Bass Traps NOT On Wall

[therealbigd]

Hi All

Was just thinking today, that bass traps are almost always found attached to walls. I really, just wondered - what effect would it have if you put it away from a wall? In the centre of a room. Would it be good (more surface area), or bad (bass tends to build up at walls more)?

If it's be a good thing, I might try it out as we have a room we're trying to tame, where we have windows all round, but no walls, and being able to hang it from eyebolts in the ceiling could be really good. But if it'd just sit and do nothing, I won't bother!

It'd be interesting to hear thoughts.

[jordanvoth]

No knowledge here, but I have seen those plant ones... they look pretty cool, I forget who makes them but hopefully someone can chime in here.

[SAC]

First, your use of the term 'bass traps' is a bit wide. There are velocity and pressure based traps.

And yes, they can be placed away from boundaries provided:
That you place them in their appropriate regions of optimal effectiveness (e.g.: in areas of high velocity or pressure respectively),
and that they are large enough, both with respect to the wavelengths targeted, and because the boundaries have a 'magnifying' effect as you are secondarily redirecting the incident energy back into the traps.

Edit: There are very practical reasons for not seeing them generally used in populated rooms, as they take up space and restrict motion and intra-room 'relationships', and we more often are concerned with managing specular reflection, not simply removing energy.

[avare]

Originally Posted by SAC

First, your use of the term 'bass traps' is a bit wide. There are velocity and pressure based traps.

And yes, they can be placed away from boundaries provided:
That you place them in their appropriate regions of optimal effectiveness (e.g.: in areas of high velocity or pressure respectively),
and that they are large enough, both with respect to the wavelengths targeted, and because the boundaries have a 'magnifying' effect as you are secondarily redirecting the incident energy back into the traps.

+1.

Andre

[RScott]

Bass pressure from all freqs terminates at walls. Various freqs will have pressure in the room itself, but the walls and corners catch the most stuff. Acoustic hanging panels are another concept that can be deployed hanging in a space. I'm not clear on the specifics of these, so www.johnlsayers.com forum would be a good place to search for info on hanging absorbers. John uses these in cavity spaces of some of his designs. The Master Handbook of Acoustics is a good starter into the field. I would probably stick to tried and true methods for acoustic treatment. Anything else is throwing darts imo.

Sent from my SPH-D700 using Gearslutz.com App

[jhbrandt]

Originally Posted by therealbigd

Hi All

Was just thinking today, that bass traps are almost always found attached to walls. I really, just wondered - what effect would it have if you put it away from a wall? In the centre of a room. Would it be good (more surface area), or bad (bass tends to build up at walls more)?

If it's be a good thing, I might try it out as we have a room we're trying to tame, where we have windows all round, but no walls, and being able to hang it from eyebolts in the ceiling could be really good. But if it'd just sit and do nothing, I won't bother!

It'd be interesting to hear thoughts.

Big D,

What specifically are you trying to tame? Tell us your problem areas - or better yet post a measurement file or snapshot of the waterfall response. What is the Dc of the room? room dimensions?

I have to quote SAC again here:

Originally Posted by SAC

First, your use of the term 'bass traps' is a bit wide. There are velocity and pressure based traps.

And yes, they can be placed away from boundaries provided:
That you place them in their appropriate regions of optimal effectiveness (e.g.: in areas of high velocity or pressure respectively),
and that they are large enough, both with respect to the wavelengths targeted, and because the boundaries have a 'magnifying' effect as you are secondarily redirecting the incident energy back into the traps.

Edit: There are very practical reasons for not seeing them generally used in populated rooms, as they take up space and restrict motion and intra-room 'relationships', and we more often are concerned with managing specular reflection, not simply removing energy.

+1 and

Cheers,
John

[therealbigd]

Originally Posted by jhbrandt

What specifically are you trying to tame? Tell us your problem areas - or better yet post a measurement file or snapshot of the waterfall response. What is the Dc of the room? room dimensions?

Not done yet.

Point is, trying to soundproof a room to the max possible, and as the building is made of wood, it doesn't do much naturally. So it's triple glazing on the sides, and the ceiling filled in with rock will covered with plasterboard. Now I get the feeling the rockwool will stop a nice amount of cymbals and snare but maybe not so much for the bassier instruments, so was just thinking of ways in which we could add trapping without the conventional wall-mounted technique (due to the walls all being made of glass). When the time comes to do it all I will happily send you some graphs and what not, this was more a 'is it possible, in theory' question, more out of interest than actual application to be honest.

