Avalon Acoustics Avatar Owners manual

Table of Contents

1 Introduction 5

2 Unpacking Instructions 6
Introduction 6
Contents 6

2.1 Opening the Crate 6

2.2 Installing the Grilles 7
Orientation of the Felt Anti-Diffraction Mask 7
3 Wiring Instructions 8
Introduction 8

3.1 Wiring Options 8

3.2 Connecting the Speaker to the Amplifier 8
Standard Wiring 9
Bi-wiring 10

3.3 Multiple Amplifiers 11
Bi-amplification 11
4 Break-in Period 12
5 Maximizing Performance 13
Break-in 13
Bi-wiring 13
Tweeter Screens 13
Grille Assemblies 13
Speaker Placement and Symmetry 14
Toe-In 14
Apex Tm Couplers 14
First Reflection Points 15
Comer Treatment 15
6 Care of Your Avalon Loudspeakers 16
Cabinet 16
Grille Assembly 16
Drivers 16
7 Warranty 17
In the Event of a Problem 17
Warranty Statement 17
8 Room Acoustics and Speaker Position 19
Introduction 19
An Optical Analogy 19
Basic Room Acoustics 19

8.1 Standing W aves 20

8.2 Flutter Echo 21

8.3 Early Reflections 21
Avoiding Early Reflections 21

8.4 Bass reinforcement 23

8.5 Summary of Recommendations 25
Flutter Echo and Standing W aves 25
Speaker Placement 26
Early Reflections 26

8.6 A Listening Room Example 27
9 Accuracy of Bass Reproduction 28
Introduction 28

9.1 Sensitivity to Time-Related Information 28
“Fast Bass” 28

9.2 Low Frequency Energy Storage.............................................................................. 29

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An Illustrative Analogy ..................................................................................... 29

9.3 Sealed Enclosures.................................................................................................. 29

Another Definition of the Q Factor.................................................................... 33

Frequency Response Effects ........................................................................... 33

9.4 Vented Enclosures.................................................................................................. 34

The Hemholtz Resonator ................................................................................. 35

A Comparison of Vented and Sealed Enclosures ............................................. 35

9.5 Passive Radiators................................................................................................... 37

9.6 Dipole Radiators..................................................................................................... 37

9.7 Servo-Systems and Electronic Equalization............................................................ 38

9.8 Rationale ................................................................................................................ 38

Anechoic Frequency Response vs. In-Room Frequency Response .................. 39

9.9 Measurements of Audio Equipment ........................................................................ 39

A Correlation with Amplifier Measurements...................................................... 39

Loudspeaker Measurements ............................................................................ 40

Designing for Accurate Bass Reproduction ...................................................... 40

9.10 Listening Qualities ................................................................................................ 41

Frequency Response Effects ........................................................................... 41

Listening for Size Distortions............................................................................ 41

Transient Response Effects ............................................................................. 42

9.11 Conclusion............................................................................................................ 42

10 Features.............................................................................................................................. 43

11 Specifications .................................................................................................................... 44

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Introduction

Your new Avalon Acoustics Avatar loudspeakers represent a true breakthrough in the development of moving-coil
loudspeakers intended for accurate music reproduction. Upon initial listening, the immediacy and presence of a live
performance becomes instantly apparent. The intent is to closely reproduce the original musical event, as opposed to
creating a “spectacular” or “exciting” sonic character which can impress upon first listening, but fail to satisfy ov er a long
period of time.

The Avatar accomplishes this goal by providing the transparency and clarity, which is lacking in many dynamic designs.
Overall smoothness is achieved without depressing the high-frequency response, a technique used in some products.
Low frequencies are rendered realistically and controlled, as opposed to a “larger than life” perspective, which can
impress, but compromises definition and harmonic integrity.

This high level of performance is retained in virtually any listening situation. The Avatar has been specifically designed
to elicit the finest possible performance from any amplifier, tube or solid-state, due to its easy-to-drive nature. Similarly,
interaction with the room has been minimized, allowing ease of placement in a wide variety of listening environments.

Your Avatar loudspeaker was designed and built to the highest standards of workmanship and performance. These
standards are preserved through the test of time by careful attention to component quality and meticulous testing of
each unit before leaving the factory. As a new owner of this Avalon Acoustics product, you can be assured that you
possess one of the few great loudspeakers the audio industry has to offer.

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2 Unpacking Instructions

Introduction

Your Avalon Acoustics loudspeakers were shipped in a heavy-duty crate to ensure their safe arrival. It is recommended
to save this crate for possible future use. Due to the weight of the speakers, it will require two persons to un-crate them
and position them for listening. Please arrange for your dealer or other friend to assist in this project.

Contents

The shipping crate contains the two loudspeaker units, one set of six Apex Tm Couplers, and the owner’s manual. The
grille assemblies are contained in an outer compartment on the side of the shipping crate.

2.1 Opening the Crate

The crate features a one-piece top assembly, which is fastened to the crate bottom with screws around the lower
perimeter. To unpack, remove the screws and lift the upper portion of the crate straight up (this will require two people).
Next, slide each speaker part way off of the crate base so that the plastic bag can be unfastened from the enclosure
bottom. Stand the speaker up and the bag can be slid off the top. Please refer to Figure 2.

Figure 2.1 - To unpack the loudspeakers

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2.2 Installing the Grilles

The grille assemblies are behind a panel on the outside of the speaker crate. Remove the screws securing the panel,
and then carefully pull the grilles straight out. The grilles are installed with friction fasteners and press into place on the
speaker cabinets. Please see Figure 2.2.

Orientation of the Felt Anti-Diffraction Mask

The grille assembly includes a felt anti-diffraction mask. Should the felt mask be removed, be sure to note the correct
inside-outside orientation when re-installing it. The tweeter opening is beveled on the side that faces the listener (away
from the speaker).

Fig 2.2 - To install the grille assemblies.

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3 Wiring Instructions

Introduction

The crossover is encapsulated in a chamber in the bottom of the speaker cabinet, minimizing the effect of vibration on
the components. The Avatar is equipped with high-quality banier terminals for connecting the speaker cables. Spade
lugs designed for #10 screws are recommended for cable termination.

WARNING- Do NOT over-tighten the screws.

3.1 Wiring Options

Separate inputs are available for each crossover section, facilitating bi-wiring. Bi-wiring the Avatar separates the ground
returns for the drivers. This reduces inter-driver modulation, and can result in a higher level of sound quality. Bi-wiring
is highly recommended as a cost-effective means to better sonics. All that is needed is one extra pair of speaker
cables. You should choose a wiring option before connecting the speakers.

3.2 Connecting the Speaker to the Amplifier

1.Place the speaker in its approximate location, and then lay the speaker on its side, using a soft
surface to avoid scratching the finish.

2.Connect the speaker wires to the terminal block on the speaker bottom, as described on the
following pages.

WARNING: Do NOT over-tighten the screws.

3. Stand the speakers up.

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Standard Wiring

(A single cable from the amplifier to each speaker)

Leave the factory-installed input jumper wires in place. Connect the wires from the amplifier to the “Low” inputs. Please

refer to Figure 3. 1.

Figure 3.1 - Bottom v iew of the speaker showing the connections from the amplifier for standard (single) wiring.

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Bi-wiring

(Two cables from the amplifier to each speaker, one for the woofer, the other for the tweeter)

Remove the factory-installed input jumper wires. Then connect one set of cables from the amplifier to the “LOW ” inputs
and the other set of cables to the “FUGH” inputs. Both sets of cables are attached in parallel to the amplifier terminals.
See Figure 3.2.

