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Home » Sponsored » Pi Speakers » 4 pi speakers + 3 pi subwoofers, pics & measurements (How to interpret the measurements?)
| 4 pi speakers + 3 pi subwoofers, pics & measurements [message #81352] |
Tue, 26 May 2015 13:29  |
vandevoordekoen
Messages: 18
Registered: January 2013
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Chancellor |
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Hello,
Two years ago I started with the 4pi project thanks to Wayne who helped me a lot with his plans and answering my questions. 
Pictures!
1. Building the 4pi speakers
2. Finishing
3. New house, made new tv furniture --> new finishing (birch)
Measurements with ecm8000 mic (listening position): very poor low-end due to room modes and resonances:
I've bought two lab12 subwoofers and made 2 testing enclosures. crossover with mini-DSP (30hz;48db/oct, 120hz;12db/oct):
A very geeky testing setup. My wife loves me when I do this kind of setups. 
Much better low-end frequency response at listening position!
When I measure full range from the listening position, there is an obvious roloff at the high frequencies. Is this something to worry about? I used the behringer ecm8000 mic, used CAL-file (which makes the roloff even steeper) and the m-audio fast track which is also calibrated by REW.
Thank you in advance!
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| Re: 4 pi speakers + 3 pi subwoofers, pics & measurements [message #81354 is a reply to message #81352] |
Tue, 26 May 2015 13:39  |
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Wayne Parham
Messages: 18786
Registered: January 2001
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Illuminati (33rd Degree) |
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Those measurements look good for the most part. But I agree with you that something is wrong above 8kHz.
To isolate the cause, try putting the microphone right in the tweeter throat and see what the response looks like. If the response above 8kHz doesn't look like what's in our published spec sheets, then something is wrong with the compression driver, crossover or measurement gear.
Normally I'd say look at the crossover first. And I suppose it wouldn't hurt to isolate it by removing the crossover. Measure the compression driver, all by itself, with just a series capacitor for protection. But honestly, if we had a crossover problem, I'd expect the response to be bad starting a couple octaves below that. This kind of rolloff looks more like a problem with the driver or the microphone.
In any case, you'll have to do a process of elimination to find the culprit.
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| Re: 4 pi speakers + 3 pi subwoofers, pics & measurements [message #81359 is a reply to message #81357] |
Wed, 27 May 2015 11:04 |
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Wayne Parham
Messages: 18786
Registered: January 2001
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Illuminati (33rd Degree) |
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I cannot help but wonder if the calibration file is wrong. One must make the inference that the microphone used to create the calibration file has rising response, so the conjugate was to reduce HF by the same amount to compensate. But from what I'm seeing in the response curves, that doesn't appear to be the case. The raw measurements look closer to what I would expect, just like you said. So I lack confidence in the measurements.
I suppose you could have done something in the crossover that would cause this, because the response droops about 10dB through the decade of operation, e.g. 1kHz to 10kHz. That's what mass-rolloff looks like generally, although it is usually flat to about 4kHz and we're seeing falloff around 2.5kHz. So that makes me wonder about the compression drivers.
If you want to isolate crossover from driver, just disconnect the crossover and measure without it, using a direct connection to the compression driver.
In any case, I think we should be suspicious of the measurements and refrain from making too many judgement calls based on them. We're just not sure if the measurements are valid.
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