Cheap Bass Traps

[DDev]

Boogs,

> What makes the Mondo traps so much better? <

We add a membrane to the front surface that 1) increases low frequency absorption over plain rigid fiberglass, and 2) reduces (intentionally) the absorption at mid and high frequencies.

Rick,

I thought Ethan answered your question about the mid/high frequency barrier as noted above. There are times when you really do want a true bass trap only and not a broadband absorber, and in those instances I think his Mondo trap design fits the bill. I have something similar that I constructed in my studio (long before Real Traps came along) and I believe it is effective, but it is hard to say since I intentionally built it in before doing any testing in the room. I also have a "poorman's" broadband corner absorber (ie. 3 rolls of R19 insualtion stacked in a corner and covered with fabric).

Anyway, I wasn't sure if your comments were based on his note or if you had missed it, so I just HAD to point it out (being the cantankerous man that I am).

Cheers,
Darryl.....

 

[RICK FITZPATRICK]

Rick,
I thought Ethan answered your question about the mid/high frequency barrier as noted above. There are times when you really do want a true bass trap only and not a broadband absorber, and in those instances I think his Mondo trap design fits the bill.

Lets look again, because this STILL doesn't answer my question.

We add a membrane to the front surface that 1) increases low frequency absorption over plain rigid fiberglass, and 2) reduces (intentionally) the absorption at mid and high frequencies.

IT IS VERY FUCKING SIMPLE. IS or IS THIS NOT A MEMBRANE ABSORBER?
IF NOT....then by WHAT principle does it INCREASE the low frequency absorption coefficient of the fiberglass, cause if its NOT sealed, it is NOT a membrane absorber. This means:
(1) The membrane has NO absorption capabilities on its own other than resonate at its natural frequency, but does NOT create a RESONATE CAVITY.
the ONLY absorption principle used is RESISTANCE absorption, and the by placing a barrier to mid and high frequencies
(2) The LF absorption coefficient is NOT RAISED because there is NOW A BARRIAR TO MID AND HIGH FREQUENCIES.....

Lets put it this way. IF, a certain RIGID FIBERGLASS has a broadband range of absorption coefficients, and you BLOCK the mid and high, you STILL have the same LF absorption coefficient. So exactly WHERE does this INCREASE come from?

So Darryl........please tell me exactly how this functions, cantankorous or not.
fitZ

 

[Ethan Winer]

Rick,

> IT IS VERY FUCKING SIMPLE. IS or IS THIS NOT A MEMBRANE ABSORBER? <

ROF,L. Yes, it really is that simple.

And yes, it really is a membrane absorber. But probably not the kind you have in mind. MondoTraps are not like wood panel bass traps, where the membrane is tuned to a specific frequency. Rather, they use a damped membrane where the membrane is bonded tightly to the rigid fiberglass. That avoids the tuned behavior almost completely, yet still offers much more absorption at very low frequencies compared to regular rigid fiberglass.

--Ethan

 

[RICK FITZPATRICK]

YEAAAAAAAAAAAA!! THANK YOU ETHAN for your concise and immediete reply. Thats all I wanted to know. Simple answer. Now how hard was that? Unlike OTHER answers YOU ask for. (You know what I mean Ethan Hey Ethan, you know me, I meant NO implications. I only search for the truth. BTW, thanks for the insight into your manufacturing technique. I applaude you as not many manufacturers will tell you their proprietary techniques. Thanks Ethan, that tells me something new.
fitZ

btw, was this discovery by accident via tests, or a calculated exercise in knowlege aquirement? Just curious

 

[DDev]

And yes, it really is a membrane absorber.

Yeah, that's what I meant to say

Thanks, Ethan, for the clarification. I guess i can stop being cantankerous now

Darryl.....

 

[Ethan Winer]

Rick (and Darryl),

> Unlike OTHER answers YOU ask for. (You know what I mean Ethan <

Actually, I have no idea what you mean. I'm a reasonable person, and I never ask anyone anything for which a direct and clear answer is not available. Unlike others who make wholly unreasonable demands on me.

