Snell Acoustics Speaker System AMC 720 User Manual

Owner’s Manual  
AMC  
720  
760  
800  
900THX  
 
AMC800  
AMC900THX  
65 Hz-20 kHz  
10–200W  
4 ohms  
78 Hz-20 kHz  
10–150W  
6 ohms  
90dB SPL  
87dB SPL  
1” Aluminum dome, ferrofluid cooling  
and heatsink. Steerable “Directed  
Power” waveguide  
(2) 1” aluminum dome, ferrofluid cooling  
and heatsink. “Directed Power” waveguide  
in dipole configuration  
n/a  
31/2” Midrange, edge-mounted in dipole  
configuration  
61/2-inch (165mm) copolymer with  
butyl rubber surround  
61/2-inch (165mm) copolymer with butyl  
rubber surround  
600 Hz, 3kHz 21/2 way  
400 Hz, 2.5 kHz, 12dB/octave  
Specialty adhesive between two  
1/4” layers of HD fiberboard  
Specialty adhesive between two  
1/4” layers of HD fiberboard  
White cloth over MDF frame  
White cloth over MDF frame  
231/4 x 131/4 x 33/4 inches  
(590 x 336 x 95mm)  
231/4 x 131/4 x 33/4 inches  
(590 x 336 x 95mm)  
22 x 12 inches  
(559 x 305mm)  
22 x 12 inches  
(559 x 305mm)  
White trim, suitable for painting  
22 lbs (10kg) each  
White trim, suitable for painting  
22 lbs (10kg) each  
AMC800  
AMC900THX  
3
 
INTRODUCTION: WHAT IS A HIGH END IN-WALL?  
The new Snell AMC series units bring a novel approach to the design and construction of  
in-wall loudspeakers, expanding the boundaries of in-wall performance.  
Our primary goal was to develop loudspeakers that delivered performance that was as close as  
possible to that of our highly regarded freestanding loudspeakers, like the K.5 mk2 and E.5 mk2.  
To do this, several issues had to be addressed.  
The bass performance of conventional loudspeakers mounted in wall cavities is very unpredict-  
able. Cavity volume can be large, which should be good for bass performance. However, with  
one very short dimension (approximately 4”) and one very long dimension (up to 8’), the wall  
cavity takes on the characteristics of a closed-end organ pipe. This creates a strong resonance  
that tends to null out the bass. Lining this cavity with fiberglass will reduce the “Q” of the  
notch but not restore the bass. What is needed is a defined volume of a more regular size. This  
is best done with fully enclosed in-wall speakers.  
The Snell AMC loudspeaker enclosure is a thin, but strong, aluminum tub. It is both damped and  
braced. This largely contains the back radiated sound of the woofer within the enclosure. An  
added benefit of containing the woofer output is a reduced chance that resonances will be  
excited in the house walls. Furthermore, sound “bleed through” to adjacent rooms is reduced.  
To minimize resonances in the Snell enclosure, the speaker baffle uses a technique first  
pioneered on our .5 and XA series loudspeakers. The baffle is a three part composite with MDF  
(fiberboard) outer layers around a thin, but highly effective, damping layer. This controls the  
panel resonances of the baffle that can obscure midrange clarity. As we have found with our  
freestanding loudspeakers, a better loudspeaker cabinet means a better sounding loudspeaker.  
Conventional in-wall speakers also suffer from poor stereo imaging. Freestanding speakers can  
be angled inward to produce a better central image and make listening position much less  
critical. In-wall speakers obviously cannot be angled in this way. Some in-wall speakers use a  
pivoting post-mounted tweeter in attempt to overcome this limitation. The pivoting mechanism  
produces reflections that adversely affect the tweeter’s response and sound. Also, the small  
baffle area of the pivoting tweeters means that only the highest frequencies can be angled  
inward.  
The Snell solution is a unique tweeter that incorporates a waveguide with a fixed 20 degree  
angle. The DPT (“Directed Power Tweeter”) waveguide design controls reflections to ensure  
smooth response. The waveguide is also large enough to function effectively over the full range  
of the tweeter. The DPT driver can be easily unfastened and rotated to any of eight positions in  
45 degree increments. This, together with the designed-in angle of the driver, lets you direct  
the sound inward to focus a stereo image. Or the sound can be directed away from the listening  
area to produce a more diffuse sound field when the AMC 720, AMC 760 or AMC 800 are used  
as surround speakers.  
In addition to these unique solutions, all traditional Snell attributes are retained. Highly  
coherent in-phase crossover networks ensure a seamless blend from driver to driver. Drivers are  
designed for smooth, wide range response and low distortion. Long sessions of listening and  
adjusting give each system that special, characteristic Snell sound. Finally, that Snell sound is  
guaranteed in every production pair by Snell’s proprietary 0.5dB production tuning techniques.  
4
 
