what causes this to happen with a BLH?
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 25th February 2012, 11:12 AM #1 gafhenderson   diyAudio Member   Join Date: Jan 2012 what causes this to happen with a BLH? what is it that causes the mega dip around 300hz when i combine the response? thanks
 25th February 2012, 11:39 AM #2 jacozz   diyAudio Member   Join Date: Mar 2009 Probably, the driver's direct output and the horn mouth's output, combined, is out of phase around 300 hz? /Jacozz
 25th February 2012, 11:51 AM #3 gafhenderson   diyAudio Member   Join Date: Jan 2012 @ 200hz it shows -126* phase response @300hz it shows -63* phase response is this what you mean? what exactly causes the combined output to be out of phase?
kctess5
diyAudio Member

Join Date: Dec 2011
Location: California
Quote:
 what exactly causes the combined output to be out of phase?
If the distance between the two sources is one half wave length apart (180 degrees) or any multiple of that (n*2pi+pi radians or n*360+180 degrees) then when the waves sum together the pressure is zero. Think adding +1 and -1 to get 0.

When they are in phase (accounting for distance at whatever frequency your talking about) it sums positively (louder) and when they are out of phase it cancels (quiet) and it varies inbetween. Also it will occur on a periodic basis as the frequency increases, this means it will happen not just at the fundamental frequency but also when n=2,3,4,5,6... this accounts for the periodic rise and fall above 300 on that graph.

I hope this makes sense

Last edited by kctess5; 26th February 2012 at 08:36 AM.

gafhenderson
diyAudio Member

Join Date: Jan 2012
Quote:
 Originally Posted by kctess5 If the distance between the two sources is one half wave length apart (180 degrees) or any multiple of that (n*2pi+pi radians or n*360+180 degrees) then when the waves sum together the pressure is zero. Think adding +1 and -1 to get 0. When they are in phase (accounting for distance at whatever frequency your talking about) it sums positively (louder) and when they are out of phase it cancels (quiet) and it varies inbetween. Also it will occur on a periodic basis as the frequency increases, this means it will happen not just at the fundamental frequency but also when n=2,3,4,5,6... this accounts for the periodic rise and fall above 300 on that graph. I hope this makes sense
yes thanks.

these things are hard to make work properly!

 26th February 2012, 04:23 PM #6 kctess5   diyAudio Member   Join Date: Dec 2011 Location: California I know the response always looks like that on paper but once you add the direct response of the driver, some stuffing, room acoustics, reflections, etc I think it will smooth out. I suppose you could eq it off of the measured response Maybe I'm off base here

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