Acoustic TReatments - What, How much, & Where?

I use "The Sheffield/XLO" test and burn in disc. It provides some tracks useful in set up including some good out of phase tracks as well as a 'walkabout' and signals for burn in use.

I also use a Stereophile Test disc, which measures low frequencies, in conjunction with a Radio Shack Sound level meter. I also use a test disc put out by Rives which is already calibrated for the RS meter.

Lastly I use a disc which is really a compilation of very simply recorded music performances which is an outstanding way of charting your progress in setting up your system and room. Its Test Disc 1, "Depth of Image" by Opus 3. It has been suceeded but is still available in a similar disc put out by Opus 3 and I understand its available on the 'net. The only negative part of owning this disc is that its a standard thats hard to meet. The will tell you on each track what to expect but you may not hear it! All that means is you still have work to do.

Have fun!

P.S. I also have the Chesky disc but I don't use it.

XLO CD is good--also the Granite Audio bass CD.

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.