Sorting out bass trap myths

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daav

daav

Flailing up a storm.
1. What is the story with needing to seal corner bass traps? I've never really felt like I've understood that.
See the attached pic i drew up. Does there need to be some seal with a 4 inch fiberglass trap alontg the entire wall, floor to sealing tohave an effective trap? I always thought that just having the panels agains the wall in the triangle formation would do the trick, but have heard otherwise lately. If they do need to be sealed, shoud they be caulked to the walls, taped, what?

2. How about the "pressure" traps? These are the cylindrical ones made from pipe insulation that are sealed on the ends and along the length. The principle touted (as i understand it, please correct my ignorance) is that since low frequency waves actually raise (?) air pressure as they travel through the room, and physics says stuff wants to go from high to low pressure, they are "attracted" to the interior of these traps and thus more actively pass through the absoptive material, and so these kinds of traps suppoosedly suck the bass right out of the room. I've read people swearing by these and other saying it is a bunch of BS. it confuses me, because since the fiberglass is not airtight at all, i would not expect there to be any real presusure difference between the inside and outside (unless there is omehting dramatic goign on from the sound passing through outside, i dunno).

3. how about the 'super chunck traps described (first i saw them) here (fantastic job on the page by the way):
http://www.radford.edu/~shelm/acoustics/bass-traps.html
Do these work well? Seem slike it would be a lot easier to just make these triangle things and stick them in corners than spend all this time and energy working out design and framing stuff to got the panel traps just right. Might take abit more fiberglass to do, but it seems like such a simple design.

I have read a TON of posts about htis stuff, and i have buyilt a few panel traps and one of those cylinder traps to try out (and seen improvements but i don't have the time right now to record sutff i want to do, let alone A/B all these traps and test them out), but i want to come up with a nice one size fits all process to work out in my studio going forward.

Thanks,
daav
 

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I did not and can't seal my traps. They still shoot down bass frequencies though.
 
I'm not an expert, but I will offer what I think I know. True "bass traps" have some sort of membrane that is air tight, and their innards or something resonate to a tuned set of frequencies thereby absorbing the bass sound waves that hit them while leaving alone the other frequencies that you don't want to be absorbed.
What you are looking to build are broadband absorbers. They aren't tuned or anything fancy like that; the sound waves just lose energy as they try to push into and through it no matter what frequency it is (dependent on the absorption characteristics of the material and the energy contained in the various soundwaves and yadda yadda). The high frequencies are easily absorbed, but the lower frequencies are harder to absorb. But these types are usually preferred for the home studio, which typically has problems with reflection points as well as bass nodes.
 
Reggie said:
I'm not an expert, but I will offer what I think I know. True "bass traps" have some sort of membrane that is air tight, and their innards or something resonate to a tuned set of frequencies thereby absorbing the bass sound waves that hit them while leaving alone the other frequencies that you don't want to be absorbed.
What you are looking to build are broadband absorbers. They aren't tuned or anything fancy like that; the sound waves just lose energy as they try to push into and through it no matter what frequency it is (dependent on the absorption characteristics of the material and the energy contained in the various soundwaves and yadda yadda). The high frequencies are easily absorbed, but the lower frequencies are harder to absorb. But these types are usually preferred for the home studio, which typically has problems with reflection points as well as bass nodes.
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Right, that is my understanding, so I guess the sealed stuff I heard was not qualified well, or i am dumb, whcih is more likely.

I wil believe that i do not need to seal antyhign unless there is another correction posted.
 
Daav,

It's true - only membrane traps need to be sealed - with these you can (with fair accuracy) take care of a single problem frequency - but with typical high density rigid fiberglass (or rockwool) you deal with a much wider range of frequencies - and there is no membrane to seal.

Item 2 is bull***t - that isn't how they work - they work on the same principal as the "sealed traps" (membrane traps) you referred to in item 1.

3. Superchunks in corners are a great way to deal with LF issues - but you will also need to deal with reflections of the walls - and could possibly use a ceiling cloud as well (all made with the same rigid fiberglass or rockwool)

This approach will give you a well rounded room.

Rod
 
My Answers

No need to seal resistance traps, membrane traps are not likely to be all that affected either.

The pressure traps thing is pure hooey, they work, but are really just resistance traps. All sound waves both raise and lower the air pressure momentarily, cause they are waves.

As for superchunk traps they will work but are not the most efficient use of a certain quantity of 703 fiberglass. Note that fiberglass traps work best if there is an air gap between them and the wall. Look at the design of the superchunk trap. Where is the air gap? The superchunk trap would work better with less fiberglass if they were only about a four to six inch deep trapezoid with the remainder of the triangular area to the corner left empty.
 
This approach will give you a well rounded room.
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Folks, you heard it from our resident expert.

Rod, welcome back and I hope your post surgery recovery is doing well. I wasn't aware of the seriousness of your condition prior to you entering the hospital. Hence my last attempt at humor regarding your stay in the hands of the HMO's. Please accept my apology for that. I understand they took very good care of you. Anyway, good to see you still find time to visit here. Thanks.

