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Author Topic: Proper delay to align mid & hi in a JBL SR4732-X?  (Read 8407 times)

Jeff Hague

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Proper delay to align mid & hi in a JBL SR4732-X?
« on: May 15, 2009, 05:11:53 pm »

I am redoing my DR260 settings for my main rig and am wondering what to use as a delay time to align the mids to the highs on a JBL SR4732-X cab. I actually already have it done and it sounds pretty nice but the tuning included with the 260 for that cab if (you use the wizard) calls for a 0.15 ms (or 0.16 ft) delay on the mid output. 0.16 feet is less than 2 inches, overall the horn/driver combination (2447 on a 2381) is 13.25 inches and the mid driver (2206) is 5" deep. I realize that the voice coils arent all the way at the back of the drivers but it seems to me that physically the offset is closer to 5" or 6" - more like 0.37 to 0.45 ms? (Assuming that the speed of sound is 0.885 ms / ft which works out to .074 ms / inch.)
Am I way off or missing something else? Am I trying to align the 2 voice coils but should instead be trying to align the 12s voice coil to the throat of the horn instead, or some other spot along the horn?
Thanks!
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Mac Kerr

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Re: Proper delay to align mid & hi in a JBL SR4732-X?
« Reply #1 on: May 15, 2009, 05:18:11 pm »

Jeff Hague wrote on Fri, 15 May 2009 17:11

I am redoing my DR260 settings for my main rig and am wondering what to use as a delay time to align the mids to the highs on a JBL SR4732-X cab. I actually already have it done and it sounds pretty nice but the tuning included with the 260 for that cab if (you use the wizard) calls for a 0.15 ms (or 0.16 ft) delay on the mid output. 0.16 feet is less than 2 inches, overall the horn/driver combination (2447 on a 2381) is 13.25 inches and the mid driver (2206) is 5" deep. I realize that the voice coils arent all the way at the back of the drivers but it seems to me that physically the offset is closer to 5" or 6" - more like 0.37 to 0.45 ms? (Assuming that the speed of sound is 0.885 ms / ft which works out to .074 ms / inch.)
Am I way off or missing something else? Am I trying to align the 2 voice coils but should instead be trying to align the 12s voice coil to the throat of the horn instead, or some other spot along the horn?
Thanks!

None of the above. You should be trying to align the phase of the horn and the mid through the crossover range. Because of the LPF on the mid its phase will be changed, which will equate to a difference in time at the crossover frequency. If you do not have a measurement system that will let you look at the phase of each speaker over that range I would go with the manufacturer's spec. That is undoubtedly how they arrived at the specified delay time.

Mac
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Ivan Beaver

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Re: Proper delay to align mid & hi in a JBL SR4732-X?
« Reply #2 on: May 15, 2009, 06:39:37 pm »

Mac Kerr wrote on Fri, 15 May 2009 17:18

Jeff Hague wrote on Fri, 15 May 2009 17:11

I am redoing my DR260 settings for my main rig and am wondering what to use as a delay time to align the mids to the highs on a JBL SR4732-X cab. I actually already have it done and it sounds pretty nice but the tuning included with the 260 for that cab if (you use the wizard) calls for a 0.15 ms (or 0.16 ft) delay on the mid output. 0.16 feet is less than 2 inches, overall the horn/driver combination (2447 on a 2381) is 13.25 inches and the mid driver (2206) is 5" deep. I realize that the voice coils arent all the way at the back of the drivers but it seems to me that physically the offset is closer to 5" or 6" - more like 0.37 to 0.45 ms? (Assuming that the speed of sound is 0.885 ms / ft which works out to .074 ms / inch.)
Am I way off or missing something else? Am I trying to align the 2 voice coils but should instead be trying to align the 12s voice coil to the throat of the horn instead, or some other spot along the horn?
Thanks!

None of the above. You should be trying to align the phase of the horn and the mid through the crossover range. Because of the LPF on the mid its phase will be changed, which will equate to a difference in time at the crossover frequency. If you do not have a measurement system that will let you look at the phase of each speaker over that range I would go with the manufacturer's spec. That is undoubtedly how they arrived at the specified delay time.

