Accurate membrane and helmholtz trap calculators?

[ggegan]

I constantly read warnings about inaccurate calculators for membrane and Helmholtz bass traps and ones that rely on an incorrect formula (actually, that may be just for membrane traps, not really sure). Anyway, there seems to a general atmosphere of insecurity on this forum about anything other than absoptive traps, but I don't want to be discouraged from considering using membrane or Helmoltz traps just because there is bad info out there and one has to be very exacting in their construction. Correct me if I am wrong, but for very low frequency modes, they appear to me to be the most legitimate solution, so I don't want to be scared off. One can follow formulas exactly and build things to very tight tolerances if they know exactly what they are.

It would really helpful if some of the expert acousticians on the forum could direct us to reliable formulas and plans for building these devices.

I understand that this is straying into the area where it is legitimate to expect people to pay experts to design and build these things. Believe me, I have so many other things I need to be spending my time doing, so if I can afford to pay someone else to handle this, I'm definitely going to go that route. A big part of my interest in this is purely intellectual curiousity, but also, even if I pay someone else to design and build something for me, I still want to understand what's going on, if for no other reason than to make sure I'm getting what I'm paying for.

[Jens Eklund]

Porous Absorber Calculator V1.58

http://www.gearslutz.com/board/6342808-post2.html

[DanDan]

I have problems when people call such device the 'only' or 'most legitimate'
It is typically accompanied with no actual construction details.
There are instances of failure in this quest by several GearSlutz.
The extremely successful results from a Helmholtz tub in MHOA page 228, appear to be completely falsified.

However to focus on some successes.
Many use the Invisible Alpha technique. i.e. the sheetboard studded partitions are themselves large panel traps.
Many use slatted broadly tuned resonators. See johnlayers.com.
Some use Limp membranes rather than tuned rigid ones. Newell does a bit of this, as does Munro.
May I point out G.E.s extensive experiments.
In particular the amazing performance of his most recent VPR type trap.
No tuning issue.
Perforated Panel with Porous Absorber trap
DD

[brandoncross]

Did you ever get the construction details of the VPR trap dan?

[DanDan]

I forgot to include the Newell/Hidley hanger design.
Takes an enormous amount of space but appears to pretty much perfection.

I did not get any details. Gernot has said that he is refining the design.
Given his past history of very extensive research and sharing all of it, I am very hopeful. My suggestion that this may be a valuable new design may have given him pause for thought though......
The performance figures are almost unbelievably good.
The corner orientation seems at odds with the usual flat mounting of VPR's which I thought was very important for their performance. See the Modex Plate and Broadband at the RPG site. This corner location is also odd considering Jens statement that performance is optimum at normal incidence.
So they should behave even better flat to the wall dealing with a low axial mode or LF reflection.
All of this suggests to me that there is something different to VPR going on.
If so, maybe something special has been invented here.
DD

[boggy]

Originally Posted by DanDan

I forgot to include the Newell/Hidley hanger design.
Takes an enormous amount of space but appears to pretty much perfection.
.........

Hm... this may sound nit picky, but what other wideband absorber construction we have that can absorb down to 20Hz with (only) 1.2m depth?

N-E design has some sort of membrane absorbers behind hangers too, btw.

Cheers,

Boggy

[DanDan]

Indeed boggy. Newell seems to throw the kitchen sink at the issue.
Limp membranes, Invisible Alpha ;-), Waveguides.........
With great success.
In answer to your question though, I don't know of any other published design, but I have a feeling that if you looked Northward.....
DD

[boggy]

Originally Posted by DanDan

...........
In answer to your question though, I don't know of any other published design, but I have a feeling that if you looked Northward.....
DD

Yes... I think about published designs only...

and I'll try to answer to original thread question...

