Triple-leaf question for the experts

[Eric_Desart]

Futhermore, if this phenomena is correct(third leaf syndrome), then John Sayers solution of a vented outer leaf in a three leaf system, actually preventing the vented leaf from becomeing a third leaf by virtue of venting, same as your membrane "third leaf senario, is actually rubbish..

I think if you ask your indirect questions less agressive, you have more chance people will respond (including your previous posts).

[rod gervais]

The edges do not have to be hermetically sealed -- remember Paul's door experiment where he held plywood in his hand in the air away from the door ?

Z,

buddy - you're mixing apples and oranges here.

In order for Ethan's traps to work as designed - they have to be sealed. It's a critical part of the design - and he points this out often on his web page.

Even small air leaks will begin to decrease the amount of attenuation with these units.

You can't equate a sealed trap to a floating membrane.

As Brian pointed out - a floating piece of plywood would have a reasonance that carried on for a while- as opposed to the fairly rapid "thunp" you hear in Ethan's recording of the sealed trap.

Sincerely,

Rod

[rod gervais]

Hmmm, I was under the impression that corners were where low frequency/ modes occilated...but maybe I'm confusing that with pressure. I also was under the impression that corners ARE a boundary:lol:

FitZ,

Corners are not a boundary - but are (rather) the intersection of multiple boundaries.

A standard "box" room has 6 boundaries.

So wall to wall you have 2 boundaries meeting - introduce the ceiling (tri-corner) and you have 3 boundaries meeting.

Hmmm, I just looked at this two hours ago. But frankly, those pictures don't jive with what you said in the quote. Your statement says

As you know, foam and fiberglass work best when spaced off the wall, because that's where the wave velocity is greater. Panel traps work best right at the boundary, where the pressure is higher, and they absorb less when spaced away.

Well, in reference to the fiberglass in a resistive absorber, and an airgap behind them, whats the difference from your membrane trap? The membrane,panel or what ever you want to call it, STILL has an ENCLOSED airgap between it and the wall leaf, no? So what do you mean by " best right at the boundary"? This is what confused me? there is NOTHING-ZILCH-.no panel, membrane, sheet, or other type "leaf" against the wall excluding the frame. the SAME as a framed resistance absorber. And since this thread was aimed at the implied "panel" becoming a third leaf, which I BELIEVED it cannot become unless there is a "hermetically sealed airgap between, I became confused. Now z60611 says the panel does NOT need to have an hermetically sealed airgap between it and a boundary...the fact that it is adacent to, parallel to, and spaced a certain
distance from, in fact now becomes a "panel absorber", no? Good grief.
Now, if placing a panel close to a boundary such as a wall, can in fact cause the TL in a two leaf system, to lower at a certain frequency, then this implies that indeed, a panel ....or picture....or cabinet, or anything with a surface of suffiecient size, can cause this effect...in essence, becomeing a third leaf....is that correct?
fitZ

Fitz,

1st…….. Z60611 is mistaken in his statement – so take that out of the equation.

2nd……… Ethan’s statement is accurate – and you are just reading too deeply into this – when it’s really quite simple.

The “Panel Trap” is created through it’s many elements. It is not just the face. It’s the Basic sub-frame- the finished face-frame- the panel and the rigid fiberglass behind the panel. All of that that creates the “Panel trap” (note that it has no “back).

Now, the “trap” is then placed against a room boundary (a wall) and the trap frames are sealed at the wall to trap intersection points to assure it works properly.

This creates the 3rd leaf of the wall system – and it is this that Brian will be testing to see if it has any appreciable effect on the TL value of a wall.

I hope this helped,

Sincerely,

Rod

[Eric_Desart]

The edges do not have to be hermetically sealed -- remember Paul's door experiment where he held plywood in his hand in the air away from the door ?

Z,

buddy - you're mixing apples and oranges here.

In order for Ethan's traps to work as designed - they have to be sealed. It's a critical part of the design - and he points this out often on his web page.

Even small air leaks will begin to decrease the amount of attenuation with these units.

Rod,

We not often disagree, but here I clearly do.

