ALESIS M1 Active Mk2 User Manual
REFERENCE MANUAL
© 2001-2005 ALESIS CORPORATION
™
Alesis M1 Active Mk2 Reference Manual
© Copyright 2001-2005, Alesis Studio Electronics, Inc. All rights reserved.
Reproduction in whole or in part is prohibited. “M1 Active Mk2” and
“Superport” are trademarks of Alesis Studio Electronics, Inc.
ALESIS CONTACT INFORMATION
Alesis Studio Electronics, Inc.
www.alesis.com
Do not use this address for repair service.
E-Mail: info@alesis.com
Website: http://www.alesis.com
Contents/Safety Warnings
CONTENTS
Introduction 2
A
BOUT THE M1 ACTIVE MK2 ...............................................................9
Unpacking and Inspection 9
Inside your new speakers 10
About Nearfield monitoring 15
S
PEAKER INSTALLATION.................................................................... 17
Avoiding reflections in the studio 17
Stereo nearfield placement of the M1 Active Mk2 20
Connections 26
Setting the Input Level control 28
S
URROUND SOUND ............................................................................ 31
About surround sound 31
Center speakers in music mixes 32
Placement of the center M1 Active Mk2 speaker in the studio 33
Placement of rear surrounds 34
Mixing for discrete six channel reproduction: matched vs. specialized speakers
T
ROUBLESHOOTING ...........................................................................39
Troubleshooting Index 39
Maintenance 40
S
PECIFICATIONS ................................................................................42
Enclosure 42
Transducers 42
Crossover section 43
Amplifier Section 43
Acoustic Section 43
General 43
I
NDEX.............................................................................................. 44
37
M1 Active Mk2 Reference Manual 1
Contents/Safety Warnings
INTRODUCTION
Thank you for purchasing the Alesis M1 Active Mk2 Biamplified Reference
Monitors. To take full advantage of the M1 Active Mk2’s operation, and to
enjoy long and trouble-free use, please read this user’s manual carefully. We
value any comments you may have about this monitor system, this manual,
your Alesis dealer or our factory service. Please take a minute now to fill out
your warranty card and tell us what you think.
HOW TO USE THIS MANUAL
This manual is divided into the following sections describing the various
features of the M1 Active Mk2. Though we recommend you take time to read
through the entire manual once carefully, those having general knowledge
about monitors should use the table of contents to reference specific
functions.
Chapter 1: About the M1 Active Mk2. Engineering specifications and
reasons why nearfield monitors have become so popular.
Chapter 2: Speaker Installation.
M1 Active Mk2s to a mixer or other line-level source and discusses proper
speaker placement for stereo operation.
Chapter 3: Surround Sound. If you are using the M1 Active Mk2 speakers in
a multichannel surround sound setup, you’ll find helpful setup and operation
information here.
Chapter 4: Troubleshooting. This chapter contains troubleshooting tips and
service information should problems occur.
This chapter explains how to connect the
✪ When something important appears in the manual, an icon (like the
one on the left) will appear in the left margin. This symbol indicates
that this information is vital when operating the M1 Active Mk2s.
2 M1 Active Reference Manual
About the M1 Active Mk2
CHAPTER 1
ABOUT THE M1 ACTIVE MK2
UNPACKING AND INSPECTION
Your M1 Active Mk2 Biamplified Reference Monitors were packed carefully
at the factory, and the shipping carton was designed to protect the speakers
during shipping. Please retain this container in the highly unlikely event that
you need to return the speakers for servicing.
The shipping carton should contain the following items:
• This instruction manual
• M1 Actives with the same serial numbers as shown on the shipping
cartons
• Two AC power cords (NEMA to CEE type)
• Alesis warranty card
filled out your warranty card and mailed it back to Alesis, please
take the time to do so now.
