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Author Topic: RTA shows big drop at 1.25khz  (Read 21162 times)

Brian Wombaugh

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RTA shows big drop at 1.25khz
« on: July 17, 2012, 05:19:04 pm »

I have been RTA'ing 2 Peavey PR12N speakers for a church.  I was able to get a flat response across the 31 bands with the exception of the 1.25khz which is falling out of spec by almost a negative 10db.  The bands on either side( 1khz and the 1.6khz ) all fall in line.  The problem is just with this one band.  I have tried correcting it with the EQ but still cannot get it in line with the rest of the frequencies.  Could this be an issue with the crossover point ?  Any info would be greatly appreciated.  Thanks -  Brian
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Kevin McDonough

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Re: RTA shows big drop at 1.25khz
« Reply #1 on: July 17, 2012, 06:13:05 pm »

I have been RTA'ing 2 Peavey PR12N speakers for a church.  I was able to get a flat response across the 31 bands with the exception of the 1.25khz which is falling out of spec by almost a negative 10db.  The bands on either side( 1khz and the 1.6khz ) all fall in line.  The problem is just with this one band.  I have tried correcting it with the EQ but still cannot get it in line with the rest of the frequencies.  Could this be an issue with the crossover point ?  Any info would be greatly appreciated.  Thanks -  Brian


hey

Crossover point sounds like a likley candidate. First however I'd recommend taking the speaker to a different location, preferably outside, and set it at a different height from what it was measured before. This'll rule out the cancellation coming from a reflection within the room your in.

However outside of this then yeah i'd say almost certainly a slight phase problem at the crossover is causing the cancellation. How is the speaker powered?  Is it an active speaker, biamped or does it use a passive internal crossover?   If it's biamped then you should be able to correct it by measuring the impulse and phase of both sections and then adding a little delay to the compression driver to line things up and bring them into phase.

However if its a passive crossover, either on its own or as part of an active speaker, then you may not be able to change the crossover settings to do this, in which case your unfortunately stuck.

k

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Brian Wombaugh

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Re: RTA shows big drop at 1.25khz
« Reply #2 on: July 17, 2012, 06:24:52 pm »

It does have a passive crossover.  The system has a BBE Sound Maximizer which suppose to allow a delay to be put on the low frequencies or the high frequencies.  I wonder if it would help to play around with that ?  Brian
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Timo Beckman

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Re: RTA shows big drop at 1.25khz
« Reply #3 on: July 17, 2012, 06:38:47 pm »

It does have a passive crossover.  The system has a BBE Sound Maximizer which suppose to allow a delay to be put on the low frequencies or the high frequencies.  I wonder if it would help to play around with that ?  Brian

You might try to reverse polarity on 1 of the drivers first (probably the high's) . If this doesn't help try to apply +/- 0,4 ms on the low driver or on the high (less likely but who knowes) .
Or even better measure the response of the loudspeaker to know for shure what's going on .
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Randall Hyde

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Re: RTA shows big drop at 1.25khz
« Reply #4 on: July 17, 2012, 07:04:03 pm »

I have been RTA'ing 2 Peavey PR12N speakers for a church.  I was able to get a flat response across the 31 bands with the exception of the 1.25khz which is falling out of spec by almost a negative 10db.  The bands on either side( 1khz and the 1.6khz ) all fall in line.  The problem is just with this one band.  I have tried correcting it with the EQ but still cannot get it in line with the rest of the frequencies.  Could this be an issue with the crossover point ?  Any info would be greatly appreciated.  Thanks -  Brian

Just a thought -- have you tried moving the RTA microphone around? It might be sitting in a NULL zone for that frequency (though I'd be surprised to find that other frequencies are all flat if this is the case).
Cheers,
Randy Hyde
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Brian Wombaugh

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Re: RTA shows big drop at 1.25khz
« Reply #5 on: July 17, 2012, 07:08:00 pm »

I have tried the microphone in different positions and have still obtained basicially the same result.  Thanks - Brian
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Ryan C. Davis

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Re: RTA shows big drop at 1.25khz
« Reply #6 on: July 17, 2012, 07:27:36 pm »

You might try to reverse polarity on 1 of the drivers first (probably the high's)...

When I was building speakers I found the same thing, usually a suck out like that was indicative of an HF driver that was out of polarity. someone recommended taking the speaker outside and measuring it, that would be a good idea just to eliminate the possibility of room interaction and interaction with the other speaker. There's always a chance someone screwed up in assembly and QA didn't catch it.
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Ryan Davis

Samuel Rees

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RTA shows big drop at 1.25khz
« Reply #7 on: July 18, 2012, 12:19:41 am »

BBE Sonic Maximizer?
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Timo Beckman

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Re: RTA shows big drop at 1.25khz
« Reply #8 on: July 18, 2012, 03:14:53 am »

I have tried the microphone in different positions and have still obtained basicially the same result.  Thanks - Brian

For measuring the phase response a RTA doesn't do the trick . You need to do phase measurements .
A RTA misses out on time vs frequency it's only amplitude vs frequency .
What kind of measurement device do you use ?
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Brian Wombaugh

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Re: RTA shows big drop at 1.25khz
« Reply #9 on: July 18, 2012, 04:52:11 am »

I use a Phonic PAA3.  If I remember correctly I think that it will do some sort of test for phase.  I will have to get my manual out and take a look.  Thanks -  Brian
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Re: RTA shows big drop at 1.25khz
« Reply #9 on: July 18, 2012, 04:52:11 am »


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