PLACEMENT OF THE FRONT CHANNEL SPEAKERS  
A home theatre system includes three loudspeakers placed across the front of the listening  
room. The distance between the left and right speakers determines the width of the stereo  
image. If the speakers are placed too close together, the image will be too narrow; too far apart  
and the blend will suffer, creating a hole in the middle. When properly placed, your speakers  
will create a continuous “virtual image” from left to right, with an illusion of sound outside, in  
front of, and behind the speaker systems.  
We recommend an angular separation between 45 degrees and 60 degrees (when viewed from  
above). This is equivalent to a separation between the speaker systems that is about 85% of the  
distance to either of the speakers.  
AMC 800  
Creation of sounds between the speakers  
requires some precise placement. The  
distance from the left speaker, right  
speaker, and center channel to the  
listener location should all be as equal as  
possible. We advise using a tape measure  
to equalize these two distances to the  
primary listening location.  
45°-60°  
Ideally the front channel speakers should  
be installed at the same height as the  
ears of a seated listener. Try to keep the  
front channel tweeters within two  
vertical feet of that height. If speakers  
must be installed more than 2-3 feet  
above or below the ideal position, take  
advantage of the DPT rotating feature.  
For example, aim the tweeter downward  
when the speakers are mounted high on  
the wall. For more information, refer to  
the “Aiming the DPT” section.  
AMC 900THX  
PLACEMENT OF THE SURROUND SPEAKERS  
There are many opinions about where surround or “rear” speakers should be mounted. The  
following is based on the findings of the best academics, and on our experience with many  
installations. These placement recommendations apply to all the AMC models, whether you are  
using AMC 900THX (dipole surrounds) or AMC 720, AMC 760 or AMC 800 (direct speakers).  
When selecting installation locations for the AMC 720, AMC 760 or AMC 800, remember that  
you can increase the diffusion of their sound by aiming their DPT drivers away from the  
listening area (see the “Aiming the DPT” section). The tweeters can be aimed toward a reflecting  
surface, or a surface that will scatter the sound, such as a shelf full of books or other irregular  
surface. The AMC 900THX tweeters should not be repositioned.  
5
 
If two surrounds are used in a standard 5.1 configuration (not 7.1 or EX), they are best mounted  
to the sides of the listening area. This means straight to the sides of the listener or in line with  
the primary row of seating, plus or minus 15 degrees. This is preferred over back wall mounting  
for several reasons: It places the surrounds at locations where the difference between left ear  
and right ear discrimination is at a maximum. This gives the maximum sense of “envelopment”  
or being surrounded by sound. Rear  
mounted speakers force a huge angular  
gulf between the front primary speakers  
and the rear speakers. The sound image  
is inherently discontinuous. Also, front  
to rear aural discrimination is not very  
strong. Differentiation between front  
and rear speakers will not be as strong  
as the effect of adding speakers to the  
side. 7.1 or EX systems that use side and  
rear speakers together overcome all of  
these obstacles and give both maximum  
envelopment and a more continuous  
surround effect.  
Optional Direct Radiation  
Surround Speaker Locations  
A second factor to consider is the evenness of sound coverage over the seating area. Most  
surround processors have features for setting the balance of all channels. A circulating noise  
signal is adjusted in each channel until the apparent or measured sound level is even. Of course,  
moving to another seat will shift this balance somewhat. Well-placed surround speakers will  
minimize the level variation from seat to seat. The best way to achieve evenness is to increase  
the distance of the surround speakers from the listening area. Mount them high on the side  
walls or even on the ceiling. As a good rule of thumb, surrounds should be on the side walls at  
least one foot above the height of a standing listener. If the speakers are ceiling-mounted, they  
should be close to the side walls, well away from an overhead position.  
If a large theater room with three or more rows of seats is planned, then more than one pair of  
surround speakers should be used to give more even coverage and a more diffuse sound field.  
We recommend that a pair of surrounds be used for every other seating row (the first, the third,  
the fifth, etc.). This follows standard cinema practice.  
Special Considerations for the AMC 900THX  
Placement of a dipole surround speaker, such as the AMC 900THX , requires another consider-  
ation. For a dipole to give a properly diffuse sound the listeners should be on or near the “null  
plane. Imagine a line running down the middle of the front of the AMC 900THX (along the  
longer dimension), between the two tweeters and across the center of the woofer. A plane  
sticking straight out from this line (at 90 degrees to the wall) defines the null plane. For any  
listener on this plane, the output of the two tweeters and the midrange will be at maximum  
cancellation. A listener at this position will hear the speaker only via multiple wall reflections.  
This is why the dipole sounds diffuse.  
So the AMC 900THX should be installed where the null plane will run through the primary  
listening area. This can be achieved either with the AMC 900THX installed in a side wall (with the  
long axis of the speaker oriented vertically) or on the ceiling (with the long axis of the speaker  
oriented across the width of the room).  
6
 
