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Author Topic: 15 and 90 degree horn speakers side by side with delay ?  (Read 2093 times)

Douglas R. Allen

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15 and 90 degree horn speakers side by side with delay ?
« on: December 15, 2020, 12:31:48 pm »

  I ran across a post on another site that claimed to "smooth out" the phase cancellation of putting 2 - 1-15 and horn 90X45  boxes that even though they were properly splayed out that if you put 3 ms of delay on the outside speaker you will smooth the comb filtering out and improve the overall response.  ???  Did I miss something in the past 30 years or so?

  Is there a basic program I could download to model 2 speakers side by side with a 100 , 200 , 400 hz tones to see how it effects the low frequency coupling?  First with both with no delay then again with 3 ms added to the outside box?  I always thought it would be best when you have 2 speakers close together you'd want to have no delay on them to keep the frequencies coupled for as long as possible. Certainly the low frequency range where they are closer than 1/4 wavelength.  I would think 3 ms or 3.5 feet of delay would keep that from happening. Down to around 90hz or so anyway.  Is this sometimes done with good results?  I would think it would lobe or steer the bass? I also would think it would make a Frequency related to delay delay comb filtering sound.  I realize that 2 - 90 degree boxes combined side by side is a bad idea but any thoughts on this? 
 
  Here to learn  :-[ as I may have simply missed this though the years even if it sounds odd.

Douglas R. Allen
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Dave Garoutte

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Re: 15 and 90 degree horn speakers side by side with delay ?
« Reply #1 on: December 15, 2020, 12:51:31 pm »

  I ran across a post on another site that claimed to "smooth out" the phase cancellation of putting 2 - 1-15 and horn 90X45  boxes that even though they were properly splayed out that if you put 3 ms of delay on the outside speaker you will smooth the comb filtering out and improve the overall response.  ???  Did I miss something in the past 30 years or so?

  Is there a basic program I could download to model 2 speakers side by side with a 100 , 200 , 400 hz tones to see how it effects the low frequency coupling?  First with both with no delay then again with 3 ms added to the outside box?  I always thought it would be best when you have 2 speakers close together you'd want to have no delay on them to keep the frequencies coupled for as long as possible. Certainly the low frequency range where they are closer than 1/4 wavelength.  I would think 3 ms or 3.5 feet of delay would keep that from happening. Down to around 90hz or so anyway.  Is this sometimes done with good results?  I would think it would lobe or steer the bass? I also would think it would make a Frequency related to delay delay comb filtering sound.  I realize that 2 - 90 degree boxes combined side by side is a bad idea but any thoughts on this? 
 
  Here to learn  :-[ as I may have simply missed this though the years even if it sounds odd.

Douglas R. Allen
It seems like a bit of delay (based on the center to center distance) would help the outside speaker blend with the inside one if you are in the CENTER of the audience.
But the point of the splay is to put the outside speaker energy to the OUTSIDE. 
The primary concern has to be at the overlap of the two patterns, so no delay would make more sense.
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Robert Healey

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Re: 15 and 90 degree horn speakers side by side with delay ?
« Reply #2 on: December 15, 2020, 01:01:48 pm »

  I ran across a post on another site that claimed to "smooth out" the phase cancellation of putting 2 - 1-15 and horn 90X45  boxes that even though they were properly splayed out that if you put 3 ms of delay on the outside speaker you will smooth the comb filtering out and improve the overall response.  ???  Did I miss something in the past 30 years or so?

  Is there a basic program I could download to model 2 speakers side by side with a 100 , 200 , 400 hz tones to see how it effects the low frequency coupling?  First with both with no delay then again with 3 ms added to the outside box?  I always thought it would be best when you have 2 speakers close together you'd want to have no delay on them to keep the frequencies coupled for as long as possible. Certainly the low frequency range where they are closer than 1/4 wavelength.  I would think 3 ms or 3.5 feet of delay would keep that from happening. Down to around 90hz or so anyway.  Is this sometimes done with good results?  I would think it would lobe or steer the bass? I also would think it would make a Frequency related to delay delay comb filtering sound.  I realize that 2 - 90 degree boxes combined side by side is a bad idea but any thoughts on this? 
 
  Here to learn  :-[ as I may have simply missed this though the years even if it sounds odd.

Douglas R. Allen

This is a technique Bob Coffeen used (calling it "optimal misalignment") and taught. He had a demo where he would play pink noise for an audience on a pair speakers that rotated so you could "sweep" the audience with the comb filtering, and it did sound smoother with the delay. Bob found it increased intelligibility in systems that required multiple loudspeakers. With EASE, you can see that it was steering the worst comb filtering artifacts to less critical areas of the audience.

I am not so sure it is valid with modern systems. When this technique was developed, the time domain was not being measured and most of the systems that were being designed then were old horn-type clusters that were completely time incoherent to begin with. Achieving intelligibility in installed systems was seen as more important than fidelity. Modern installed systems are much more music-focused, and we know a lot more about how the time domain affects fidelity and have an active goal of preserving it - especially with the use of coaxial designs and FIR filters.

Either way - it is worth a try, especially if you have a cluster of traditional 15" + horn boxes.