Oh, btw folks, for those of you who are looking for GREAT information on studio building, Rod has a new book out regarding said subject, which from my understanding is absolutely "the studio building bible". :D I haven't ordered mine yet, but I will soon. Although, at this point my studio is almost done...Doggone Rod, I wish you could have published it 5 years ago. :eek: :p
Anyway, heres a link to some info on it.
http://www.johnlsayers.com/phpBB2/viewtopic.php?t=5670&sid=e697fcc9fae3d17de528d123a07d38fc
 
Innovations said:
As for superchunk traps they will work but are not the most efficient use of a certain quantity of 703 fiberglass. Note that fiberglass traps work best if there is an air gap between them and the wall. Look at the design of the superchunk trap. Where is the air gap? The superchunk trap would work better with less fiberglass if they were only about a four to six inch deep trapezoid with the remainder of the triangular area to the corner leftempty.
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Innovations,

No disrespect intended - but you are mistaken.

Here's a thread regarding this - with data from tests performed at Riverbanks that indicates that the superchunks outperformed a trapazoid 703 (4" thick) by far.

http://forum.studiotips.com/viewtopic.php?t=536

Now - I will agree that the added performance has it's cost - BUT - if space is an issue - it is certainly a more effective manner to gain a lot of added absorption without giving up any added room in your room.

Sincerely,

Rod
 
Rod Gervais said:
Innovations,

No disrespect intended - but you are mistaken.

Here's a thread regarding this - with data from tests performed at Riverbanks that indicates that the superchunks outperformed a trapazoid 703 (4" thick) by far.

http://forum.studiotips.com/viewtopic.php?t=536

Now - I will agree that the added performance has it's cost - BUT - if space is an issue - it is certainly a more effective manner to gain a lot of added absorption without giving up any added room in your room.

Sincerely,

Rod
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I don't think that we are really in disagreement. Not that my statement was that for a given quantity of 703 it was not the most efficient.

So a floor to ceiling SuperChunk requires a full bale of 703. With the same bale you can create six four-inch thick broadband traps. Even if you say that the single superchunk absorbs more than the six typical panel traps the superchunk treats ONE corner. Other corner pairs in the room are still untreated. You can take the SIX panel traps that you made with the bale of 703 and place them around the room, damping down all the potential problem spots.

So, my statemet essentially was, if somebody gave you a bale of 703 and said 'treat this room' would you use it all to treat just one corner?
 
id treat as much of the room as possible, hell home recording is a lot different than commercial recording. take what you are given and the tricks involved, that's home recording. gotta love it!
 
Innovations said:
if somebody gave you a bale of 703 and said 'treat this room' would you use it all to treat just one corner?
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In general, I would treat multiple locations - corners, first reflection points and see if it was meeting my needs. if not, I could always cut up some of the 703 and make super chunks out of it.

I think overall you have to measure your room and surrounding environment to be sure of what your issues may be and then whether or not you are moving in the right direction with your treatments.
 
Innovations said:
I don't think that we are really in disagreement. Not that my statement was that for a given quantity of 703 it was not the most efficient.
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Inno,

I was responding more to this statement - which is incorrect on it's face:

Look at the design of the superchunk trap. Where is the air gap? The superchunk trap would work better with less fiberglass if they were only about a four to six inch deep trapezoid with the remainder of the triangular area to the corner left empty.
Click to expand...

That is (simply put) - not true.

Thus - although Iwill agree that (with imited funds) you can treat more of the room with the same amount spread out - - and that in the end- that same product spread out will give you greater absorption than the single super trap - that does not change the fact that a supertrap works better than a trapazoid with air behind it.

So, my statemet essentially was, if somebody gave you a bale of 703 and said 'treat this room' would you use it all to treat just one corner?
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Well that would depend on my present financial status - if I could afford to do my corners with super traps - and then treat my reflection points - I certainly would do that.

The reason for that is this - it is so simple to treat frequencies above 200Hz, and the same amount of product spread out will handle all of those issue - but that same amount (spread out)will hardly touch the lower frequencies - which are what create your modal issues.

So you end up with a room that is bass light (or heavy depending on your listening location) and you have to constantly correct for that in your mixes - so in my mind dealing with the real issues is the most important thing - it makes life so much easier during the mix down process - at which point it becomes much more fun - and a lot less like work.

And I don't know about you - but for me - the music is supposed to be something I do that relaxes me after a hard day's work - not something that taxes me.

Sincerely,

Rod
 
People often have that misconception that you have to have air behind it. It's not the air - it's the distance from the front face to the hard boundary. If that space is filled with absorbtion, the distance does not change but you get more of the wave in absorbtion.

Even on the walls, when you space a 2" panel out 2", it's not the air - it's the distance. You're getting closer to the 1/4 wavelength of lower frequencies. That said, 4" on the wall will outperform 2" spaced off the wall 2".

Rod.

Welcome back.

