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Re: On multiple tweeters

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In Reply to: On multiple tweeters posted by Paul Joppa on January 31, 2000 at 14:01:09:

Is that spacing center to center?
It may be a lobing issue, but the beaming I'm mentioning is really beaming, I think, because the effect is noticable even on a single driver speaker, that is, say if you run the woofers full range to 15 kHz, there is a noticable drop off in HF as you get off axis, to one side.
I think the lobing issue is more likely to create a bit of vague imaging or recession at certain heights, as certain frequencies dip, while the beaming effect is noticed more off to one side.

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Re: On multiple tweeters Paul Joppa 17:50:35 01/31/00 (3)
Yes, center to center. I should have been more clear, sorry.
OK, it's beaming then.
Lobing is probably more of a problem with tweeters, which remain wide dispersion at high frequencies. Incidentally, this problem resolves itself if the array is tall enough and you sit close enough - the difference in speaker-to-ear delay times spreads the apparent directivity. You can also do this with a gently curved baffle if you want to sit further away.
The real problem with severe lobing is that small head movements give large changes in the first-arrival spectral shape. You want the principle lobe to cover at least +/- 15 degrees generally, so that there is a sweet spot bigger than your head.
- Re: On multiple tweeters Doc B. 08:42:23 02/01/00 (2)
  Bigger than my head? You're asking a lot.
  In fact we are enjoying sitting close to the straight 8s. I measured last night and the current listening position is at 8 feet from the middle of driver array, with about 6.5 feet between them. I did a lot of neck craning and shifting around in my seat, and while there's a definite sweet spot, there doesn't seem to be any lobing effect - it doesn't really seem to change the character of the speaks as you move.
  - Re: On multiple tweeters Paul Joppa 10:03:10 02/01/00 (1)
    Ummm - not sure if this was clear, but that's my point exactly. The Str8-8s would lobe above 4kHz if they were not crossed over to a single-point tweeter. An array of tweeters, spaced 6" apart like the Str8-8, would have some problems, too; IMHO they would have to be spaced much closer to work out well.
    - Re: On multiple tweeters Doc B. 10:57:19 02/01/00 (0)
      Sorry, I was trying to support your point, bud. You may recall that I initially ran the 4 driver FIM model 4 midwoofs all the way up to 15 kHz, and crossed the tweeter in with a 1 mfd cap. When we improved the tweeter damping and could then move to a lower crossover point, as used in the Straight 8, things got a lot more coherent.

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