AIMING THE DPT (AMC720, AMC 760 and AMC800 only)  
In addition to providing an extremely clean wide range response, the DPT have the added  
feature of an adjustable waveguide (in 45 degree increments). This unique Snell feature  
provides the opportunity to toe-in conventionally mounted in-wall systems or compensate for  
the less than ideal placements that occur in the real world. This feature will greatly improve  
imaging.  
To adjust the DPT rotation,  
remove the four wood  
screws with a 5/64” allen  
driver and rotate the driver  
to the desired positions.  
Three examples of how the DPT waveguide tweeter  
can be rotated in 45° increments.  
MULTIPLE DISPERSION PATTERNS (AMC 800 only)  
The AMC800 can be set to reproduce two dispersion patterns. You determine the dispersion  
pattern by selecting which of the two bass units will operate as the midbass driver. The  
dispersion pattern can be seen as an ellipse, whose length is a line perpendicular to the  
tweeter/midbass combination as shown below.  
Dispersion Pattern A  
Dispersion Pattern B  
MID/BASS  
MID/BASS  
WOOFER  
WOOFER  
7
 
Setting the Dispersion Switch  
The illustrations below show the recommended Dispersion Switch setting for most common  
placement options for the AMC 800.  
Horizontal Placement  
Vertical Placement  
*Note: When the AMC 800 is used as a center channel speaker and is placed horizontally, the  
dispersion switch may be set in either position.  
INSTALLATION INSTRUCTIONS  
IMPORTANT: This manual assumes that the installer possesses skill in the proper use of  
hand and power tools, knowledge of local building and fire codes, and a familiarity  
with the environment behind the wall or ceiling in which the speakers will be installed.  
Optional preconstruction brackets are available for each model.  
PAINTING THE SPEAKERS  
If you intend to paint the speakers, it is best to do so before installation.  
1) Remove the speaker grille.  
2) Mask the baffle.  
3) After painting, carefully remove the paint mask.  
Note: Custom paint and grilles are available for an extra charge.  
8
 
PREPARING FOR INSTALLATION  
Map out the wiring paths from the speakers to the amplifier. We recommend 16-gauge wire for  
runs up to 25 feet, and 14-gauge wire for longer runs. Be sure the speaker wire does not rest or  
rub against any sharp or pointed objects.  
The speakers should be mounted on a flat surface to form a good seal between the speaker  
flange and the mounting surface.  
When connecting more than two speakers per amplifier channel, you should use series/parallel  
wiring. In all cases, make certain that the total impedance does not fall below the amplifier’s  
rating. If you are not sure, contact your Snell Acoustics dealer.  
You will Need:  
1) A utility knife, an electric jigsaw, or other means of cutting a hole in the mounting surface.  
2) A #2 Phillips screwdriver.  
3) A wire cutter or stripper for preparing the speaker wires.  
With the supplied hardware, the speaker can be installed in existing walls or ceilings from 1/2”  
(12mm) to 11/2” (38mm). For thinner walls, you will need to use spacers for the mounting legs  
(contact your Snell dealer for this optional rubber part).  
INSTALLATION  
For convenient installation, the Snell AMC720, AMC760, AMC 800 and AMC 900THX use a dog-  
leg mounting system (see illustrations below). This provides a quick and clean install. Further-  
more, the dog-legs can be removed if a particular situation requires to speaker to be directly  
attached to a stud.  
Note: As an added security feature, the speaker tubs can be pre-mounted without the baffle,  
drivers, and crossovers installed. This will allow you to protect the delicate speaker components  
from debris if significant construction work is being done near the speaker installation location.  
1) Make an appropriate size speaker mounting cutout in the wall material.  
2) Run the wire from the amplifier to the cutout. Allow an extra foot of wire at the cutout.  
Strip 1/2” (12mm) off the wire, and tightly twist the wire strands together.  
3) Remove the speaker grille.  
4) Insert the speaker wires into the spring  
terminal binding posts.  
Important: Typically, one side of the wire is  
smooth. Connect this side to the – (black)  
speaker terminal. The other side has a rib or  
stripe. Connect this to the + (red) speaker  
terminal. Connect wire at the amplifier in  
the same way. Failure to do so will result in  
degraded sound.  
Warning! To prevent electrical shock, always  
switch off the amplifier or receiver when  
making connections to the speaker system.  
Continued  
9
 
