From the Desk of Art Noxon

Art Noxon is a fully accredited Acoustical Engineer with Master of Science degrees in Mechanical Engineering/Acoustics and Physics. A Professional Engineer since 1982, he is licensed in Oregon to practice engineering in the public domain with the specialty area of acoustics. A prolific inventor, he developed and patented the iconic TubeTrap, the original corner-loaded bass trap/treble diffuser, 150 other acoustic devices, and counting. Lecturer, writer, and teacher of acoustics, he has presented 7 AES papers, numerous magazine articles, white papers and blogs. He is president of Acoustic Sciences Corporation, the company he founded in 1984.

TubeTrap History

Arthur Noxon, Father of the TubeTrap bass trap, 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 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.

This diagram shows the acoustic circuit of a TubeTrap bass trap. This bass trap uses acoustic “time constant” technology to achieve high efficiency unlike membrane, Helmholtz and quarter wavelength bass traps.

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.

Schematic of Ripple Tank, using speakers to generate the waves.

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 until 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 genius speaker designer famous for high end quality, that he should check these out.

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,

Finally, the TubeTrap was born.

The first Tubes, sold as a set of 8 that were 9" x 36", featured mated pairs with a unique built-in diamond base similar in shape to a "home plate" used in baseball. This gave the stacked Tubes a nice finished look and contributed to the "furniture look" that Bradford's wanted.

These first TubeTraps didn't feature the classic reflectors that create the now familiar live side/dead side found on all subsequent TubeTraps. These were the only TubeTraps made by Mr. Noxon prior to the formation of ASC, and once they became ASC TubeTrap, the reflectors were included.

As with the TubeTraps of today, these did feature a wire cage to add strength as well as to help dampen twang. The fabric covering, much like today, was a sleeve stretched over the cage assembly. The end caps were 1/4" plywood, and the base units permanently attached. The stacking feature relied on three dowels to keep the two Traps properly lined up and prevent toppling.


*This is the very first TubeTrap bass trap, then the only real bass trap that could be moved in and out of the corner, tuned with ease.

*The base plate shape for the original TubeTrap supported the bass trap in the corner while providing designer angles for the eye.

A Sonic Tsunami: Born in the front end of your listening room.

Comment recently added to Sunday Morning HiFi #4 blog by Spencer Holbert in Absolute Sound on room acoustics:

Room Breakup, Curse of the Audiophile (2007)

Nothing, not even audio, is perfect all of the time.  But most of the time, the audio system seems to behave just fine.  Still, if you crank the volume up just one notch too high, in most systems, something changes and the system no longer sounds musical.  What you are hearing is not cone breakup but room breakup.    Yes, rooms too can be overdriven and more easily than we might suspect.  

There are limits, even in Audio

What's with HiFi These Days (2015)

What’s with Hi Fi these days?  Nothing much, except it’s a new generation of people who are discovering it…  It started in NYC in the early 50’s and kind of died out in the 90’s because of computers, home theater, downloads and ear buds. 

Buy Subwoofers instead of Soundproofing

Dec 2014, comments submitted to Audiophile Review supporting Brent Butterworth’s article about multiple subs. 

Good work Brent...

There are other reasons to have multiple subs than just to minimize mode coupling.......more subs can also mean quieter modes, less power delivering the same sound level, noticeably improved musical clarity and reduced bass boom next door.  

With one subwoofer you will set the volume for a satisfactory sound level. 

More On Early Reflections

Comment to Audiophile Review, Roger Scoff, 6/19/14, Room Acoustics,  "What gets you more, $10k ..."

Art Responds to Studio Performance Questions on Gearslutz

Studio performance...Yes, FFT analysis has gotten pretty inexpensive since those early days in the mid 1980’s when we had to buy the Crown Techron 12 or 20 for something well over $10k...but regardless of when or how much it cost, once you have the FFT analysis, then what? 

If the FFT waterfalls look smooth and fast, does that mean the studio sounds good? 

If the freq response measures pretty flat, does that mean your mix will hold together?

What is the connection between the output of FFT analysis and being able to mix a record? Isn’t that the bottom line? 

