Me WM8 Installation Instructions Manual

Marchand Electronics Inc.

PO Box 18099, Rochester NY 14618

Tel:[phone] Fax:[phone]

[e-mail] www.marchandelec.com

(c)1997....2005 Marchand Electronics Inc.

WM8 Installation Instructions

CONTENTS

Specifications

Introduction

Installation
Separate Components
Biamping

Operation
Setting Qs
Setting Fs
Setting BOOST
Setting Qb
Vented Speakers
Final Adjustments

Technical Description
Circuit
Options

Assembly (kit version)
General Wiring Practice
PC Board Assembly
Chassis Wiring

Appendix A - Schematic Diagram
Appendix B - PC Board Layout
Appendix C - Chassis Layout
Appendix D - PC Board Parts List
Appendix E - Overall Parts List

Appendix F - Troubleshooting

SPECIFICATIONS*

Frequency Response
(Boost=0, Qs=Qb) 2 Hz-100kHz
Harmonic Distortion <.01% (1 kHz)
Signal/Noise Ratio >110 dB (Ref. 10 V)

Input Impedance 80 kΩ
Output Impedance 10 Ω

Maximum Output Voltage 25 V (P-P)

Output Load Capability 100 Ω (min.)

Bass Boost Range 0-24 dB
Net Q Range .25 - 1.0
Dimensions 17"W x 8.5"D x 3.5"H
*Specifications subject to change without notice.

INTRODUCTION

The BASSIS is a specialized electronic
equalizer which enables acoustic-suspension
(closed-box) loudspeakers to take on a wide
range of alternative bass responses improving
some vented (bass-reflex) designs.
By adjusting the front panel controls, the line­level audio signal is equalized as the exact
inverse of a given loudspeaker's bass response,
and the new bass cutoff frequency and damping
are defined. The filtered signal is then passed to
the power amp and on to the speakers, where the
existing bass response is cancelled and replaced
by the desired bass response. Figure 1 illustrates
the frequency response at various points in the
signal path.

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INSTALLATION

There are several ways of connecting the

BASSIS to you system, depending upon your
present setup. In any case, make sure all

components are turned off while making
connections, and read the rear panel labelling
carefully. Do not apply power to the unit when

installation is complete. You must make the
adjustments described in "Operation" first.
SEPARATE COMPONENTS
If you own a separate preamp/power amp
combination, you can use the arrangement shown
in Figure 1, where the OUTPUT from the preamp
is connected to the BASSIS' INPUT jacks, and
the BASSIS' OUTPUT jacks are connected to
your power amp's INPUTs. The BYPASS switch
removes the BASSIS circuitry from the signal path
by connecting the INPUT directly to the OUTPUT.
This allows easy evaluation of the equalizer's
effectiveness.
If you own an integrated amplifier or receiver
with PREAMP OUT and POWER AMP IN jacks,
the same connection as for separates can be
used.

MULTIPLE TAPE LOOPS

If your integrated amp or receiver has an
unused tape loop (or a dedicated signal­processing loop), you may connect the BASSIS
as shown in Figure 2, below.

Be sure to press the TAPE 2 MON button on your
receiver. You can remove the BASSIS from the
signal path in two ways now: (1) turn off the
TAPE 2 MON button on your receiver, or (2) use
the BYPASS switch on the BASSIS.

BIAMPING
If you wish to equalize the response of
independently amplified woofers or subwoofer(s),
you may use the BASSIS solely in the low­frequency signal path, using the arrangement in
Figure 4.

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OPERATION

The various controls on the BASSIS must be
adjusted to match your system's requirements
before power is applied to the unit. If the 24 dB
(factor of 16) maximum BOOST setting is applied
incorrectly, damage to your speakers and/or
amplifier may result.