[Hannes_F]

If you want to effectively block bass waves with treatment not attached to the wall you need an airtight shell all over the area. This shell needs to have mass in it.

Single elements like big gobos and the like will be surrounded by the bass waves. The problem is not that they would not have any attenuating property at all, they have. But something between -1 dB to - 3 dB in the bass range will probably not help you much.

BTW what can realistically be achieved with such shells is an improvement of 6 to 10 dB. The effect is limited because of the flanking paths.

[SAC]

Hannes is correct. Internal treatments are NOT going to be effective in mitigating ingress and egress. In other words, they won't do a thing regarding isolation!


Gypsum Board Walls: Transmission Loss Data
By Halliwell, R.E.; Nightingale, T.R.T.; Warnock, A.C.C.; Birta, J.A.
www.nrc-cnrc.gc.ca/obj/irc/doc/pubs/ir/ir761/ir761.pdf


System Details That Work (Leaks and Flanking)
by David Quirt
www.nrc-cnrc.gc.ca/obj/irc/doc/leaks-flanking.pdf

Guide for flanking sound transmission in wood framed construction - airborne sources
by Nightingale, T.; Quirt, J. D.; King, F.
http://www.nrc-cnrc.gc.ca/obj/irc/do.../nrcc49468.pdf

[jhbrandt]

Originally Posted by therealbigd

Point is, trying to soundproof a room to the max possible, and as the building is made of wood, it doesn't do much naturally. So it's triple glazing on the sides, and the ceiling filled in with rock will covered with plasterboard....

-- Just in case you did not understand Hannes or SAC above ---

You are mixing up treatment for room acoustics, (which we were all talking about earlier), with sound-proofing / acoustic isolation.

Room acoustics and room-to-room sound proofing do not use the same techniques.

You can not treat the acoustics in a room and change the acoustic isolation of that room. - That would be like having an aquarium with a leak and deciding that cleaning the algae will solve the problem.

You'll need an air-tight box... ir761 will give you some idea as to what is required.

Cheers,
John

[therealbigd]

Originally Posted by jhbrandt

-- Just in case you did not understand Hannes or SAC above ---

You are mixing up treatment for room acoustics, (which we were all talking about earlier), with sound-proofing / acoustic isolation.

Room acoustics and room-to-room sound proofing do not use the same techniques.

You can not treat the acoustics in a room and change the acoustic isolation of that room. - That would be like having an aquarium with a leak and deciding that cleaning the algae will solve the problem.

You'll need an air-tight box... ir761 will give you some idea as to what is required.

Cheers,
John

Thanks John, was just interested that's all.

Going to post a serious question later on!

[Hannes_F]

Originally Posted by jhbrandt

You are mixing up treatment for room acoustics, (which we were all talking about earlier), with sound-proofing / acoustic isolation.

Or, to try another analogy: Does the use of an umbrella block light? Yes it does, to a certain extent. But can you construct a photographic darkroom with a handful umbrellas? No way, you need to seal that really tight.

[Hannes_F]

For all that are interested here are measurement results for the transmission loss of a wall with (blue) and without (red) a closed shell in front of it. These measurements are done in a diagonal test bench that include flanking paths.

Note that while the overall transmission loss is bigger with the shell ... nevertheless the bass loss is reduced, something that does not seem to be unusual near the resonance frequencies of such systems.

Also note that transmission loss bigger than 35 or 40 dB around 50 Hz is very hard to achieve, no matter what you do. The nominal attenuation is 60 dB without and 70 dB with the shell ... but in a situation where the bass counts these numbers do not really help much.

Wall: 24 cm sand-lime brick, 10 mm plaster on both sides
Shell: 50 mm polystrol plus 12.5 mm gypsum board
Measurement method: Diagonal test bench
Data source: Hartmut Schröder, Fraunhofer-Institut für Bauphysik, St uttgart: Verbesserung der Längs-Schalldämmung durch Vorsatzsschalen

[Torea]

Originally Posted by jhbrandt

Room acoustics and room-to-room sound proofing do not use the same techniques.

You can not treat the acoustics in a room and change the acoustic isolation of that room. - That would be like having an aquarium with a leak and deciding that cleaning the algae will solve the problem.

Cheers,
John

I like that analogy =D

[DanDan]

Based on the classic theories I have sometimes recommended 'off the wall' solutions. e.g. A large fibre filled seat at the mix position or fibre filled couch at room centre. At some stage in discourse with Andre he referenced some BBC research which illustrated that such placements were perhaps only about one third as effective as the high particle velocity would suggest.
I may be remembering incorrectly, but if not, another intriguing anomaly IMHO.
Andre?


