Corner Trap Nonsense

[olieb]

So using an airgap is really never the best option.

Here are two different uses of 100 mm porous absorber panel modeled for normal and random incidence.
I took the geometry from the panels @Randyman... described above. 4" of rather dense fibre and 4" gap.
Green is with gap, blue is without. Which use of the absorber gives better efficiency in bass?
(A gap of 8" would be even more efficient, but one would be getting into that "middle of the room" problem.)

Porous Absorber Calculator

Secondly, when the sound energy is not contained it will flow and not be absorbed. We know this now based on newer studies.

Well I have no clue, what you are saying here. Is the energy flowing like water? Or like heat? Or in a different way?
I am very much interested in those newer studies as the theories behind the modeling from acousticmodelling.com from above must be moot now.

 

[Bjorn]

I know what those simulation show and they are wrong. Newer studies, newer knowledge

 

[HiMu]

I know what those simulation show and they are wrong. Newer studies, newer knowledge

Sincerely interested, please provide a source or link to those studies, if they are published!

 

[Wolf11Man]

A layer of some absorbent on a wall has no effect on low frequency. You can tune simulations with unrealistic data or program them to prove the opposite, but that is exactly the kind of sales lies that are told.
If you want to know what a material does, look at the manufacturers data. You will then understand that the claims of these snake oil sellers are pure nonsense. They do not manufacture anything by them self's, but only use industrial materials that are used in huge amounts in buildings. The larger a building gets, the more of these relative cheap materials is used. Think of hotels, schools, hospitals, bureaus, cinemas and concert halls. Just because some audio crooks re-label it and ten-fold it's price, no material gets any magic abilities.
Of course room treatments can change the acoustic environment, but there are close limits and frequency regions. Some problems in some rooms simply can not be cured by putting any material or resonant boxes at walls, the ceiling or in corners.

If you are a professional or educated DIYS speaker builder, you may know what material has what effect, because you use them inside your builds. Porous materials only work in the medium and high frequency range. So any claims of them reducing something like a 60Hz mode effectively, are simply wrong.
You can't beat physics, even if some claim to do so.
The best way to improve a problematic bass reproduction is to use hardware in the signal chain. There are various, well working solutions, like Anti Mode, some Audessey version, Dirac and REW.
DSP's have made things a lot simpler and better, before that the parametric equalizer was a possible cure.

 

[olieb]

I know what those simulation show and they are wrong. Newer studies, newer knowledge

Yeah, these studies that you will not reference and this "newer" knowledge nobody knows.
"Secret science" only for the initiated and those in the "know". "Flowing energy" and such.

 

[Wolf11Man]

If you are a seller of such stuff, you have another kind of view on physics, influenced by your bank account.

 

[jlo]

The best way to improve a problematic bass reproduction is to use hardware in the signal chain. There are various, well working solutions, like Anti Mode, some Audessey version, Dirac and REW. DSP's have made things a lot simpler and better, before that the parametric equalizer was a possible cure.

Hardware won't work with modal notches : it can correct a peak but cannot compensate an acoustical cancelation.
Only basstraps, resonators (or PSI AVAA) can, under some conditions, fill a deep notch.

 

[Tim Link]

A tube trap is a silly design since it doesn't cover the corner properly and has a small diameter. It's basically a fancy commercial product for eye catching.

We try to make them look nice, but few people are attracted to TubeTraps specifically for their visual appeal. We also sell a rectangular corner bass trap. It takes more work to put one of those together, so they end up being more expensive. Being square they are less adjustable in terms of aiming the high frequency reflecting side.
The diameter can be a number of sizes. The big ones are about the diameter of a 55 gallon drum. A lot of rooms don't have space for something that big.

Speaking of 55 gallon drums, they could be square too, but they are typically tubular.

The following quote from here: https://www.acousticsciences.com/tubetrap-history/

"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. "

 

[Tim Link]

It doesn't work that way. First of all, a big airgap leads to a loss in absorption in parts of the frequency area. So using an airgap is really never the best option. Secondly, when the sound energy is not contained it will flow and not be absorbed. We know this now based on newer studies.

The best way to use porous material for bass trapping is using the correct material vs the thickness and flushed against the wall. Something done below in a room I designed where red graph is before and blue after bass trapping applied. As can be seen, porous can work really low when done correctly.
View attachment 403650

Looks intriguing. Any more info on the size of the room and amount of material used to treat it?