M1 Active Mk2 Reference Manual 9
✪ It is important to register your purchase; if you have not already
The M1 Active Mk2s are designed as mirror-imaged pairs. If you have
received a pair where the tweeters are both on the same side, contact your
dealer immediately.
About the M1 Active Mk2
INSIDE YOUR NEW SPEAKERS
✪ If you’re in a hurry to get started, skip ahead to Chapter 2,
“Speaker Installation”, for connection and placement tips.
ABOUT POWERED MONITORS
The M1 Active Mk2s combine a speaker and amplifiers in the same compact
cabinet. Powered monitors are growing in popularity over the traditional
separate amplifier and speakers for a number of reasons, convenience and
ease of hookup being only one of them. You can connect a powered speaker
directly to any line-level source (normally, the control room output of a
mixer) simply by connecting a patch cord.
Another benefit is improved sound quality. With careful design, the speaker,
amplifier and electronic crossover can be optimised for each other. The M1
Active Mk2s are biamplified, meaning that low frequencies and high
frequencies are handled not only by separate speakers (the tweeter and the
woofer), but by separate amplifiers. A pair of M1 Active Mk2s contain a total
of four power amplifiers. Because of the increased efficiency of
biamplification, these are much louder than a single-channel power amplifier
of the same wattage feeding a passive crossover, as in other designs. New
technology makes it possible to make these high-wattage amplifiers small
enough to fit inside the speaker cabinet, with very little weight or size gain.
Since the M1 Active Mk2s are self-powered, DO NOT connect them to
the speaker output of another amplifier (such as a powered mixer or hifi receiver). Connect them only to the line-level outputs of such devices
(+4 dBu nominal, +24 dBu maximum).
10 M1 Active Reference Manual
About the M1 Active Mk2
TONE
Tonally, every effort has been made to create a powered monitor that is as
linear as possible, representing a flat frequency response from 50Hz to 20KHz
±2dB. (see p. 21) Additionally, the use of electronic crossovers within the
critical upper midrange frequencies has reduced phase and time delay
anomalies often associated with passive crossovers. By including discrete
woofer and tweeter amplifiers and application-specific electronic high and
low pass crossover filters in the same enclosure the tonal accuracy of the M1
Active Mk2 will always remain constant.
ABOUT THE DRIVERS
The M1 Active Mk2’s 6.5” woofer cone is made of proprietary non-woven
carbon fiber. This material is 25% lighter than polypropylene with twice the
stiffness for quicker transient response in the low-to-midbass region and
vastly improved midrange intelligibility (over polypropylene at 2000 Hz).
The non-woven carbon fiber cone, along with the closed cell synthetic rubber
surround, are both nearly impervious to ozone, direct sunlight, heat and
humidity. Therefore, after an initial break-in period, the sound should remain
virtually unchanged for the life of the product.
Alesis’ proprietary-design tweeter features a special wave guide baffle to
improve polar response, a silk dome, and low viscosity ferrofluid formulated
specifically to retain the best balance of transient response to power handling.
The shielded tweeter utilizes a vented pole piece with a separate rear
chamber to lower the free air resonance. The low 2000Hz crossover point of
this tweeter produces a very widely dispersed, low-distortion signal within
the critical midrange frequencies. It is these frequencies which are often the
most problematic to get “right” during a mix. The tweeter is designed for an
optimal response for non-fatiguing, long term, high level, nearfield
mixdowns. This design results in a flat, linear mix when played back on home
or car systems from appropriate distances.
MAGNETIC SHIELDING
Your M1 Active Mk2s are at home in recording environments wherein video
is a major component. They are magnetically shielded for use in fairly close
proximity (3” minimum) to a computer monitor or video screen. (Nonshielded components can make the colors of a screen “smear” or appear out
of focus if the speaker is too close.) Magnetic shielding was designed into
both the woofer and the tweeter from the beginning so that the system
exhibits about low magnetic leakage. Shielding of both the woofer and the
tweeter is accomplished by the use of a second opposing-field-oriented
“bucking” magnet.
