This page is a history of my quest for the best playback system possible.
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Pictures of The Wall of Sound
High School
I built a front-loaded horn system with a large infinite baffle behind two
15" low frequency drivers. I had saved my money to buy two Stromberg Carlson
15" drivers with bright red cones and fairly large voice coils. I was
disappointed to discover that they had relatively high free-air resonances. I
steamed some thin plywood boards and bent them into roughly an exponential curve
as per plans I found in an early edition of Audio Magazine. The
high-frequency section was an
Altec Lansing horn whose model
was an
811B,
and the driver was a
288C. I only had
monophonic sound, but it certainly could achieve high sound pressure levels, at
least above 50 Hz.
College
While in college, I improved the front-loaded horn by doubling the volume in
the infinite baffle, but this system still lacked the bass response I longed
for. I also tried to build a system called "Ton-and-a-Quarter of Sound" from a
design in Audio Magazine. This system used thin-wall concrete for both the bass
and treble sections of exponential-sectoral horns. The high frequency unit used
an
Altec 288C as the driver and the bass horn used two Jensen 15" drivers.
Despite significant help from the author, I never completed the moulds from
which the enclosures themselves were to be cast.
Employed
After having worked a couple years, I was able to purchase the Infinity IRS or Infinity Reference Standard.
(Picture of left side) (Great
web site for Infinity Systems) I was the proud owner of serial number 4. This was a beautiful Rosewood system with
two towers containing six 12" woofers each, and two curved
panels with electromagnetic flat panel drivers. There were, as I remember, 24 of
them in a vertical linear array per side. The response above 40 Hz or so, was
flat, and extended beyond my hearing range to something like 40 KHz they claimed.
These physically beautiful speakers did not reproduce organ tones down in the
low registers at adequate volume levels. The low frequency towers had built-in
amplifiers and there was an accelerometer glued onto one woofer of each side.
After a week of playing the system, I remember the start of many problems in
their design, beginning with the left side's glued-on accelerometer falling off of the
cone. Infinity supplied me with the schematics of the system, and I had numerous
repairs and modifications to their electronics, most of which were in the
accelerometer amplifier and integrator stages. I re-glued the accelerometer onto
the voice coil dust cover and also touched-up the other side, which ended the
physical problems. I paid $22K for this system and unloaded it for $14K a couple
years later to some guy in Santa Monica who was thrilled to obtain it. Just the
packing crates alone, all custom made and felt lined, were something to behold.
2nd Last Attempt
I was still enamored with horns and purchased an
Altec Lansing theater system
(similar to the A6 shown in the link, but twice as many drivers)
with four very imposing plywood enclosures, and two large aluminum horn high
frequency units. The low frequency units had four 15" drivers per side,
front horn loaded with a bass reflex design for frequencies below 100 Hz or so.
The high frequency horns were exponentials with
291-16A drivers. Everything was bi-amped.
The SPLs were very impressive, the response was anything but flat, and I still
had negligible response below 50Hz.
Final Design
I knew from this many previous attempts, that I would need some low frequency
drivers that first of all, had a lot of cone area, and second of all, had a low
free-air resonance. I picked the
Electro Voice 30W driver (no longer in
production) because of its 30" cone diameter and also because its free-air
resonance was around 15 Hz. To get the proper SPLs to match the JBL mid and high
frequency drivers (see below), I choose three 30" drivers per
front side, for a total of six drivers. I enclosed them in concrete to keep any
wall resonances to a minimum, and also to attempt to keep the sound enclosed and
away from my neighbors tender ears. I borrowed from Infinity, the idea of smoothing-out the response with
an accelerometer, and have one
per side glued to the outer-most driver of the trio. I use about 20 dB of
negative feedback and have a flat response to about 12 Hz where the system drops
off rapidly. I deliberately force the response to be 24 dB down at 5 Hz to keep
the cone motion in control where there is no back-air loading. Unlike the
Infinity IRS servo which was completely analog, my design digitizes the low
frequency channels of the
JBL
DSC-280 electronic crossover and my FIR filters, integrators, and feedback
servo, are all done with DSP. My sample rate is only 8 kHz because I'm dealing
with less than 100 Hz signals. (24 dB per octave)
I cross this sub-woofer system over at 62 Hz, and above that, is a pair of
JBL
4675C-8LF theater loudspeaker systems. This is a really flat
(specs), efficient,
speaker system, THX qualified for use in theaters, and not really expensive. I
just don't understand why they are not more popular with serious audiophiles.