Figure 3.2 - Bottom v iew of the speakers showing the connections from the amplifier for bi-wiring. The speaker cables are
connected in parallel at the amplifier terminals. The input jumper wires have been removed.

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3.3 Multiple Amplifiers

It is possible to use more than one amplifier to drive each speaker. Doing so may result in a slight additional sonic
benefit over bi-wiring, as the inter-driver modulation due to the amplifier’s finite output impedance is eliminated. All
amplifiers are driven with a full-range signal from the pre-amplifier, and the frequency division is performed by the
passive crossover.

It is important to use identical amplifiers when bi-amping. If this is not possible, then the gains of the amplifiers must be
adjustable and matched within 0.1 dB. Mismatched gain levels can significantly alter the tonal balance of the Avatar
and lead to poor sound quality. It is also important to be aware of the absolute polarity of the amplifiers. If any of the
amplifiers invert phase, be sure to compensate by reversing the polarity of the speaker leads at the amplifier’s output
terminals.

Bi-amplification

Follow the instructions for bi-wiring (above), except connect the speaker cables to separate amplifiers. The amplifiers
are driven with the full-range signal from the pre-amplifier. If your pre-amplifier only has one set of output jacks, use a
“Y” connector to tie the inputs of the amplifiers in parallel.

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4 Break-in Period

Your new Avalon Acoustics loudspeakers have an initial break-in period. They will not perform to their full sonic
potential when first installed in your system. This is due to a residual polarization of the dielectric materials used in
the crossover capacitors and internal wiring. (See note 1) As music is played through the loudspeakers, the electrical
signal will gradually anneal these materials. Similarly, the suspensions of the drivers will reach their optimal
mechanical properties as the speakers are played. Only after the break-in period will the full performance of your
Avalon Acoustics loudspeakers be realized.

The break-in process will occur naturally as music is played through the system. To reduce the time required, it is
recommended that the system be played continuously, using either a digital source in the repeat mode or an FM
broadcast signal. The recommended break-in procedure is as follows:

Initial warm-up: three to six hours of quiet music.

Extended break-in: 200 to 300 hours of loud and dynamic source material.

During the break-in period, the sonic properties of your loudspeakers may undergo several gradual shifts as the various
components break-in at different rates. It is therefore suggested that the fine-tuning of the system be delayed until after
the break-in period is completed. However, during the final phases of the break-in period, the sonic image will open up,
the sound-stage will gain specificity, the bass control and impact will increase, and the overall sound will have a more
relaxed, involving presentation.

(1) A high-voltage test is applied to wiring and capacitors during their manufacture. This results in a residual polarization
of the dielectric materials.

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5 Maximizing Performance

These details are imperative to obtaining optimum results from your Avalon Acoustics loudspeakers.

Break-in

The break-in period is critical to maximizing sonic performance and should take place before other adjustments (see the
discussion on page 12). The break-in should begin with three to six hours of quiet music, followed by 200 to 300 hours
of loud and dynamic source material.

Bi-wiring

Bi-wiring of the Avatar is strongly recommended. The sonic benefits include increased bass articulation, midrange
definition, image solidity, and ambient information retrieval. Please refer to page 10 (Tri-wiring) for further information.

Tweeter Screens

The tweeters are equipped with a screen to protect the fragile titanium dome. The screens slightly reduce (1-2 dB) the
tweeters’ maximum diffusion characteristics above 10,000 Hz. They are held in place by the magnet of the tweeter, and
may be removed if your system requires additional energy in the highest octave.

WARNING: The titanium domes are thinner than a human hair and are
easily damaged. Remove

To remove the screens, firmly grasp their tapered sides with the thumb and forefinger,
and carefully pull the screen straight out. It is recommended that they be replaced if the
speakers are to be transported. W hen replacing the screens, be sure to hold them
securely, as the magnetic attraction from the tweeter will tend to pull them from your
hand, which can damage the dome.

the screens at your own risk.

Grille Assemblies

The grille assemblies, with their felt anti-diffraction masks, are integral elements of the loudspeakers’ design. Unlike
many other products, Avalon Acoustics loudspeakers are designed to be used with the grilles in place while listening,
and removing them will degrade the system’s performance. It is extremely important that the felt anti-diffraction masks
make physical contact with the face of the loudspeakers, as air space between the felt and the speaker face will
adversely affect sound quality.

WARNING: Be extremely cautious positioning the felt in the tweeter area, especially if you have removed the
tweeter screens.

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Speaker Placement and Symmetry

Selecting the proper room position for your Avalon Acoustics loudspeakers can dramatically improve their performance.
The following points highlight the fundamental concepts in loudspeaker positioning from the in-depth discussion in
Chapter 8, Room Acoustics and Speaker Position (beginning on page 19):

• Left to right room symmetry aids in producing a balanced sound stage.

Image depth is enhanced when the distance to the rear wall is increased.

• The most even bass response will be attained when the distances to the side and rear walls are not overly similar.

Toe-in

Adjusting the toe-in angle of the speakers is useful in tailoring the sound to best match the
characteristics of your system and listening room.

When the speakers are facing straight forward, they tend to create a large, expansive sound­stage, painted with broad brush strokes. As they are rotated toward the listening position, the
image becomes more compact, with increased focus, creating a greater sense of intimacy.
Pointing the speakers inward is also helpful in situations where strong reflections from the side
walls are a problem.

Start with the loudspeakers facing straight forward, and play either a mono source, or a stereo
source with a distinct center image, through both channels. Carefully rotate the loudspeakers
inward in small increments to bring the image in precise center focus (small adjustments can be
made with the speaker on Apex Tm couplers). Toe-in adjustment is rather delicate, and
experimentation is necessary to achieve the proper angle for your listening situation. The
optimum angle is usually between three and ten degrees inward.

Apex- Couplers

Supplied with your Avalon Acoustics loudspeakers are six Apex Tm couplers, used to couple the speakers to the floor,
thereby minimizing time-smearing resonance effects. The result is an increase in focus and solidity of the sonic images.

On hardwood floors, use a large coin, such as a quarter, to protect the floor from the pointed spike

Once you have located the proper position and toe-in angle for your Avalon Acoustics loudspeakers, place the couplers
under the speaker bases. It is easiest to install the couplers with the assistance of a friend. Lean the speaker forward
first, and position two couplers pointing downward, one under each rear comer. Then lean the speaker backward and
place one Apex Tm coupler under the front center of the base.

In rare instances, the additional coupling established by the Apex Tm couplers can cause increased excitation of low­frequency resonances in the floor. If the bass quality decreases with the couplers in place, it may be worthwhile to
experiment with soft rubber isolation disks, such as Sorbothane.

.

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First Reflection Points

Since the ear/brain system tends to integrate the sounds arriving within a 10 millisecond time window, it is important to
control the early reflections arriving from the sidewalls to the listening position. A hard-surfaced wall can produce a
strong frequency-dependent reflection that can interfere with the reproduced sound-stage, as well as change the
perceived tonal balance of the system. Therefore, damping these first reflection points in strongly recommended.
Please refer to Section 8.3, Early Reflections, beginning on page 21, for further information.

Corner Treatment

It is important to control the first reflections of low frequency sound, which normally occur at the comers behind the
loudspeakers. These reflections can cause significant distortions in phase and amplitude, resulting in muddy bass
definition and smeared bass transients. Placing Tube-Traps (available from Acoustic Sciences Corporation) at the room
comers can significantly control these bass colorations and restore the quickness of bass transients.