EV used to have an Excel based cluster prediction program - not sure if it is still available.
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Helge A Bentsen

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Re: 15 and 90 degree horn speakers side by side with delay ?
« Reply #3 on: December 15, 2020, 02:22:23 pm »

I've done that several times, but I used delay AND level to match boxes with reduced splay angle.
There is a formula somewhere in Bobs book to calculate splay angles when you reduce level between two identical boxes, I just use Smaart and roll with whatever measures "right" at the time.


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Caleb Dueck

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Re: 15 and 90 degree horn speakers side by side with delay ?
« Reply #4 on: December 16, 2020, 12:01:24 am »

I've done that several times, but I used delay AND level to match boxes with reduced splay angle.
There is a formula somewhere in Bobs book to calculate splay angles when you reduce level between two identical boxes, I just use Smaart and roll with whatever measures "right" at the time.

I've played with this a few times.  It merely steers the nasties a bit outside the pattern of one box, but screws with impulse response and comb filtering.  Whether or not it's better - it depends.
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Ivan Beaver

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Re: 15 and 90 degree horn speakers side by side with delay ?
« Reply #5 on: December 16, 2020, 04:54:30 pm »

When you have 2 sources arriving at different times at the same time you WILL have combfiltering.

YES, you can "fix it" for 1 location with delay, but you will make other locations worse.

You have to choose what is most important.
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Bradford "BJ" James

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Re: 15 and 90 degree horn speakers side by side with delay ?
« Reply #6 on: December 16, 2020, 07:05:28 pm »

When you have 2 sources arriving at different times at the same time you WILL have combfiltering.

YES, you can "fix it" for 1 location with delay, but you will make other locations worse.

You have to choose what is most important.
Ivan,
Back when I had a Versarray and hung out on the PV forum, there was a hot headed PV designer who always advised to run either the outside or inside pair a few dB lower to kill (or maybe just slightly maim) any comb filtering when using 1 pair of wide dispersion trap boxes/side. Doesn't that simply move the area of combing more towards the listening area of the attenuated boxes?
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Caleb Dueck

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Re: 15 and 90 degree horn speakers side by side with delay ?
« Reply #7 on: December 16, 2020, 10:30:03 pm »

Ivan,
Back when I had a Versarray and hung out on the PV forum, there was a hot headed PV designer who always advised to run either the outside or inside pair a few dB lower to kill (or maybe just slightly maim) any comb filtering when using 1 pair of wide dispersion trap boxes/side. Doesn't that simply move the area of combing more towards the listening area of the attenuated boxes?

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. 
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Ivan Beaver

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Re: 15 and 90 degree horn speakers side by side with delay ?
« Reply #8 on: December 17, 2020, 09:30:24 am »

Ivan,
Back when I had a Versarray and hung out on the PV forum, there was a hot headed PV designer who always advised to run either the outside or inside pair a few dB lower to kill (or maybe just slightly maim) any comb filtering when using 1 pair of wide dispersion trap boxes/side. Doesn't that simply move the area of combing more towards the listening area of the attenuated boxes?
As Caleb says, the freq of the combfilters will not change, just how deep and high they are.

You get maximum combfiltering  when both arrivals are equal in level.  As soon as either one goes down in level, the depth of the notch (and the peak of the sum) is reduced, but the freq stays the same.

The basic math is this.  The spacing of the notches (the peaks are between the notches) = the difference in time of arrivals.  So if the arrivals are 1ms apart (about 1'), they will be spaced at 500Hz intervals.  The first notch will be at 1/2 of the time difference, or in this case 500Hz.  1ms=1,000Hz. 

So you will have notches at 500hz, 1KHz, 1.5KHz, 2KHz, 2.5KHz, 3KHz, 3.5KHz etc
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Bradford "BJ" James

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Re: 15 and 90 degree horn speakers side by side with delay ?
« Reply #9 on: December 17, 2020, 08:52:01 pm »

Great explanation. Thanks.
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Scott Helmke

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Re: 15 and 90 degree horn speakers side by side with delay ?
« Reply #10 on: December 18, 2020, 11:54:45 am »

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.
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Jim McKeveny

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Re: 15 and 90 degree horn speakers side by side with delay ?
« Reply #11 on: December 18, 2020, 12:45:55 pm »

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!"
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Chris Hindle

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Re: 15 and 90 degree horn speakers side by side with delay ?
« Reply #12 on: December 18, 2020, 02:25:57 pm »

"I specifically requested No Comb Filtering seats, young man!"
Like anybody other than us knows what that even means??? ::)
Chris
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Michael Lawrence

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Re: 15 and 90 degree horn speakers side by side with delay ?
« Reply #13 on: December 18, 2020, 02:55:49 pm »

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.
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Douglas R. Allen

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Re: 15 and 90 degree horn speakers side by side with delay ?
« Reply #14 on: December 18, 2020, 03:55:07 pm »

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
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Michael Lawrence

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Re: 15 and 90 degree horn speakers side by side with delay ?
« Reply #15 on: December 18, 2020, 09:12:03 pm »

   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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Re: 15 and 90 degree horn speakers side by side with delay ?
« Reply #15 on: December 18, 2020, 09:12:03 pm »


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