 

[krabapple]

Interesting that people can't even seem to agree on what is nonsense and what is not, on this topic.

 

[Wolf11Man]

There are alternative facts for bass traps. Those who sell them offer an alternative to reality. If the customer agrees, everthing is fine. Not only in the US alternative facts have become increasingly popular for a mentaly different audience.

Because there is scientificaly correct room treatment, the snake oil industry just bends reality to their financial favor. This is why it is so hard for many, semi educated in the science, to come to a truthfull and realistic conclusion. "Maybe they have found something new, you don't know" is what you hear from the believers.
They can not see the hard border between evolving technology and physical impossibility.

If you have science based company selling only working sound proofing, the stupid customer will not choose you, but the crook promising him whatever he wants. Customer stupidity is not limited to poor customers, but found under many rich ones as well. So you have to decide to die honest or sell lies and live.

You find this behavior in all aspects of life. Just think of those people with terminal illness, that fall for the false promises from criminals offering wonder healing.
An ill sized listening room is just similar, it is impossible to correct it in all aspects without breaking down walls. You can't make money by telling the audiophile in a square, badly modal room, the ugly truth.

 

[basscleaner]

Which is also a corner ("a place or angle where two sides or edges meet"), no?



A single tube trap for a 34Hz room mode. What size of tube trap do you have in mind, and do you have any measurements to show us how effective it is at these frequencies?

Yes, of course. As you know, shoebox room has 8 corners.
It is a very good question. We know, that any tube has your own modal frequency, which is determined by its longitude. You make sure for yourself in this phenomena. Some years ago I simply took a piece of cardboard tube and it just so happened, that there was coincidence between one resonant mode for the room and the tube frequency due to longitude. The effect was very strong. I had sensed vibrations of the tube wall by my fingers. The tube diameter was 1 ft. After this I have used lids, which can be titled at the tube ends to shift absorption peak. But, unfortunately, I didn't have opportunities to investigate this effect further and had some successful attempts to use such a construction at some control studio rooms. It was an attempt to construct telescopic tube, which was used in some cases more or less successfully.

 

[basscleaner]

Well, anything else would have been close to miraculous.
To absorb sound below 100Hz you need quite a bit of fibrous material. How thick were your sheets/panels?

Porous Absorber Calculator

And even if you achieve considerate absorption this will only produce a (global) attenuation of sound, because you do this at the mouth of a horn (more or less one point in space) and absorption is not selective in frequency. The modes in the room will stay the same (that is valid for the horn cavity, too). Only small changes might happen.
And about the plastic sheet moving only a little bit. That is just the way sound is. That is not different with a "big" volume in the corner where air is pressed into by the bass wave. A 104dBSPL signal (already quite loud) has a pressure peak of 28Pa, that is 1/3600 of the air pressure. If you have a corner volume of 200 liters, then only about 50cm3 will be moving in and out. That is all the movement for the absorption to work upon.

There is one effective technique to fight with QF narrow SPL peak for LF range. You could take piece of tube with such a longitude (diameter 1' or bigger), which correspond to 340 m/sec divided by frequency to be damped and than divided by 2. By means of SPL-meter you need to find place in the room volume, where is the maximum of SPL (there may be some of them) and place tube such a manner, to place end of tube there. You need to measure FR in the listening point before and after this. It may will require to try some positions for tube in vertical or horizontal locations. There is important to have free space between ends of tube and hard surface not less than 1 ft. It is good to use hard movable lids on these tube ends to control damping capacity. Sometimes it works very impressive

 

[Wolf11Man]

You forgot to mention the magic wand that directs the energy into your resonator. This is the point where all bass traps hit the impenetrable wall of physics.

Compare it to a sack full of fleas. It is very easy to open it up and release all the tiny buggers, but near to impossible to put them back.
So once you released sound pressure into your room, it will not go back into a single opening (of a bass trap).
Case closed one could think. If there was not that much money to be made with snake oiled corner boxes. Not only the seller of these expensive nonsense promote them, also the poor fools that bought them and don't want to admit they have been scammed.

 

[Tim Link]

You can't make money by telling the audiophile in a square, badly modal room, the ugly truth.