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6 Care of Your Avalon Loudspeakers

Cabinet

Your Avatar loudspeakers are finished with a high quality furniture lacquer. This is a modern finish which is beautiful yet
durable, and requires only minimal attention. The speaker should be dusted with a soft, non-abrasive cloth, using
furniture polish.

Grille Assembly

The grille assembly may be removed from the cabinet and gently vacuumed to remov e dust. If the felt insert is
removed, please note the inside-outside orientation when re-installing it. The hole for the tweeter is beveled on the side
toward the listener, to provide optimal dispersion characteristics.

Drivers

The drivers (woofer and tweeter) require no regular maintenance. Do not attempt to clean the tweeter dome, as it is
easily damaged. If desired, you may remove dust from the woofer cone by using a small, soft dusting brush.

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7 Warranty

Your Avalon Acoustics loudspeakers are warranted against defects in workmanship and materials for a period of five
years, provided that the enclosed registration card is returned to the factory within seven days of the purchase date.
If the registration card is not returned within the seven day period, this warranty is null and void, and you will not be
notified of future updates. In the unlikely event that you did not receive the registration card with your loudspeakers,
please contact the factory immediately so that we may send you a replacement card. This warranty is transferable
to subsequent purchasers within the original five year period. A complete statement of warranty is given below.
Please take the time to fill out and return the enclosed warranty registration card.

In the Event of a Problem

In the unlikely event of a problem with your Avalon Acoustics loudspeakers, the component most susceptible to failure is
one of the driver units. If driver replacement is required, have your dealer contact Avalon Acoustics. The individual
performance curves of the drivers in each pair of loudspeakers are kept on file at the factory. This enables Avalon
Acoustics to supply an exact replacement unit, ensuring continued operation at the highest level of performance. The
defective driver must then be returned to the factory for inspection to determine the status of the warranty claim. This
on-site replacement of the driver units eliminates the time and expense of shipping the entire speaker to the factory for
repair. All warranty claims must be made through an authorized Avalon Acoustics dealer or distributor,

Warranty Statement

1. Avalon Acoustics warrants the materials, workmanship, and proper functioning of this product for a period of five
years, provided that the completed registration card is returned to Avalon Acoustics within seven days of the date of
purchase. If the registration card is not returned to the factory within the seven day period, this warranty is null and
void. If any defects are found in the materials or workmanship of this Avalon Acoustics product, or if the product
ceases to properly function within the appropriate warranty period from the date of first purchase, the unit will be
repaired or replaced by Avalon Acoustics or its authorized agent after receiving authorization from the factory or
dealer.

2. Purchaser must return the product, packaged in the original shipping carton, freight prepaid to:

Avalon Acoustics

2800 Wilderness Place

Boulder, Colorado 80301

[phone]

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3. Avalon Acoustics reserves the right to inspect any products which are the subject of any warranty claim

prior to repairing or replacing. Final determination of warranty coverage lies solely with Avalon Acoustics.
Any products which do not conform to this warranty shall be repaired or replaced by Avalon Acoustics as
soon as possible following receipt of the product and claim, but in no event later than 30 days after receipt
of the product. Out-of-warranty claims will be billed for labor, materials, return freight, and insurance as
required. Any product for which a warranty claim is accepted will be returned to the purchaser and cost of
shipping and insurance will be factory prepaid within the boundaries of the USA. Units to be shipped
outside of the USA will be shipped freight collect only. This warranty gives specific legal rights. The
purchaser also has implied warranty rights, and may also have other rights, which vary from state to state.

4. This warranty is extended to the purchaser and any purchaser from him for value.

5. Avalon Acoustics strives to manufacture the very finest possible equipment, and therefore

reserves the right to make changes in design and improvements upon its products, without necessarily
assuming an obligation to retrofit such changes upon its previously manufactured models.

6. The above warranty is the sole warranty given by Avalon Acoustics, and is in lieu of all other warranties. All

implied warranties, including warranties of merchantability or fitness for any particular purpose shall be strictly
limited in duration to five years from the date of original purchase, and upon the expiration of the warranty
period (five years), Avalon Acoustics shall have no other obligation of any kind whether express or implied,
including but not limited to merchantability. Further, Avalon Acoustics shall in no event be obligated for any
incidental or consequential damages as a result of any defect or any warranty claim, whether express or implied.
Some states do not allow exclusion or limitation of incidental or consequential damages or limitations on how
long implied warranties last, so the above limitations and exclusions may not apply to you.

7. Avalon Acoustics does not authorize any third party, including any dealer or sales representative to assume any

liability for Avalon Acoustics, or make any warranty for Avalon Acoustics. The unit must not have been altered
or improperly serviced or repaired. The serial number on the unit must not have been altered or removed.

8. Warranty registration cards must be completed and mailed to Avalon Acoustics within seven days of date of

purchase; otherwise, this warranty is null and v oid. Avalon Acoustics may, at its option, require from the
purchaser valid proof of purchase (dated copy or photocopy of dealer’s original invoice).

9. If this product is used in a commercial or industrial application, then special warranty exclusions may apply.

Contact your dealer or Avalon Acoustics for commercial warranty policies.

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8 Room Acoustics and Speaker Position

Introduction

The listening room forms the final link of the playback system, as important as any other component in the chain. Just
as an otherwise superb system is handicapped by an inferior pre-amplifier (for example), so can a well-matched system
be hindered by poor room acoustics. It is not necessary to listen to your system in a specially-designed sound chamber
in order to enjoy it. In fact, a dedicated listening room usually requires additional sound treatment, due to a lack of other
items in the room that can help provide proper acoustics. However, attention to the listening environment can greatly
increase your system’s performance.

Listening in a properly set-up room can be a startling experience. Due to the limitations of the two-channel format and
the listening environment, the illusion of actually being transported to the recording site cannot usually be achieved.
However, an uncanny sense of realism can be created. Perhaps it is best described as if the front half of your listening
room has been removed, so that it now opens out into the recording site.

To optimize your equipment set-up and the listening-room acoustics requires a basic understanding of the principles that
affect the propagation of sound in the room. Also, we will discuss the way in which our brain interprets spatial cues, and
how the room acoustics can affect our sonic perceptions.

An Optical Analogy

Let us use an optical analogy to aid our understanding of acoustics. Imagine that you are in a room that is lit only by a
candle in its center. There is a uniform amount of light cast in all directions. If a large mirror is held closely to candle,
one half of the room becomes darkened, while the other half receiv es twice as much light. This is because there are
effectively two candles now illuminating that half of the room, the real candle, and the virtual (or reflected) candle. The
energy that had been sent to both sides of the room has now been concentrated in one side only.

If we repeat the same experiment using a large piece of black cloth instead of a mirror, the results will be somewhat
different. The side of the room behind the cloth is darkened, just as before, but the level of light on the side of the
candle remains unchanged. This is because the light is absorbed by the cloth, rather than being reflected back into the
room.

Thus we can see that the energy can either be absorbed or reflected. A similar situation occurs with sound waves,
although we must account for the much greater wavelengths of audible frequencies. Of course no material is a perfect
absorber or an absolute reflector. Furthermore, the sonic absorption coefficient of a given material usually varies with
frequency.

Basic Room Acoustics

The great majority of all listening rooms are rectangular, with parallel surfaces. The walls and ceiling are typically hard
surfaces, which are acoustically reflective. These large areas

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are the predominating factors in the ov erall room acoustics, although the other items in the room (furnishings, carpeting,
wall hangings, doorways, etc.) will also play a role. Without going into excessive detail, there are four primary areas of
potential concern:

1. Standing waves.

2. Flutter echo.

3. Early reflections.

4. Bass reinforcement

The first three items are problems that should be reduced or eliminated. The last item, bass reinforcement, needs to be
matched to the entire system for proper tonal balance.