DD

[avare]

Originally Posted by DanDan

Based on the classic theories I have sometimes recommended 'off the wall' solutions. e.g. A large fibre filled seat at the mix position or fibre filled couch at room centre. At some stage in discourse with Andre he referenced some BBC research which illustrated that such placements were perhaps only about one third as effective as the high particle velocity would suggest.
I may be remembering incorrectly, but if not, another intriguing anomaly IMHO.
Andre?

You are correct. It is not off the wall, it is reality against standard "academic myths." The BBC paper is RD 1985-11.

Andre

[Rod Gervais]

Originally Posted by avare

You are correct. It is not off the wall, it is reality against standard "academic myths." The BBC paper is RD 1985-11.

Andre

It may not be "off the wall" - but it is literally "off the wall"

Rod Gervais
Director of Education
GIK Acoustics
Gik Acoustics USA
Gik Acoustics Europe
Tel.(US)1.888.986.2789
Tel.(UK)+44(0)20.7558.8976

[jhbrandt]

Originally Posted by TheBlueberryRoom

1-3db would sure help ...say...recording a kit in an otherwise terrible live room where you absolutely have to get the session done and there is bleed from the band next door

I would take 1-3dB reduction in lows around the close mics in that situation.

So. What is your point?

You are now quoting Hannes out of context.

Read post #10 - better yet, buy and read "The Master Handbook of Acoustics" - it is basic, easy to read, without confusing math, and most people with an IQ above 90 should be able to understand it.

You keep pushing your pet theory that gobos will affect transmissions loss - which is insane to put it mildly.

You keep arguing with professionals on a public forum... - You are annoying the teachers and will be asked to go sit in the hall...

--- Do you have an astounding new paper to present here? -- or to the AES?
Have you found some magic beans? -- or some VooDoo that works?

It is posts like that that keeps the poor souls that come here looking for an answer - in the dark... with at least with some hope that they can sit on their asses and wish their problems away.

~ Folks, this is not the first time that Blueberry Room has tried to tell people that Gobos will fix their sound ingress / egress issues.

And the point of my scolding is to try to stop the land-slide of myths that are pushed everyday day by unscrupulous sound-proofing foam dealers and the true believers... Once a ball this big gets rolling, it is nearly impossible to stop. - Mainly due to the psychology of group-think. And what makes it so easy for these dealers is that people too often want easy/instant gratification. Easy & Cheap.

People, do not confuse Room Treatment with Acoustic Isolation or Sound-Proofing. By the way, Sound-Proofing is Acoustic Isolation. Ignorant store owners that sell foam acoustic room treatment call it sound-proofing which is wrong at best. - And that brings me to the subject of changing the meaning of words by stupid people and the world/media just follow along.

Here are two examples:
Sound-Proofing = will make your room sound better.
Gender = a polite way of saying sex. (you will see this silly error on U.S. tax forms and every time I see it, I understand that I am dealing with idiots. It's like Hitchhikers Guide to the Universe...)

For those who do not understand the English language, which includes people from Texas, the word gender is used to describe words. ie; the gender of the word he is male. A man has no gender. He has a sex. Cattle have no gender they are determined male or female by their sex.

I hope that you all have enjoyed my little rant. If you would like to know more about acoustics; read and study and listen and experiment. -by experiment, I mean test for yourself the things that are known and proven. I have a tiny fraction of this good information posted on my site. Also, see the recommended reading list on my publications page.

FYI, I spent my childhood in Texas...

Cheers,
John

[jsipich]

Originally Posted by SAC

First, your use of the term 'bass traps' is a bit wide. There are velocity and pressure based traps.

And yes, they can be placed away from boundaries provided:
That you place them in their appropriate regions of optimal effectiveness (e.g.: in areas of high velocity or pressure respectively),
and that they are large enough, both with respect to the wavelengths targeted, and because the boundaries have a 'magnifying' effect as you are secondarily redirecting the incident energy back into the traps.

Edit: There are very practical reasons for not seeing them generally used in populated rooms, as they take up space and restrict motion and intra-room 'relationships', and we more often are concerned with managing specular reflection, not simply removing energy.

+1

- Jack

[flyingworld]

Originally Posted by jhbrandt

-- Just in case you did not understand Hannes or SAC above ---

You are mixing up treatment for room acoustics, (which we were all talking about earlier), with sound-proofing / acoustic isolation.

