Originally Posted by mcnarus
I'd be interested in sdurani's take on this question, since he seems most firmly convinced that the weight of evidence argues against treatment.
Apparently I've given the wrong impression to some, so let me try to clarify. To start with, this isn't a binary argument: "against treatment" vs for treatment. If you're going to set up a recreational listening space based on your preferences, then the amount and type of treatment should be like Baby Bear's porridge: just right.
As I mentioned in my last post, the Klippel experiments found that a flawed sense of spaciousness was preferred over too little spaciousness. But that's not an argument for wide dispersion speakers with terrible off-axis response, it just points out what was preferred when limited to those two choices. Olive's tests show that the most preferred speakers are the ones with wide dispersion AND consistent off-axis response (early reflections off the side walls sound similar to the direct sound from the speakers). Listeners like spaciousness that early reflections deliver, they like it even more when those reflections are consistent with the direct sound.
Likewise, when limited to a choice of too much absortion vs too little absorbtion, the latter tends to be preferred. But that's not an argument for treating your room incorrectly, just points out why listeners would prefer a recreational listening space that sounds more like a typically furnished living room rather than a more absorbent recording studio, when limited to those two choices. The optimal solution is somewhere in between, where the right type of treatments are used, in the right amounts, at the right locations to give the listener the sound he likes.
The oft-posted graph above shows the detection thresholds for early reflections. If you compare the red trace to the blue line, you'll see what is required to hear a reflection as a separate event: during the first 30ms or so, the reflected sound would have to be significantly louder than the direct sound. That's not going to happen in a typcially furnished living room. Worst case scenario would be a reflection as loud as the source (like in Haas' early experiments), but that still won't be detected as a separate sound (echo) unless it arrives almost 40ms later. Typcal living rooms aren't large enough to create such long-delayed AND high-gain early reflections.
If you compare the green trace to the blue line, then you'll notice that within the first 10ms, early reflections in a small room can easily be loud enough to fall above the image shift threshold, especially if you're using speakers with wide and consistent off-axis response. So we lock on the direct sound and won't hear multiple copies/echos of it, but we will get a broader soundstage. Recording engineers might not find this useful for work, but most listeners tend to find it pleasing; like increasing the size of your display to get a larger, more immersive image.
Ando looked into direction vs preference and a consensus has developed since. A couple of supporting quotes, first from Mathias Johanssen of Diarc "Reflections from the front and the rear (within ±40º) are perceived as detrimental to sound quality, whereas side reflections (within reasonable levels) often improve the perceived sound quality."
and from Floyd Toole of Harman "Front–back symmetry in binaural hearing implies that these desirable effects will exist for sounds arriving at angles of 40–140º."
So the difference between my preference and Ethan's (if he's willing to admit his is a preference) isn't a case of no treatment vs treatment, but instead what we would use and where we would put it. Where he might absorb lateral first reflections, I leave them alone (maybe a little diffusion) and instead pile my absorbers on the front and back walls within roughly ±40º (see Johanssen and Toole quotes above). I certainly wouldn't absorb early reflections around ±55-60º, since those contribute most to spaciousness. Both of us use absorbtion, just a difference of where.
Finally, a word about testing for statistical preference: just because evidence points to listeners preferring lateral early reflections, it doesn't guarantee that you will prefer them as well, any more than the song that sits at #1 on the Top 40 charts is guaranteed to by your favourite as well. The data offers a good starting point: if you're human, then you'll likely prefer what other humans do; doesn't mean you absolutely will. But let's not pretend a consensus doesn't exist.