SETTING Qs

Figure 5 shows the bass response of various
acoustic-suspension loudspeakers. If the
speaker's Q is greater than 0.7, the response may
reach a peak at the "resonant frequency", then fall
off at a rate of 12 dB/octave at lower frequencies.
If your speaker has a "boomy" or "heavy" sound,
then it is likely that it Q is in the "underdamped"
range from 1.0 to 1.6. On the other hand,
speakers whose Q is .5 or .6 will be "well­damped", with a "tight" or even "lightweight"
sound (due to the prematurely-falling bass
response).

speaker's value for Qs is .5, then Figure 5 shows
that its -3 dB point is near 1.6 x Fs. Thus, if your
specs indicate a -3dB poi9nt of 75 Hz, then a
setting of Fs = 75/1.6=45Hz should be used. On
the other hand if your speaker has Qs= 1.4
(boomy-sounding), then Figure 5 indicates its -3
dB point is near .65 x Fs. Hence if its
specifications indicate a frequency response like:
"52 Hz to 22 kHz + 3dB", then you should use a
setting of Fs + 52/.65 = 80Hz. Finally, if you
assume Qs = .7 for your speakers, then Fs
equals the specified -3 dB point.

You must adjust the Left and Right channel
controls labelled Qs (Speaker Q) according to
your own speakers' characteristics. (You will
ordinarily use the same settings for Left and Right
channels.) Choose a value which approximates
the damping for your speakers, as suggested
above. If in doubt, use a setting around .7,
corresponding to the value most speaker
designers aim for. You can later fine-tune the
setting if necessary.
Setting Fs
You must now set the Left and Right channel
Fs (Speaker Corner Frequency or -- less
accurately -- Resonant Frequency) controls. If
you have frequency response specifications for
your loudspeakers of the form:"55 Hz to 18 kHz +
3dB" or ".3 dB point at 75 Hz", you can
approximate Fs by making use of Figure 5 and
your estimate for Qs. For example, if your

If you have no frequency response specs for
your loudspeakers, or if the specs are of the form
"50 Hz to 20 kHz" (without + x dB limits) then you
will have to estimate Fs. Most medium-size
"bookshelf" speakers have Fs around 65 Hz;
compact speakers (enclosure less than 14" high)
may have Fs closer to 80 Hz; large speakers
(greater than 30" high) may have Fs around 40­50 Hz. For those tiny die-cast speakers like
Radio Shack's Minimus 7, try a value of 100 Hz or
higher for Fs, with Qs around .8 or .9.
While these settings are not too critical, it is
important to get in the ballpark of the correct
setting before using the BASSIS. The settings
may be fine-tuned later if necessary. As an
example of the effect of a severe mismatch,
suppose your speaker has Fs = 50 Hz, and Qs =
1, and suppose that you incorrectly set the
BASSIS according to Fs =100 Hz, Qs = .5. If you
make the remaining adjustments (Boost and Qb,
as described below) to try to extend the bass
response, the BASSIS will give a 6 dB boost

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In the net response at 100 Hz and more than 12
dB too much bass at 50 Hz. (This speaker would
be nearly flat to 50 Hz. without equalization.) The
unnecessary bass boost will give a very "heavy"
sound to most recordings, and may damage the
speakers or cause distortion when listening at
high levels.

SETTING BOOST

Once the correct settings of Fs and Qs have
been made to match your loudspeakers, you may
never need to readjust these controls. However,
the remaining controls -- BOOST and Qb -- may
be adjusted to give the best results with your
choice of listening levels and source material.
BOOST indicates the amount by which low
frequency signals are amplified. If the Fs and Qs
setting are correct, only those frequencies where
your speaker is deficient will be amplified, so that
the effect is to extend bass response. (In

contrast, the BASS control on your receiver or
preamp indiscriminately boosts the entire low­frequency portion on the signal, often leading to a
"boomy" or "heavy" quality.) A setting of BOOST
= 0 dB will not extend the bass, but will allow you
to effectively adjust your woofer's damping by
changing Qb as described below. A setting of
BOOST = 12 dB will extend bass response one
octave lower, and a setting of BOOST = 24 dB
will extend bass by two octaves.

SETTING Qb

The best setting for Qb is largely dependent
upon your taste and on the listening-room
acoustics. This control adjusts the Q (see Figure

5) of the new bass response dictated by the
BASSIS. If you want a very "tight" sound, choose
a Qb = .5 or smaller. If you want a "looser", more
"full" bass, use Qb = 1. Qb = .7 gives the
"maximally-flat" response. Figures 6 and 7 show
the results when the BASSIS is used to correct a
somewhat boomy-sounding speaker whose
response drops below 60 Hz (Qs = 1.4, Fs = 60).
In both cases BOOST = 24 dB is used, but in
Figure 6 a setting of Qb = .7 is used, while in
Figure 7 Qb = .25 is used.
It is interesting to note that settings of Qb< .5 give
a transient response with absolutely no "ringing",
so that the BASSIS allows you to achieve a "non­resonant" bass response without need for a
refridgerator-sized "transmission-line"
loudspeaker enclosure.

