Corner Bass Traps - Always beneficial?

[microstrip]

It is simple mathematics of sound. If you put the two speakers flush to the side walls, you get two nulls at 25% point. The theory says that if you put the speaker then int he nulls, they vanish. Hence the 25% rule. Now whether that is optimal otherwise, is another matter . I am just talking about bass performance.

Amir,
As far I see the problem you only get these nulls at one frequency. This is not bass performance at all. Or I am seeing it wrongly?

 

[microstrip]

Again, you can see real improvement down to very low frequencies. And this is real measurements, not a simulation or "theory." BTW, the traps were flat against the walls, not spaced way out into the room or even straddling corners.

--Ethan

Ethan,

Can you give us details on what type of bass traps (membrane, porous or a mixed type), what was the total area of the traps and the volume of the room?

 

[mep]

Sounds plausible and I cannot argue with the laws of physics, but the upshot would be the entire "bass trap industry" is selling snake oil, because no bass is actually being trapped.

Sadly it is true. From Dr. Toole's CEDIA presentation:

""Sometimes these (modular bass absorbers) are called "bass traps." The problem with the name is that some of them don't "trap" much of anything excpet cash from unwiiting purchasers."

I have to say I’m a little surprised that this thread has determined the bass trap industry is selling “snake oil” with no less than a quote from Dr. Toole. I don’t know how many times the subject of the importance of bass traps has come up on this forum and I have never seen their capabilities or lack thereof taken to task until now. Don’t we have at least one member on this forum who derives their living from selling bass traps?

 

[microstrip]

I have to say I’m a little surprised that this thread has determined the bass trap industry is selling “snake oil” with no less than a quote from Dr. Toole. I don’t know how many times the subject of the importance of bass traps has come up on this forum and I have never seen their capabilities or lack thereof taken to task until now. Don’t we have at least one member on this forum who derives their living from selling bass traps?

Mep,

Please read carefully the posts. No one had said what you are concluding. It is just said that most absorbers sold by SOME manufacturers do not extend their performance in the bass frequencies as should be expected from a bass trap and are really "snake oil" in the bass. Many manufacturers sell good quality bass traps and supply data about their products. There is not such a thing as the bass trap industry - IMHO such generalizations are misleading. Although I openly disagree a lot with Ethan about sound reproduction, the measurements and specifications of his products seem straightforward and well documented. But we will happily diverge on its specific application in listening rooms.

 

[NorthStar]

 

[NorthStar]

 

[Bruce B]

Bass traps you hang on the wall are a waste of money. To get "good" bass trapping, you need SPACE! Triangulate the corners about 4-6'. False walls with 6' space behind them or creating soffits with hundreds of cubic feet. THATS bass trapping.

 

[NorthStar]

 

[amirm]

Amir,
As far I see the problem you only get these nulls at one frequency. This is not bass performance at all. Or I am seeing it wrongly?

That frequency is your room mode. The one that you would be interested in solving. There will be others, e.g. in the other direction, that this won't solve. It is poor man's multi-sub solution after all .

 

[JonFo]

I will attest to the efficacy of bass traps, Real Traps in my case, as being extremely effective in managing room resonances.

It does take a lot of trapping devices to achieve good results in a decent sized room, but the results are worth it, and easily measurable.

Layer on room correction (Audyssey Pro in my case) and most LF problems are well mitigated. Bass is now truly 'articulate'.

So I do believe that straddling the corners with 6" thick limp-mass based absorbers will be helpful in managing bass modes in most rooms.

 

[mep]

Mep,

Please read carefully the posts. No one had said what you are concluding. It is just said that most absorbers sold by SOME manufacturers do not extend their performance in the bass frequencies as should be expected from a bass trap and are really "snake oil" in the bass. Many manufacturers sell good quality bass traps and supply data about their products. There is not such a thing as the bass trap industry - IMHO such generalizations are misleading. Although I openly disagree a lot with Ethan about sound reproduction, the measurements and specifications of his products seem straightforward and well documented. But we will happily diverge on its specific application in listening rooms.

I don't know how I could read what was stated and come to any different conclusions no matter how many times I read it.

