SL3 horizontal dispersion...

[eaf]

Short version: sidewall 1st-reflection points for toed-in speakers -- important or not?

Long version: I'm researching room acoustical treatments and have a question regarding the horizontal dispersion and sidewall 1st-reflection points for my SL-3s. I have a 23'L X 14'W room (drywall walls and ceiling; carpeted concrete floor), positioned for listening along the long axis of the room (i.e., front wall is 14', sides are 23'). My speakers are ~8 feet into the room from the front wall, and my listening spot is ~8 feet from the back wall. Speakers are ~3 feet in from the side walls, and are toed-in to obtain the "listen to the inner third of the panel" orientation.

It is my understanding that SL-3s have a horizontal dispersion of 30 degrees. Is that (a) 30 degrees from an imaginary focal line located behind the ESL panel, (b) 30 degrees on-axis from the centerline of the ESL panel, (c) 30 degrees centered on perpendiculars across the whole front of the curved ESL panel, or (d) something else? If it is (c), wouldn't that achieve around 90 degrees or more of overall dispersion from the whole panel?

I've read conflicting user information about treating the sidewall 1st-reflection points for the curved ESL panels. Geometrically, with a 30-degree launch, I'm not sure the sidewalls get any direct sound from toed-in speakers ... but if it's more like the 90-degree launch, then maybe there are 1st-reflection point concerns...

Or am I just obsessing?

Thanks in advance,
-Ed

 

[JonFo]

Short version: sidewall 1st-reflection points for toed-in speakers -- important or not?
...

Or am I just obsessing?

Thanks in advance,
-Ed

Hi Ed, well, you’re not obsessing enough IMHO

Let me help you a bit on this, yes, important topic

The real issue in your setup will be the rear wave reflections. As the toe-out will make them bounce of the front wall, ricochet off the side walls (at 8 feet, I guessing they will reflect a point behind the speaker) and come back to the listener.

Now, 8 feet of distance (both ways, so total 16+ feet) is a good distance, as those reflections will be way outside the usual ‘smearing window’ of <10ms, and slightly above the clear-cut 15ms window for humans detecting it as a separate sound.
However, because it’s a reflection of the exact same audio as the front of the speaker, it will cause comb-filtering, which is not such a great thing.

Also, it's like having a reverb effect on full time. On some music its great, on others, not so much.

My usual recommendation is to absorb the rear wave with two strategically placed absorbers.
One at the first incident point on the front wall (where the rear wave first hits) and another at the side wall behind the speaker were the first reflection point from the front wall ricochet would be.

If you really want to go nuts reading, check out these two threads that go on and on about placements and treatments. The guy leading these threads is obsessed about acoustics, so caution

http://67.19.167.226/~tdacquis/forum/showthread.php?t=5435

http://www.martinloganowners.com/~tdacquis/forum/showthread.php?t=6931