8.1 Standing Waves

The parallel surfaces of most listening rooms can lead to a potential problem in the low frequencies. A sound wave can
be repeatedly reflected from opposing surfaces, back and forth. If the distance between the surfaces is an integral
multiple of one-half the sound wavelength, a standing wave will be set up. This means that the incident and reflected
waves combine with each other so that a stationary pattern of high and low sound pressures is established in the room.
This irregular distribution of sound level is caused by cancellation and reinforcement between the reflected and direct
sound waves.

At high frequencies, this pattern of high and low sound pressure levels within the room becomes too finely spaced to be
discerned. However, when the dimensions of the room are comparable to the wavelengths of the musical notes, there
will be obvious changes in the intensity of certain bass notes in different locations within the room. Additionally, the
existence of the standing wave implies a resonant condition where acoustic energy is stored in the room. This energy
storage can result in “heavy”, “muddy”, or “slow” bass.

Since the presence of standing waves is caused by parallel reflective surfaces, practically every listening room suffers
from this problem to some degree. However, several factors are working in our favor here. First, as the room size
increases, the affected frequencies become lower and thereby less audibly apparent. Second, the presence of shelving
or furniture against the walls will break up the large surfaces, reducing the magnitude of the problem. Third, upholstered
furniture can absorb a significant amount of bass, diminishing the build-up of resonant energy. Fourth, typical wall
construction is not completely reflective at low frequencies.

However, in some cases audibly objectionable standing waves will still be present in the listening room. This can be
noted by large variations of the intensity of certain bass notes in different areas of the room. Another indicator is an
unevenness of loudness of different bass notes. (This is sometimes what is actually on the recording, so be sure that this
is consistently a problem on a variety of recordings.)

If you wish to reduce or eliminate standing waves that may exist in your room, it will be necessary to reduce the low­frequency reflectiveness of at least one of the parallel opposing surfaces. The most effective method is to use Tube­Traps, available from Acoustic Sciences Corporation. Experimentation will be needed to determine the optimal
locations.

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8.2 Flutter Echo

These same parallel, reflective surfaces can also produce a different audible problem. If there is little absorption at
higher frequencies, a musical transient containing high frequencies, such as a hand clap or the strike of a percussion
instrument, can be heard bouncing repeatedly between the surfaces. Called flutter echo (or slap echo), these
multiple reflections can obscure musical detail. The situation is analogous to standing between two parallel mirrors,
when the outline of your reflection becomes more difficult to discern, due to the additional reflected images present.

Again, it is only necessary to reduce the reflectiveness of one of the surfaces in each pair of surfaces to eliminate
flutter echo. Since we are concerned with the high frequencies, any soft material is appropriate. Drapery or fabric
wall hangings are quite effective on the walls. Bookshelves also work well by breaking up the flat surfaces.
Carpeting should eliminate potential problems between the floor and ceiling.

8.3 Early Reflections

Another situation that can reduce the subjective quality of reproduced sound is the presence of early reflections. By
early reflections, we are referring to reflected sound waves that reach the listener within I0 to 20 milliseconds of the
direct signal from the loudspeaker.

When a reflected sound reaches the listener more than 40 milliseconds later than the direct sound, the reflection is
heard as a discrete echo. However, if the reflected sound arrives within around 20 milliseconds of the direct sound, the
ear/brain system integrates the two sounds so that only one sound is heard. This integration is done in such a way that
spatial information is preserved, providing an acoustical “picture” of the physical space that created the reflections.

However, the source recording also contains ambient information that portrays the original recording site. Early
reflections in the listening room will tend to obscure the ambient information in the recording, leading to a loss of
dimensionality or spaciousness. Secondary arrivals within the first 10 milliseconds are especially problematic, becoming
less troublesome as the arrival time lengthens to 20 milliseconds or so.

Avoiding Early Reflections

The speed of sound is approximately one foot (30 cm) per millisecond. Therefore, to preserve the natural soundstage
on your recordings, there should be no reflected sounds arriving at the listening position with a path length less than ten
feet (3 meters) longer than the direct path from speaker to listener (see Figure 8. 1). This means that if the speaker or
listener is placed closer than about five feet to a wall or other surface, that surface should be covered with sonically
absorbent material.

Since the floor is within five feet of the speaker, it is best to have a carpeted floor to absorb floor reflections. A thick,
dense carpet and pad will absorb lower frequencies more effectively than a thin one. Due to their complex structure,
carpets and pads of natural materials, such as wool and jute, will exhibit a more uniform absorption over the frequency
spectrum than synthetic materials will.

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It is not necessary to acoustically treat the entire room to achieve good results. Strategic treatment of specific locations
can realize considerable benefits. Remember that when sound wav es reflect from a flat surface, the angle of reflection
is equal to the angle of incidence, just as a mirror reflects light waves. Therefore, the most important location for sound
absorbing material is the point where the sound waves reflect to the listener (see Figure 8.2).

Figure 8.1 - The reflected sound must travel further than the direct sound, and therefore reaches the listener at a later

time.

Figure 8.2 - The sound is reflected at the same angle that it struck the surface; i.e., Angle X = Angle Y. Since light
waves obey this same rule, a mirror can be used to find the point that can be acoustically damped to avoid early
reflections.

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8.4 Bass reinforcement

By bass reinforcement, we mean the effect of the room boundaries on the propagation of sound.
It is widely known that speaker placement relative to the floor and walls can affect the relative
amount of bass that the system produces.

To make this interaction more clear, let us refer to the optical analogy of the candle. Similarly to
the way that the mirror reflected the light of the candle, so can the surfaces near the loudspeaker
reflect the sound waves back into the listening room. However, when the path-length-difference
of the reflected wave is short relative to the wavelength of the sound, the reflected wave is
substantially in-phase with the original wave. When this condition is met, the coupling

coefficient between the speaker diaphragm and the air increases, and the speaker
efficiency increases. This changes the actual frequency response of the speaker, and is
not attributable to standing waves or other room resonances.

By selecting the distance from the speaker to the reflective surface, we can determine the
frequency at which the bass reinforcement takes effect. Please see Figures 8.3 and 8.4.
Furthermore, there are typically three reflective surfaces near each speaker, the floor, the rear
wall and the side wall. Each of these surfaces produces its own reflection, and hence additional
bass reinforcement.

Figure 8.3 - Change in frequency response resulting from placement of speaker 3.3 feet from a reflective surface
(relative to an anechoic environment).

Figure 8.4 - Same conditions as above, except speaker is 6.6 feet from the reflecting
surface. Note how the reinforcement now occurs at a lower frequency.

23

By properly selecting the distances to each surface, we can extend the in-room bass response of the speaker much
deeper than its anechoic response. Please see Figure 8.5. This is because the bass reinforcement provides a boost
which is complementary to the bass roll-off that would be present in an anechoic chamber.

Figure 8.5 - Anechoic response of the Avalon Acoustics Avatar, and in-room response with the speaker placed 4.6 feet
from the rear wall, and 3.0 feet from the side wall. Note how the bass response is extended by the room reinforcement.
Conversely, improper placement of the loudspeakers can result in uneven frequency response. This results in
diminished bass quality. Please refer to Figure 8.6.

Figure 8.6 - Uneven frequency response caused by improper placement of the speakers. In this case, the speaker is 2.0
feet from both the side and rear walls.

In order to take full advantage of the bass reinforcement to provide the most uniform and extended bass response, the
anechoic response of the speaker must be known. The Avatar is designed so that proper bass reinforcement occurs
when the speaker is placed between two and five feet from one of the walls (side or rear), and between three and ten
feet from the other wall.