 

[JonFo]

Bass traps you hang on the wall are a waste of money. To get "good" bass trapping, you need SPACE! Triangulate the corners about 4-6'. False walls with 6' space behind them or creating soffits with hundreds of cubic feet. THATS bass trapping.

No question that very low frequency (under 60hz) trapping takes massive volume or customized tuned and placed Helmholtz resonators. Which is why room correction PLUS whatever physical trapping one can add is a fairly realistic solution for most people.

 

[amirm]

I have to say I’m a little surprised that this thread has determined the bass trap industry is selling “snake oil” with no less than a quote from Dr. Toole. I don’t know how many times the subject of the importance of bass traps has come up on this forum and I have never seen their capabilities or lack thereof taken to task until now. Don’t we have at least one member on this forum who derives their living from selling bass traps?

As microstrip correctly stated, no one is against general use of acoustic products for bass. It is tempting for consumers to think that by merely putting a panel on the wall they have helped the bass response. As I explained, the physics of simple velocity based absorbers just doesn't allow that. You talk about Ethan. This is a chart from his web site:

For "classic" bass, we care about the first three lines as the graph starts at 50 Hz and by the next three ticks we are already at 80 Hz. As you see, the performance falls very quickly there. Compare the simulation of a panel on wall with the data above:

Look at the the dashed blue line in Ethan's specs which is the panel on the wall (as opposed to in the corner). His chart is not in percent but total absorption. If you compute the percentage in his graph, you see that the dashed blue line is only slightly better than the simulation (by my math at 0.15 vs .10).

Now, the absorption is not zero so if you put a pile of them there, eventually they will provide enough absorption. The issue there other than accommodating many of them is whether you have made the room too dead because you have substantial amount of absorption at higher frequencies now (and gotten rid of some beneficial reflections).

To wit, Ethan can confirm but I believe the measurement he has put forward is from his own living room which looks like this:

As you see, there are quite a few products there. And the fact that so many are spaced away from the wall even when placed on horizontal surfaces.

 

[microstrip]

Diaphragmatic absorbers put is the corners can be much more effective than the porous absorbers. As the distance from the panel to the corner is variable the peak of absorption is broad and can cover a large bandwidth. You can find a chart for designing the details needed to build them in the book The Master Handbook of Acoustics of FA Everest.

Also we can use Bruce strategy and built some large corners!
http://www.whatsbestforum.com/showthread.php?5893-Speaker-Room-calibration&p=93347&viewfull=1#post93347

 

[mep]

As microstrip correctly stated, no one is against general use of acoustic products for bass.

I didn’t say anyone was against using them. I’m only referring to the comments that I quoted that stated they aren’t effective at bass frequencies. I didn’t fabricate the quotes so I’m not sure where any misunderstanding lies here. I’m not the one that said:

…but the upshot would be the entire "bass trap industry" is selling snake oil, because no bass is actually being trapped.

To which you replied:

Sadly it is true.

 

[amirm]

I didn’t say anyone was against using them. I’m only referring to the comments that I quoted that stated they aren’t effective at bass frequencies. I didn’t fabricate the quotes so I’m not sure where any misunderstanding lies here. I’m not the one that said:

To which you replied:

What is generally being sold as "bass trap" does not perform that function. Bass is difficult to absorb let alone "trap" completely. But the phrase "bass trap" is such a great marketing phrase that it is used routinely against the capabilities of the product itself. This was behind my comment and that of Dr. Toole. If this is clear enough, let's move on .

 

[edorr]

OK. I bit the bullet and committed funds. Just ordered 4 six packs of 2" corning 703 to make my own corner traps, using this the design:

http://forum.studiotips.com/viewtopic.php?t=535

This will be a bit of work, but get me a lot more absorbing mass in my corners than using the standard 24" triangular traps. I'll do some treated and untreated measurements and report my findings.

 

[amirm]

Sounds good. Look forward to the report back!

 

[JackD201]

I wonder if GIK's "added feature" is a membrane.

 

[Ethan Winer]

Can you give us details on what type of bass traps (membrane, porous or a mixed type), what was the total area of the traps and the volume of the room?

As I said earlier, this was a lot of treatment in a small room. Full details in this video:

Hearing is Believing

Again, you don't need that much treatment to make a real improvement below 100 Hz.

--Ethan