About the low end of corner bass traps

[Ydope]

Hi,

as I want to build some DIY bass traps i read a lot of the information that can be found.
I plan on going for the fiberglass panels-straddling-the-corners solution.
But theres one question:

How can a corner trap that's got a maximum distance of 60cm/2ft from a wall absorb frequencies below (343/(0.60*4))=142Hz?
[343m/s speed of sonic; multiplied by 4 because a quarter of the wavelangth has to be reached]

Do they have to be bigger in order to reach lower frequencies or can't the low-end be calculated like that?
I did a lot of searching but I couldn't find an answer to this.

Massive thanks in advance.

[Ethan Winer]

Originally Posted by Ydope

How can a corner trap that's got a maximum distance of 60cm/2ft from a wall absorb frequencies below (343/(0.60*4))=142Hz?

Even a piece of paper towel absorbs something at 20 Hz.

So then what matters is 1) how much is absorbed, and 2) what does that amount of absorption do for the room? Also, you don't need 100 percent absorption to make a big improvement! Even 25 percent will help a lot. So what really matters is covering enough corner surface with traps. If you line every single corner with traps that absorb 25 percent, that will still help a lot.

--Ethan

[Ydope]

Ethan, thanks for your answer.

If I place 703, 10cm thick and 60cm wide, straddling a corner (no tri corner), would you dare a rough guess down to about which frequency this construction could absorb 25% or more? To 140, 110, 80 or 50Hz?
I want to do this right and I think I lack a bit of 'feeling' for this. The described installation would be the least effective I am considering. I can improve all other parameters like density, thickness and size, but your guess would give me some base.

Thanks

[Ethan Winer]

Originally Posted by Ydope

If I place 703, 10cm thick and 60cm wide, straddling a corner (no tri corner), would you dare a rough guess down to about which frequency this construction could absorb 25% or more? To 140, 110, 80 or 50Hz?

Yes, somewhere down there.

Seriously, it's impossible to know without measuring that exact material in your particular room. It's well known that thick 703 works well, so I suggest you get started and see where that takes you. Also, it's better to cover more total corner surface with less effective traps, than use fewer traps that each absorb more. See my Density Report for more on this:

www.ethanwiner.com/density/density.html

--Ethan

[Ydope]

Hahaha!
OK I see it's impossible to bring some hard numbers to the table.

Thank you very much for your answer.

[Ethan Winer]

Originally Posted by Ydope

Hahaha!
OK I see it's impossible to bring some hard numbers to the table.

Thank you very much for your answer.

Not impossible. But expensive.

--Ethan

[Scott R. Foster]

Originally Posted by Ydope

Hi,

as I want to build some DIY bass traps i read a lot of the information that can be found.
I plan on going for the fiberglass panels-straddling-the-corners solution.
But theres one question:

How can a corner trap that's got a maximum distance of 60cm/2ft from a wall absorb frequencies below (343/(0.60*4))=142Hz?
[343m/s speed of sonic; multiplied by 4 because a quarter of the wavelangth has to be reached]

Do they have to be bigger in order to reach lower frequencies or can't the low-end be calculated like that?
I did a lot of searching but I couldn't find an answer to this.

Massive thanks in advance.

Y:

No... your panels don't need to be bigger to work below 142 Hz... the calculation you are making is not valid in context [max depth from panel back side to apex of corner = quarter wave of the low frequency limit].

The construct you describe [corner straddling, non tri-corner mounted, 100mm thick, 3 lbs. density semi-rigid fiberglass] will achieve an absorption coefficient well above .25 at 63 Hz [.40 in fact - or about 3.2 Sabines per 2x4' panel], and about 2.0 [about 16 Sabines per panel] at 140 Hz.

See attached graph.

This data arises from experiments done at the Riverbank Acoustical Laboratories by our firm using the mounting technique shown below which is consistent with your question.

More here:

http://www.readyacoustics.com/index.php?go=acoustics-advice.acoustic-data

PS: The intrinsic absorptive properties of this material are a constant that does not vary from "room to room" . When properly installed, the material will perform predictability.

Happy bass trap building!

[Glenn Kuras]

Originally Posted by Ydope

Hi,

as I want to build some DIY bass traps i read a lot of the information that can be found.
I plan on going for the fiberglass panels-straddling-the-corners solution.
But theres one question:

How can a corner trap that's got a maximum distance of 60cm/2ft from a wall absorb frequencies below (343/(0.60*4))=142Hz?
[343m/s speed of sonic; multiplied by 4 because a quarter of the wavelangth has to be reached]

Do they have to be bigger in order to reach lower frequencies or can't the low-end be calculated like that?
I did a lot of searching but I couldn't find an answer to this.

