.73 ratio for Left/Right measured from?

[Jonnyozero3]

This is an odd question I thought of a long time ago but never asked. The .73 ratio mentioned in the Ascend manual for separating the stereo mains...where exactly do I measure from? Do I measure from the corresponding left/right sides of the speakers to determine the ".73" distance, or do I measure from the midpoint of the speaker enclosure? Does that make sense? I'm assuming I should measure from the center/midpoint of the drivers, but I thought I would check.

Silly question, I know.

PS: Yeah, I get in the tweaking mood now and then

[curtis]

I just assume the midpoint of the speaker/driver.

I know it is only a guideline, but I always wondered how the suggestion of .73 came about.

[Jonnyozero3]

Yeah, I think I assumed the sides of the speakers last time I tweaked placement because it's what worked better for my setup, lol. I'll have to go remeasure. I am so anal about this stuff...

Anyhow, I am also really curious how that ratio came about? Must have to do with the dispertion patterns and axial response right? This is one of those times I'd love to have Dave's personal design notes to read

[azanon]

What should the ratio be in the case of a phantom center? The same? Lower? (closer together).

[Jonnyozero3]

I don't know, but I'd venture a guess that if the .73 ratio gets you the best stereo image, then it would work best for the phantom center as well. But I don't really know...

[davef]

Hi Guys,

Good discussion here... and I am happy to contribute.

The .73 multiplier is really just simple geometry. Multiplying the distance you are seated from the midpoint between the speakers by .73, yields a recommended separation distance between the left / right speakers that places each speaker at a corresponding 20 degree off-axis angle from you. Combining that with the 5 degree toe-in angle I generally recommend and each speaker will be at an off-axis angle of 15 degrees. The range of 0 through 15 degrees off-axis yields the most accurate response from the loudspeaker.

The .73 multiplier is the simplest way to determine the maximum separation distance between the left/right speaker that will position the listener within the most ideal listening window.

Note: in this example, the distance between the speakers is measured from center to center (typically, tweeter to tweeter)

Of course, this is just a rule of thumb but it is a very good starting point.

Hope this helps!

[Jonnyozero3]

Great info. Thank you, Dave. You covered all my questions

[Grayson73]

If distance from listening position to center between L/R is 10 feet, the L and R should be 7.3 feet apart?

[Jonnyozero3]

7.3 ft tweeter to tweeter, yup.

[nickmo]

Since I've moved into my new house in May I have been unable to set up my Sierras properly due to a number of factors(money, newly crawling baby, etc.,...). Before last night I had my front three Sierras sitting on the edge of a long (~5') low (~14") coffee table about two feet away from the wall. There was less than two and a half feet between the center and either of the L/R speakers. I found that center channel dialog was almost impossible to understand, and I was always bumping up the the center channel volume +5-6 in order to hear it clearly. Of course this made any effects coming from the center channel uncomfortably loud. So last night before watching RocknRolla on Blu Ray I moved my right channel on to the top of my Rythmik D15 which sits in the front corner of my room. WHAT A HUGE DIFFERENCE!!!!! Dialog was clear, effects panned across the front soundstage so much better, I was grinning the whole movie.
Then this morning I swing by the forums and do a search for speaker placement and find this thread. I sit ten feet from my speakers so according to the .73 rule of thumb my speakers should be 7'4" apart for best imaging. I just measured them in their new locations and it came out to 7'2" tweeter to tweeter. Amazing. Really I can't do the increase in sound quality justice with my description. WOW!