Arthur
Noxon, Father of the TubeTrap, demonstrating bass trapping concepts
at Recording Arts Center, Eugene, Oregon in 1985.
The TubeTrap
is the world's first commercially manufactured corner loaded bass
trap. Acoustic Sciences Corp. was founded in 1984 by Arthur Noxon
to build and sell the TubeTrap. The TubeTrap was also the world's
first portable bass trap, opening up an entirely new field in
acoustics, namely audio acoustics. Coupled with recent new advances
in audio speakers and solid state electronics, the necessary ingredients
for explosive growth in high end audio were at hand.
Unlike
any other bass trap, the physics behind the TubeTrap are based
on a capacitive-resistive circuit. The acoustic capacitor (C)
is the air chamber inside, the bigger it is, the more efficient
the TubeTrap is at low frequencies. The acoustic resistance (R)
is DC impedance matched to the radiation (LC) impedance of a freely
radiating soundwave. Because of this design feature, the TubeTrap
is more than 100% efficient.
Another unique
feature is the adjustable diffusion grid built into the TubeTrap.
The specular diffusion panel that covers half of the TubeTrap
is an acoustic choke (L) which is sized, ported and mass loaded
to backscatter the treble range.
Before
The Beginning Shortly after graduating in 1981 with a Masters
in Engineering, Mr. Noxon had established a small acoustic engineering
firm doing local projects in the Eugene, Oregon area. In the course
of his work, he was hired to take care of a huge lecture hall
at the University of Oregon. The lecture hall had a serious resonance
problem at 125 Hz, not good for speech intelligibility. So he
set out in search of a suitable bass trap.
Mr.
Noxon had always been interested in low frequency acoustics since
his college days and endless hours observing wave theory using
a ripple tank (see picture). As he researched the availability
of bass traps, he found they only existed as custom units built
for recording studios. As he pondered and searched, he was frustrated
by the total avoidance of bass trapping within the acoustics field,
as though it didn't matter.
In an epiphany,
he could think back to his ripple tank days and "see"
the acoustic waves. That led to the concept of the acoustic resistor,
something that nobody had thought of till Mr. Noxon. Yes, bass
traps existed, but they relied on membranes to deal with the pressure
wave. Now it was time to test out Mr. Noxon's novel idea of applying
a resistive-capacitive circuit to low frequency acoustic waves.
Could he apply in practice this theory to the job at hand, the
huge lecture hall at U of O?
Almost
The First TubeTrap Mr. Noxon searched for suitable materials
for his bass trap, and knew he needed a porous walled cavity
to experiment with. He found some 2" semi-rigid fiberglass
duct board and experimented with it for a while. Then he found
the circular fiberglass pipe wrap which became the basis for
the familiar TubeTrap. The pipe wrap was easier to work with
since the cavity didn't have to be made, it was already there.
The problem was the resonance of the pipe wrap itself, the twang,
would cause resonant dips at certain frequencies. After much
experimentation, it was found that a wire mesh cage would muffle
the twang, much like holding a bell muffles the ring.
So, now Mr.
Noxon could place columns of his new TubeTraps in the corners
of the U of O lecture hall, and fix the 125 Hz resonance problem.
But as he looked over the test data of the lecture hall, he
noticed that the numbers didn't check out for a room that size.
Something wasn't quite right, the resonance at 125 Hz couldn't
be caused by the room itself. So he went back to the hall to
take a closer look. It turned out that the desk tops and the
tiered design of the room were the real cause of the resonance,
and the fix was to structurally strengthen the desk tops. The
TubeTraps would have to wait for another opportunity.
The
First TubeTrap One
day the phone rang and it was the local hi-fi shop getting ready
for a remodel. They had Magneplanar speakers and they sounded
awful in their demo room. The folks at Bradford's
wanted something furniture-like, and Mr. Noxon figured maybe
his TubeTrap might be the ticket. Sure enough, they made those
Maggies sing, and Bradford's was thrilled. Now, 25 years later,
Bradford's still uses TubeTraps in their demo room.
Mr. Noxon bought those
first TubeTraps back from Bradford's, and replaced them with
newer ones. The originals are now safely stored in the TubeTrap
Archives for posterity, and Mr.
Noxon recently showed them off.
At the time, Mr. Noxon's
day job was as a sanitation engineer for the city, spending
most of his time underground in the sewers. While it paid well,
it wasn't all that much fun. Meanwhile, several speakers reps
visiting Bradford's took note of the TubeTraps and really liked
what they heard. Some time later, word reached John Dhalquist,
a genious speaker designer famous for high end quality, that
he should check out these TubeTraps.
Mr. Noxon gets a phone
call from New York, it's John Dhalquist wanting to order 4 TubeTraps
to "try out". Mr. Dhalquist liked them, but they were
too dead in the treble range. So, along came the now familiar
reflector (which originally was made of aluminum with holes
drilled). However, there was more to it than everyday hi-fi
tweaking. Mr. Dhalquist was getting ready to unveil his new
DQ-10 speakers at the upcoming CES Show, and placed an order
for 30 TubeTraps to be delivered at the show, and set up by
Arthur and two associates.