Sonic Couch Driver
In the beginning the world of
acoustic fidelity was flat and without extended bass extension. The
heavenly deities of audio were sad and searched the world for a hero to
bring bass to the sonic deprived masses, but they could find none. Then
after all hope was exhausted a great disturbance in the universal force
was felt. It could mean only one thing...
Martin was back in town and he had stopped in to see me.
This is the journey of two men, eight drivers, several hundred pounds
of reclaimed lumber, drywall screws, and a cat.
On the afternoon of July 24rth,
2004 I received a telephone call from my friend Martin. He wonders if
he can drop by and pick up a vacuum tube. Although this is the reason
for the visit, we both know that its only an excuse to spend several
hours discussing turbo chargers, robotics, and of course exotic audio.
I was not be disappointed, and much discussion occurred concerning
multi-driver line sources. I lamented the fact that I really had no
where to actually set up such monoliths of acoustic splendor.
Its no secret that my sound system is lacking in low end response.
Which isn't a big deal since I don't listen to a lot of music with a
real deep bass beat, but it would be nice to have a fuller sounding
cannon fire when I toss the 1812 overture onto the turntable. Now we
originally had an insane idea to build a Sonic Bass Bed, out of an
array of about a gazillion inexpensive 6x9 surplus auto speakers. Since
I never got around to building the bed, the Sonic Bass Bed was never
built, but I did have 4 pairs of brand spanking new 6x9's. The outcome
was obvious (if only to us). The epic adventure was to begin the next
morning. Which in Martin speak means the next afternoon.
ENTER THE SONIC COUCH
Well my couch was designed by people with legs 4" long, so it could
stand to be raised up. We scaled back the original design and ended up
with a 'sub' approx 7' by a bit less than 4'. Instead of being open on
both sides as orginally called for, the back was turned into a giant
port. (Or a huge air pump, wind tunnel whatever...) The drivers are
arranged in 4 pairs. The operation is described as we go.
Martin finally realizes the scale of this venture...
Martin poses for a quick pic, as we do a quick mock up.
I cut lawn, Martin cuts holes...
One complete segment. The drivers are driven out of phase so that when
one driver is pushing the other is pulling. Its basically just a real
high volume air compressor.
Direction of air flow with proper phasing.
All four segments in place. The front of the 'sub' is toward the floor,
the top will enclose a giant port which will be located toward the
Its about 8:30, and Martin is in deep kaka, since he should have headed
home about 2hrs ago. We agree to meet up again in two weeks and Martin
departs leaving we with a half finished giant, and no room left to
After Martin departs, I struggle on and hook up the wiring harness
(Twice). The first attempt resulted in nearly zero output. How can you
have 8 drivers, and no output?! .Although the phasing was perfect, the
impedance was not... Hmm 2 ohms, that ain't right. Seems they are 4 ohm
speakers not the 8 I designed for... Yeah... I knew that. Seems I
remember telling the class that a 2 ohm load impedance was bad, when
the amp thinks its driving 4... Proof of concept.
All righty then... Phasing? Check. Impedance? 8 ohms, Check. Bleeding
ear drums? Check. --sorry what was that?
Top and bottom in place, looking at it from the front. My God Martin...
What have we done...
Well if all else fails Marbles the cat can use it as a play house.
On the floor, and in position.
Theres that giant port in the back. You could dock your ship in that
Well here it is with the couch in place. Its just a bit high now,
although its just about the perfect height to use with my laptop now.
Pleminary testing seems to show that the low frequency cutoff is...
Huh... It should be here some where... It makes one heck of an air pump
at 1-2Hz. We'll be sure to do complete testing when I get back from
There is significant flex, and vibration in the port, and will require
further structural reinforcement. Of course there is significant
vibration and flex of the house as well...
The design is such that it can be 'sub-graded' with an additional 16
drivers, bringing the total for the finished project to 24 drivers.
Does it work?
Can it reproduce bass...?
Check the seismology reports for the morning of July 26th, and you will
have your answer.
Impulse testing, and specifications to follow in 2-3 weeks time.