M1 Active Mk2 Reference Manual 11
About the M1 Active Mk2
THE M1 ACTIVE MK2 BI-AMPLIFIERS & ELECTRONIC
CROSSOVERS
The M1 Active Mk2 uses a 75W woofer amp and a 25W tweeter amp along
th
with 4
order high and low pass electronic crossover filters centered at
2000Hz. Electronic crossovers, which separate the frequencies before being
sent to the amplifiers, have fewer phase problems and less power loss than
the traditional passive crossover used after the amplifier. Fourth-order filters
are steep (24 dB per octave), which minimizes the interaction between woofer
and tweeter near the crossover point. Additionally, the high pass (tweeter)
section of this system employs an electronic time alignment circuit. Thus the
“launch” of frequencies from both the woofer and the tweeter will originate
at exactly the same time.
There are several advantages to using built-in amplifiers and active
(electronic) crossovers versus a passive network system, most of which have
been previously enumerated in Vance Dickason’s “Loudspeaker Design
Cookbook”:
• Lower intermodulation distortion due to amplifier operation over a more
narrow bandwidth. Also, clipping caused by low frequency overload is
reduced, being limited to only one driver within a two driver system.
• Increased dynamic range. The M1 Active Mk2’s 75W and 25W amplifiers
in their bi-amp setup will clip at about the same levels as one 200W
amplifier operating into a passive crossover.
• Improved transient response.
• Better amplifier/speaker coupling for woofers.
• Better crossover performance working into a constant impedance load.
• Better subjective sound quality than high level (passive) networks.
• Easier control over driver sensitivity differences.
• Easier manipulation of phase, time delay, resonance, and various kinds of
shaping, contouring and equalization.
• Specifically in the case of the M1 Active Mk2, the wide, mid-frequency
polar response of the tweeter can be utilized down to a low 2000 Hz
thereby mating more cohesively with the 6.5" non-woven carbon fiber
(NWCF) woofer. This low crossover point is only possible through the use
of a steep, electronic fourth-order (24 dB per octave rolloff) high pass filter.
12 M1 Active Reference Manual
About the M1 Active Mk2
THE M1 ACTIVE MK2 POWER SUPPLY
The M1 Active Mk2 employs a regulated switching power supply. This type
of supply has previously only been available in amplifiers sold at the very
high end of the Pro Audio market.
Most power amp customers are familiar with the large transformer and
output capacitors in high quality amplifiers. These large components are
used to keep the amplifier’s supply rails as close to DC as possible. For
traditional supplies, bigger is better.
But by using Pulse Width Modulation (PWM) and output voltage feedback in
the M1 Active Mk2, we have the equivalent of near-infinite transformer and
output capacitors, but at a fraction of the cost. PWM provides protection
from line voltage surges that would otherwise destroy the amplifier. No
user-replaceable fuse is required because nuisance tripping is eliminated.
And finally, PWM practically eliminates hum because the line frequency (60
Hz) transformer is replaced with a very high frequency (130,000 Hz)
transformer.
The regulated supply rails increase the amplifier dynamic range and reduce
clipping distortion under heavy loading. The compact size of the supply does
not significantly reduce the internal air volume of the speaker cabinet. And
lastly, full power can be maintained even with low or “flat-topped” line
voltages.
Note, however, that this switching supply is NOT a universal voltage
type that may be used with any input voltage in any country simply by
changing the cord. If you wish to use the M1 Active Mk2s in a country
whose line voltage is other than 120 volts AC, they must be internally
modified or used with a step-down transformer.
THE CABINET AND PORT DESIGN
The M1 Active Mk2 cabinet construction employs vinyl composite material
laminated to a .625” MDF (medium density fiberboard) core for the four sides
and the rear. The front panel is 1” thick MDF, to withstand the greater
demands of the drivers mounted on it. The entire cabinet is braced
extensively in random fashion to dissipate intramodal vibration.
