Snell Acoustics AMC 760 - Manual (Page 4)

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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.