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Old 18th June 2017, 10:00 PM   #31
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Originally Posted by ICG View Post
No, that's completely wrong. Because you've still got all the tools to get the crossover parts correct, and measuring mics actually are very linear, they mostly differ just at the ends of the measuring range. That means, all you have to do with your ears is to realize how much the upper end is off. It doesn't matter if it's +x dB, it will always the same +x dB and once it fits your ear there, keep developing it to the same level there.

So, no time waste and especally no 'total blind'.
Sorry but don't understand. This is the cal file of the mike i am using. How can i guess that i have a 2db bump around 8khz? How do i know that i am wrong 2db and not 5db or 0.5db?
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File Type: png calmic.png (10.3 KB, 65 views)
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Old 18th June 2017, 10:10 PM   #32
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Originally Posted by ICG View Post

@Piersma: What amp do you use for measurements? Do you always keep the same level on the amp aswell as on the mixer and Holmimpulse? Any preamp there? Please post the whole measuring chain again.
Any input or output transformer lurking in signal path, no matter if silver wound or amorphous cored?
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Old 18th June 2017, 11:37 PM   #33
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Originally Posted by GDO View Post
Sorry but don't understand. This is the cal file of the mike i am using. How can i guess that i have a 2db bump around 8khz? How do i know that i am wrong 2db and not 5db or 0.5db?
At 8kHz you will still have a 2dB bigger bump (or 5dB or 0,5dB). It will not make a 2dB bump only 1dB more. The calibration makes it lniear, that means, your measurements of an uncalibrated mic are not linear but you can still measure the difference of 2 or 5dB. If you microphone can't reproduce that difference in sound pressure level, then it's not suitable as a measurement microphone. By that I don't mean the maximum spl it can measure distortion free.

With 0,5dB it's a bit different though because that's most likely within the expected repeat measurement tolerance.
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Old 19th June 2017, 05:18 AM   #34
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Well, why not using a gated measuring instead of absorbing material on walls/floors? If you already do, the gate is too long or you got still something reflective in too close proximity to the mic or the speaker.
Because I like to push the first reflection as low as possible
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Old 19th June 2017, 11:04 AM   #35
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@Piersma: What amp do you use for measurements? Do you always keep the same level on the amp aswell as on the mixer and Holmimpulse? Any preamp there? Please post the whole measuring chain again.[/QUOTE]

I use Current Feedback amplifier for measurements, during measurements I keep equal levels all the time. I use a passive resistive potmeter to set the SPL outputlevel.

Attached: frequency response, gating time 4 ms.
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File Type: png Tweeter resp. gating 4 ms.png (43.1 KB, 52 views)
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Old 19th June 2017, 12:58 PM   #36
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Passive preamps have high output impedance which combined with cable capacitance can produce severe HF roll off, varying morevoer with volume level setting.

Did you check the FR of your setup with a loopback measurement?
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Old 19th June 2017, 06:31 PM   #37
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Quote:
Originally Posted by Piersma View Post
I use Current Feedback amplifier for measurements, during measurements I keep equal levels all the time.
That's not how you measure speakers. You need a constant voltage! Where's the list of the rest? List it all!

Quote:
Originally Posted by Piersma View Post
I use a passive resistive potmeter to set the SPL outputlevel.
You mean before the amp?

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Originally Posted by Piersma View Post
Attached: frequency response, gating time 4 ms.
The polarity is still switched on one measurement. Did you do the tests of the soundcard? I'm really annoyed you only do one thing and not what's requested. I'm really tired and fed up with typing everything 5 times!
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Old 19th June 2017, 06:43 PM   #38
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Passive preamps have high output impedance which combined with cable capacitance can produce severe HF roll off, varying morevoer with volume level setting.
Exactly! The output impedane of the pre has always to be lower than the input impedance of the amp, about 1/20th. With a passive solution you're sabotaging your measurements yourself.

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Did you check the FR of your setup with a loopback measurement?
I already asked for that twice.
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Old 19th June 2017, 06:47 PM   #39
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I'm really tired and fed up with typing everything 5 times!
Welcome to the whatamidoinwron' (fake dummy?) game!
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Last edited by GDO; 19th June 2017 at 06:53 PM.
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Old 19th June 2017, 06:56 PM   #40
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Originally Posted by Mario Pankov View Post
Because I like to push the first reflection as low as possible
You have to gate it to exclude it. The absorption material is frequency dependent, so it's most effective on high frequencies (where the gating could be much shorter and you don't need it) while it's much less effective at lower frequencies, where it's really needed. Try and measure how much dB it's damping. I doubt it will be much more than 2-3dB.
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