Room acoustics and room-to-room sound proofing do not use the same techniques.

You can not treat the acoustics in a room and change the acoustic isolation of that room. - That would be like having an aquarium with a leak and deciding that cleaning the algae will solve the problem.

You'll need an air-tight box... ir761 will give you some idea as to what is required.

Cheers,
John

AMAZING! ALL OF THESE POST ARE JUST AMAZING.I'M NOT GONNA SOUND PROOF THE WALLS AT THIS TIME.I'M JUST TRYING TO GET A MORE ACCURATE ROOM,WILL THE AURORA TRIANGLE BASS TRAPS HELP MY CORNERS? AND SHOULD I DIFFUSE FROM THE SPEAKERS? AND ABSORB THE REST?

Sent from my PC36100 using Gearslutz.com App

[DanDan]

Well, I have issues about who may be the Real Big D, obviously...
However,

I really, just wondered - what effect would it have if you put it away from a wall? In the centre of a room. Would it be good (more surface area), or bad (bass tends to build up at walls more)?

The answer is probably in the BBC paper which Andre, as ever kindly, provided. I tried to read it quickly, but research papers don't respond to that, plus to be frank my physics ain't really up to it.
Andre, would it be fair to say that fibrous absorption does not behave as well as might be expected from some theories, at areas of high particle velocity, i.e. off the wall....
Or as my memory suggests, about a third of such expectations.
Disappointing as this may seem, I like the real world and relish such anomalies. If I may be so bold, could you, Andre, draw a simple conclusion from the BBC work?
DD

[jhbrandt]

Blue,

I had assumed that Hannes was talking about Damping rather than attenuation and said nothing before... as we were talking about room acoustics and not transmission loss through barriers.

You will not get 1-3db of attenuation at frequencies that are equal to or larger than the size of the gobo... and only if the gobo is made of concrete. If the gobo is a porous absorber with no mass, it will do nothing to attenuate bass frequencies at all but will only attenuate frequencies that have a length up to twice the thickness of the trap/gobo.

You will have a 'shadow' in the ray region, but this does not apply to the wave region and even in the shadow area, you will still get diffraction into the shadow.

I am sorry if you feel that I 'got on you' too hard. It just seemed to me like you were pushing a point about gobos or treatment affecting the STL of the room partitions. -- and the last time I looked, you were still arguing about it. So, forgive me for jumping onto you so quickly.

Cheers,
John

[Hannes_F]

Originally Posted by jhbrandt

You will not get 1-3db of attenuation at frequencies that are equal to or larger than the size of the gobo...

+ 1. The deeper the frequencies are, the steeper the wave will diffract into the shadow behind the gobo. Sorry man.

The 1 - 3 dB number was just a ballpark to indicate that room treatment indeed has a shielding effect if you look at it physically (especially with thick closed layer absorption and/or heavy shields) but it will not suffice for your demands in the bass range.

Room isolation vs. room treatment is not a question of black and white if you look closely ... but the grey is too much away from black in the most cases, unfortunately.

However, if somebody knows what he does (which must include measurements) he can use those grey shadows to his advantage, that is what I wanted to say. In one case it worked very well for me.

In case you don't know exactly was diffraction is and how it works and can really measure what you do, listen to J. H. Brandt. He is the expert (have recommended him several times for projects and will do that any time again).

[avare]

Originally Posted by DanDan

Well, I have issues about who may be the Real Big D, obviously...
However,
The answer is probably in the BBC paper which Andre, as ever kindly, provided. I tried to read it quickly, but research papers don't respond to that, plus to be frank my physics ain't really up to it.
Andre, would it be fair to say that fibrous absorption does not behave as well as might be expected from some theories, at areas of high particle velocity, i.e. off the wall....
Or as my memory suggests, about a third of such expectations.
Disappointing as this may seem, I like the real world and relish such anomalies. If I may be so bold, could you, Andre, draw a simple conclusion from the BBC work?

That is exactly my conclusion. At the worst locations, porous materials will absorb about 1/3 as much as in ideal locations (for absorption). Applying this
to acoustic treatment strategies, ths is why I recommend as thick as possible for all absorbers. When looking at the complete cost of absorbers including labour, the addtional cost of going from 4" to 8", remembering that lighter material, or 4" of 7903 type material gapped can be used, is minimal compared to the additional low end absorption obtained. Depending on the prices of the 2 different density materials, the deeper absorber may even be more inexpensive!