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VENTED SPEAKERS

The BASSIS can be used to reduce the
boominess of poorly tuned vented ("ported",
"bass-reflex", or "passive radiator") speakers. In
this case, use a setting of BOOST = 0 dB (never
boost the bass below the resonant frequency of a
vented speaker!), Qs = 1.4, and adjust Qb to your
taste. Or, you can plug the vent and forego the
efficiency advantage of the vented design,
allowing you to use the entire range of
equalization options as you would for an acoustic­suspension loudspeaker.

extend smoothly into the lower bass, particularly
when using high-quality source material.
On the other hand, extending the bass
response will make your system more sensitive to
"standing waves" in the listening room. You may
have to experiment with new locations for your
loudspeakers or listening seat to obtain the
smoothese overall bass response.

TECHNICAL DESCRIPTION

The equalization offered by the BASSIS can be
described in terms of the biquadratic transfer

function:

FINAL ADJUSTMENTS

You are now ready to apply power to your
system including the BASSIS. Advance your
VOLUME control slowly to make sure the unit is
working properly. If you have difficulties, see the
"Troubleshooting" section of this manual
(Appendix F). There are a few additional points to
keep in mind to obtain optimum performance.
If your source materialis LP records, you should
test your system's sensitivity to record warps.
Remove the grilles from your speakers. With the

VOLUME control set low and the BASSIS set with
BOOST = 24 dB, play the silent lead-in observing

your woofer cones. If a significant "pumping"
motion is visible at your normal VOLUME setting,
engage the 20 HZ CUT filter on the BASSIS.

Even when properly adjusted, the bass
extension offered by the BASSIS must be used
with discretion. While the BASSIS can give a 6­1/2" woofer the same bass response as that of a
12" woofer, it cannot increase the power handling
of small speakers. Do not engage your preamp
or receiver's LOUDNESS button or make
excellive use of the BASS tone control while
using the BASSIS. When listening at high
VOLUME levels to material with significant low­bass content, it is wise to reduce the BOOST
setting, reduce Qb, or BYPASS the unit entirely.
Fortunately, the low-bass content of most
recordings is much smaller than the content of
the remaining frequency range. In these cases
the low-frequecy boost applied by the BASSIS will
not impair the speaker or amplifier power
capabilities.
When using the BASSIS, don't expect to hear
the sort of elevated bass produced by turning up
your preamp or receiver's BASS tone control or
pressing the LOUDNESS button. Instead, the
mid-bass will be reproduced with impoved
neutrality and "openness", and the response will

2

w

+ 2 dswss + s

s

2

G(s)= --------------------------------------

2

w

+ 2 dbwbs + s

b

where ws and ds are the corner frequency
and damping ratio of the woofer and wb and d

are the new corner frequency and damping ration
chosen by the user (w =2piF and d =0.5/Q). The
numerator cancels the 2nd-order high-pass effect

of the acoustic-suspension woofer and the
denominator defines the new 2nd-order cutoff.

CIRCUIT

The circuitry for each channel of the BASSIS is
contained on an individual printed circuit board
(PC board), using high-speed op-amps and close­tolerance passive components. A power supply is
contained on a third board. The schematic
diagram of a single channel is shown in Appendix
A.
The heart of the circuit is a 4-amplifier
biquadratic filter, supplemented with additional op­amps to allow the independent adjustment of the
damping and cutoff frequency pararmeters. Op­amps IC1, IC2 and IC3 provide the equalization,
while IIC4A is part of the 20 Hz CUT filer. Op­amp IC4B provide low output impedance and high
current capability, to allow long cable runs with
minimal loading effects.
Dual potentiometer VR3 adjusts the frequency
matching the speaker's corner frequency over the
range: Fs = 30 Hz to 130 Hz. Potentioometer
VR2 adjusts the damping which exactly cancels
the speaker's response, for speakers with Qs
from .4 to 1.6. Potentiometers VR1 and VR4 set
the corner frequency and damping of the new
bass response over the range: Fb = Fs to Fs/4
and Qb = .25 to 1. Since each octave of bass
extension requires 12 dB of amplification at low

2

b

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