Massive thanks in advance.

As Scott pointed out that a 4" of 703 will do OK below 142hz, but you can see how starts to really drop at 100hz or so. If you really want o hit below 100hz you may want to cut the 703 into triangles and stack them from floor to ceiling.

Glenn

[Ethan Winer]

Originally Posted by myfipie

If you really want o hit below 100hz you may want to cut the 703 into triangles and stack them from floor to ceiling.

Or buy/build a membrane-based bass trap.

--Ethan

[Scott R. Foster]

Membrane - you mean a layer of fabric don't you?

Hardly seems right to pretend covering the mineral fiber with fabric deserves a fancy name like "membrane" - given that virtually everyone who makes porous absorbers - either commercially or DIY - adds upholstery.

Doing so not only strikes me as a bit silly, but also more likely to mis-lead people than inform.

If you insist on using the term "membrane" for fabric liners I suggest you at least remove the cryptic element. Perhaps you should go on to explain the trivial nature of what it is you are talking about, lest someone mistakenly suppose you have brought up a design element of some import, as opposed to a "distinction without a difference".

[DrDeltaM]

Originally Posted by Scott R. Foster

Membrane - you mean a layer of fabric don't you?

Maybe he actually means to build/have build a true membrane based bass trap tuned to the room, like specialised acoustic services offer.

He's not implying that he's talking of his own products. I personally don't know if they are membrane based or not, they're not tuned to a room anyway, as they are standard models, like all the affordable acoustic solutions.

A real membrane based basstrap would be a good solution anyway, so his advice is correct actually.

Thanks.

[Glenn Kuras]

Originally Posted by Ethan Winer

Or buy/build a membrane-based bass trap.

--Ethan

very true.

Glenn

[Ethan Winer]

Originally Posted by Scott R. Foster

Membrane - you mean a layer of fabric don't you?

No, I mean a membrane. And there's no need to be rude - yet again.

The use of a limp mass membrane is a unique and valuable attribute of RealTraps products. We do use fabric, of course, but it's the membrane that gives our traps their unique and specific curve of absorption versus frequency.

--Ethan

[Slaytex]

Isn't the FRK on 703 a membrane? I have 703 that is doubled (4" thick) with FRK on the front from floor to ceiling in my corners with the impression that the FRK helps absorb more low end.

[Scott@RealTraps]

Originally Posted by Scott R. Foster

Membrane - you mean a layer of fabric don't you?

Hardly seems right to pretend covering the mineral fiber with fabric deserves a fancy name like "membrane" - given that virtually everyone who makes porous absorbers - either commercially or DIY - adds upholstery.

Doing so not only strikes me as a bit silly, but also more likely to mis-lead people than inform.

If you insist on using the term "membrane" for fabric liners I suggest you at least remove the cryptic element. Perhaps you should go on to explain the trivial nature of what it is you are talking about, lest someone mistakenly suppose you have brought up a design element of some import, as opposed to a "distinction without a difference".

Yo . . . Scott Foster . . . you got some evidence to back up that claim there, fella? If you don't, it's libelous. You and your partner, Joel DuBay, have made this statement numerous times, but . . . seriously, man . . . WTF? Where are you guys getting this?

If perhaps you happened to get your hands on one of our traps and pulled it apart to see what's inside, and you did not find a membrane underneath the fabric, then I can only assume you ended up with a HF version of our traps.

We sell them both ways, you know . . . both with and without the membrane, because there are times when it's more appropriate to have greater absorption of the highs and mids across the face of the traps.

Man, I gotta tell ya . . . the fact that your and your partner's marketing campaign seems to be based so much around viciously (and gratuitously) attacking your competitors and their products is not only annoying as hell, it's incredibly unprofessional. And the fact that Joel likes to try to play innocent while having taken the incredibly slimy (not to mention cowardly) action of sending PMs to other forum members containing libelous statements about Ethan, RealTraps, etc. . . . well, it just says a lot . . . ya know?

It makes for a very hostile environment not only for those of us who work in this industry, but also for all of our customers, and for the many members of these forums.

Oh . . . and I saw your comment over at studiotips . . . something about "Ethan Winer and his home made crap". WTF is *that* about? I mean, what the hell kind of statement is that, especially coming from a company that sells fabric bags for people to make their own bass traps? And even so . . . how are RealTraps products any more "home made" than your "firm's" products? We have a full manufacturing plant in Connecticut, with real employees and everything -- we even pay them proper wages.