The measurements are made from the wall to the center of the woofer cone. The exact distances are not overly critical,
although the two distances should not be within about 20% of each other. For example, if the distance to the side wall is
four feet, then the distance to the rear wall should be at least five feet.

24

Figure 8.7 - In-room response of Avalon Acoustics Avatar when the speaker is placed 2.3 feet from the side wall, and

3.9 feet from the rear wall.

Figure 8.8 - In-room response of Avalon Acoustics Avatar when the speaker is placed 3.6 feet from the side wall, and

6.6 feet from the rear wall.

8.5 Summary of Recommendations

Now that we have looked at some of the common problems of listening rooms, as well as their remedies, let us
summarize our findings and recommendations.

Flutter Echo and Standing Waves

These situations are the result of the room having parallel, reflective surfaces. The potential problems are independent
of the audio system, and need to be addressed at the source. This means that at least one surface in an opposing pair
of surfaces needs to be made less reflective and/or non-parallel.

• Low Frequency Absorption

If a problem exists with standing waves, it is the low frequencies that will need to be addressed. Remember that the
absorption spectrum of different materials and objects is not uniform. That is, some items will absorb only high
frequencies, and some objects may only absorb the middle frequencies. At low frequencies, about the only common
item that can absorb a meaningful amount of energy is heavily upholstered furniture. Another effective means of
absorption is the use of Tube-Traps, from Acoustic Sciences Corporation.

• High Frequency Absorption and Room Symmetry

25

Since flutter echo is a high-frequency effect, it becomes much easier to manage potential problems in this area. Almost
any item attached to the walls will be less reflective at high frequencies than the bare walls themselves. Draperies, wall
hangings, paintings, bookshelves and other items will normally be present in the room, and will usually eliminate any
possible problems. If flutter echo is still audible, a fabric wall hanging provides an effective and attractive cure.

Additionally, it is desirable to maintain a degree of left/right symmetry in the room to preserve a balanced acoustic
“space”. For example, if your listening room has full length draperies along the right wall, and the left wall is bare, slap
echo will not be a problem. Nonetheless, the sound-stage may be somewhat distorted, and it could be beneficial to
place a fabric hanging or tapestry on the wall opposite the draperies.

• Parallel Surfaces

Although it is not generally possible to make the walls non-parallel, the same effect is achieved by breaking up the large,
flat surfaces with furniture and shelving.

Speaker Placement

Although your Avalon Acoustics loudspeakers may be placed in a wide variety of positions relative to the walls of the
room, it is still wise to experiment a bit to achieve optimal results. The suggested minimum distances for the Avatar are
two feet from one wall (side or rear), and four feet from the other (all distances are measured to the center of the woofer
cone). This will provide the proper degree of bass reinforcement, as well as minimize early reflections.

The suggested maximum distances for the Avatar are five feet from one wall (side or rear), and ten feet from the other.
As the distance from the speaker to the nearby walls increases, early reflections become less of a problem, and the
sound-stage becomes more spacious. However, regardless of the absolute numbers used, the most ev en bass
response will be attained if the distances from the side wall and the rear wall are not overly similar.

Early Reflections

When arranging the furnishings in your listening room, remember that reflective objects should not be within a five foot
radius of either the speaker or listener to avoid early reflections. This suggests the possibility of a dual-purpose room,
with one end devoted to music reproduction, and the other end for another use, such as a study or office. In this way,
the area behind the listener will contain items that will reduce problems with standing waves and/or flutter echo, while
the zone around the speakers remains relatively free from reflective objects.

If you wish to achieve an even more spacious sound-stage, it may be useful to place a sonically absorbent material on
the side and rear walls near the speakers. This can be particularly effective at the points where the sound wave is
directly reflected to the listening position (a mirror can be used to determine these points, as illustrated in Fig. 8.2). As
the distance to the wall becomes smaller, the suppression of these reflections becomes more important.

Early reflections will tend to diminish the soundstage in the direction of the reflections, i.e. early reflections from the side
walls tend to reduce sound-stage width, while early reflections from the back wall will reduce image depth. W e have
found that a strong sense

26

of depth enhances the feeling of involvement when listening, due to the three-dimensional solidity of images.
Therefore, it is more important to have a greater distance from the speakers to the rear wall than to the side walls.
Typically, this is easier to achieve if the speakers are placed along the short wall of the listening room.

8.6 A Listening Room Example

In order to make these points more clear, an example of a room layout is given in Figure 8.9, illustrating the
principles we have given.

Figure 8.9 - Example listening room. The area around the speakers is free of objects that would produce early
reflections. A tapestry is hung opposite the draperies to absorb the reflection from the side-wall and to help maintain left
right symmetry. The area behind the listening position contains items which help break-up standing waves and flutter
echoes. Heavily upholstered sofas will help avoid low-frequency standing waves, while a carpet absorbs early
reflections from the floor.

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9 Accuracy of Bass Reproduction

Introduction

We hav e all had the experience of listening to speakers with poor bass quality. Perhaps the bass was muddy, or ill­defined. Possibly the bass was exaggerated or bloated. These distortions are distracting and keep us from enjoying the
full measure of the performer’s intent.

Concerning the reproduction of low frequencies, Avalon Acoustics pursues a different design goal than most other
speaker manufacturers. Specifically, we believe that the complete absence of stored resonant energy is of paramount
sonic importance. First, we will discuss some of the technical aspects of bass reproduction and perception, and then
explain how this relates to the listening experience.

9.1 Sensitivity to Time-Related Information

The human ear/brain system is extremely sensitive to time-related distortions. This is because directional (and spatial)
information is provided by inter-aural time (and phase) differences. During the period of man’s evolution, the ability to
accurately determine the direction and distance of sound sources conferred a survival advantage, hence our present day
aural acuity.

This sensitivity to time-related information is apparent in the terms used to describe the quality of a system’s bass
reproduction. Many of the terms refer to temporal properties. A system with poor low-frequency transient response is
described as “boomy”, heavy “sluggish”, or “slow”. When the transient response is accurate, the bass is characterized
as “tight”, “clean”, “quick”, or “fast”.

“Fast Bass”

The term “fast bass” would seem to be an oxymoron. After all, it is the “slowness” of a note that makes it a low
frequency. Nonetheless, the term provides an accurate description of our subjective impression. Many people have
erroneously ascribed “fast bass” to the use of a light diaphragm or the use of a powerful energizing system. (See note 1)
In fact, it is not how fast the diaphragm can be set into motion that imparts a speaker with “fast” bass. Rather, it is how
fast that motion can be stopped, how quickly the stored energy can be dissipated, that results in the sensation of “fast”
bass.

___________________________________________________________________________________________

(1) The acceleration of an object is equal to the force exerted upon it, div ided by the mass of the object. Since a
loudspeaker is used above its fundamental resonance, it operates in what is known as the mass-controlled region. In
this region, high acceleration (large driving force and/or small driven mass) does not imply extended high frequency
response or fast transient response. Instead, high acceleration confers high efficiency.

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9.2 Low Frequency Energy Storage

Avalon speakers use the only practical bass loading system that results in the complete absence of low frequency
energy storage. (2) This is a sealed enclosure with a Q factor equal to 0.5. (3)

no stored resonant energy in the system. All other low-frequency loading systems (including sealed
enclosures with a Q factor greater than 0.5, vented enclosures, and planar speakers without enclosures)
deliberately add a low-frequency resonance to improve frequency response in an anechoic chamber.

However, a resonance is, by definition, due to energy storage. The resulting time-related distortion is audible.

