I'm at page 121 and read your name once - keep counting 😉
Do you remember the title of Schultzes paper? Alternatively feel free to send me a copy of your book to my email
Do you remember the title of Schultzes paper? Alternatively feel free to send me a copy of your book to my email
gedlee said:
Belive me, Earl - not only for *small* rooms....
😉
What I read from the german forum (thanks for the link, Markus) no one did it DIY yet.
I guess I should use the Basotec I just bought for experimenting with acoustic lenses a'la Raal to give this one a try.
Reading quickly through the patent its basically a 1-2mm front plate consisting of metal (steel or aluminium = low absorbtion) kompletely glued to a BASOTEC like acoustic foam (=high absorbtion plus porous) of 100mm and up.
Nothing else - especially no cassette in order to not hinder any modal movement of the front metal plate (= becoming somewhat "broad band" absorbtive) and to allow sound energy to enter also from the back of the steel plate (through the acoustic foam).
Markus, the whole thing has to be glued *over its full area* to the wall / ceiling or to something rigid (MDF plate for example) IMO - though I din't found that outlined?
Greetings
Michael
Greetings
Michael
Yes the foam should be glued to something rigid. MDF will do. You'll find people at casakustik that did tests. But they all didn't follow the original specs and so their experience was rather bad. As with all passive absorption only more is better. At least 10% of a rooms surface is needed, 30% is better.
Best, Markus
Best, Markus
gedlee said:
No - this thread is about loudspeaker perception. I don't want you to "prove" something, but I would like to "hear" some well reasoned arguments why an open baffle midbass *might* be beneficial, OTHER THAN what has been already offered.
"Dawned on me"? "..isn't that possible?" 😉 Now who is being "disrespectful"? (..no, don't answer - it was rhetorical, moreover it isn't really important.)
You may well have thought this through, but you haven't discussed anything different here on this subject then you have in any other multitude of posts (..here and on other forums). At least in this respect then, all I can assume is that you have "thought it through" ONLY SO FAR, and *perhaps* - NOT FAR ENOUGH. (Note: that in fact on several occasions I recall statements made by you that have been contrary to this (i.e. professing some degree of ignorance to open baffle dipoles at lower freq.s), BUT that was over a year ago, AND I'll accept that it could well have been sarcasm.)
As for "agreement" - I *never* asked for you to agree with me on this subject matter.
Let me state this as clearly as I possibly can: I AM NOT LOOKING FOR AN *AGREEMENT* (..with regard to any beneficial property of an open baffle mid-bass design that I or others might perceive).
What I would *like* are some *arguments* (as stated above in my first paragraph, and as I've stated previously).🙂
Is that clear enough?
Markus
When I do panel absorbers now I use Constrained Layer Damping as it very effective in this application. I'm suprised that the commercial products don't do this.
When I do panel absorbers now I use Constrained Layer Damping as it very effective in this application. I'm suprised that the commercial products don't do this.
gedlee said:
A good cheap way of doing this is:
Sealing the room:
1. use an exterior grade (with seal) door for the room.
2. use a close-loop hvac for the room ("tied into" venting, typically a single-room "euro" unit)
3. don't use "pot" lighting, instead use separate add-on fixtures.
4. Make extensive use of caulking (transition between walls, ceilings, and floors, and doors as well as electrical/hvac "connections").
"Plate absorption":
Select a very compliant fire retardant carpet padding and adhere it to the walls and ceiling with a low fire rating adhesive (spread thinly).
Then adhere a layer of sheet rock to the carpet padding on the walls and ceilings (same adhesive) - but do NOT "join" the walls to the wall corners, or the ceiling (and of course it isn't something that you would do to the floor anyway). Note that the adhesive needs to specifically allow for a very small amount expansion and contraction so that the walls don't "fall off" over time.
Cosmetic treatment at minor "gap" transitions to "taste".
🙂
markus76 said:
Yeah – a rough guess from Wallace C. Sabine' formula
http://www.sengpielaudio.com/calculator-RT60.htm
BTW I re-read the patent - Fuchs and Zha were not decisive about suspension. They state that the absorber (metal plate plus foam plate) can be suspended from the ceiling / walls in any form you like *or* can be glued to walls / ceilings (I'd rather doubt that the acoustic foam will carry the load of a 10-30kg metal plate securely for ever)
markus76 said:
DBA - as far as I can tell - is the only "active absorber" that works – under very stringent conditions. (bwaslo thanks for pointing to the thread at AVS)
It uses cancellation to *absorb* the original wave that was thrown out. Something quite impossible with random placed subs.
Markus, the *ringing* in the plots you mentioned are pretty low and I'd expect them to be from imperfections in room symmetry / wall losses. From theory – when the sound is turned off the delay (back wall subs) turns off later so the "pitch and catch" isn't compromised and decay should be quick (immediately in ideal).
If it were suitable for OB operation I'd possibly give it a go – still searching for a sub approach – maybe the closest to OB :
Quasi - IB – DBA (at front and rear walls – what an overkill !).
