Acoustical Treatments Master Thread - Page 295

Originally Posted by GRBoomer

The idea with constant directivity waveguides (CD) such as Procella, Pi Speakers and the SEOS thread (in the DIY speaker forum) is that there is much less acoustical energy in the vertical so you do not have a typical high energy short delay reflection bouncing off the ceiling towards you. Yet, you get good, well controlled horizontal dispersion, to create a wide listening sweet spot. With waveguides, you do not have to correct, what's not there. Prevention versus cure.

In fact well defined horizontal control from waveguides also lessens the absolute, blind need for absorption at the first reflection point and starts to muddy the equation to diffusion being more beneficial to preserve the energy content in the room instead of trying to bury it all with fiberglass.

Originally Posted by dragonfyr

Lots of problems.

First, treatment for specular reflections (behavior above ~250 Hz) should be broadband.

Otherwise you only EQ the reflections and change the timber of the perceived sound - all while doing nothing to resolve the anomalies created by superposition of high gain reflections.

And 1" of porous absorption is good for little other than flutter echo.

Secondly, what should one imagine if the treat the rear sides and back of the room with absorption other than to create a deader space - to the degree that it EQs the reflections and fails to stop the destructive superposition?

Yes, you can guesstimate as to the polar dispersion of the speakers and you can guesstimate as to the optimal location for reflection control without knowing where the actual early arriving high gain reflections are incident - and simply deaden the room more than necessary in the quest and very possibly miss the actual high gain indirect paths.

And you can also figure out what acoustic response model you desire - but if you are placing absorption all over the rear and sides its hard to imagine you are interested in a later arriving diffuse soundfield that provides a sense of envelopment or spaciousness!

But after you figure out what kind of response you like, you can use (free) RoomEQWizard, (along with a calibrated Dayton EMM6 mic from Cross Spectrum and an ART Dual USB Pre mic preamp from B&H Photo for ~$69 delivered along with a mic cable , adapter and an RCA cable), to measure the room modes and adjust the seats forward or back to avoid the nulls, and you can make ETC measurements to identify the actual paths of the actual high gain early arriving reflections and place adequate broadband absorption at those points of boundary incidence and verify their effectiveness.

You can also determine if you want to control the later arriving reflections with absorption resulting in a 'dead room', or with diffusion, helping to preserve a sense of envelopment and space.

Depending upon the desired response, the ETC will provide a means to precisely place such absorption or diffusion treatment and will allow you to ascertain the spatial/temporal quality pf the resulting soundfield.

Originally Posted by myfipie

I really would invite you to read the following about early reflections before thinking diffusion is the way to go. The point is to hear that is coming out of the speakers not the speakers plus the ceiling reflection.
http://www.gikacoustics.com/news_020209.html

Originally Posted by dragonfyr

Oh, so the problem is that the reflections are not 'massive' enough???? LOL!
In my haste you definitely caught me!



Hmm...so we either need to figure out how to dim them, or to enable them to gain some weight... Let me get back to you regarding the latest best practices...

Your post is a veritable tar baby of double entendre!!!

Originally Posted by GRBoomer

I did not say diffusion was the way to go. It is just with better controlled speakers, you may have other options than just trying to kill all the sound with absorption. And you lessen the influence of the ceiling reflection by not throwing energy at it in the first place.

I agree, measure and determine a strategy.

Originally Posted by R Harkness

Sound issues aside: Will this create any difference in terms of heating or cooling in the room? In other words will heat tend to build up more around the projector due to it being curtained off in it's space behind the sofa? Or can I presume air, heat, etc, will transfer through the acoustic material roughly as sound will, and that there will be essentially the same thermal characteristics to the room as before?

Originally Posted by dragonfyr

If its not acoustical terms its basic English....
Look up the meaning of a "double entendre".

Originally Posted by dragonfyr

...And if you have to explain the joke...

Originally Posted by sdurani

The thermal insulation properties of a single layer of acoustically transparent cloth are likely negligible, so I doubt you'll notice any temperature changes even with the material draped across three walls (left, right, back).

Originally Posted by dragonfyr

I have already made reference to some of them. If you can't see them even after several having been pointed out, well, then you are unable to identify double entendre.

I am glad you understand the definition, if not the actual 'thing'. Sorry if the references sailed past you...

But take a light hearted comment oh so seriously and in so doing call into question the understanding of the term itself as well.

Originally Posted by LeBon

Some bass traps also use a sheet of kraft paper or 3-mil plastic film over the front. This reflects higher frequencies, and keeps the bass trap from absorbing them.

This is for a flutter echo problem in a living room, so I dont want to use the plastic on the front of it. I thought perhaps the membrane was something special that was firm(ish) and relatively AT (but 500hz and up reflection isn't helpful).

Originally Posted by Dennis Erskine

In your case, likely true; however, while the membrane meets a couple of purposes with respect to LF performance, it is also used where additional LF absorption is desired but additional HF absorption would not be beneficial.

Originally Posted by Dennis Erskine

In your case, likely true; however, while the membrane meets a couple of purposes with respect to LF performance, it is also used where additional LF absorption is desired but additional HF absorption would not be beneficial.

Originally Posted by Brad Horstkotte

Is there any resource you can point to Dennis that would help me wrap my head around why adding the membrane onto the face of a bass trap helps improve LF absorption?