Advent The Advent Loudspeaker Brochure
The
Advent
Loudspeaker…
and The Smaller
Advent Loudspeaker
First of All, Who and What Is
Advent?*
Advent Corporation is a new company formed to
develop new kinds of home entertainment products. Most
of us involved have had long prior experience in making
and marketing high-performance audio products for the
home. We are in business now to produce new home entertainment products, both audio and visual, that go well
beyond the generally limits generally accepted at any
given moment, and explore new or significantly different
approaches to design. One of our main product objectives
is a color television system that uses a projected image
instead of a conventional picture tube, producing a picture
of 41/2 by 6 feet.
Our President and General Manager, Henry E.
Kloss, was previously President and a founder of KLH
Research and Development Corporation, and, prior to that,
General Manager and a founder of Acoustic Research,
Incorporated. He has been directly responsible, over the
past fifteen years, for a major proportion of the important
and lasting audio products for the home, including roughly
half of the total number of loudspeaker now in use across
the country in component stereo systems and high-performance three piece music systems, radios and phonographs. His credits would be embarrassingly long to present complete, but they include:
• The longest lived best selling component speaker system on the market, unchanged in design and undiminished in popularity after twelve years.
• The revolutionary miniature full range speaker
that made it possible to provide sound of high quality in
radios and phonographs of modest size.
• The first high performance FM radio.
• The first high performance portable stereo
phonograph.
• The development of the three piece compact
stereo system as a primary medium for home audio.
All of us at Advent share with him some convictions developed over several years of working together,
about the way in which products can and should be developed. The Advent Loudspeaker is one result of those convictions, and we will have some more to say about them as
we describe the speaker.
What is the Advent Loudspeaker?
Our first Product, the Advent Loudspeaker, is
based on a premise that is not easy to accept. We believe
that it is possible to produce a speaker system, for a moderate price, that will be nothing Iess than the right, completely satisfying choice for most people with a demanding
interest in music and sound. The Advent speaker is
designed to combine the following objectives:
• To fit the highest category of loud speaker quality, with overall performance at least the equal - in every
audible and useful respect - of the most expensive speakers available.
• To do that for about half the average cost of the
speakers now generally considered the best available.
• To be small enough, unobtrusive enough, and
uncritical enough in placement to fit gracefully and usefully into a home.
• To produce enough output at low distortion to
permit listening to music at satisfyingly loud levels in even
the largest living room.
• To be driven comfortably by the majority of
good amplifiers and receivers now available, with a power
margin sufficient for the most demanding musical material.
• To sound convincing not only on the best recordings, but on the great majority of recordings of all kinds.
In developing the Advent Loudspeaker, our initial
interest was in the category just below the “ultimate” in
performance and a long way below it in price - the category in which most serious listeners, believing that further
improvements are not worth the added cost, decide to buy.
We knew that we could produce a speaker that would be
both significantly better and significantly less expensive
than the speakers considered the best value in that category. Our aim was to do that and establish a new point of
diminishing returns that would be closer to the highest
level of speaker performance.
But as we began to apply some new thinking
about old concepts and to take advantage of new materials
and manufacturing techniques, it became really clear that
we could provide a really tremendous gain in performance-per-dollar. So much, in fact, that the difference
between something very good and the highest level of performance was essentially nonexistent in actual cost. It
made no sense, then, to stop short of a speaker in the best
category.
We didn’t stop short of that point. As difficult as it
may be to believe of a speaker system of this cost and
apparent simplicity, we know of no way to make any useful improvement in its performance.
*About our name: When you form a new business, and are eager to get on with things before the lawyers get all the papers signed
and the incorporation proceedings over with, you (our) lawyers call you “an advent company”. We decided the term suited our continued desire to get on with things, so we appropriated it for our permanent company name.
How is all that possible?
The performance of the Advent Loudspeaker is
due in great part to some important specifics of design and
construction. But the key to all of them, and to the entirely
new level of value the system represents, is that it is the
first loudspeaker system to exploit the full potential of two
way loudspeaker design.
For just about as long as home audio has been of
real importance, it has been assumed that the three-way
speaker system, which assigns at least one specialized
speaker to each of the three segments (low, middle, high)
of the frequency range, is a necessity for optimum sound.
The two-way system has been accepted as a “good” medium-price expedient, but the idea of extra speakers and further specialization for optimum quality fits in both with
the idea of separate, specialized audio components and
with the widespread feeling that “more is better”. But the
superiority of the three-way system is one of those
“absolutes” that remain true only so long as no one really
challenges them. After a thorough review of today’s materials and manufacturing technology, we knew that the old
assumption no longer need be true.
The trouble with the concept of the three-way system - a crucial one - is that it’s based on the limitations of
an earlier generation of loudspeakers. When high fidelity
first gained wide interest for home listeners, the only suitable speakers available for use in a home audio system
were those used in theater and public address systems. The
individual speakers in theater systems were specialized
and restricted in range for the purpose of maximum powerhandling to fill large public spaces, and they converted to
full-range use in home systems only in three-way designs.
As new cone materials and new techniques were
developed specifically for home loudspeakers, the need for
three-way systems has disappeared. It’s simply no longer
true that if a woofer is to be able to deliver excellent bass
response, it will not have enough mid-range output, or that
a tweeter can not combine excellent high frequency and
mid-range response. Nor is it true that the three-way system is somehow capable of wider range or subtler characteristics.