The good news is that modes aren't the only issue, and they take time to build up, and musically are not always the problem they're made out to be. To excite and hear all the modes you have to put a speaker in a tri-corner and then put your head in another tri-corner. Who does that? In real listening setups here are other problems that can be measured and addressed to good audible effect.

 

[Tim Link]

You forgot to mention the magic wand that directs the energy into your resonator. This is the point where all bass traps hit the impenetrable wall of physics.

No magic wand. Just the room. The bass can't be kept away from the resonator, and the mode requires strength of the reflections to be built up. If something out of phase with that build up enters the equation it's going to supress the overall strength of the mode. How well it will work depends on a number of factors. You'll have to do the math to see what the results will be, or actually set it up and test it. Problematic modes are often sub bass, which is below 60 Hz. Bass traps are not necessarily effective in sub bass ranges for obvious reasons. A bad mode way down in that sub bass range can be eq'd down. We don't hear timing so well down there so the lack of clarity because of resonance is not as important at 34 Hz as it is above 100Hz. Above 100 Hz bass traps can be made at reasonable size and fit in to a room to make measurable and audible improvements in clarity.

 

[Mschn]

I know these BBC reports have already been referred to in other threads but it seems (to me) they are worth mentioning here too:
The Design of a Modular Sound Absorber for Very Low Frequencies
A Modular Wideband Sound Absorber

I have one comment regarding the online absorber calculators: They model 'one dimensional' absorbers by which I mean they only take the depth dimension into account. Introducing and an air-gap behind a porous absorber of finite width and height will not work as well as those calculators predict. This is not to say the gap is always useless. Sealing the edges should improve things.

Cheers,
/Martin

 

[Wolf11Man]

If you read the BBC report because you want to construct any kind of "bass trap" from it, you will be very disappointed. Hitting a certain frequency is near to impossible and an area of 10 square meters (!) or 110 square feet is needed just to measure some results. A convenient size, tucked away in some corner, is useless. That is what is sold on a regular base as a bass trap: Useless. Snake oil.
The important point is, the BBC build something from a theory, but the absorbers working frequency were different from the calculation. These random results were measured and noted as success. If they only had measured the predicted = wanted frequency, the result would have been a simple fail.
The used wood materials will change resonance frequency with temperature and humidity, which is another unwanted result.

 

[Tim Link]

If you read the BBC report because you want to construct any kind of "bass trap" from it, you will be very disappointed. Hitting a certain frequency is near to impossible and an area of 10 square meters (!) or 110 square feet is needed just to measure some results. A convenient size, tucked away in some corner, is useless.

Keep in mind that for making measurements in a reverberation chamber you have to have enough of the material compared to the size of the reverberation chamber for the measurement to be reasonably accurate and meaningful. Also depending on how the material is spread around the chamber you will get a different calculated absorption coefficient for the same traps. We had our products tested at NWAA labs up in Washington. They have a very large reverberation chamber so we had to bring an adequate number of corner traps to get a good measurement, in accordance with established standards. While we were testing, the facility manager offered to do another free test to learn more about how the traps perform. He wanted to see if the same number of traps would perform as well if scattered randomly on the floor in the middle of the chamber. The result was the reverberation in the room was better controlled with the traps in the corners.
I think we brought 16 traps for that test session. That room is humongous compared to a standard home listening room. TubeTraps are not tuned to hit a specific frequency.

 

[Wolf11Man]

I allways thought ASC meant "Alternative Science Crooks". I see you gave it another meaning to trapp more audiophiles into buying your cardboard rolls?
You needed 16 traps to measure anything. Can you tell us what 16 of these cost? Just like the BBC had to use a huge multiple of what they had planed for when they started. At that point you change the volume and dimensions of the room from disposing all these useless money trapps inside it. You could as well have stacked a numper of moving boxes instead of your cardboard rolls to get the same result.

For the poor fools that thinks about buying such nonsense trapps: Just get some plain cardbox rolls from Home Depot. Place them inside your listening room at the rate you are shown (dozends of them!). It will have the same result by diffusing the audible sound. The only difference is the price, saving you an amount not worth mentioning, maybe like 10000$. And remember: If 10 don't work, buy another 10 and try again. The seller will be happy to assist in taking $ loads from your wallet.

I'm sure in a country of 335 millions, every morning some idiot wakes up and decides to throw a handfull of money out of the window. Why not with ASC, you are right. I just didn't think about that.