Monday, January 24, 2011

Chair position adjustment and The Near Field

While it was a big improvement in audio realism to move my new listening chair from the far wall to the center of the room last year, I had some difficulty determining how far back into the room (from the speakers) to place the chair.  I ended up with a kind of compromise position.  Compared to other systems I have heard, it does not give me the widest possible separation.  I think it's just shy of 60 degrees angle between the speakers, perhaps 55 degrees.  But it is way more separation than I had been accustomed to, having previously listened only from the back of the room.

But it seemed to me that when I placed the speakers even closer to the speakers, the center image fell apart, and that was the main reason for not positioning the listening chair even closer to the speakers.

I've also had a longstanding problem with the center image (usually the lead vocal) not being exactly in the center.  When I notice the lead being off to the side in some way not intended, it bothers me a lot.  During the past year, I've found that speaker positioning to the nearest 5mm, or delay adjustments as small as 0.03 milliseconds can make a difference in center image stability.  But the best thing to insure center image stability is (1) exact chair and speaker positioning, and (2) subwoofer levels.  For some reason, the subwoofer levels have an uncanny effect on the center image.

So now that's I've got those problems "solved",  and since I am still procrastinating on doing a new Room Correction with Tact, I thought I'd look at the chair position issue again.

I tried a position about 10 inches closer to the front of the room (I define "front" as where the speakers are) than my current position.  It did have a noticeably (though not compellingly) wider stereo image.  And center image position and stability (assessed by playing Supertramp Crime of the Century) seemed OK.  But now what seems irksome is that it appears possible to "hear" the supertweeters as a distinct source.  My new much higher supertweeter levels contribute to that.

I tried fiddling with the supertweeter crossover adjustments to make it work better.  Of course, I had to increase time delay because of the angles involved.  But that wasn't enough.  I raised the crossover point.  It helped if I raised crossover up to 14.8kKz, but that still didn't make the supertweeter disappear.  16.5kHz did make the supertweeter invisible, but then I loose all the new WOW factor of my fully extended highs which I am really beginning to appreciate.

What is happening is that when I get too close to the speaker (this position was 5 feet from the panels) I start listening from something like "the near field" which tends to exaggerate highs and bass.  The room acoustics interact little and are relatively unimportant.  In some ways this is good, but most recordings and speakers aren't designed to sound good this way.

So I went back to my "old" position, or really a new "old" position that is still about 5 inches closer to the speakers than last year.  It is indicated by my ears lining up with the back edge of the largest side bookcase. This is about 6 feet back from the speakers.  Last year I had my ears line up with the forward edge of the next bookcase.

Now I have completed the preliminaries to Room Correction.  I have set up low and high frequency crossovers and chosen a listening position.  System is sounding very good even without correction, though slightly weak in the 100-500Hz region, lumpy in the deep bass around 45Hz, and just a little too prominent in the upper highs starting at 10K.  Those are exactly the kinds of issues that can be solved with room correction.  What my RCS 2.0 system cannot do is set up the crossover optimally, but that work is now done, at least good enough for this time around.

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