> I applaude you as not many manufacturers will tell you their proprietary techniques. <

Well, I didn't tell you the weight and density of the membrane, or how we attach it, or anything else that would help someone duplicate the huge amount of low frequency absorption we pack into a MondoTrap.

> was this discovery by accident via tests, or a calculated exercise in knowlege aquirement? <

No accident, I assure you! We did a lot of tests, some time consuming (but free) in our own "lab" room, and some at IBM's acoustics lab - which is very expensive - to verify what we measured in our lab.

--Ethan

 

[RICK FITZPATRICK]

Actually, I have no idea what you mean.

Hmmm, doesn't the term "edge effect" bring SOMETHING to mind? I was just teasing you, so don't take me wrong Ethan. I'm STILL researching that one. And I'm STILL not convinced of certain "information" being the ONLY answer. Anyway, I think you know what I meant now. No harm intended, in fact, I'm agreeing with you on that one.

Well, I didn't tell you the weight and density of the membrane, or how we attach it, or anything else that would help someone duplicate the huge amount of low frequency absorption we pack into a MondoTrap.

Well now that you mention it, how bout tellin us?? (just kiddin) Thanks for what you DID share with us.

fitZ

 

[Ethan Winer]

Rick,

> doesn't the term "edge effect" bring SOMETHING to mind? <

Here's a better way to look at that situation:

Over at the SOS forum I proposed that when a 2x4 foot absorber panel is 4 inches thick, the edge adds a full 50 percent to the total absorbing surface. So using common sense only it's easy to see that a thicker panel will have more absorption than a thinner panel of the same length and width.

Now, some self-proclaimed "expert" comes along and says that the increased absorption measured is not due to the additional surface area, but rather is caused mainly by heat losses due to diffraction around the edges. I can't imagine that much "heat" is generated by sound waves wrapping around the corner of a piece of soft foam, but that's another matter.

My point is I asked them to explain how much of the increase is due to diffraction and how much is due to the simple fact that there's 50 percent more surface.

Did you see an answer from them? Neither did I. And, of course, it's well known that this self-proclaimed "expert" has a long history of challenging everything I say just to make trouble and try to make himself look superior. As I've said many times, you can always tell who knows what they're talking about and who is full of crap by seeing who sticks to the facts and who resorts to name calling. I'm sure you saw all the extreme name-calling from that "expert," yes? I rest my case.

--Ethan

 

[RICK FITZPATRICK]

I totally agree Ethan. In fact, to illustrate further,I posted a thread at Studiotips dealing with this exact question, and I STILL didn't get a SUBSTANTIATED answer. In fact, one could draw a conclusion that there is something really wierd going on.
First off, if their answer really made sense, if you considered the entrance of the earcanal as a perforation on the surface of a skull, you wouldn't hear wavelengths longer than the perferation diameter . OR if you had a pinhole in a wall, the only wavelengths that would propagate through this hole would be proportionate to the diameter of the hole, which is totally against what Everest says. I'm no expert, but even Everest suggests the edge effect is due to exposed edges, and the more you cut up a given square footage of material into patchs, the more edge area you expose which translates into more absorption. So, who do you believe? Anyway, I just wanted to let you know "I" agree with you.
However, there is one little piece of information I was able to find, that puts a WHOLE NEW light on this absorption issue, which I am working on right now.
I have sent a couple of emails to certain people asking questions in regards to the VECTOR FORCE of air molecules when subjected to the surface of an absorber, and how this force works WITHIN an absorber. If what they showed in their web page is true, then it suggests a whole different concept in regards to resistance absorption, the edge, and diffraction, as what they showed is EVERY SURFACE is subjected to vector force PERPENDICULAR to the surface, regardless of angle of incidence. As far as I understand it though. We'll see.
fitZ