Today’s three-way systems fall into three categories:
• Those that sound genuinely excellent.
• Those designed that way because of the severe
limitations or their individual (and outmoded) drivers.
• Those that simply throw in an extra speaker or
two because It looks better as a selling point.
Of these three, only the second has to be a three-
way system.
The Two-Way System
We began the design of the Advent Loudspeaker
with the knowledge that the two-way system had basic
advantages, both theoretical and practical, over any other
way of designing a full range speaker system for the home.
They include:
• Less interference between drivers than any other
practical system, Yielding more uniform characteristics
over the listening area. A single speaker would be better
here as an ideal, but lacks either the range or power-handling required in the ‘“best”’ category, or both.
• A better transition between drivers than the
three-way system, because there is no need to sharply cut
off the operating range of any driver. Whether such a cutoff is made for good reasons or simply to satisfy the arbitrary parameters of three-way design, its ill effects are
audible.
• One simple crossover network instead of the two
more complex networks needed in a three-way system.
• A cost significantly lower for excellent sound
than that of an equivalent system of three-way - or any
other - design.
Those advantages are important enough in themselves, but there is an overall advantage that seems even
more important to us. It is that simplest feasible approach
to an objective produces the best kind of engineering - a
concept not too far from the notion that the shortest distance between two points is either a straight line or the one
that is straightest under the circumstances “Over-engineering is a common problem in audio equipment, and one for
which the customer often pays heavily in many ways.
Good design to us is represented by the simplest approach
that permits reaching an objective without compromise,
not by an over-elaboration that makes the buyer pay for
our painting the lily.
If the two-way system has effective limitations,
they apply to the tremendous power-handling required for
use in a theater auditorium or in some laboratory applications. An extra driver provides (all other things being
equal) both greater power-handling for these purposes, and
the extra radiating area helpful both for radiating power
and dispersing sound over a large public area. But those
are the only significant limitations of two-way design.
They have no importance in the design of the best possible
speaker system for use in a home.
The Specifics of the System
The Advent Loudspeaker is a “system” in the
fullest sense of the term. All of its components, including
the cabinet, have been designed from the outset for no
application other than this one, and all of them are interdependent. That interdependence is worth stressing here. The
relationship of cabinet size and speaker size, for instance,
is critical. If the size of the low frequency driver were
increased (all other things remaining equal), the result
would be less bass: a larger driver in the same cabinet
would raise the effective stiffness of the air in the enclosure and would establish a higher bass roll-off frequency.
Some other factors are equally important and we
will try to make them clear as we go along.
The Low-Frequency System
The operating range of the low-frequency driver
extends from the lowest frequency of musical importance
to the upper crossover point of 1,000 Hz. To achieve this
objective, we chose to build the driver on a standard 12inch frame that provides at low cost the width and frame
depth needed for maximum cone excursion at lowest frequencies and highest power. The piston diameter of the
cone combines maximum usable response at 30-35 Hz
with a maximum of dispersion in the upper part of the
operating range.
The driver’s capabilities at lowest frequencies is
made possible in great part by a new outer suspension
design of thermally-formed fiber-reinforced poly-urethane.
The new suspension, a highly durable and reliable centering design, permits long linear cone motion, yet remains
an effective airtight seal that maintains the full operating
effectiveness of the system’s sealed cabinet. In the
acoustic-suspension design used for low frequencies in the
system, the mechanical rigidity of conventional suspensions is replaced by a combination of a free-moving suspension and the stiffness of the air trapped inside a sealed
enclosure. For optimum performance both at first and over
years or continuous operation, the free moving suspension
of the speaker should have no tendency to develop air
leaks, however small. The new suspension of the Advent
Loudspeaker is more effective than any in our experience.
The felted cone of the low frequency speaker is
formed by a low-vacuum process developed to assure high
uniformity from speaker to speaker and the proper resistance to the transmission of excess energy through the
cone, (The “live” energy-transmitting cone still used in
many speaker systems is a prime source of the kind of distortion generally called cone “break-up”). The composition
of the cone is as important as any other factor in achieving
the smooth operation of the driver in the upper part of its
range.
The heavy magnetic structure of the low-frequency driver is designed to provide “critical damping” for the
speaker in its specific cabinet volume - that is the amount
of damping that could not be increased without rolling off
bass response unnecessarily). (Like everything else in
speaker design, the improvements secured from increasing
the weight and flux density of a magnet go only so far;
increasing beyond that point just rolls off bass response).
Also part or the magnetic system is a double-wound, fourlayer voice coil that is significantly longer than the magnetic gap in which it operates. This is to allow a uniform
portion of the coil to stay in the gap at all times, even
when cone and voice coil make their longest excursions,
and is a vital factor in keeping bass harmonic distortion
low at even the highest listening levels.
The efficiency of the system has been carefully
chosen to provide for reproduction of the lowest usable
frequencies with amplifiers and receivers of good quality
and medium power. While efficiency is lower than that of
some comparably priced speakers of more limited range,
and will require a slightly higher setting of a volume control for the same acoustic level, it is no more likely to tax
the actual power capabilities of the amplifier or receiver
used in a home. This doesn’t hold for auditoriums or, in
many cases, for large (and sometimes noisy) audio showrooms, but it is emphatically so for home listening at even
the highest usual loudness levels.
The Advent Low-Frequency Driver
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