Acoustic TReatments - What, How much, & Where?

As integral as test CD's are... Just how do you determine, for example, the coefficient of the absorbers/diffusers needed? Many of the ones I've looked at post their own measurements of NRC ratings at different Hz....

Also, what's best behind the speakers, absorption, or diffusion?

Re last question, see my comments to Tboooe's thread on Room treatments if you're interested in my opinion.

I'll defer to Rives on your first question - I'm sure he would know - thats why he get paid the big bucks. :-)

There is a common misconception being perpetrated here.

The reflected acoustics off the side walls are NOT out of phase and will not destroy stereo image provided the speakers are an equal distance from the side walls and the listener is sitting in the middle with ear level at the height of the mid range.

Although the reflected sound will not be in phase with the primary signal reaching your ears directly from the speakers, the reflected sound off each wall will be in phase with that from the opposite wall and therefore still present a stereo image that allows you to pinpoint the sound position source between the speakers.

The critical factor is to ensure that the reverberant field has enough delay relative to the direct sound so that your brain can distinguish it from the direct energy....i.e. do NOT place the speakers right up against the side walls as the reverberant field becomes completely mixed up with the primary field and the brain can't figure it all out resulting in a poor stereo image...

I find that placing the speakers three feet away from side walls is a safe distance.

Shadrone, In reference to your first sentence. I must say I'm at a loss as to the nature of the common 'misconception being purpetrated' here, unless of course you believe that setting up the speakers as you have described, or as you have in your systems photograph, is the definitive or only way of setting up speakers and there is only one possible end result.

In my experience there are many ways of setting up speakers which present a satisfactory stereo image to a particular group of listeners. I'm not talking multi channel, home theater systems, which is an entirely different issue/sound. Just simple two speaker stereo.

My personal choice is a sound which is pinpoint source specific which reproduces most accurately the sound of the recording. This requires exacting set up (as far away from all walls as possible, especially the rear wall, having a triangulated listening position, and the elimination of as much of the room's reflected sound as possible, including (most importantly) deadening as much as possible 1st reflection points. This set up, properly executed, gives you exactly what is on the recording, nothing more, and little less. I reemphasize that is my personal choice and when I discuss set up, that is my point of reference. I don't care much for a set up which presents a larger 'apparent' sound stage by utilizing room surfaces. Again, MY choice - MY preference.

Many folks prefer a different sound (whether they really even know that they do because they may have never actually heard a set up as I descrbibed) and that is a 'bigger apparent sound stage'. This will include a good sense of presence of the musicians between the speakers and as well, provide for a greater sense of ambiance created by the reflected sounds from room surfaces. In fact this sound is so preferred by so many that speaker manufacturers make speakers to specifically produce that result, such as panels, many electrostats, bipolar's using dynamic cones, as well as Omni's.

Now regarding the 'in-phase' and 'out of phase' issue. You have admitted that the information which comes from the outsides of the speakers is out of phase with the direct sound between the speakers (as I stated in my post), but you conclude that in a perfect set up it is in-phase with itself and does not effect the quality of the central stereo image. I have no problem with that statement in itself (other than I don't agree that it doesn't effect the quality of sound from the recording), however I fail to see how in any way it supports your statement about someone perpetuating (I think that is the word you meant to use, not perpetrating) a misconception.

As I said in my other post, folks have preferences, and I have mine as you yours. Interestingly, what I describe and what I personally prefer, only came after I was exposed to a system that was capable of that level of performance. Until then I really didn't understand what folks meant by 'specific' depth of image comments, I thought it was all about equipment hype by salesmen as I only heard a more 'generalized' sense of depth of image, much as I thought break in being a bunch of hype by salemen and manufacturers.

Now, since you have joined this thread why not share with us your views of how both Blindjim and Tbooose can set up their systems - you will note both have sidewall problems (one speaker near a wall and another near an open space) and at least Tbooose has a backwall issue as well.

BTW, I looked at your system and photos. What a great looking HT system. Looks like you put in a lot of effort. Congratulations...........

I use test CDs to give me an idea of what's going on. For the final details I use listening tests and intuition.