Originally Posted by ggegan

I constantly read warnings about inaccurate calculators for membrane and Helmholtz bass traps and ones that rely on an incorrect formula (actually, that may be just for membrane traps, not really sure). Anyway, there seems to a general atmosphere of insecurity on this forum about anything other than absoptive traps, but I don't want to be discouraged from considering using membrane or Helmoltz traps just because there is bad info out there and one has to be very exacting in their construction. Correct me if I am wrong, but for very low frequency modes, they appear to me to be the most legitimate solution, so I don't want to be scared off. One can follow formulas exactly and build things to very tight tolerances if they know exactly what they are.

Yes, you are right,... but I think that you understand "warnings" in a wrong way.

In this case you may be careful instead of scared, and you must prepare some ways for checking your design.

For example, you need a good method for measurement absorption coefficient... something like Jens Eklund describe in
http://www.gearslutz.com/board/6493935-post13.html... it is really good for starting point.

Second thing that you possibly need is a decent accelerometer, to find a resonant frequency of your membrane absorber.

Material that we use for absorbers may not be consistent from time to time, or from country to country,

Even if we know some published characteristics... they may not be true in our case....

Errors in material characteristics leads us to errors in resonant frequency, and if we miss a resonant frequency, resonant absorber is waste of time and money.

So... if we must tune our abosrbers, then we must be prepared for this... and I think that this is a reason why people spread "insecurity" about resonant absorbers here... and with a good reason.

Instead of this... using porous absorbing methods is much easier and virtually error-free, even for (careful) amateurs.

I try to help people with method of measurement Helmholtz abosrbers I described at R/E/P PSW forum:
Measuring Helmholtz absorber resonant frequency in non-anechoic space.
and it's useful for tuning even if this calculator works surprisingly well

Originally Posted by ggegan

It would really helpful if some of the expert acousticians on the forum could direct us to reliable formulas and plans for building these devices.

If you need formulas, Jans Eklund already leads you... but bear in mind that you must be always able to measure where you are with your construction... models aren't fully accurate, mostly theoretical, and we don't have better (for now)...

Originally Posted by ggegan

I understand that this is straying into the area where it is legitimate to expect people to pay experts to design and build these things. Believe me, I have so many other things I need to be spending my time doing, so if I can afford to pay someone else to handle this, I'm definitely going to go that route. A big part of my interest in this is purely intellectual curiousity, but also, even if I pay someone else to design and build something for me, I still want to understand what's going on, if for no other reason than to make sure I'm getting what I'm paying for.

Hm... from my perspective, to pay someone for some service that you need, and to pay someone to learn you what going on, are usually different things.

Cheers

Boggy

[brandoncross]

Oklloklllkko

[bassjam]

Originally Posted by DanDan

I have problems when people call such device the 'only' or 'most legitimate'
It is typically accompanied with no actual construction details.
There are instances of failure in this quest by several GearSlutz.
The extremely successful results from a Helmholtz tub in MHOA page 228, appear to be completely falsified.

However to focus on some successes.
Many use the Invisible Alpha technique. i.e. the sheetboard studded partitions are themselves large panel traps.
Many use slatted broadly tuned resonators. See johnlayers.com.
Some use Limp membranes rather than tuned rigid ones. Newell does a bit of this, as does Munro.
May I point out G.E.s extensive experiments.
In particular the amazing performance of his most recent VPR type trap.
No tuning issue.
Perforated Panel with Porous Absorber trap
DD

Maybe some of us who pay a large amount of money for construction designs for our membrane absorbers and Helm Holtz absorption panels, don't want to share the exact drawings and details with everyone? maybe we are protecting our and our architects intellectual property?

If you want to know how to do it properly then hire a designer to tell you what to do with your room!

And for those of you who want proof of the results then please feel free to book some time with us, if your not happy then you can have you money back.

[audiothings]

Hm... this may sound nit picky, but what other wideband absorber construction we have that can absorb down to 20Hz with (only) 1.2m depth?