5) Place the speaker into the rough opening.  
6) Level the speaker and tighten the screws, being careful not to over tighten them. See  
diagram below for details.  
Turn the mounting  
clamps against the  
enclosure, then  
place the speaker  
in the mounting  
hole. Use a phillips  
head screwdriver  
to deploy the  
mounting clamps  
and pull them  
against the back  
of the drywall.  
7) Replace the speaker grille.  
Note: The AMC 900THX is sold in pairs. On the cabinet, near the input terminals, is a temporary  
label to specify screen direction. The response will be slightly superior in this direction. Install  
the two AMC 900THX’s so that the arrows BOTH point toward the screen. If listeners are not  
going to be located on or near the center axis of the speaker, the speaker should be oriented  
with the arrow toward the listener location (even if this is away from the screen).  
LISTENING LEVELS AND POWER HANDLING  
The power recommendation for the system assumes you will operate the amplifier in a way that  
will not produce distortion. All speakers can be damaged by even a modest amplifier if it is  
producing distortion. If you hear a gritty noise or other signs of strain, turn down the volume.  
Prolonged or repeated operation of your speakers with a distorted signal can cause damage  
that is not covered by the warranty. It is especially important that you do not overdrive the  
bass capability of smaller speakers. Watch for noises, such as pops, caused by the music’s bass  
line. Use of the loudness control and/or full bass boost at louder volumes is likely to overdrive  
the woofer. Use such controls sparingly.  
HOW TO CARE FOR YOUR SPEAKERS  
Use a soft terry cloth towel slightly dampened with water, glass cleaner, or a diluted mild  
detergent. The towel should be just damp enough to wipe the surface clean without leaving  
a trail of moisture.  
Do not use abrasive cleaners or any cleaner containing chemicals harsher than those found  
in glass cleaner.  
10  
 
LIMITED WARRANTY  
For five years from the date of purchase, Snell Acoustics will repair for the original owner any  
defect in materials or workmanship that occurs in normal use of the speaker system, without  
charge for parts and labor.  
Your responsibilities are to use the product according to the instructions supplied, to provide  
safe and secure transportation to an authorized Snell Acoustics service representative, and to  
present proof of purchase from an authorized Snell dealer in the form of your sales slip when  
requesting service.  
Excluded from this warranty is damage that results from abuse, misuse, accidents, shipping,  
repairs, or modifications by anyone other than an authorized Snell Acoustics service  
representative. This warranty is void if the serial number has been removed or defaced.  
This warranty gives you specific legal rights, and you may also have other rights that vary from  
state to state.  
If Service Seems Necessary  
Contact the dealer from whom you purchased the speaker system. If that is not possible, call us  
at 978-538-6262, or write to:  
Snell Acoustics  
300 Jubilee Drive, PO Box 3717  
Peabody, MA 01961-3717  
We will promptly advise you of what action to take. If it is necessary to return your speaker  
system to the factory, please ship it prepaid in the original factory packaging. Please note that  
Snell Acoustics will not be held liable for shipping damage due to improper packaging. After it  
has been repaired, we will return it freight prepaid in the U.S. or Canada.  
11  
 
300 Jubilee Drive, P0B 3717  
Peabody, MA 01961-3717  
phone: 978-538-6262  
fax: 978-538-6266  
©2002 Snell Acoustics. All Rights Reserved.  
Specifications are subject to change without notice.  
Covered by patents issued and/or pending.  
Part #542-1026  
 

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