When this condition is met, there is

An Illustrative Analogy

To more clearly understand the concept of stored resonant energy, consider the case of an analog voltmeter. The meter
might have a movement that moves freely, or it could have some damping present in the form of silicone-damped
bearings. The Q factor refers to the amount of damping (mechanical resistance) present in the system.

Let us examine the behavior of the meter when it is connected to a battery. If the meter is underdamped (Q factor
greater than 0.5), the meter needle would swing past the correct voltage of the battery and tend to fluctuate before
settling down at the proper value. If the meter is overdamped (Q factor less than 0.5), the meter would be slow to
respond and take a relatively long time to reach the final reading. If the meter is critically damped (Q factor equal to

0.5), the needle would quickly reach the correct reading with essentially no overshoot.

9.3 Sealed Enclosures

An analogous situation occurs with sealed-enclosure loudspeakers. Please refer to
Figures

9.1 through 9.5. This shows the resultant sound pressure level versus time when various sealed enclosure systems are

subjected to a step (pulse) input. All of the systems display a similar behavior in the initial phase of the pulse, but it is
when the input signal has reached a steady state that the differences are seen. The system with Q = 0.5 undershoots
the zero level slightly, and then immediately returns to zero. As the Q factor is increased, the transient response
becomes worse, and the system exhibits increased oscillatory behavior (ringing).

(2) A properly designed horn-loaded system can be free of energy storage effects, but will be impractically large for
extended bass response. A transmission-line design can theoretically operate as an infinite-baffle (infinitely large sealed
enclosure), although no experimental analysis exists to support this claim. All commercially available transmission-line
designs are made to practical size considerations and appear to operate as damped bass-reflex (vented) systems. In
either instance, the absence of low-frequency energy storage is not assured.

This refers to the condition when a damped resonant system has a damping coefficient exactly equal to the square

(3)
root of the quantity four times the moving mass times the suspension stiffness.

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Figure 9.1 - Transient response of a sealed enclosure loudspeaker with 0=0.5 when subjected to a step-pulse. After the
signal undershoots the baseline, it returns to zero with an exponential decay. This represents perfect transient
performance.

Figure 9.2 - Transient response of a sealed enclosure loudspeaker with 0=0.7 when subjected to a step-pulse. Note the
greater amount of undershoot, caused by the cone motion continuing after the input has become static. Although
difficult to discern on this plot, the pressure again rises above zero after the initial undershoot.

30

Figure 9.3 - Transient response of a sealed enclosure loudspeaker with Q=1.0 when subjected to a step-pulse. The
increasing Q factor indicates that there is insufficient damping to control the cone’s motion after the input signal has
become static.

31

For a Q factor of 0.7, the system appears to have a well-behaved transient behavior. However, the system now exhibits
a damped oscillation at a defined frequency. This is one form of a time-related distortion. In this instance, the woofer
contains stored resonant energy and the cone continues to oscillate after the input signal has become static. Almost all
commercially available sealed enclosure systems have a Q factor between 0.7 and I.O.

Another Definition of the Q Factor

An alternate interpretation (not mathematically precise, but nonetheless helpful) of the Q factor is to regard it as
approximately the number of cycles that the system will ring after it has been excited by a transient. For example, a
dipole woofer with a Q = 4 will oscillate for roughly four complete cycles before the speaker’s damping stops the motion.
A speaker with a Q = 0.7 will oscillate for most of a cycle, giving the ear enough information to determine a tone
associated with the resonance. When the Q factor drops to 0.5 or less, there is no tone identified with the speaker’s
resonance, as one-half of a cycle does not determine a frequency.

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Frequency Response Effects

Figure 9.9 shows the anechoic frequency responses of sealed enclosures with different Q factors. The system with a Q
factor of 0.5 produces relatively less bass near the system resonance than those systems with higher Q factors.
However, the situation is more clearly seen from the opposite point of view. That is, if a Q factor of 0.5 represents
perfect transient response, then what is the magnitude of error created by a higher Q factor? One can examine the
graph and see that a system with a Q factor of 0.7 produces 3 dB of additional output at resonance, while a Q factor of

1.0 produces 6 dB extra output. A resonant peak of 3 to 6 dB in the midrange of a speaker would be justifiably

criticized, but it is traditionally (and we believe incorrectly) accepted in the bass response of most speakers. To
sum up, increasing the Q factor above 0.5 increases the magnitude of the bass response at the expense of decreased
transient performance.

Figure 9.9 - Frequency response characteristics of sealed enclosure systems with the following Q factors (top to bottom):
Q=2.0, 0=1.4, 0=1.0, Q=0.7, 0=0.5. At resonance, each curve is 3 dB from its neighbor.

33

9.4 Vented Enclosures

For comparison, the frequency response and the transient response of two popular vented-system
alignments are shown in Figures 9.10 through 9.12. The most commonly used vented alignment is B4
(fourth order Butterworth). The QB3 (third order quasi-Butterworth) alignment is often touted as
possessing superior transient response. While better than the B4 alignment, its transient behavior is
poorer than typical sealed enclosures, even those with relatively high Q factors.

Figure 9.1 0 - Frequency responses of vented enclosure loudspeakers.

Figure 9.11 - Transient response of a v ented enclosure loudspeaker with B4 tuning when subjected to a
step-pulse. Although a 0 factor cannot be assigned to vented systems, the transient response is similar

to a sealed system with Q=1.4.

34

Figure 9.12 - Transient response of a v ented enclosure loudspeaker with a QB3 tuning when subjected to

a step-pulse. This transient behavior is similar to a sealed system with 0=1.1.

The Helmholtz Resonator

The source of this transient ringing is the vented enclosure acting as resonant cavity, technically referred to as a Helmholtz
resonator. Another example of a Helmholtz resonator is an empty soda-pop bottle, which produces a tone when one blows
across the opening. The resonant frequency of the soda-pop bottle is determined by the mass of the air in the mouth of
the bottle and the compliance of the air "spring" in the body of the bottle.

In the case of the vented loudspeaker, the resonant frequency of the enclosure is determined by the mass of the air in the
vent (port), and the compliance of the air enclosed by the cabinet. It is at this frequency that the vent contributes its
maximum output.

A Comparison of Vented and Sealed Enclosures

In approximate terms, the vented enclosure is tuned so that it resonates (and increases the system output) at the point
where the output from the woofer would be falling off if the enclosure were sealed. This is demonstrated in Figure 9.13,
which compares the anechoic frequency response of a woofer mounted in a vented enclosure to the same driver in a sealed
enclosure of the same volume. The vented enclosure is tuned to a fourth-order Butterworth response. The sealed
enclosure is identical except for the lack of the vent, which results in a Q factor of 0.57.4

35

Figure 9.13 - Frequency response characteristics of a v ented enclosure loudspeaker with a B4 tuning, and the same
system except with the vent blocked, creating a sealed system. Note that while the presence of the vent increases the
system output in the vicinity of the enclosure resonance, it decreases the system output at lower frequencies.

It should be noted that closing the vent of a vented enclosure does not automatically result in a Q factor of 0.57. This is only true for the
case of the B4 tuning, which is achieved only with one specific set of woofer and enclosure parameters.

The vented enclosure has greater output at the enclosure resonance, but below the enclosure resonance,
the vent output becomes out of phase to the woofer output, and reduces the total output below that for
the sealed enclosures Furthermore, the presence of the vent severely degrades the transient
performance. This is shown in Figure 9.14. The designer of a vented enclosure is clearly seen to be
trading improved anechoic frequency response for inferior transient response.

