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Author Topic: Speaker measurements  (Read 8254 times)

Kent Thompson

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Speaker measurements
« on: July 29, 2012, 01:21:34 am »

I thought I would move a question of mine out of an existing thread and put it here like I should have done to begin with...



The measurement I took was at about 8' the microphone was positioned about mid cabinet (dual 15s and horn) on axis at about the top 15 level below the horn.  It would be nice to know what causes this whether I am measuring wrong or something is wrong with the speaker.

I probably should have had the microphone mid way between the top speaker and horn... I am gonna take another measurement in a couple days when its my turn to run the system again.



It was suggested I take measurements at different places. So I did.
These are from various places on axis andslightly off axis(around 10 degrees), close and far.
The black trace is an average.
the dip is pretty consistent from every position.
What I think I see...at the crossover point there is a pretty good phase shift. Is this causing the dip or something else I am not understanding?
« Last Edit: July 29, 2012, 01:35:50 am by Kent Thompson »
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Timo Beckman

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Re: Speaker measurements
« Reply #1 on: July 29, 2012, 03:47:07 am »

Without seeing the individual respons of all drivers i'm guessing but @ about 200Hz the phase trace goes up meaning the low end of the system is ahead in time compared to the synchronization point of the analyzer . @ about 900Hz the high driver is starting to kick in . @ the point of the frequency dip both drivers have equal level but are 180dg out of phase (might be 540dg but i don't think that's the case here).
So you might try delaying the low's and maybe polarity revers on the high's but as to the polarity thing can't say for sure untill i see the solo respons of individual drivers...

http://sdrv.ms/LW9ck4

Could you sent me a personal mail . I did a edit on the screen shot but for some reason i can't post it here .
« Last Edit: July 29, 2012, 04:29:59 am by Timo Beckman »
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Paul Tucci

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Re: Speaker measurements
« Reply #2 on: July 29, 2012, 08:47:50 pm »

Kent,

Pick a spot, close is good. Can you get within a few feet of the speaker? On axis, halfway between the horn and the closer of the two woofs.
Measure, document it.
Move nothing.
Disconnect/mute the lows.
Measure the highs, document it.
Move nothing.
Reconnect/unmute the lows.  Disconnect/mute the highs.
Measure the lows, document it.

It is imperative that the TF measurements are all done from the same place in time, so don't go redoing an impulse response when the highs have been muted/disconnected. What we want to see is what is the phase response of the lows and the highs are by themselves so that we can see if differing phase responses are destructive to rather than reinforcing each other. Chances are this is the case, just look at those two smiley face phase traces.

One has choices to make in speaker designs. This appears to be an impulse alignment. The bulk of each driver's range is relatively flat phase, indicating alignment with that offset time.
Another choice would be to give higher priority to the crossover region. This comes at the expense of even more phase misalignment elsewhere.
Another choice would be to make it as flat phase as possible at the expense of DSP and latency.
Make youir choice, pay the piper.

Your best advice will come from us examining the phase traces individually. It's worth the effort.

PT
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Kent Thompson

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Re: Speaker measurements
« Reply #3 on: July 29, 2012, 11:54:58 pm »

Well this is a passive crossover so I can't really measure them separately now. There are connections to bi-amp but, will have to make a cable for that. So for now I guess I am just practicing measurements lol.
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Ryan C. Davis

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Re: Speaker measurements
« Reply #4 on: July 29, 2012, 11:57:56 pm »

Well this is a passive crossover so I can't really measure them separately now. There are connections to bi-amp but, will have to make a cable for that. So for now I guess I am just practicing measurements lol.

you're not off the hook cowboy... disconnect the drivers from inside the cab. It will take some time to do all the measuring but if the data is good it will definitely be worth it.
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Ryan Davis

Paul Tucci

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Re: Speaker measurements
« Reply #5 on: July 30, 2012, 12:13:47 am »

Well this is a passive crossover so I can't really measure them separately now. There are connections to bi-amp but, will have to make a cable for that. So for now I guess I am just practicing measurements lol.

You most certainly can measure them separately. As many people have said, ( I read the other posts from the other thread) you have to get inside the cabinet and disconnect post crossover.
Secondly, if you measure in a biamp situation, markedly different from what you are now doing, EVERYTHING changes. You will have eliminated the passive crossover from the equation. That would provide different data, not neccessarily valid to your question.

PT
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Ales Dravinec

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Re: Speaker measurements
« Reply #6 on: July 30, 2012, 07:21:26 am »

Well this is a passive crossover so I can't really measure them separately now. There are connections to bi-amp but, will have to make a cable for that. So for now I guess I am just practicing measurements lol.

Kent,

You should do as Paul suggested ...

I'm offering a simplification :
Instead of disconnecting the driver(s) you are not using in the measurement, just COVER it (them) with thin sheet of wood ot something ....
Follow other steps exactly as mr. Tucci suggested and report back, please.

Respectfully.

P.s.: Btw, phase response (except for anomaly) is painfully flat .... kinda weird for a box of that rank ... I'd also say that HF polarity needs reversal ...
« Last Edit: July 30, 2012, 07:44:21 am by Ales Dravinec »
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Paul Tucci

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Re: Speaker measurements
« Reply #7 on: July 30, 2012, 12:40:03 pm »

...mr. Tucci ...

Kinda formal for this playground, don't you think?

PT

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Tim McCulloch

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Re: Speaker measurements
« Reply #8 on: July 30, 2012, 01:24:16 pm »

Kinda formal for this playground, don't you think?

PT

"Oh Great Guru Tucci" has too many syllables. ;)

Paul, what I find interesting is the uniformity of results regardless of measurement coherence.  Also, since the OPs are measuring boxes with passive crossovers I wonder *why* a manufacturer would ship such products; i.e. I think the OPs need to contact the OEM and ask "is this what I should be seeing?"

I'm yet to be convinced we're looking at valid measurements.
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"Practicing an art, no matter how well or badly, is a way to make your soul grow, for heaven's sake. Sing in the shower. Dance to the radio. Tell stories. Write a poem to a friend, even a lousy poem. Do it as well as you possible can. You will get an enormous reward. You will have created something."  - Kurt Vonnegut

Kent Thompson

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Re: Speaker measurements
« Reply #9 on: July 30, 2012, 01:29:48 pm »

Kent,

You should do as Paul suggested ...

I'm offering a simplification :
Instead of disconnecting the driver(s) you are not using in the measurement, just COVER it (them) with thin sheet of wood ot something ....
Follow other steps exactly as mr. Tucci suggested and report back, please.

Respectfully.

P.s.: Btw, phase response (except for anomaly) is painfully flat .... kinda weird for a box of that rank ... I'd also say that HF polarity needs reversal ...

Did not think of that! I had thought of opening them up but I did not really want to because they are new and they don't belong to me so this gives me the alternative I need. I will be running sound for the owner of these boxes on occasion so this is also a getting to know the cabinets session for me.
« Last Edit: July 30, 2012, 01:41:07 pm by Kent Thompson »
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ProSoundWeb Community

Re: Speaker measurements
« Reply #9 on: July 30, 2012, 01:29:48 pm »


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