Mac


+1  I have seen systems in which the horn driver is the deepest driver in the cabinet and have STILL delayed it.

The reason-to achieve a good PHASE response.

There is A LOT more to performance/sound quality than amplitude!
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Jeff Hague

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Re: Proper delay to align mid & hi in a JBL SR4732-X?
« Reply #3 on: May 15, 2009, 08:58:03 pm »

Mac Kerr wrote on Fri, 15 May 2009 17:18

None of the above. You should be trying to align the phase of the horn and the mid through the crossover range.
Mac

Ivan Beaver wrote on Fri, 15 May 2009 18:39


+1  I have seen systems in which the horn driver is the deepest driver in the cabinet and have STILL delayed it.
The reason-to achieve a good PHASE response.
There is A LOT more to performance/sound quality than amplitude!


So way back (in the early 80s?) when delay on crossover outputs became common on MI grade gear, the manufacturers just said you were trying to time align them because of the distance offset? Were we too stupid to understand those things then?
I understand that there is a phase issue in the crossover region but I still thought the delay was to time align the drivers due to the distance offset... If its a phase thing that isnt related to distance, why does DBX give you the option of setting in ms or feet? Would the amount of delay needed change as you change the crossover freqs and slopes of the mid and hi outputs as well?
In any case, I am not profficient  enough with Smaart to feel comfortable getting it right that way so I will go with DBXs recommendation for the time being. The "wizard" applies no delay on the lo output, I guess I should leave that alone too?
Thanks!
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Mac Kerr

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Re: Proper delay to align mid & hi
« Reply #4 on: May 15, 2009, 09:11:26 pm »

Jeff Hague wrote on Fri, 15 May 2009 20:58

So way back (in the early 80s?) when delay on crossover outputs became common on MI grade gear, the manufacturers just said you were trying to time align them because of the distance offset? Were we too stupid to understand those things then?
I understand that there is a phase issue in the crossover region but I still thought the delay was to time align the drivers due to the distance offset... If its a phase thing that isnt related to distance, why does DBX give you the option of setting in ms or feet? Would the amount of delay needed change as you change the crossover freqs and slopes of the mid and hi outputs as well?
In any case, I am not profficient  enough with Smaart to feel comfortable getting it right that way so I will go with DBXs recommendation for the time being. The "wizard" applies no delay on the lo output, I guess I should leave that alone too?
Thanks!


Who said it wasn't related to distance? Yes the signal delay is used to compensate for a difference in position of the drivers, but the solution is not the measured distance between the drivers. What you want is maximum summation through the crossover region, and you get that when the 2 drivers are in phase with each other. I have no idea why dbx (who have no capitol letters in their corporate name) has feet and ms other than that has been the standard on delay units for years.

Yes, the amount of delay will change as you change the type of crossover filter. The phase change of the signal will be determined by the number of poles in the filter. Steeper slopes will have more phase shift.

If you have Smaart it is not a difficult procedure, and has been explained in detail on these forums recently (in the last week or two). Give it a try and see how your measured results compare with dbx's published specs.

Mac
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Ivan Beaver

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Re: Proper delay to align mid & hi in a JBL SR4732-X?
« Reply #5 on: May 15, 2009, 09:12:41 pm »

I would use the recommended settings-unless you have a specific reason to change them-and how you "feel" is not one of them Laughing

There are a lot of things that go into a proper alignment-physical displacement-electronic delay-phase shift of the different crossover filters/types-phase shift of any eq around the crossover region-intended zero axis of alignment-amplitude response of the individual passbands etc.

It is not just one or two things-but the combination that makes the final settings.

You also have to understand that the overall knowledge base in audio has gone through leaps and bounds since the 80's.

With very few exceptions, almost all crossovers back then used the same freg for adjacent bands.  Mainly because it was easy.

