Arthur Noxon

Selected General Acoustics Correspondence From the Founder of ASC


"I recommend this school to anybody who wants to work on the acoustic side of the audio industry."


From a student designing a studio for his senior project

What is impedance matched?

Art Responds:

To impede means to stop what's going on.

If I have a 20" thick strip of building insulation, like you'd use in the attic, and you cut it to just fit into a doorway, 30" wide by 6'-9" long. You attach this fluffy material to the edge of the doorway? so it just hangs there, plugging up the doorway. Imagine that.
Now, you and a friend position yourselves on either side of the doorway and talk to each other. the sound is slightly muted but you guys can hear each other pretty well. The material in the doorway has low impedance, it doesn't stop what is going on and sound travels right through it pretty much without being absorbed either.

Now you somehow compress all that 20" of glass fiber down to a thickness of 1/8th inch, compressing it by a factor of 160. You now have a lot of material tightly compacted together. You have made something like a fiberglass boat hull or car body. this material has the weight density equal to water. Compress it in half again and you actually make glass, a 1/16th thick glass window. we all know that a thin heavy sheet of material blocks sound. This will probably provide STC 15. Sound bounces off it. that means it has high impedance, the path of sound is reversed, but not absorbed.

In both cases hi or lo impedance, sound interacts with the material and no energy is lose due to the interaction.

Now, we loosen up the clamping machine, letting the fiberglass expand and we stop it when the fiberglass is 2" thick. that would be a compression of building insulation by a factor of 10. we have a 2" thick panel plugging up the doorway. We talk and our voice is barely heard on the other side. We measure an STC 10. But no sound is actually reflected off the panel. We've made a sound panel.

An "impedance matched" sound panel.
1) sound does not reflect off it
2) sound does not pass thru it.

If the sound didn't bounce off and it didn't pass thru, what happened to the sound? It got absorbed. sound energy was converted into making warm air, heat, by friction between the movement part of a sound (actually acoustic) wave and the fiberglass fibers.

Arthur Noxon

from an audiophile bass lover

Hello: After searching the net for info on bass traps etc, I obviously came across the SubTrap. As I have a small living room to which I just added a sub I now have immense problems with poor bass balance, some notes are much louder than others.

Could you advise as to the availability of the SubTrap in Australia, as I have been unable to find any other similar product in Australia, except for acoustic foam corner bass traps.

I look forward to your response.

Regards Craig

Art Responds:

Hello Craig,

I see that you were asking about SubTraps and that you have a Velodyne subwoofer.

If you want some help with your listening room, we write up an order for some engineering time. You send photos of your room and equipment list, and floor plan, over email. We study things and ask questions and make recommendation. We also have a more complicated option which is to run certain test CDs over your system and make recordings of the result and send them to us. We analyze them and share results with you and make recommendations.

As for the SubTrap, it is a specially made TubeTrap, suitable to put Subwoofers on. It isolates sub vibrations from the floor. It raises sub out of the floor pressure zone so it does not couple to the first few vertical modes in the room and lastly it damps out any modes that do get developed. It smooths out the sub bass, removes the one note bass effect and turns the sub into a musical instrument, with clean dynamics, tonality and increased bottom end punch.

What we do, in general, with the TubeTrap product line, is remove the shudder, the after shock, the shaking of the air in the bass range that immediately follows each and every dynamic sonic event. What you get is a much improved signal to noise (air shudder) ratio. This improves musicality and imaging because we lower the sound masking noise floor, the one that interferes with your perception of the inner detail in each musical attack transient.

So, if you want to get to work on your system, let me know.

Arthur Noxon

from an audiophile soundproofing customer


I read about ASC WallDamp in the book: "The Complete Guide to High-End Audio". I am in the process of constructing a listening room in the basement. It is a 350 square foot room with brick walls and a roof with 2x6 inch wood with isolation and a wooden floor on top. I assume that the best solution will be to build the walls and possibly also the roof using your WallDamp system. Do you send outside the US? Any dealers Europe, Scandinavia, or maybe even Norway? :-)

Best regards, Armand

Art Responds:

1) Yes, we ship world wide.