Figure 9.14 Transient response comparison between vented enclosure loudspeaker withB4 tuning and

the same system with the vent blocked, thereby creating a sealed system. The stored energy needed to

create the resonance of the vented system is released after the initial transient has passed.

36

Note: Sometimes speaker measurements of vented designs are given showing the contributions from the woofer

cone and the vent separately on the same graph. However, these fail to take into account the phase difference
between these two sources, and are therefore inaccurate and misleading.

9.5 Passive Radiators

The passive radiator (also known as a drone cone, auxiliary bass radiator, fluid-coupled
subwoofer, etc.) operates in very nearly the same manner as the vented enclosure. In this case,
the mass of the passive radiator replaces the mass of the air in the vent. The major difference is
a sharpening of the low-frequency comer of the frequency response curve, caused by the
additional element of the passive radiator's suspension compliance. This results in even greater
overshoot and ringing compared to the equiv alent vented enclosure. However, there are
benefits to be gained relative to vented enclosures, especially the reduction of turbulent wind
noise which can exist in vents.

9.6 Dipole Radiators

Normally the low frequency response of a dipole radiator (panel or planar-type speaker) falls off at
6 dB per octave, due to increasing cancellation from the anti-phase rear wave. The frequency at
which the cancellation begins to occur is dependent upon the physical dimensions of the baffle,
and is between 100 and 200 Hz for typical commercially available systems. To compensate for
this roll-off, virtually all manufacturers design the diaphragm to have a low-frequency mechanical
resonance, often using distributed or staggered multiple resonances. The resonance of the
diaphragm boosts the system output where it would otherwise be reduced due to cancellation from
the rear wave. A Q factor between 2 and 5 is typically required to achieve the necessary
correction and represents a significant amount of energy storage and attendant transient
inaccuracy.

37

9.7 Servo-Systems and Electronic Equalization

Although not achieving widespread acceptance, there always seems to be at least one servo­controlled or electronically equalized woofer system available on the market. These types of
systems do not provide miracle cures for the maladies of bass reproduction; rather, they are
alternative design concepts, with their own set of advantages and disadvantages.

The main benefit of both techniques is that, for a given frequency response, a smaller enclosure
can be used than would otherwise be needed. This comes at the expense of requiring greater
amplifier power, that is, a lower effective efficiency of the woofer. This can be a valid design
choice in certain situations, although in many cases cone excursion or thermal dissipation
becomes the limiting factor in achieving extended bass response.

The servo-controlled system also has the capability to correct for non-linearities in the low­frequency driver itself. At Avalon Acoustics, we believe that the superior approach is to use a well
designed driver that needs no correction, just as a well-designed amplifier can be built with no
negative feedback.

Concerning transient response, there is no advantage to using either of these systems compared
to a non-equalized system. This is because the transient response merely describes an alternative
view of the frequency response. In other words, by utilizing a servo-controller adjusted to obtain
the perfect transient response of a sealed enclosure with a Q factor of 0.5, the frequency response
will necessarily be the same for both systems, regardless of how that response is attained.
Although these electronic methods allow for easier adjustment of the system parameters, most
systems are designed for impressive anechoic frequency response at the expense of accurate
transient response.

9.8 Rationale

There is an old saying, "There's no such thing as a free lunch." There are many trade-offs in
speaker design, as in almost any area one can think of. In this case, the trade off is between
transient response and anechoic frequency response (the speaker's frequency response in an
anechoic chamber). Almost all manufacturers have chosen to sacrifice transient response for
improv ed anechoic frequency response.

At Avalon Acoustics, we have chosen to pursue a goal of complete freedom from resonances
and stored energy to ensure transient accuracy. Although this results in a slight sacrifice in one
traditionally measured area, we feel that the resulting gain in areas not traditionally measured
results in audibly superior overall performance.

38

Anechoic Frequency Response vs. In-Room Frequency Response

It must be remembered that very little listening actually takes place in anechoic chambers.
Placement of the speakers in a real-world listening room will boost the bass response of the
speaker, as explained in Section 8, Room Acoustics and Speaker Placement, beginning on page

19. Since a loudspeaker with perfectly flat anechoic frequency response will exhibit a low­frequency boost in a normal listening environment, a loudspeaker with a gradual bass roll-off (in
an anechoic chamber) can exhibit more accurate in-room frequency response. Avalon Acoustics
loudspeakers are carefully designed taking these factors into account. When placed in a variety
of representative positions in the room, Avalon loudspeakers will produce deep, accurate, and
unexaggerated bass response, with complete freedom from stored resonant energy.

9.9 Measurements of Audio Equipment

It should be recognized that measurements are not the final arbiter of sound quality of audio
components. Often times a measurement standard has evolved because it is easily performed,
or because it is easily repeatable, or it has shown some link to certain audible characteristics.
Unquestionably, it is the latter criterion which is the most important one. After all, the listener is
not concerned with how a piece of audio equipment measures, he is only concerned with the
faithful recreation of the original musical event.

On the other hand, measurement techniques that correspond to audible effects are an invaluable
tool to the designer. However, it is the degree of correlation with the subjective experience
which is important, and anechoic bass response does not have a high correlation with musical
accuracy in the listening room. In-room frequency response and transient accuracy are both
significant factors in determining subjective quality. Nevertheless, anechoic frequency response
is by far the most prevalent measurement used to characterize speakers.

A Correlation with Amplifier Measurements

A striking parallel exists in the measurement of audio amplifiers. The power output and
distortion of an amplifier is invariably measured into an eight-ohm resistor. It is widely
acknowledged that this standard is far removed from the actual conditions in which the amplifier
will be used. One doesn't listen to resistors, one listens to loudspeakers, and the load that the
speaker presents to the amplifier is nearly always highly reactive (varies with frequency). The
eight-ohm resistive load has developed as a standard because it somewhat approximates a
speaker load, is easily reproducible by different testing facilities, and it represents something of a
lowest common denominator. That is, while everybody recognizes that a different load should
be used for amplifier testing, nobody can agree as to what that alternative should be.

In the last decade, there has been a growing awareness of the importance of an amplifier's
capability to drive a real-world loudspeaker. This is the reason we have seen the emergence of
amplifiers with high current output capabilities, and a lack of current-limiting or similar protection
circuitry. The ability to drive reactive loads has been accepted as having a higher correlation
with audible qualities than the traditional measurement into a load resistor.

Note: The cynic will also note that a resistive test load produces the most impressive measurements for use in

advertisements.

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Loudspeaker Measurements

Returning to loudspeakers, a similar situation has developed. Although nobody listens to music in an
anechoic chamber, loudspeaker measurements are commonly performed in them (1). Although various
proposals have been made for performing low frequency measurements in a more realistic setting, there
has been no agreement as to what that setting should be. Loudspeakers continue to be measured in a
test chamber that is equivalent to the absence of any room at all.

There is a developing appreciation that this traditionally performed measurement is not an accurate
predictor of the performance actually attained in the listener's room. Certainly, in-room frequency
response is more important than anechoic response in determining a speaker's tonal accuracy.
Placement of the speaker within a room will cause changes in the frequency response compared to the
anechoic conditions (2). At lower frequencies, the speaker's output is modified by the acoustic loading
presented by the walls and floor. However, when making measurements, it is difficult to separate the
effects of a room's bass reinforcement from standing waves and other resonances associated with that
room.

