Sound pressure in time domain

jamikl · 24th March 2006, 02:30 AM

Could anyone help with an explanation on this as shown in the mathcad simulations. I favour blh enclosures but as mentioned by MJK in one of his papers the double burst shown in this graph has made me wonder a bit. Also, would there not be a similar pattern shown in a bipole MLTL and what effect would this have at a normal listening distance.
Thanks for any help, Mike.
jamikl

lndm · 24th March 2006, 04:37 AM

If the back wave has to travel through the horn first before meeting with the front, it will be out of phase by then. The old sound that was playing momentarily before is now meeting with the current sound from the front.

The time delay is somewhat constant for all frequencies as its main cause is the fixed length horn. This, however, is a different portion of a wavelength for different frequencies.

Where the difference is a small portion of a wavelength, there will be no real problems. Where the difference is half/one and a half etc, there will be nulls. Where there are several wavelengths in it (at higher frequencies) there will be an echo like effect in theory.

If you consider the frequency where the difference will cause your first null, you may be rolling off your blh by then anyway.

Still, I like mine. At the end of the day, it sounds great, even with deep complex organ music with natural reverberation on the recording.

If I remember rightly, Nelson Pass may have mentioned the horn delay was not as bad as it seems on paper.

IMHO, don't try to stop the effect by stuffing your horn. Well, maybe a little, but it really kills it. I prefer to roll off the bass using my electronics if necessary.

jamikl · 24th March 2006, 11:21 AM

Thanks for the reply Indm. I understand what happens with the BLH but am still wondering if the same thing happens with a bipole when moved out 2 - 3 feet from the wall. I did appreciate the BLHs I had years ago and am now tossing up between a Bipole MLTL and the horn. Particularly looking at the Solo with perhaps a mid range using a 3.5" to 4.5" full range speaker in a homebuilt horn as discussed with Colin in an earlier post. General opinion is NOT to mount a front loaded mid and upper horn on a driver that is BLH mounted for bass. I'm open to opinions on this though!
Mike
jamikl

jamikl · 25th March 2006, 08:55 AM

Does any member of the forum have expeience of building with a mid-hi horn on front of a speaker and a BLH for the bass?
Mike
jamikl

lndm · 25th March 2006, 10:39 AM

http://home.vicnet.net.au/~macinc/alf1.htm

jamikl · 26th March 2006, 01:15 AM

Thanks for the reply Indm. I had forgotten about that horn! What you have shown on the link looks great. How low does it go in room?
jamikl

lndm · 26th March 2006, 02:11 AM

I don't know, but probably all the way if done right.

I use my corners. The horn design goes back into the corner and turns inside out over itself and uses the room walls as the mouth. I have to EQ to quieten 20Hz and I'm only using a 7" driver.

24th March 2006, 02:30 AM	#1
jamikl diyAudio Member Join Date: May 2005 Location: Melbourne	Sound pressure in time domain Could anyone help with an explanation on this as shown in the mathcad simulations. I favour blh enclosures but as mentioned by MJK in one of his papers the double burst shown in this graph has made me wonder a bit. Also, would there not be a similar pattern shown in a bipole MLTL and what effect would this have at a normal listening distance. Thanks for any help, Mike. jamikl

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24th March 2006, 04:37 AM	#2
lndm diyAudio Member Join Date: Mar 2006 Location: nsw	If the back wave has to travel through the horn first before meeting with the front, it will be out of phase by then. The old sound that was playing momentarily before is now meeting with the current sound from the front. The time delay is somewhat constant for all frequencies as its main cause is the fixed length horn. This, however, is a different portion of a wavelength for different frequencies. Where the difference is a small portion of a wavelength, there will be no real problems. Where the difference is half/one and a half etc, there will be nulls. Where there are several wavelengths in it (at higher frequencies) there will be an echo like effect in theory. If you consider the frequency where the difference will cause your first null, you may be rolling off your blh by then anyway. Still, I like mine. At the end of the day, it sounds great, even with deep complex organ music with natural reverberation on the recording. If I remember rightly, Nelson Pass may have mentioned the horn delay was not as bad as it seems on paper. IMHO, don't try to stop the effect by stuffing your horn. Well, maybe a little, but it really kills it. I prefer to roll off the bass using my electronics if necessary.

24th March 2006, 11:21 AM	#3
jamikl diyAudio Member Join Date: May 2005 Location: Melbourne	Thanks for the reply Indm. I understand what happens with the BLH but am still wondering if the same thing happens with a bipole when moved out 2 - 3 feet from the wall. I did appreciate the BLHs I had years ago and am now tossing up between a Bipole MLTL and the horn. Particularly looking at the Solo with perhaps a mid range using a 3.5" to 4.5" full range speaker in a homebuilt horn as discussed with Colin in an earlier post. General opinion is NOT to mount a front loaded mid and upper horn on a driver that is BLH mounted for bass. I'm open to opinions on this though! Mike jamikl

25th March 2006, 08:55 AM	#4
jamikl diyAudio Member Join Date: May 2005 Location: Melbourne	Does any member of the forum have expeience of building with a mid-hi horn on front of a speaker and a BLH for the bass? Mike jamikl

25th March 2006, 10:39 AM	#5
lndm diyAudio Member Join Date: Mar 2006 Location: nsw	http://home.vicnet.net.au/~macinc/alf1.htm

26th March 2006, 01:15 AM	#6
jamikl diyAudio Member Join Date: May 2005 Location: Melbourne	Thanks for the reply Indm. I had forgotten about that horn! What you have shown on the link looks great. How low does it go in room? jamikl

26th March 2006, 02:11 AM	#7
lndm diyAudio Member Join Date: Mar 2006 Location: nsw	I don't know, but probably all the way if done right. I use my corners. The horn design goes back into the corner and turns inside out over itself and uses the room walls as the mouth. I have to EQ to quieten 20Hz and I'm only using a 7" driver.

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