Jeez, man . . . grow up already, willya?

This kind of thing just alienates people, and it is harmful to the community at large. Or maybe you are more concerned about pursuing your own personal vendetta than actually being concerned for the community?

Enough is enough is enough is enough . . . ! Seriously.

[Glenn Kuras]

Originally Posted by Slaytex

Isn't the FRK on 703 a membrane? I have 703 that is doubled (4" thick) with FRK on the front from floor to ceiling in my corners with the impression that the FRK helps absorb more low end.

Yes the FRK will act as a limp membrane on the panel..

Glenn

[Ethan Winer]

Originally Posted by myfipie

Yes the FRK will act as a limp membrane on the panel

Just to be clear, FKR is a membrane, but it's not a limp mass. We used to build MiniTraps with 705 FRK (years ago), and it's a lot better than plain rigid fiberglass or fiberglass in a sack. But the flexible plastic material we use now for all of our products is even better, and has a higher "crossover" frequency as it transitions from extreme bass trapping to the lesser absorption at mid and high frequencies. That is, the increased absorption from our limp mass membrane extends to the top of the bass range, rather than petering out around between 150 and 200 Hz as happens with FRK.

--Ethan

[Glenn Kuras]

Ethan wrote:

"That is, the increased absorption from our limp mass membrane extends to the top of the bass range, rather than petering out around between 150 and 200 Hz as happens with FRK."

Do you have old lab numbers that you might be able to post with the FRK panels straddling the corners? I have never seen them and could be helpful to others.

Glenn

[Ethan Winer]

Glenn,

Originally Posted by myfipie

Do you have old lab numbers that you might be able to post with the FRK panels straddling the corners? I have never seen them and could be helpful to others.

I do but there's more to the story than I'm willing to relate here in front of you-know-who. Send me an email reminder when you get a moment and I'll be glad to you all about it. As long as you promise to keep it to yourself, of course!



--Ethan

[macmod]

Originally Posted by Ethan Winer

No, I mean a membrane. And there's no need to be rude - yet again.

The use of a limp mass membrane is a unique and valuable attribute of RealTraps products. We do use fabric, of course, but it's the membrane that gives our traps their unique and specific curve of absorption versus frequency.

--Ethan

What about the thin ply on the front of the bass trap, Ethan. Can we call this a limp mass? I've made a couple of those using the info on you great site, but they seem out of vogue in this forum. Don't understand why...

Macmod

[bpape]

The thin ply version is a sealed type of absorber where the ply (membrane) is allowed to vibrate freely and is not (and cannot) be damped. The tuning is based on the mass of the front panel and the depth of the cavity behind (determines the springiness of the air cavity). These work over a relatively narrow range of frequencies - maybe a couple of octaves so in many smaller rooms, they're simply not feasible. In small rooms, you need a more broadband approach since you only have so much wall/corner space to play with.

An unsealed damped membrane like FSK causes some reflection of frequencies above a certain frequency and a peak in absorbtion at a center frequency based on the stiffness of the material it's bonded to and it's own mass/tightness. It still however, operates over a much wider range than a sealed membrane does. General usage in a small room is to:

- increase aborbtion at a target frequency
- minimize the amount of upper mid/high frequency absorbtion to avoid having the room too dead sounding.

Bryan

[Ethan Winer]

Originally Posted by macmod

What about the thin ply on the front of the bass trap, Ethan. Can we call this a limp mass?

Bryan already gave you the right answer. Also, to be "limp" the material really does need to be soft and flexible. Think of very thick plastic food wrap.

--Ethan

[Glenn Kuras]

Originally Posted by Ethan Winer

Bryan already gave you the right answer. Also, to be "limp" the material really does need to be soft and flexible. Think of very thick plastic food wrap.

--Ethan

Or "limp" like a.......

Glenn

[Slaytex]

Originally Posted by myfipie

Or "limp" like a.......

Glenn

Aren't there pills for that?

Why don't you put (E.D.) next to the traps you sell so that we can distinguish the ones that use a limp membrane.

[Glenn Kuras]

[quote=Slaytex;1165329]Aren't there pills for that?

QUOTE]

There might be but I am to young to take them YET!!!!

Hey I see you are from Charlotte? We are playing at the Milestone April 20th. I believe it is the Cash Bash pre party. You should come on out.

Glenn