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45 degrees

Posted by Duke (D) on March 14, 2013 at 23:34:02

In Reply to: Toe in question posted by JeffH on March 13, 2013 at 22:36:52:

I design my speakers to be toed in about 45 degrees, such that the axes criss-cross in front of the listening position. If the speakers have a roughly 90 degree (-6 dB limits) radiation pattern in the horizontal plane, along with good pattern uniformity, this setup can give you an exceptionally wide listening area. Let me explain:

The ear localizes sound by two mechanisms: Arrival time and intensity. If your speakers have little or no toe-in, for the off-centerline listener the near speaker wins both arrival time and intensity, the latter because he is more on-axis of that near speaker. So the image tends to be pulled strongly towards the near speaker.

If the speakers are toed-in such that the axes criss-cross in front of the center sweet spot, then for the off-centerline listener, the near speaker of course wins arrival time BUT the far speaker wins intensity, because he is well off-axis of the near speaker but on-axis of the far speaker. The two localization mechanisms roughly average out, and center vocalists do a much better job of staying centered even if the listener is off to one side. The secret to this working well is, the near speaker's SPL must fall off fairly rapidly and uniformly as we move off-axis. This calls for more aggressive radiation pattern control than we normally see in home audio speakers.

A second benefit of this configuration is, more uniform tonal balance throughout the listening room, as the highs are spread around more evenly rather than concentrated up and down the centerline.

And finally, both imaging and a sense of envelopment are improved (especially if the room surfaces are fairly live and diffusive) because the first strong sidewall reflection of the left speaker is the long-delay bounce off the right side wall, and vice versa. It is psychoacoustically beneficial for the first reflection of the sound that first hits the left ear to arrive from the right side, and vice versa, as that way the reflection is interpreted as spaciousness instead of coloration and/or image shift.

I did not figure out all of this on my own. It was all taught to me by Earl Geddes.

Duke

Me being a dealer makes you leery?? It gets worse... I'm a manufacturer too.

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