Very few loudspeakers will have the same crossover points for adjacent bands.
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Danley Sound Labs

Jeff Hague

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Re: Proper delay to align mid & hi in a JBL SR4732-X?
« Reply #6 on: May 15, 2009, 10:14:28 pm »

Mac and Ivan - thanks for the replies.
I have played with Smaart quite a bit but havent been able yet to get a coherence trace that makes me feel as though its giving me accurate information. Until I can figure that part out, I think I will be more comfortable using the tools Ive always used - what I can read, what I can learn from other folks and what my ears tell me...
I have used the DR260 "wizard" settings ever since I got the thing and the rig did sound OK but I have been told not to use them - that the preset tunings arent very accurate for my particular rig because the SR-X series predates the DR260. The settings were sort of "imported" from an older piece of JBL gear and dbx didnt spend much time on them. I have to admit that, although my own settings are similar to what the wizard recommends, the system does sound better to me.
I think the bands will all be late for the outdoor gig I have tomorrow anyway so I might have some time to play with it.
Thanks again!
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Mac Kerr

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Re: Proper delay to align mid & hi in a JBL SR4732-X?
« Reply #7 on: May 15, 2009, 10:24:12 pm »

Jeff Hague wrote on Fri, 15 May 2009 22:14

Mac and Ivan - thanks for the replies.
I have played with Smaart quite a bit but havent been able yet to get a coherence trace that makes me feel as though its giving me accurate information.

If you are measuring the components within a single speaker system you should have the mic about 3' away from the speaker, with the speaker raised up enough that any reflection path will be significantly longer than 3'. The mic should probably be on the center between the 2 drivers being measured. You should be able to get good coherence under these conditions.

For a simple impulse measurement you can you can use the IR mode and get the impulse timing from each driver. While this is not a good method to use with low frequency drivers it may be fine at the crossover between a mid and high driver. You will be comparing the highest range of each driver rather than the highest range of the low driver and the lowest range of the high driver, but with the short wavelengths of the high driver it may be fine. It would be interesting to compare with the dbx specs in any case.

Mac
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Jeff Hague

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Re: Proper delay to align mid & hi in a JBL SR4732-X?
« Reply #8 on: May 15, 2009, 11:29:50 pm »

Mac Kerr wrote on Fri, 15 May 2009 22:24

If you are measuring the components within a single speaker system you should have the mic about 3' away from the speaker, with the speaker raised up enough that any reflection path will be significantly longer than 3'. The mic should probably be on the center between the 2 drivers being measured. You should be able to get good coherence under these conditions.
Mac


Ill try that as soon as the wife gives me the garage and enough time  Confused.
The garage is 30 by 24 with a concrete slab and is pretty much wide open in the middle. What I have done is lay the top cabinet on its side with blocks under the "back" so its perpendicular to the floor - its a trap cabinet. Then place the measurement mic about 10' away pointing down, directly at and about 1/2" from the slab. This arrangement is what I thought I read is optimum to eliminate floor bounce. Should I instead stack the top cab on one of the lows (4' tall) like I would do for a gig and put the measurement mic on a stand, 3' away and pointing directly at a point midway between the mid and hf drivers? That makes much more sense to me but it seems contrary to what Ive read. That arrangement would allow me to do this stuff "on gig" especially at outdoor stuff. That sure would be nice!
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Mac Kerr

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Re: Proper delay to align mid & hi in a JBL SR4732-X?
« Reply #9 on: May 16, 2009, 09:48:01 am »

Jeff Hague wrote on Fri, 15 May 2009 23:29

What I have done is lay the top cabinet on its side with blocks under the "back" so its perpendicular to the floor - its a trap cabinet. Then place the measurement mic about 10' away pointing down, directly at and about 1/2" from the slab. This arrangement is what I thought I read is optimum to eliminate floor bounce. Should I instead stack the top cab on one of the lows (4' tall) like I would do for a gig and put the measurement mic on a stand, 3' away and pointing directly at a point midway between the mid and hf drivers? That makes much more sense to me but it seems contrary to what Ive read. That arrangement would allow me to do this stuff "on gig" especially at outdoor stuff. That sure would be nice!

What you have done is fine. The mic should be closer to the slab, maybe an 1/8" or less at the closest point, and not 10' away, try 3' away. I do not point the mic straight down, but at a 45
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