M1 Active Mk2 Reference Manual 13
About the M1 Active Mk2
WHY THE TWEETERS ARE OFFSET
The M1 Active Mk2 speakers have been developed as a mirror-imaged pair
with dual front mounted ports and an offset tweeter. In some applications,
an extremely wide dispersion tweeter, such as used in the M1 Active Mk2,
will exhibit response dips if mounted exactly on center. Wave-guide style
tweeters, used in other products, purposely limit dispersion and thus can be
center mounted. But as hi-end audiophile speaker companies have found, a
high quality dome tweeter, offset in the cabinet toward the stereo “image
center” (between the left and right speakers) will have a flatter characteristic
frequency and power response. This (flat power response) more closely
characterizes the way humans hear.
On a horizontal polar response curve of the M1 Active Mk2, with the cabinet
placed vertically, the tweeter response at one meter stays essentially
symmetrical on either side of the cabinet’s centerline. This is because the
angle subtended between the cabinet-centerline-to-tweeter-centerline (.5”),
and the nominal nearfield listening distance (1 meter or 39.375”), is only 1.27
degrees. Thus, acoustically speaking, the offset tweeter design has no
negative effects, only the positive of smoothing the frequency response in the
2KHz-4KHz range.
In the tradition of the Alesis Superport design, which uses the energy from
the back of the speaker to enhance bass performance, the M1 Active Mk2s use
dual, front baffle mounted, long folded ports. The dual ports on the M1
Active Mk2 are also non-symmetrical with relation to their distances from the
woofer. In developing the M1 Active Mk2, Alesis engineers determined that
dual ports, offset to the outside of the stereo image center gave the most
coherent and extended low bass augmentation. The ports are flared on the
front baffle to provide smooth and quiet exit airflow while inside they are cut
with a 45° angle and faced toward the amplifier’s internal heat sink. This
arrangement aids in keeping the internal amps working at a more constant
temperature. At the same time, this 45° angle increases the port’s air entry
efficiency.
14 M1 Active Reference Manual
ABOUT NEARFIELD MONITORING
In the early days of recording, most recording studios used big monitor
speakers almost exclusively. Unfortunately, they also required high powered
amplifiers and expensive acoustic treatment (often poorly done) of the entire
control room. Still, a well-constructed big monitoring system really was
impressive to listen to, a fact not overlooked by the studio owners who
wanted to impress the record company executives who paid for the big
studio's time. These big systems had big level control knobs, and clients
enjoyed "cranking-up" the volume. Fortunately, recording engineers and
producers eventually learned that this was not the best way to accurately mix
music because it wasn't the way most people listened to their radios, cassettes
and CD players. Also, big monitor systems and the costs for the required
control room acoustic treatments were going through the roof (no pun
intended), particularly beyond the budget limits of smaller project and home
studios which were growing in numbers. A new way of accurate monitoring
was needed: nearfield monitoring.
Nearfield monitors, by their definition, are intended for mounting close to the
listener. The idea here is to improve the direct acoustic path between the
speaker and the listener by making it shorter, thereby giving less opportunity
for the always present indirect (reflected) sounds to get back in and muddle
things up. With nearfield monitoring, the surrounding acoustic environment
becomes a much less significant factor in establishing the monitor system's
sound character.
A good set of small monitors properly placed in a reasonably non-reverberant
room and properly powered will yield surprisingly accurate results at budget
prices. Carried to another studio, the same monitor should also provide
repeatable results. In fact, some recording engineers carry their own speakers
around because they know how they will sound in almost any room. Now,
even the big studios use smaller speakers to augment their big monitoring
systems, and nearfield monitors have become proven tools in the recording
business.
About the M1 Active Mk2
M1 Active Mk2 Reference Manual 15
About the M1 Active Mk2
16 M1 Active Reference Manual
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