2) For good sound, we need to add flexible walls and ceiling to your room. The IsoDamp wall and ceiling system is mounted to the more rigid walls and ceiling you now have. The IsoDamp wall and ceiling system will handle all sound in the first 1 1/2 octaves, between 20 and 60 Hz. .

3) Once the room is built, then we will need to add bass traps in the corners to handle bass between 60 and 250 Hz.

4) Treble range acoustics are usually wall panels and wall diffusion, which we also supply.

5) To begin this project, I need photos of the room and a floor plan, list of equipment and where you plan to set up the speakers and listening position. We also need a small deposit which is fully applied to future purchases. With this, we can begin the design process.

Sincerely, Arthur Noxon

We recieved this inquiry about the soundfence


I think your product MIGHT solve my problem. I want to talk to you about it and I might even conduct my own experiment before I proceed. I have an 6 foot perimeter fence. My street has gotten very busy. I need some plan to mitigate the traffic noise. Here are some specifics. My house is on a hill 3-4 feet above street level. Then I have a six foot fence. My house is two feet off the ground. I can raise the fence up and make an 8 foot fence. I have read that you need a 12 FOOT LINE OF SIGHT BARRIER. To mitigate sound.

I think that means that 4 feet above grade + 6 foot fence – 2 foot house above grade= 8 foot. Will your product work?

I am thinking about testing it by stacking hay bales against the fence to six foot. If that works then your product might too.

What do you think?

I am interested in your thoughts on this

Thanks, Kevin

Art Responds:

Hay bales work as a sound absorbing barrier.

Using plywood works as a sound reflecting barrier. Plywood leaks a lot of sound over the top of the fence. A plywood or concrete block fence adds an echo to your back yard. It also reflects back onto the house sound that slips over the top of the fence, hits the house and bounces back towards the fence. Sound absorbing barriers get rid of the sound once and for all and do not create a backyard echo.

Most traffic noise comes from tires, which is at street level. For good noise control, you want to break the line of sight between the noise source and the listener by about 2 feet. This means that in most cases a 4 or 5' fence is more than adequate.

Next problem, not so severe is car exhaust pipe noise, radiator fan and engine noise which is generally 1 to 2; off the ground. Again, a 4 to 5' acoustic fence blocks the noise effectively.

What isn't handled so well is the big truck exhausts pipe that is directed towards the side of the road and is located about 10' above the ground. This noise is dumped right over most any fence and the only thing you can do about it is to ensure you do not further amplify the noise by having a sound reflecting fence.

In good weather, you can buy or rent plywood and moving blankets. Prop up the plywood to make a fence 4' high and and drape moving blankets over both sides. This should approximate the effect of a sound absorbing fence. If you like what you hear, you'll love our fence.

You are welcome to send plot plan, address and photos, we'll assess your lot and the road and take a look at what can be done.

Arthur Noxon
Acoustic Engineer

We recieved this inquiry about the soundfence

Dear ASC;

I have a shadow box fence that has red cedar slats and a space in-between. We have a neighbor's side load garage near the side of our house with windows. We want to reduce some of the noise that bounces between their house and ours. I think the SoundFence may be the solution..

Our cross piece is only 1 1/2"thick, and will not accommodate the standard 3" thickness that the SoundFence comes in.

The height is about 44" and the length will vary from 7' to 8'. I would need at least four panels.

Can I order 1 1/2" thick panels at specific heights and lengths?


Art Responds:

Yes, we can make a thin model. However, one side of the panel will have to be semi reflective and the other side will be absorptive. Do you want the absorptive side to face your house or the neighbor's house?

The cost is discussed here and the covering is green.