Church Carpet Not Good For Organist

Question: I’m the organist at a church with a beautiful pipe organ in a historic stone church. I’m sure it sounded great in the old days they covered the floor with beautiful carpet years ago and lost the sanctuary lost its reverb. They won’t remove the carpet to get the reverb back….Do you know of any clear paint I can use to remove the carpet’s acoustics so I can get the reverb back into the sanctuary?

Limp Mass Membrane Bass Traps?

The formula f = 170/sqrt(m x d) is often quoted as applying to membrane bass traps. The m term is surface weight (lb/sqft) of the membrane and d is the depth of the air cavity behind the membrane. See Home Recording Studio, Gervais, Fig 9.10 (Panel Trap Formula).

Do Audio Measurements Correlate with Sound Quality?

Sometimes yes, but usually not, depending on the kind or version of the Audio Measurement being made. My primary experience with audio measurement is in the realm of room acoustics so this will be the context of my response to this question.

What is MTF for sound?

The sonic MTF is how the clarity of sound or intelligibility of speech is physically measured. A similar system exists for measuring the clarity of lenses in optics.

It appears as a 3-D plot with the Modulation Level (dB) on the vertical axis, the Modulated Tone (Hz) on a horizontal axis and the Modulation Rate (Hz) on the other horizontal axis. A typical data point would be a Modulation Level of 15 dB for a Modulated Tone of 250 Hz at a tone burst or Modulation Rate of 8 Hz.

How many people could Jesus talk to at once using his natural voice?

Back in 2009 I received a philosophical question, something not too different from "How many angels can dance on the head of a pin?" It's about how many people could hear the voice of Jesus at one time. Below I show the actual question followed by Section 1 of my answer. Here I idealized the physical listening conditions so that I could establish the maximum possible number of listeners. In later sections, which I will soon publish, I work towards more practical answers.

Ever wonder what to do about Sub Bass Energy?

Sub bass is the frequency range the subwoofer make, typically below 45 Hz. It’s pretty difficult to buy bass traps large enough to absorb the power being put out by subwoofers. A subwoofer might be rated at 1000 watts. One horsepower is about 750 watts, so a subwoofer is rated as a 1¼ horsepower air pump. What happens to all that power anyway?

A Sonic Sculptured Listening Room: Big Demo Room and no TubeTraps

One time I was asked to dial in a huge hifi demo room at a high end audio show in Newport, CA without using TubeTraps. The room was a large conference room, with a 12’ ceiling and the width and length were both in the 50 to 60’ range. It was a huge room and it would take a truck load of TubeTraps to try to get this room to play. It was running big Magico speakers, Spectral electronics and MIT cables and that package deserved to sound great.

What is Sonic Shimmer?

When it comes to measurement or assessment tools in acoustics, we have a problem when the tools we have do not agree with subjective interpretations. In this case we need a shimmer meter to better study and understand concert hall acoustics and guitar pedal sound, because in both venues, the concept of shimmering sound is a valued commodity.

Remove a corner bass trap and the “suck-out” went away?

It happened to Bob Hodas once and it was so unusual that he mentioned it in a MIX article on room acoustics. Actually, what he ran into could easily have been a live example of a technique we use in the design and set up of listening room and control room acoustics.

Why is sonic clarity more important than a flat frequency response in your room?

Contrary to popular belief the big problem with bass in hifi is not lumpy bass, standing waves, room modes, hot spots and suckouts. The big problem is sound masking.

That’s right, sound masking is what happens when an unwanted sound overpowers our ability to hear and discern the fine details of a wanted sound.

Michael Jackson and Acoustic Sciences Corporation

Bruce Swedien had recorded and mixed Thriller in 1982 and by 1987 he was still the top recording engineer in the world.

During the time Thriller was being made, I was graduating from college, my second masters degree, this time in physics, prior degree was Mechanical engineering/acoustics. I couldn’t get a real job, had 3 wonderful kids and ended up working in the city sewer, stringing and pulling an inspection video camera through the pipes.

Persian Rug Acoustics

The timeless image of HiFi is a high flying Persian carpet sporting a listening chair and a pair of loudspeakers. Yes, it’s true. A good sound system set up on a Persian carpet can transport any audiophile into a wonderful adventure in some other place and time.