I'm very sure that small leaks in Ethans design will not influence attenuation that much. I even believe it's not even worth it to seal them so accuratly with caulck or silicone as often described, assuming they are made relative good. And the shift in frequency caused by such minor leaks is probably smaller than the uncertainties involved in the whole construction of the trap versus his background, stiffness, wool filling etc.

I've build traps, wittingly spaced from the walls (without backing) to get my frequency low enough. I DO use this shortcut of the air enclosed by the trap and its frame with the environment to tune them.

What Ethan wrote on his page and in his related articles is based on his related knowledge at the time he wrote it. And that became an axiom, but a wrong one.
I even remember clear at RO that somebody explained Ethan how they could be calculated. Ethan at the time had no idea about these physical principles on which they worked. He just knew they did from empirical experience.
Ethan learned about that formula in Everest's book long after he wrote his articles about it.

If I should make a paneltrap to solve specific problems as per those drawings on Ethan's page, I should tune them theoretically somewhat too high, don't provide them with a backing and use whatever solution (screws, conic pieces of wood, whatever) to tune them after placement, which probably means I should wittingly create a gap all around while tuning them.
This is not an assumption, When using them (only to solve specific problems) I standard provide the option to tune them afterwards, because I know how difficult it is to get them theoretically right. And a shortcut with the surrounding environment is one of the logical options to obtain that.

In a later stage, after related discussions about it, and before MiniTraps substituted the PanelTraps completely Ethan even played with the thought to provide vents in his paneltrap designs.

While Z goes to the other extreme here, in principle he's right. And that's not comparing apples with oranges. You can not take Z comments out of the equation.
I'm rather convinced that the mistuning of paneltraps by the assumption of an infinite mass in these stylized formulas, and the mineral wool filling is much more significant than all these discussions I saw before about perfect sealing with caulck at those edges and connections.

This whole thing is a mass spring system. What you do with shortcuttig the air behind the trap with the surrounding environment is altering the properties of the spring, which is very much related with the law of inertia.

I recently saw Steve also somewhere telling here that the difference of sealing panel traps or not, is that they become easier to calculate. And Steve is right. It's not easy to bring this inertia into the equation.
But while Steve brought it as an uncertainty making that approach risky, he forgot that the same principle also provides some additional flexibility to tune them after real life placement.

This is exactly comparable with the vent of a speaker. A closed cabinet will show a resonance where the woofer cone act as the panel. By introducing a vent you can alter the resonance of that speaker cabinet. But the wool has a very large impact on that as well. And altering the vent design allows altering the resonance frequency.

It's all a matter of the dynamic stiffness and damping of the airlayer.
If we could that easily get rid of this defining mass-spring resonance caused by this dynamic stiffness of this airlayer by applying a shortcut, which could be damped then we could build superior walls, with double leaf systems.
But we hardly can, as little as we can't get rid of a speaker cabinet resonance with a vent. We can use it to alter things.

Warm regards

[msikio]

Thanks Eric, so intersting, and so logical too...

[rod gervais]

Rod,

We not often disagree, but here I clearly do.

Eric,

thanks for the education - I stand corrected and learned something new today - this has been a good day indeed.

Sincerely,

Rod

[Ethan Winer]

Eric,

> I'm very sure that small leaks in Ethans design will not influence attenuation that much. I even believe it's not even worth it to seal them so accuratly <

I don't doubt that. When I was selling a commercial version of those traps it occurred to me that the fiberglass inside could be replaced by a controlled amount of air leakage. In a tuned electrical circuit the Q is lowered by adding a resistor to the circuit. The wood panel is the same as an inductor, and the air trapped inside is equivalent to the capacitor, so adding a leak intentionally is like adding a resistor. Besides lower the Q and absorbing over a wider range, a leak will also help damp the panel's vibration to avoid "after" ringing. But it was easier and cheaper to keep building them as we knew worked, versus spending time and money to experiment with controlled leaks.

--Ethan

[Brian Ravnaas]

I have some analagous data.

