What have I done wrong?

[igorot]

I just finished creating and mounting the traps I created based on the designs I gathered around here. However, something weird is happening. I noticed that a trap or 2 is making some sort of a "whistle" sound when I try to play my guitar's lower string/bass strings (e/a/d). It might also happen with a bass guitar.

 

[pdadda]

What are the traps resting against? Anything metal?

 

[RICK FITZPATRICK]

I just finished creating and mounting the traps I created based on the designs I gathered around here.

Tell us what you used for materials and the design, and how/where they are mounted. I can't imagine "traps" whistleing. Unless these are membrane absorbers. What is not told around here usually, is they can actually do more harm than good, by resonating certain frequencies back into the room. But if these are resistance absorbers....hmmm.
fitZ

 

[Ethan Winer]

Rick,

> membrane absorbers ... can actually do more harm than good, by resonating certain frequencies back into the room. <

It may be that a membrane bass trap can ring for a short time at very low levels after the sound stops. Especially if it's not built properly and has too little internal damping. I've never measured that so I can't say it won't ever happen. But the notion that a properly built membrane bass trap can do "more harm than good" is preposterous.

--Ethan

 

[RICK FITZPATRICK]

Especially if it's not built properly and has too little internal damping.

By Jove, I think you have it there Ethan. Expecially the "not built properly" part.

I've never measured that so I can't say it won't ever happen.

Apply those 2 statements to this next one and it might demonstrate something.

But the notion that a properly built membrane bass trap can do "more harm than good" is preposterous.

As the ad for Guiness Beer says......BRILLIANT!

The catch here is "NOT built properly" vs "properly built". IF one is "built properly", it stands to reason that it is doing the job it is designed for, which is absorption of a TARGET frequency plus or minus. That is IF I understand the point of Membrane absorpters correctly, as they are NOT broadband. It also stands to reason, if one is built IMPROPERLY, as in ARBITRARY design,,"IMPROPERLY", assumes that one has no target in mind, which implies it is intirely possible to "do more harm than good".
Ethan, I mean no disrespect here as you are the "expert" here. However, if memory serves me, more than one OTHER expert has posted the possibility of "doing more harm than good" on other forums. Including a Physicist. If need be, I will search for his and other expert statements on other forums as I have read these in the past. If I remember correctly, the point was RE introducing resonance of UNWANTED frequencies back into the room, which to my way of thinking, is IF the device is NOT doing the job it was designed to do(improperly built), and actually put sounds(ringing) back into the room which is EXACTLY what Igorot stated....then WHAT damn part of my STATEMENT is PREPOSTEROUS? I mean..lets look at his statement..........

I noticed that a trap or 2 is making some sort of a "whistle" sound when I try to play my guitar's lower string/bass strings (e/a/d).

Which part illustrates they are built "correctly". IF indeed they are actually membrane absorbers.
I rest my case.
fitZ

 

[Ethan Winer]

Rick,

> The catch here is "NOT built properly" vs "properly built". <

Yes, but all I meant is having the right amount of damping inside the trap. It's not like someone shaves 1/32 inch too much off a side rail and all of a sudden the panel starts ringing. It's not difficult to build these correctly!

> IF I understand the point of Membrane absorpters correctly, as they are NOT broadband. <

I consider the membrane bass traps in my Plans article to be broadband, at least in comparison to a Helmholtz design that is often made to have a very narrow bandwidth to target a single mode. Each membrane trap type absorbs over a useful range of about one octave. More to the point, the system of traps described in my article is broadband because together they work over much/most of the bass range. So while they're not broadband in the sense that rigid fiberglass is, they're not really "narrow band" either.

> more than one OTHER expert has posted the possibility of "doing more harm than good" on other forums. Including a Physicist. <

To my knowledge only one person has ever suggested that membrane bass traps can do more harm than good. And as far as I know that fellow is not a degreed physicist, though I can't be certain because he never reveals his credentials. What I am certain of is his motive, even going so far as to make up stupid stories about membrane bass traps doing more harm than good if there's a chance it will make me look bad. Think about that.

Last time I checked Alton Everest was still alive. You might send him a letter asking if the membrane bass traps described in his book do more harm than good. Likewise, you could email the BBC who has done extensive research on bass trap types and, as far as I know, never concluded that membrane traps are a poor choice.

--Ethan

 

[RICK FITZPATRICK]

all I meant is having the right amount of damping inside the trap. It's not like someone shaves 1/32 inch too much off a side rail and all of a sudden the panel starts ringing.

Ethan, I have seen pictures of membrane traps 30' long. Who knows how someone built theirs. My point was, without knowing what it is you are trying to absorb, you could POSSIBLY be wasting your time and money, or even making things worse than without them.

As to other experts, the person you are thinking of was NOT who I am talking about. Give me a while and I'll research where I read this and WHO the expertS were. Like anything else, I can only TRUST the word of SELF PROCLAIMED experts, even such as yourself. If they "purportedly" have credentials, who wants to dispute them? Certainly not me.

To my knowledge only one person has ever suggested that membrane bass traps can do more harm than good

You're taking this out of context Ethan. I suggested IMPROPERLY designed and built ones POSSIBLY could do more harm than good. Look, I'm NOT an expert, but if I read something written by an expert, and another "expert" disagrees, so be it. That doesn't prove one way or another. And this DISAGREEMENT crap is exactly what pisses me off at Acoustical "consulting". If disagreement exists on primary acoustical subjects, then WHO the hell does one believe? IF they can't prove something, then that tells me NIETHER of them are right as it is ONLY opinion.

you could email the BBC who has done extensive research on bass trap types and, as far as I know, never concluded that membrane traps are a poor choice.

I NEVER SAID THAT, so don't put words in my mouth Ethan, it really fucking irritates me. I only implied what we have disgusssed. And speaking of disgussed, I'm getting damn disgussted with ALL this crap.

fitZ

 

[pdadda]

Settle down fellas.

 

[Ethan Winer]

> Settle down fellas <

Indeed. No need for anyone to get riled. It's just audio, after all.

 

[Dani Pace]

Whistling sound? Could this be the result of moving air? A port in the trap might solve the problem if moving air is the cause. Of course this could be an idea which would defeat the purpose of the trap. You need to isolate the source of the annoying noise, then do whatever it takes to eliminate it.