We would need length of all 4 sides of each panel and the diagonal dimensions of each panel, a total of 6 dimensions for each panel. The dimensions need to be given as measured when facing the absorptive side of the panel, not the semi reflective side. When fitting panels to old fences, the fences tend to not be square.

Remember, you have to seal the fence below the lower rail all the way to the ground. Use a 2x6 or 2x8 between the bottom of the lower rail and the ground.

We'd like photos of the install and a report back from you about how well it worked. If you want to send photos to us so we can see what you are planning, please feel free to send them. We'll let you know if we see anything odd or in the way. If you want to see a sample of the fabric, send over your mailing address.

Sincerely, Arthur Noxon

from an audiophile ready for the next level

Dear Sirs,

I am a music lover and audiophile. Yesterday my wife moved the carpet 10cm to the right and that had a profound effect on the soundstage. It widened. So now I am interested in acoustical improvements.

With best regards, Eric

Art responds:

Congratulations Eric,

Usually it is the wife who keeps the audiophile from exploring acoustic upgrades. Here, yours has introduced you to the vulnerability and delicacy of the room acoustic imprint on the sound stage.

Here's how we work to voice your room. First, send over a floor plan showing speaker locations, listening position, and doors and windows and ceiling height. Then take at least 8 to 10 photos of your room showing us what your room looks like.

Include as list of the main gear in your room, speakers, amp and cable. Finally, what you like about listening. The music or the imaging. Yes, we all like both but with me for example, it's the imaging that really makes my day. I guess I assume the music sounds ok with a good system but when I get into imaging, then it really makes me happy. Now I know that the sound may be ok but the dynamic tracking of the sound may well not be OK. We have the MATT a test for dynamic stability, a musical intelligibility test that you'll also have fun with.

Each step costs some money. A small fee covers the initial setup of the file (floor plan and photos) and assessment for hifi room. The fee is fully applied to future acoustic product purchases.

We've been doing this for 20 years and you'll be glad you trusted us with your room.

Arthur Noxon

from a soundproofing customer


I live in an older home, with lath and plaster walls, and quite close to outside traffic. I am planning to replace an older window in the master bedroom which faces on the traffic and at the same time am most interested in the feasibility and possible effectiveness of applying WallDamp to at least three of the walls with a layer of drywall applied over that. Am I on the right track?

Recognizing that a number of factors are always involved is there nonetheless some way of estimating the potential sound reduction I might hope to achieve? As well, would applying one of the sound-deadening paints as a base coat to the final paint finish be helpful? ANY suggestions, recommendations or insights would be very much appreciated.

Thank you, BR

Art responds:

Hello BR,

1) Replacing windows that face traffic is tricky. Use thick glass or if you are going to put in modern double glazed windows be sure that one of the sheets of glass is significantly more heavy than the other. Modern thin thermal windows leak traffic noise badly.

2) If you are removing lath and plaster, and going to replace it with sheetrock, you are in for a big disappointment. Lath and plaster is heavy and both sound and vibration absorbing. Replacing it with sheetrock leaves you with a hollow sounding house, that traffic noise easily penetrates. I have an 1886 Victorian and I've been through this.

If you are removing lath and plaster, add insulation to the inside of the wall, or buy our Wall Wool for maximum absorption. Then add WallDamp to face of studs, blocking and plates. Add 3/8 sheetrock. Add WallDamp squares on 12" centers or less and add 1/4" sheetrock on top. This pretty much replicates the feel and soundproofing of lath and plaster.

If you are leaving lath and plaster, then YES, add WallDamp squares on 12" centers or less and cover over with one layer of 5/8 type X sheetrock for maximum absorption.

We always provide engineering support along with the needed materials for these jobs. Send photos and floor plan and sketches of what you are planning. We'll help you think it through so you get the best results for the budget you have to work with.

In general, sound deadening paint doesn't work on thick walls.

Arthur Noxon
Acoustic Engineer