What you see in the graph is the result of punching about 2" holes in one side of a steel stud wall to "vent" the cavity. Basically no change in the behavior at the MSM is observed.

a steel stud wall is not the best choice of wall for this kind of experiment. In walls with steel studs, resilient channel, sound clips, or spring hangers used for decoupling, the studs or channel/clips/hangers provide some spring force which affects the location of MSM. This is most pronounced in channel and steel stud walls.

The best choice of wall for this test would be a double stud wall.


With respect to the seal quality on the panel traps, it should take only a few seconds to deliberately change the seal quality from very well sealed to poorly sealed and another minute to test noise reduction again.

I'm going to post a proposed assembly at studiotips. I'll post it here as well.

[Eric_Desart]

Eric,

thanks for the education - I stand corrected and learned something new today - this has been a good day indeed.

Rod many thanks for your kind words

But it was easier and cheaper to keep building them as we knew worked, versus spending time and money to experiment with controlled leaks.
--Ethan

Yes Ethan,

But you used panel traps as a part of a broadband absorption approach(set of 3 combined types), before the MiniTraps.
Hence people didn't/don't bother about exact tuning.

But for a huge amount of panel traps I see in groups, people try to target them to certain problem frequencies,
In those cases you, and others refer to your related page and further to the standard formula integrated in the Master Handbook of Everest.
As became more clear lately based themselves on an over-simplified formula, assuming that perfect sealing and respecting that formula should solve their problem.

Well it doesn't. They have a fixed inflexible device, and only luck will have it tuned exactly.

That formula assumes an:

1. infinite stiff or heavy backing;
2. an empty cavity;
3. a plain wave
4. at straight incidence;
5. the panel seen as a mass which freely moves as a piston.

Basically it's nothing else than a simple calculation of a mass-spring system where all those real life factors hardly come into play.

For walls it's simple: Get MSM as low as practically possible. For panel traps to solve problem frequencies the aim is: Get it as accurate as possible.

Important is that your design was just meant as a low frequent absorber (part of a whole room treatment), not exactly defined to which frequency it is tuned.
Therefore the mini changes (if any to speak off) by caulking them or not can not be rated in better or worse. Therefore in most cases it hardly has sense to caulk them.

On the net they interpreted/interpret it as some water tightness they need to obtain, simultaneously taking any 'after tuning' possibility away, (wrongly?) assuming that by following the rules and a simple formula they create exactly what they targeted.

Based on some recent discussions at Studiotips I come to a shift of a factor of ca 0.85 to 1.00 for the resonance frequency ranging between filled and empty cavity. (still unlucky and uncertain with my own approach)
John in another thread shows that the way the panels were fixed influenced the MSM.

Hence your design is OK as part from your original goal (room treatment) but your related articles and plans, and the numerous references in groups are used as guidelines for a panel trap as a concept without reference to all these uncertainties, and the often occurring need for tuning.

Hence in this very thread you said that if the outcome of Brian's tests (which I'm grateful for and very interested in) will show an influence on TL you'll make a notice of that in your articles.
But then why don't/didn't you make such a notice already for standard double leave systems where you have a panel in front of a single wall?
While the effect of a third leave is interesting in this context, for double leaf systems there's no doubt whatsoever.
If your question is about influence on TL, then why only discussing triple leaf with a bit strange behavior, and leaving out double leaf with much clearer behavior?

As I noted in this thread, I get the feel if the effect of a triple leaf principle is minor that that becomes another axiom:
A panel trap hardly influences TL.

[msikio]

..., and only luck will have it tuned exactly.

What about creating the panels with a higher theorical center frequency and then installing a tuning/damping device like on a snare drum ?

Alternativly, a sharp panel could maybe be tuned by affixing a certain amount of roofing felt on the membrane, down to pitch.

Using a contact microphone a blast of pink noise and a spectrum analyser should help to fine tune for a specific frequency.

My feeling is some commercial membrane traps (RPG Modex) works on this principle, maybe using an ajustable spring ?

Any other though on fine tuning those beasts ?