The best designs for acoustic treatment are not always the most expensive.

Thanks Dan.

Andre

[Torea]

Hey all, it appears I'm pretty late to the party with this, but maybe it'll still be relevant. I'm not requesting help with this (aka not a hijack), I'm just trying to point out my tests of bass traps in the middle of the room.

This was all done before properly orientating my room (12'x16'x8'); I was facing the 16' wall. That said, the SPL responses looked better than I thought they'd be. I made three traps, 2'x4'x4". Also, my speakers have their low cut at 70Hz, explaining some of the poorness in the bass. So first, untreated...

When I first built my bass traps I did some tests just for fun. Since I only had two framed, I only used those two. I decided to put them parallel to my chair, a few inches wider than the speakers. I also put them in a few different places but none of them were radically different so I took the average. I thought it odd that they moved the dip from 100Hz to 200Hz. This is the (hopefully) relevant test, because the traps were almost in the center of the room...

Lastly, I placed the traps in the back corners of my room. They were maybe 7-9 feet back from the mix position. Also, there was one trap standing on my desk, between the speakers, in the vertical position. It was maybe 6-8 inches from each speaker...

[therealbigd]

Originally Posted by DanDan

Well, I have issues about who may be the Real Big D, obviously...

Meaning?

[Hannes_F]

Originally Posted by Torea

Hey all, it appears I'm pretty late to the party with this, but maybe it'll still be relevant. I'm not requesting help with this (aka not a hijack), I'm just trying to point out my tests of bass traps in the middle of the room.

This was all done before properly orientating my room (12'x16'x8'); I was facing the 16' wall. That said, the SPL responses looked better than I thought they'd be. I made three traps, 2'x4'x4". Also, my speakers have their low cut at 70Hz, explaining some of the poorness in the bass. So first, untreated...

When I first built my bass traps I did some tests just for fun. Since I only had two framed, I only used those two. I decided to put them parallel to my chair, a few inches wider than the speakers. I also put them in a few different places but none of them were radically different so I took the average. I thought it odd that they moved the dip from 100Hz to 200Hz. This is the (hopefully) relevant test, because the traps were almost in the center of the room...

Lastly, I placed the traps in the back corners of my room. They were maybe 7-9 feet back from the mix position. Also, there was one trap standing on my desk, between the speakers, in the vertical position. It was maybe 6-8 inches from each speaker...

Hi Torea,

thank you for your contribution. I understand you placed traps rather in the middle of your room than at the walls and it changed something in the frequency response.

For really understanding your measurements it would be good to have a sketch of your setup ... where were (approx.) the speakers, the mic, the traps?

Also, did you move the mic between measurement 1 and 2?

What exactly is measurement 3?

Without these informations I would have difficulties to draw any conclusion at all.

Second step, in case the informations asked for above were available, would then be to look at waterfall diagrams, too. The frequency response does only tell a little part of it.

[Torea]

Originally Posted by Hannes_F

Hi Torea,

thank you for your contribution. I understand you placed traps rather in the middle of your room than at the walls and it changed something in the frequency response.

For really understanding your measurements it would be good to have a sketch of your setup ... where were (approx.) the speakers, the mic, the traps?

Also, did you move the mic between measurement 1 and 2?

What exactly is measurement 3?

Without these informations I would have difficulties to draw any conclusion at all.

Second step, in case the informations asked for above were available, would then be to look at waterfall diagrams, too. The frequency response does only tell a little part of it.

So here are a few pictures of my setup for those tests. Obviously, my mix position (computer and blue cubes for speakers) isn't oriented as it should be, but it's what I had at the time.

I did all the tests on different days, but made sure to use a tape measure to get the mic in the same spot. I believe all three are averages, moving the mic a few inches to the front, back, left, and right (even if the REW thing doesn't say average).

Measurement 3 is with traps in the back corners of my room, and one on top of my table. You'll see from the pictures here. Also, for the second picture (sides) that corresponds with measurement 2, I think the traps may have been a few inches wider apart, but you get the idea from the picture.


The yellow rectangles are the 2'x4'x4" traps.

[Torea]

And the waterfalls for my measurements. Green is the empty room, Red is traps parallel to the mic, and Orange is traps in back corner/on tabletop.

[localhost127]

is it just me or is that pretty significant for only 3 traps?? especially on the low end. granted, there's still lots of problems to tend to, but pretty big change for only 3 traps!