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[Scott Helmke]

Changing the level doesn't shift the nasties, that's what delay does.  What lowering the level does is makes the nulls slightly less deep.  Rather than have +10 and -10 signals combine for 0 (0dB SPL, IE pure comb filtering) - you have +10 and -7 signals combine for -3 - it's still bad, at the same locations, but the nulls aren't quite as deep.  The peaks are slightly less high, but that isn't as noticeable.

The tradeoff with changing levels is shortchanging the people who happen to be sitting only in the coverage area of the speaker that is turned down.

[Jim McKeveny]

The tradeoff with changing levels is shortchanging the people who happen to be sitting only in the coverage area of the speaker that is turned down.

"I specifically requested No Comb Filtering seats, young man!"

[Chris Hindle]

"I specifically requested No Comb Filtering seats, young man!"

Like anybody other than us knows what that even means???
Chris

[Michael Lawrence]

There is a kernel of truth to this concept - as has been pointed out already, two sources are most interactive where they are equal in level. If one source is attenuated, the location where they are equal in level has changed (it has moved closer to the attenuated source).

Now your equal-level point is no longer an equal time point (because it's closer to one source), and that new location where they are now equal in level (spatial crossover) can be cleaned up with delay. It's a little bit unintuitive but this can result in a net positive effect. Yes, you will move the combing around, but at other locations, one source has a level advantage so it's not as severe.

Bob's book address this well, although I can't find the relevant page at the moment.

EDIT: Left out a word.

[Douglas R. Allen]

There is a kernel of truth to this concept - as has been pointed out already, two sources are most interactive where they are equal in level. If one source is attenuated, the location where they are equal in level has changed (it has moved closer to the attenuated source).

Now your equal-level point is no longer an equal time point (because it's closer to one source), and that new location where they are now equal in level (spatial crossover) can be cleaned up with delay. It's a little bit unintuitive but this can result in a net positive effect. Yes, you will move the combing around, but at other locations, one source has a level advantage so it's not as severe.

Bob's book address this well, although I can't find the relevant page at the moment.

EDIT: Left out a word.

   Wouldn't this level and delay have to be engineered in?  The reason I asked my original question was that a person was told "Add 3 ms" and your problem will be solved. Without proper measurements with known splay angles isn't a " one delay fits all " advice not really possible or is 3ms to the outside speaker a given standard average setting?  This is with only 2 speakers a side splayed and delay added to the outside speaker. It does seem clear that adding delay will give you the expected different result that no delay at all gives but I don't see it as a one delay fits all speakers and setups.  I thought the advice given was too unclear and didn't cover both sides of the coin. The comments here in general were roughly what I expected to get.    "It depends"    although I expected there would be more negative than there was. It does give me something to think about and research. To me though it feels like a bandage that is only moving the problem of two speakers that are not really designed to work together to a different location. On the other hand I've learned something about a setup I thought would never work and I may just give it a try in the future just to see the results I get. This can easily be done in a informal test environment to see. Handy to know.
   
   Thanks to everyone who took the time to reply. Certainly has given me something to look into anyway.

Kindest Regards;
Douglas R. Allen

[Michael Lawrence]

   Wouldn't this level and delay have to be engineered in?  The reason I asked my original question was that a person was told "Add 3 ms" and your problem will be solved. Without proper measurements with known splay angles isn't a " one delay fits all " advice not really possible or is 3ms to the outside speaker a given standard average setting?  This is with only 2 speakers a side splayed and delay added to the outside speaker. It does seem clear that adding delay will give you the expected different result that no delay at all gives but I don't see it as a one delay fits all speakers and setups.  I thought the advice given was too unclear and didn't cover both sides of the coin. The comments here in general were roughly what I expected to get.    "It depends"    although I expected there would be more negative than there was. It does give me something to think about and research. To me though it feels like a bandage that is only moving the problem of two speakers that are not really designed to work together to a different location. On the other hand I've learned something about a setup I thought would never work and I may just give it a try in the future just to see the results I get. This can easily be done in a informal test environment to see. Handy to know.
   
   Thanks to everyone who took the time to reply. Certainly has given me something to look into anyway.

Kindest Regards;
Douglas R. Allen

That's exactly right, Doug. Your instincts are right on the money. The physical design of the box, the amount of splay, and the amount of level offset are all variables here. The workflow would be to find the angular location where both boxes are matched in level (at HF) after the desired attenuation has been done, and delay the earlier (attenuated) box to align the two arrivals at this point. My guess is that whoever is selling this 3ms idea saw that done once, 3ms happened to be the correct timing needed in that one particular instance, and off you go.

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