"Single bass array" would also do maybe as I'm definitely more interested in short reverberation time than in uniform FR over the room.
But there is still left my desire to have stereo down to the bottom
(and YES, I already know that this is nonsense for most ....)
Greetings
Michael
ScottG said:
So you read my book 🙂 - this is almost exactly what I propose there.
I tend to use mufflers in the HVAC system as this isolates the HVAC sound from the room as well as the room from the HVAC system. When you use a stand alone system you still need mufflers to quiet it down.
I recommend USG RC-1 resiliant channel for the walls as this issolates better than the carpet pad and there isn't the "falling off" problem. Two sheets of drywall with CLD between them are hung on that. This construction is sound proof and very well damped especially at LFs.
gedlee said:
Again, yes - we understand those that don't favor the design.
You can't "think" of any? Or are you not willing to try? (I'll of course accept either.)
Hmm, (broadly speaking):
How about any fundamental differences in pressure vs. velocity operation?
How about any additional mechanical resistance added via "stuffing"?
(As Elias hinted at) - How about a marginal increase in apparent L/R separation at somewhat lower freq.s?
How about the perception of significant sp-loss/(lack of boundary) at the 90 degree positions (..accepting some degree of rotation)?
etc..
Note that I'm NOT proposing that all, or even any of the above are necessarily arguments in favor of an open baffle midbass design, in fact there could well be arguments in favor of a monopole here. But they *might* be in favor of an open baffle midbass and they haven't really been discussed.😉
gedlee said:
Not yet! But yes, when I start to travel (about a year and a half from now) I'll get around to it. 🙂
Hmm, independent thought reaching similar conclusions..😀
Scott,
I believe nobody on this forum has a duty to publish all and everything he has thought or found out about loudspeakers, even if asked. And nobody has a duty to enter into discussions opened by others. I´ve followed these OS CD waveguide threads for quite a while and remember that Earl more than once stated that dipoles might be an option in theory for some applications, but for him would practically not justify the added cost/complexity. Such a decision is always one of personal preference in the first place, but has to be accepted as that.
If one of us believes in the superiority of a dipole solution, he would have to convince Earl by his priorities – not ours. And certainly with a proof of concept , not *how abouts* or *might* be´s.
I believe nobody on this forum has a duty to publish all and everything he has thought or found out about loudspeakers, even if asked. And nobody has a duty to enter into discussions opened by others. I´ve followed these OS CD waveguide threads for quite a while and remember that Earl more than once stated that dipoles might be an option in theory for some applications, but for him would practically not justify the added cost/complexity. Such a decision is always one of personal preference in the first place, but has to be accepted as that.
If one of us believes in the superiority of a dipole solution, he would have to convince Earl by his priorities – not ours. And certainly with a proof of concept , not *how abouts* or *might* be´s.
JPV said:
Small ? – not sure – well, at least as small as a 200+ seat cinema actually is.
Basically it was full range as there were roughly a dozen surround speakers each side available.
Though I tailored the frequency response to taste. If too much HF the result doesn't convince of.
For home use – no, I didn't
For LF only is a pretty hypothetical case as you don't easily get into a situation where you have more LF absorption in small rooms than HF absorption
Greetings
Michael
Rudolf said:
Well said!
*If* Earl would be in cars he would have to beat my ultra compact sub first.
😀
Rudolf said:
You are COMPLETELY misunderstanding me.
There NEVER is a "duty". Nor is there even an expectation.
What there was (and still is) - is a *REQUEST*.
Nor do you "have to" or even "need" to convince Earl of any superiority.
I'm simply asking for OTHER aspects of a particular design that *may* result in a perception of superiority by others - and perhaps some insightful discussion from those other aspects. You know, a major premise of a forum like this.😉
The "how abouts" were there to simply "get the ball rolling". Otherwise what we have is the same old discussion that you can search for in any number of threads on this forum and in others. If you enjoy this repetition then there is certainly an abundance to choose from.
Rudolf said:
You are quite correct. I don't believe that I have ever argued against OB on a purely theoretical basis, only that the "apparent" advatages do not "appear" to outweigh the "apparent" disadvantages. I find them impractical and problematic to work with. I find the need for active crossovers and multiple amps a very bad use of limited funds in a sound system setup. If cost were no object I would sell lots more speakers than I do. The fact is that cost IS ALWAYS a major factor. The OB pushes up the costs far more than I believe it would push up the performance.
ScottG said:
Scott, I can actually think of lots of reason for "a perception of superiority by others". Its just that none of them are acoustic - they are all psychological. (And I prefer to avoid those kinds of discussions because its not my field.)
ScottG said:
To me OB does 2 things that give it a sense of superior subjective purity in the power region 200-800Hz over a box. 1. Does not smear the 1st msec as much. 2. Gives a means of radiation control there. I.e. figure of 8 is a type of control.
It asks for more space and money, but that is a discussion of another order.
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