[Ethan Winer]

Eric,

> Hence people didn't/don't bother about exact tuning. <

Those traps are pretty "broadband" when fitted with insulation as shown in my plans. Each style (low, high) covers about an octave, so there's a fair amount of tolerance built in. More to the point - and I've built three different studios using those traps - they work very well for their intended purpose as bass traps. Could a different design work even better? Maybe. There are dozens of bass trap designs including all the variants, and I have direct experience measuring only a few of them.

> if the effect of a triple leaf principle is minor that that becomes another axiom: A panel trap hardly influences TL. <

Well, if it turns out that adding a series of high-bass and low-bass panel traps on a standard sheet rock wall does not reduce transmission loss by much, then "hardly influences" is the correct conclusion, no?

--Ethan

[Eric_Desart]

Eric,

> Hence people didn't/don't bother about exact tuning. <

Those traps are pretty "broadband" when fitted with insulation as shown in my plans. Each style (low, high) covers about an octave, so there's a fair amount of tolerance built in. More to the point - and I've built three different studios using those traps - they work very well for their intended purpose as bass traps. Could a different design work even better? Maybe. There are dozens of bass trap designs including all the variants, and I have direct experience measuring only a few of them.

> if the effect of a triple leaf principle is minor that that becomes another axiom: A panel trap hardly influences TL. <

Well, if it turns out that adding a series of high-bass and low-bass panel traps on a standard sheet rock wall does not reduce transmission loss by much, then "hardly influences" is the correct conclusion, no?

--Ethan

You only read what you want to read don't you .....??????

In fact that low bass trap showed a very high 1 1/3 octave behavior, and how high that peak exactly was is hidden by the way a lab measures as I mathematically simulated at Studiotips.

My comments were NOT that these traps didn't function in relation to the purpose of alternative broadband absorption. Hence you don't need to repeat what I said myself.

But I contribute for others. I DO know your way of reasoning. I know you're looking for a new slogan, which I why I reactivated this thread after your first reply to Brian, which was more than enough answer for you already.
How people interpreted your pages in function of solving problem frequencies and what a panel trap is all about, is easily to check all around the net, including here at this forum, even in this very thread.

[Ethan Winer]

Eric,

> You only read what you want to read don't you .....?????? <

Are you not able to discuss anything without insulting me?

> In fact that low bass trap showed a very high 1 1/3 octave behavior <

Okay, we'll call it 1 1/3 octaves. And your point is?

> how high that peak exactly was is hidden by the way a lab measures <

That has been my point for many years now. Unless you measure an absorber at a resolution much greater than 1/3 octave, it's impossible to identify what it's really doing.

My comments were NOT that these traps didn't function in relation to the purpose of alternative broadband absorption. Hence you don't need to repeat what I said myself.

But I contribute for others. I DO know your way of reasoning. I know you're looking for a new slogan, which I why I reactivated this thread after your first reply to Brian, which was more than enough answer for you already.
How people interpreted your pages in function of solving problem frequencies and what a panel trap is all about, is easily to check all around the net, including here at this forum, even in this very thread.

Blah blah blah.

Please let me know when you're ready to carry on a civil discussion about the science of audio. Thanks.

--Ethan

[Eric_Desart]

That has been my point for many years now. Unless you measure an absorber at a resolution much greater than 1/3 octave, it's impossible to identify what it's really doing.

Please explain what I exactly was referring to (I not you), before telling it was your point for years.

[myfipie]

Eric wrote:

"I'm very sure that small leaks in Ethans design will not influence attenuation that much. I even believe it's not even worth it to seal them so accuratly with caulck or silicone as often described, assuming they are made relative good. And the shift in frequency caused by such minor leaks is probably smaller than the uncertainties involved in the whole construction of the trap versus his background, stiffness, wool filling etc.

I've build traps, wittingly spaced from the walls (without backing) to get my frequency low enough. I DO use this shortcut of the air enclosed by the trap and its frame with the environment to tune them. "

Ok dumb question, but would then that be a Hybrid device at that point? Sorry just was reading Rods book and read your post almost at the sametime.. Very cool idea, BTW.

Glenn