Warming up, burning in, diffusing, firming up

[WMcD]

Not to argue with Art?

I did not wish it to challenge any of your valuable insights. I think we're on the same wavelength (ahem).

It was about the following, if I may quote you.

"and the diffusor thing.......less is less. If you are experiencing a particular problem at a particular location, your spot treatment approach may solve the problem provided its confined to middle/treble frequencies. However, most acoustical problems also involve the bass range which is aprox half of the audible musical spectrum. Devices which are large enough to affect the bass frequencies will also affect the higher frequencies (this is called "broadband") and is really the way to approach an acoustical problem, not by attempting spot treament of specific frequency ranges in very small surface areas. "

"Emphasis added", as we say in the legal world.

- - - - -

I was thinking that Toole is saying that 200 Hz is line of demarcation (it is deliberately hazy in his illustration) is the border between bass and treble effects, and by implication are affected by different treatment structures.

The issue I'm discussing, here, is the extent to which there are structures which affect one or the other -- and the extent to which some structures have efffects in both worlds.

- - - -

If I understand correctly, the bass effect is standing waves and very large absorbers must be positioned in corners to be effective. Sort of like corner loading of speakers, in reverse. Pressure is localized in corners and thus corners are the only place where low freqs can be absorbed by what is essentially something which evens out pressure at low freqs. The room is getting to be small in terms of bass wavelenghts but so are absorbers.)

OTOH, treble is affected by raw flat walls which are very large in terms of treble wavelengths. Absorbers - ones of reasonable size - on the walls can be effective. But dispursion through curved surfaces are more in keeping with the goals in treble manipulation described by Toole. Those are the goals of Apparent Source Width (ASW) and Listener Envelopement (LEV). I'll have to let anyone read his book.

- - - -

I see that Art is also discussing the possibility of cylindrical diffusers with absorbing material behind. That was of interest to me too. See the articles posted by me in

http://forums.klipsch.com/forums/p/66726/653030.aspx#653030

Some of the data for stuffed polys looks very good.

- - - -

One thing I'm not knowing but wondering about, is whether a long stretch of shallow absortive material can affect bass freqs. This is to discuss two situations.

One is the three cubic feet block of absortive material in a corner. That is a typical corner bass trap.

The other is a a 3 inch deep, 36 inch wide, but 12 foot long array on one or two, or four walls. One theory is that the three inch depth will not do anything for bass absorption because it is too shallow. On the other hand, we have the long expanse of 12 feet. And this could be behind an array of polys.

Art's installation is of to greater thickness and overall dimensions. Still you have have to wonder if the smallest dimension of a long absorber is getting in the way of absortion. Maybe not.

There is something like this in the radio antenna world. The Beverage Antenna. http://en.wikipedia.org/wiki/Beverage_antenna

If long but thin antennae can transmit and aborb r.f., so maybe can acoustic treatments.

My rant for the night.

Wm McD

The treble is

[artto]

One thing I'm not knowing but wondering about, is whether a long stretch of shallow absortive material can affect bass freqs. This is to discuss two situations.

One is the three cubic feet block of absortive material in a corner. That is a typical corner bass trap.

The other is a a 3 inch deep, 36 inch wide, but 12 foot long array on one or two, or four walls. One theory is that the three inch depth will not do anything for bass absorption because it is too shallow. On the other hand, we have the long expanse of 12 feet. And this could be behind an array of polys.

Art's installation is of to greater thickness and overall dimensions. Still you have have to wonder if the smallest dimension of a long absorber is getting in the way of absortion. Maybe not.

There is something like this in the radio antenna world. The Beverage Antenna. http://en.wikipedia.org/wiki/Beverage_antenna

If long but thin antennae can transmit and aborb r.f., so maybe can acoustic treatments.

My rant for the night.

Wm McD

"The other is a a 3 inch deep, 36 inch wide, but 12 foot long array on
one or two, or four walls. One theory is that the three inch depth
will not do anything for bass absorption because it is too shallow. On
the other hand, we have the long expanse of 12 feet. And this could be
behind an array of polys"

I've tried that. It doesn't work. The way I described and showed the Sonex mounted behind the polys have no audible effect.

There also is 1" Celotex rigid insulation behind the polys. This material is not as "broadband" sound absorptive as the Owens Corning stuff or Roxul. I plan on installing Roxul behind the cyclinders, fitting the curved panel snuggly. Some of the panels that overlap might even be pressed against each other, sort of like a shock absorber. This should stiffen up/dampen any bounce of the panel due to vibration. At the same time, because of the depth of the cylinders, and their length across the entire room they should also add to bass trapping.The larger curved panels already aid somewhat in breaking up standing waves. With full depth absorption behind them they should provide an increase in bass trapping performance.

Since these polys are arranged in a louvered fashion, sort like, well, a gill (no pun intended [] ) , my thinking is that the shorter wavelengths will be captured in the Roxul behind the poly "gills". My objective here is to try and keep the reverberation time consistent as volume level increases, so that excessive reflections around the room at high volumes don't start making things sound harsher. Will it work? We shall see [8-|]

[artto]

Art's installation is of to greater thickness and overall dimensions. Still you have have to wonder if the smallest dimension of a long absorber is getting in the way of absortion. Maybe not.

There is something like this in the radio antenna world. The Beverage Antenna. http://en.wikipedia.org/wiki/Beverage_antenna

If long but thin antennae can transmit and aborb r.f., so maybe can acoustic treatments.

My rant for the night.

Wm McD

This does work ~ to some extent. For instance, I have some Auralex bass traps installed across the back wall/ceiling corner. These are the regular sized trianglar Lenrd traps. The length of these is 16' (8 two foot sections). Because of the length I could easily hear the difference. It had an effect to lower frequencies than the "specs" of one trap section. Likewise, if you stack two or three Auralex MegaLenrd the combined units will be able to absorb to lower frequencies. However, if the absorption material is so thin as to not affect bass frequencies, you are going to need an awful long wall of this stuff to have any impact. Not very efficient. Best to nip it in the bud and not build a room with parallel walls in the first place. And thats why I use polys. [Y]

[garyrc]

Artto,

Are your polys made of masonite, or somethig else? How thick is the masonite or other material?

Do they just press up against cleats?

Thanks, Gary

[artto]

Artto,

Are your polys made of masonite, or somethig else? How thick is the masonite or other material?

Do they just press up against cleats?

Thanks, Gary

The large ones are 1/4" tempered Masonite. The smaller ones are 3/16". They are all screwed to "L" shaped clips which are screwed to the ceiling. They will tend to bend in the winter time because of heat flow from the forced air heating, so they must be secured. There's detailed pictures on my thread in the Architectural section ~ I know you've been there because you were the last post []