Sure they are large and imposing, especially the exponential-sectoral horn, but
their response is so flat, they are hard to ignore. (For good prices on JBL
professional equipment, look to
this site) I cross the 15" drivers and
the horn over at 500 Hz. All
speakers are separately amplified and the electronic crossover is a
JBL DSC-280
as mentioned.
The 280 allows for time-alignment of the non-planer speaker cones to keep the
response smooth. I highly recommend the DSC-280 as an electronic crossover.
My high-frequency amplifier and my mid-frequency amplifier (left and right
front) is a pair of
Yamaha M-85s which I'm guessing are around 250 watts per channel each. Each
set of Electro Voice 30W drivers (3 per set) is driven from one Adcom GFA-555.
Each GFA-555 is a pair of 200 RMS Watt amplifiers. I use two additional
GFA-555s for the front and rear surround amplifiers.
I have no preamp. The output of the CD player which is a Yamaha CDX-5000,
feeds the JBL DSC-280 directly, thus avoiding any superfluous electronics in the
playback path. I set the volume by using the remote for the CD player. The
DSC-280 takes care of all the Linkowitz-Riley phase and amplitude crossover
responses, plus the shelf amplitudes of each band-limited channel. It also
includes a limit function which I didn't used to invoke, but after feeling the
front pane-glass window excursion on some playback material, I now have it set.
What about specs?
With regard to flatness, from 62 Hz through 16 kHz, the JBL THX spec allows
for a 3 dB variation. The listener must be within 20 degrees of on-axis to the
horns to get the 16 kHz which I always am where I listen. From 12 Hz to 62 Hz, I
have a 5 dB variation, probably due to the room's contribution to standing
waves. The big advantage to this design over other "over-the-top" designs, is
the sound pressure level (SPL) in the 16 to 64 Hz that this one can achieve. I
have heard no other system reproduce the low C (16 2/3 Hz) to C (33 Hz) octave
at such high SPLs. With heavy pipe organ music, I can not tell the difference
between being in a large cathedral and being in my living room, which is why I
went to all the trouble in the first place. I can play the volume realistically
and truly duplicate the sound I hear live, or crank it up, and vibrate the
pictures off the walls. There is the lead-in to the Telarc CD "Time Warp"
(CD-80106) which includes a synthesizer producing the low notes from Richard
Strauss' "Also Sprach Zarathustra", that at high SPLs scares me because the
front pane-glass windows are moving about one-quarter inch at their centers. I
realize at some excursion, they will sustain an expensive crack, so on this CD,
Wellington's Victory, and any 1812 Overture CD, I pre-play the tracks to find a
safe volume level.
After all this expense and effort, am I happy?
This system is my final system. I have had it untouched for going-on five
years, and will die with it, although it may get transported to a new home when I
move. I have added surround, and will recreate it when I
move to my retirement home. I will make one modification to the design when I
move, and that is to excite the room with the low frequency energy from the
corners of the room. I now have the low frequency drivers on a flat surface
(see
pictures) and suffer from room standing waves. Exciting the corners and
carefully picking the room dimensions will lessen this phenomenon. My planned
playback system/home theater room is 42'W x 57'L x 30'H.
All pictures of the system...
FAQs- Via e-mail I have been asked several common questions. Here they are
with answers.
