John Sayers' Recording Studio Design Forum Archive

Glenn,

For me a panel trap in the context discussed here refers to a mass-spring system where the mass is a panel resonating on a spring which is the air layer.

For me there is nothing hybrid about what I describe. I cause a panel to absorb at the resonance frequency of that panel.

That for me is a panel trap.
Ethan's design is a design of a panel trap, not THE design of a panel trap making other things a hybrid of the real thing and some diversions.

I don't want to go into the use of the word trap here (disputed by John before), for me one can call it absorber, trap, whatever.

myfipie wrote:Very cool idea, BTW.

Glenn in fact I tell the same thing for years already, only when pushing it seems to have some effect.

You interpret the idea as cool, because since you came on the net the panel trap idea/concept was mainly defined in groups by pages and articles from 1 author with enormous penetration on the net.
And for me the sealing obsession, when I read all these discussions and absolutes about it, were just one of these typical axioms from the first moment I saw them.

There's nothing cool about my idea, it's just applying basic principles as I did from long before these articles existed.
I know on what these formulas are based. I know the uncertainties. I am confronted with these uncertainties from the beginning, knowing it's difficult to grasp them all theoretically. Hence for me the logical thing ALWAYS was having some possibility to tune/adjust these things, when it mattered. And in basics there are only 2 things to work with, that's the mass or the spring or a combination of both.

I don't make a hybrid. I make a panel trap, that's a physical principle/concept, not a predefined object or construction. Ethan's plans are an approach, not THE approach.

Just so I understand what you are saying about this kind of panel. Basically you would build it the same way as EW wood panel trap but leave the back open to space it off the wall to what ever frequency you want? If that is right how you do know how to space it to get a curtain target frequency?
Sorry I did not mean to label that panel, but found it funny that I was reading Rods book about Hybrid panels just about at the same time I read your post.

Glenn

myfipie wrote: Sorry I did not mean to label that panel, but found it funny that I was reading Rods book about Hybrid panels just about at the same time I read your post.

Glen,

remember - my book discussed velocity and pressure devices - the hybrid reference was in regards to treatments that work on both principles..........

Plywood faced panels are pressure devices regardless of whether they are 100% sealed or not........ any of the Helmholz " traps" are also pressure devices - and they couldn't be sealed and work properly........

Just something to keep in mind.........

Sincerely,

Rod

Rod wrote:

"remember - my book discussed velocity and pressure devices - the hybrid reference was in regards to treatments that work on both principles.......... "

It seemed like the panel Eric was talking about was on both principles, is it not? Like I said I was sorry for labeling them, and I really do not care what label you put them under, just thought it was a great way to build a panel.
BTW Rod, really a great book. I bought a copy before, but really the first time I have had the time to read it all the way through. Very easy to understand. Can not wait for the next one!!!! Oh and thank you for page 215 thru 219

Glenn

myfipie wrote:Just so I understand what you are saying about this kind of panel. Basically you would build it the same way as EW wood panel trap but leave the back open to space it off the wall to what ever frequency you want? If that is right how you do know how to space it to get a curtain target frequency?
Sorry I did not mean to label that panel, but found it funny that I was reading Rods book about Hybrid panels just about at the same time I read your post.

Glenn

Glenn,

A panel trap for me can be a lot of things.

It can be mounted in between studs which are also used to mount standard absorption, which then are covered by continues fabric, hence you can't recognize or see them. It can be panels laid/mounted between the bottom flanges of I or H beams, it can look as the Ethan plans. It all depends. John also referred to an application he described here.

How to know?
First calculate it as good as possible theoretically, where by definition for closed panels I start from the wall MSM formula as entered in that Bob's thread, I adjust it listening to my belly knowing much more than I do, and depending on the situation. I ONLY should use the traditional formula (Everest and others) on very heavy walls, NEVER on drywall.
I take care that I easily can adjust things. Hence if I don't integrate some standard posibility, I mount it temporary in a way I can easily adjust things until happy with the results.

I once tried to aim for about 32 Hz (if recalling correctly) and then gave up, because once it was tuned correctly and damping high enough, it hardly absorbed anymore (was a costly, time consuming experiment).

And I have the advantage of doing narrow band sound AND vibration measurements, but with single walls, which I have more experience with here than double walls you can also see it with narrow band sound measurements on the other side of the wall too (DIP in isolation)**.
Hence you measure it with whatever and however it's practical.

I easily can imagine that with pure sinus tones scanning the relevant frequency range you can find it back as well.
It's like playing a sweep in a living room. Once you hit the resonant frequencies of different objects they start rattling/vibrating. Only with a sweep you don't know exactly the frequency (passing through).

In DSSF3 sits a very extensive signal generator with some fun possibilities.
In the freeware version a lot of function stop working after 30 days but the signal generator remains functional (is meant as freeware).
http://www.soft32.com/download_13520.html

++++++++++++++++++++++++++++++++++++++++++++++++

** For triple leaf systems the TL method is too uncertain too my taste (not enough experience with.
The first time I was confronted with the TL behavior of triple leaf systems by adding an additional layer on the outside of a wall was between '80 to '84 somewhere (can't remember exactly).
I helped people from a company called Agglorex which produces this bonded foam. The idea was to start using it as resilient skin walls to be glued to existing walls (hence the only connection is the foam itself).
There are also mineral wool versions of this principle.
The logical test back then was to check also (note that brick walls are standard here in private housing) how this should behave on drywall to improve TL (offices and utility buildings are made a lot here with non-load bearing drywall as separation). There I was first confronted with this strange triple wall behavior. In general the curve remained comparable with some dips at certain frequencies and others a bit better.
Overall it became worse. But the traditional behavior one could expect from a theoretical stylized mechanical MSMSM system was far from recognizable.

But the conclusion was: Don't do it. It doesn't work in function of TL. But that behavior isn't that clear for walls.

This triple leaf system however does work nicely as the theory predicts on decouplers. I once worked for a factory which sold such decouplers mainly/often for elevator constructions (a lead block in between springs). It did what it was expected to do: Increasing high frequent insulation significantly, but it simultaneously increased the MSM frequency, which wasn't a problem since located far enough below the frequency of interest.

Thanks Eric for your reply

Glenn

Glenn,

You're welcome.

I think it's worth to play with this signal generator. It's the most extensive I know (and free).

You can e.g. scroll a pure tone back and forth, really scanning a limited area and searching.
You can do a lot with that thing, and it's really fun to play with.

You can phase and time shift two speakers, have a piano keyboard in that generator. to play correct musical frequencies and so on.

Eric
.

So, discussion closed?

After reading I couldn't help myself thinking; "There should be a new and improved article/book about trapping/absorption". (or something, u get the idea)

The accoustics faq on EW's site, also discussing paneltraps etc, is a very nice article. Helped me have some more inside. But as Eric mentioned, it's one side of the story. And who are we to pick a side. It's good stuff to discuss and debate about (without calling eachother an ass)

So with input from more than just one pers, a dedicated article/thread/faq whatever should be written. idea?

2 cents