Bryan
 
bpape said:
People often have that misconception that you have to have air behind it. It's not the air - it's the distance from the front face to the hard boundary. If that space is filled with absorbtion, the distance does not change but you get more of the wave in absorbtion.

Even on the walls, when you space a 2" panel out 2", it's not the air - it's the distance. You're getting closer to the 1/4 wavelength of lower frequencies. That said, 4" on the wall will outperform 2" spaced off the wall 2".

Rod.

Welcome back.

Bryan
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yes but the two inches of air are free. A four inch trap with two inches of air behind it may not outperform a six inch trap against the wall, but the two inches of air are essentially free.

Moreover there is a matter of diminishing returns. You can't absorb more than ALL of the sound that hits a trap. A trap has no ability to draw sound to it.

Bass builds up between corners in a room. (Actually it builds up between opposite corners because that is the longest dimension in the room.)

So somebody puts a whole bale of 703 in two corners of their room in the form of Super Chunks. Meanwhile the OTHER corner pairs have NOTHING. Is the bass problem solved for the room? No. If the same bale is used to make six four inch traps covering all the major corner pairs in the room is the bass problem solved for the room? Most likely yes as well as any problems with mids and highs too.

That's why I think it deserves to be in the 'bass trap myths'...that you can solve your bass trap needs by putting a ton of stuff in just one corner.
 
Innovations said:
That's why I think it deserves to be in the 'bass trap myths'...that you can solve your bass trap needs by putting a ton of stuff in just one corner.
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Inno,

No one has ever made the claim that "you can solve your bass trap needs by putting a ton of stuff in just one corner" - but rather that (while taking up exactly the same amount of real estate in a room with either treatment) you can dramatically increase the amount of effective bass trapping through the use of super-chunks versus 4" trapazoidal corner treatments.

Obviously anything you do that gives you a dramatic increase has a cost associated with it - but cost doesn't make it a myth - thus it doesn't belong with myths.......

It's another good approach (of many) with tested results from a respected independent laboratory.

If someone can't afford it that doesn't change the fact that it works.

RealTraps work........... Auralex traps work.............. GIK traps work........ whether someone can afford them or not is irrelevant - they work......

Trapazoidal traps work - you can see the test results -

Super Chunks work - you can see the test results..........

how many one will need is based strictly on how many sabins of absorption is required in one's space - the is no myth involved with any of these treatments - but there is one hell of a cost difference involved.

sincerely,

Rod
 
how many one will need is based strictly on how many sabins of absorption is required in one's space
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Rod, exactly what determines the TOTAL required absorption? And how does one determine how many sabines of absorption are in effect before treatment? Such as furniture, membrane absorption by walls/ceilings, and material absorption such as wood flooring?

In other words, what tells you a given room needs X sabines of absorption at X frequency?

And what tells you how to get it with X square footage of X brand of absorption material? Using coefficients alone seems to overlap absorption of high and mid hz absorption into the Low hz absorption domain, as if X sabines are required at 100 hz, use of X brand of absorption material to get it may absorb TOO MUCH at 6000 hz simply because the absorption coefficient at 100 hz is rated say at .4 while the coefficient for the same thickness and specimen size is rated say at .9 at 6000 hz? Or is that plain silly :D

Actually, are you saying to ACHIEVE a target RT-60, it would require a certain x sabines of absorption?
 
RICK FITZPATRICK said:
Rod, exactly what determines the TOTAL required absorption? And how does one determine how many sabines of absorption are in effect before treatment? Such as furniture, membrane absorption by walls/ceilings, and material absorption such as wood flooring?
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Rick,

I am basing this on desired RT60 - fo which I use the ITU recommendation found in their publication: RECOMMENDATION ITU-R BS.1116-1

This give you the calculation to be used for small critical listening rooms.

For anyone who purchased my book - it's lists 2 sites where one can go to download a spreadsheet I created to calculate this - you just inut the dimensional info for your room (it's only good for rectangles) and then the room construction (I listed a farily large amount of absorption coefficients for various materials and furnishings) and then it will show you your target RT60 for each of the individual frequencies -

Figure out what you want to use and then input the data for that product - this spreadsheet will show you when you reach your goals.

This is really an estimating tool - but will give you a pretty good idea of where you'll be once it's dome.

Sincerely,

Rod
 
Hello Rod. Ok, I did a search on it..HOLY COW! :eek: 107 pages..well, needless to say I need a little time(of which I have zero at the moment :D )to read it or pin down the sections of relevance. Other than that, I'll have to get your book as soon as I can. I do want your assessment on my rear wall conundrum. I'll start my own thread this weekend so you can see what I am confused about. Well, work beckons, so thanks again for your insight.
fitZ :)
 
Rick,

> exactly what determines the TOTAL required absorption? <

Below about 300 Hz, the more the better. Anything short of filling the entire room with absorption will still leave some response skewing and some ringing. Otherwise, the goal is for a relatively short and even RT60 over as wide a range of frequencies as possible. but you already knew that, yes?

--Ethan
 
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