Bogic, please correct me if I'm wrong... I am under the impression that the 1.2 m waveguides absorb down to about 80 Hz. The damped walls are acting as membrane absorbers below that range, requiring an additional 30-45 cm air gap, to absorb down to 20 Hz.

[boggy]

Originally Posted by audiothings

Bogic, please correct me if I'm wrong... I am under the impression that the 1.2 m waveguides absorb down to about 80 Hz. The damped walls are acting as membrane absorbers below that range, requiring an additional 30-45 cm air gap, to absorb down to 20 Hz.

I tried to explain this here, http://www.gearslutz.com/board/6795721-post41.html
Width of hangers is used to define lowest frequency, membrane absorbers isn't included in this simple model/formula, and 1.2m depth in my calculations is only for hangers.

Cheers

Boggy

[DanDan]

A piezo pickup will work fine as an accelerometer. Shadow make robust ones which can be blu taced on. The guitar/mandolin one is good.
These need a high impedance input otherwise they have low level and no bass response. An active DI with 1 Meg or more will do fine.
For Mac users, Labmeter by rustykat.com is a remarkable frequency meter.
Yet another warning I am afraid. A tuned trap may have a different resonant frequency in different locations, so as boggy said, tweak it in situ.
BTW, these 'warnings' are to prevent innocent DIYers from building traps that don't work. About four of these have appeared recently.
Conversely the calculators, resonance finding tips, and tuning techniques, are obviously meant to provide encouragement and help to those who boldly go there.

Again I recommend G.E. extensive explorations here on GS.
It's all there from no effect to various levels of performance, to eventually a really good panel performance. Soon the innovated VPR, I hope.

In my experience, almost all treatment yields great rewards. From the simple duvet hanging on a mic stand boom, to full size SuperChunks, all simple, impossible to go wrong techniques. When we get to the level of really addressing LF fully with any of the enhanced techniques, it gets Pro.


DD

[PaulP]

Originally Posted by bassjam

Maybe some of us who pay a large amount of money for construction designs for our membrane absorbers and Helm Holtz absorption panels, don't want to share the exact drawings and details with everyone? maybe we are protecting our and our architects intellectual property?

If you want to know how to do it properly then hire a designer to tell you what to do with your room!

And for those of you who want proof of the results then please feel free to book some time with us, if your not happy then you can have you money back.

If there were any kind of real applied science involved it would be extensively covered in publicly accessible research documents. The basis of science is that if you can't prove it, it doesn't exist.

As far as I'm concerned, real, useful, practical helmholtz absorbers for small room use don't exist. Membrane absorbers don't have much of an existence either. All I smell is snake oil.

[JP__]

Originally Posted by PaulP

As far as I'm concerned, real, useful, practical helmholtz absorbers for small room use don't exist. Membrane absorbers don't have much of an existence either. All I smell is snake oil.

Is it like that? I've seen several good working DIY helmholz resonators(passive and active). I´ve postet results of a small panel absorber (made out of garbage) and GE has also implemented several projects successfully.
The problem is more that there exists no detailed guidance or can exist ...

So we had to use our brain, understand the principle and then just do it.

But, of course there are less sophisticated things to use if waste of space isn´t a issue...

[DanDan]

You've been burned Paul it seems. Sounds like over-reaction though.
How about the Modex Corner and Primacoustic Max Traps? Both Membrane and both with good looking numbers.
The BBC research is pretty comprehensive and trustworthy also.
DD

[bassjam]

Originally Posted by PaulP

If there were any kind of real applied science involved it would be extensively covered in publicly accessible research documents. The basis of science is that if you can't prove it, it doesn't exist.

As far as I'm concerned, real, useful, practical helmholtz absorbers for small room use don't exist. Membrane absorbers don't have much of an existence either. All I smell is snake oil.

Come over to our place paul, Ill show you it all working.

You gonna come???

[Dange]

I don't think PaulP was being serious.........

[Jens Eklund]

Originally Posted by Dange

I don't think PaulP was being serious.........

+1

(I hope! )