Designing for Accurate Bass Reproduction

How, then, does one arrive at the goal of a loudspeaker that provides tonal accuracy in the listening
room? The answer, in large part, comes in the form of the digital computer. It is possible to create a
mathematical model of a listening room, and predict the response of a given speaker in that room. With
the computer model, it is quite easy to change the position of the speaker in the room, or other
parameters of the model. In this way, a composite picture can be created of a wide variety of rooms and
speaker locations. This enables one to design the speaker so that it interfaces properly with the listening
environment and prov ides correct bass response in real-world environments.

The accuracy of the computer model must also be tested in the physical world, using pink noise, warble
tones, and time-delay spectrometry for verification. The final, and most important check, is the listening
test. Theory and measurements become useless if they do not agree with what our ears tell us. Even
the best measurement methods provide little more than a simplified, one-dimensional translation of what
is, in reality, an extremely complex, multi-dimensional experience. Again, the goal is the recreation of a
musical event, and the faithfulness of that recreation can only be determined through listening.

1 Since an anechoic chamber which performs accurately to low frequencies is extremely large and expensive,

other measurement methods are also commonly used. These include near-field measurements, when the
microphone is extremely close to the driver, and half-space measurements, when the speaker under test is
buried with its front baffle flush with the ground, facing upwards. Both of these methods are equivalent to
anechoic measurements below the frequency at which the speaker baffle appreciably changes the acoustic load
to the woofer, typically between 100 and 200 Hz. Note that these conditions are also non-representative of an
actual listening situation.

2 Since this discussion is concerned with the reproduction of low frequencies, we will not delve deeply into the

high-frequency variations between the anechoic response and the in-room response of a loudspeaker. Briefly,
the interaction of the dispersion pattern of the speaker with the reflective surfaces in the room (and the variation
of both with frequency) creates an in-room frequency response that may vary markedly from the anechoic
response.

40

9.10 Listening Qualities

We have seen how many speaker systems store resonant bass energy, resulting in ringing and
poor transient accuracy. We have also seen that a sealed enclosure with a Q factor of 0.5 can
yield complete freedom from energy storage effects, as well as provide more accurate in-room
frequency response. Now we will turn our attention to the listening experience, and describe how
these measurable properties correlate with our subjective impressions.

There are two main factors which affect subjective low-frequency accuracy, frequency response
and transient response. At low frequencies, these two descriptions are different aspects of the
same event. (1) Nevertheless, for the purposes of this discussion, we will treat these two topics
separately as much as is possible.

Frequency Response Effects

As you listen to music, images of the instruments that created the sounds are elicited. For
instance, one can tell the approximate size of a drum from the sound it produces. On a high­resolution playback system, finer details can be heard; i.e., is the head made of plastic or
calfskin? Is the player using light sticks or heavy ones?

A relatively broad-band emphasis (or de-emphasis) of a given frequency range can tend to
exaggerate (or diminish) the relative size of the instruments playing in that range. A useful tool
for evaluating these distortions of size is a recording of a small group of unamplified acoustic
instruments made with a simple microphone set-up. One superb example is the series of
acoustic jazz recordings available from Chesky Records. These are made with a single-point
stereo microphone, and feature a photograph of the recording session that shows the location of
the players.

Listening for Size Distortions

Play a recording of this type, with the volume adjusted to achieve a natural playback level. As
you listen, create a mental image of the players based on sounds being recreated. Then ask
yourself, "Does this sonic image correspond to the musical instruments that generated these
sounds?"

Is the portrait a natural one, or are certain elements distorted? Does a stand-up bass sound like
the correct size, or is it exaggerated, sounding like it is ten feet tall, or as if the strings are the
size of ropes? A speaker with excessive in-room bass response can create these effects. On
the other hand, a speaker system with rolled-off bass can shrink the size of instruments, turning
the same stand-up bass into a cello-sized instrument.

1 Below about 200 Hz, virtually every woofer operates as a minimum-phase device. This means that the

responses in the time-domain and the frequency-domain are inextricably linked, and that the one generates the
other. Thus, two woofers with the same frequency response will necessarily exhibit the same time (phase)
response. However, many crossover networks display non-minimum phase response, and will thereby alter the
phase response of the woofer in the speaker system.

41

Transient Response Effects

A speaker with poor transient response will store energy, releasing it after the initial musical
transient has passed. This causes a loss of detail and obscures important musical information.
Also associated with poor transient response is a narrow-band resonance, which can emphasize
specific notes.

When listening for the low-frequency transient accuracy of a speaker, it will be useful to utilize a
broad variety of recordings. Try playing a rock or jazz group, and listen to the interplay between
the drummer and the bassist. Is it easy to distinguish the kick drum from the bass, or is there a
blurring of low-frequency detail caused by the speaker's time-smear?

To listen for narrow-band low frequency resonances, use a recording with the bass line played by
a synthesizer. As you listen to the bass line, are the individual notes of equal level, or are some
of them more prominent than others? Electronic instruments can be more useful for this test
since acoustic instruments have resonances of their own which can hide flaws in the speaker,
unless you are intimately familiar with the instrument and the recording. Similarly, an electric
bass that has been recorded by miking its speaker/amplifier will exhibit the resonances of its
speakers, which are inevitably considerable, masking defects in the loudspeaker under
evaluation. (1)

9.11 Conclusion

Most loudspeakers have been designed to perform well in the frequency domain when measured
in an anechoic test chamber. We have seen how this design paradigm produces audible bass
distortion and exaggeration. W hile these exaggerations may sometimes seem impressive in the
short term, they quickly prove to be distracting from the musical intentions of the composer. At
Avalon Acoustics, we design all of our speakers to produce transient-perfect bass response. As
you listen to music on Avalon Acoustics loudspeakers, your enjoyment of the music will grow as
you hear the full measure of low-frequency detail, without exaggeration, and come close to the
heart of the artist's intent.

1 There is a technique known as "direct injection" where the signal from an electric instrument is connected

directly from the amplifier to the recording console, bypassing the speakers. In this instance, an electric bass
will prove to be a consistent low-frequency source. The difference between direct injection and miking of the
speaker/amplifier is easily audible with high-quality speakers.

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10 Features

Advanced light weight driver diaphragm materials minimize energy storage and time domain distortion.
Each driver individually tested and matched for optimum performance.
Moderate impedance characteristic allows for ideal interface with any amplifier.
Star-grounding techniques eliminate signal modulation.
Crossover circuitry is hard-wired with surface-only conductors, eliminating deleterious sonic effects of printed-circuit
boards.
Oxygen-free copper conductor air-core coils provide ideal inductor properties.
Oversize screw terminals allow access to individual crossover section inputs, allowing bi-wiring.
Crossover coils carefully oriented to minimize interaction of magnetic fields.
Polypropylene capacitors used exclusively to minimize energy storage.
Proprietary damping circuit controls the tweeter’s electrical parameters, reducing interaction with the amplifier.
Encapsulated crossover circuitry to prov ide isolation from vibrations.
Constrained-mode damping system absorbs cabinet vibrations.
Three and one-half inch thick front panel supplies acoustically inert wave-launch platform.
Acoustically-engineered grille assembly decreases edge diffraction effects.
Distinctive faceted cabinet design provides optimal polar characteristics.

Specifications

Driver Complement I" titanium dome tweeter

8 1/2" Nomex-Kevlar composite cone woofer

Sensitivity 85 dB (2.83V, I meter)

Impedance 6 ohms (5.5 ohms minimum)

Frequency Response 45Hz to 24kHz (+/- 1.5 dB, anechoic)
(In room, typical -3 dB point is below 35Hz)

System Resonance Q=0.5

Recommended Amplifier Power 30 to 200 watts

Wiring Methods Four position terminal block
(providing bi-wiring options)

Dimensions 34" high
9 1/2" wide
13" deep

Weight 65 pounds (each)

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