Q on ZaphAudio measurement conditions

[weinstro]

Hi,

Does anyone know the mic distance used for the frequency response measurements at ZaphAudio? The distance appears to be specified for harmonic distortion of the various drivers, but not for frequency response.

Thanks - much appreciated.

Rob

[xavier]

why not just ask him?

[benchtester]

why not just ask him?

That can be problematic

http://www.zaphaudio.com/email.html

Plus he has been particularly busy with work recently.


Here is his description of general testing:

http://www.zaphaudio.com/setup.html

The "Infinite Baffle" section gives a brief description of the mic distance selection.

[evilskillit]

Ive read about his measurement setup before, maybe seen pictures. IIRC its pretty big, like 4x8 or bigger. I know recently he said its big enough that he wrenched his back out and cant use/move it currently. If you search hard enough the info might be out there somewhere. If I see/recall it I'll post it.

[evilskillit]

Actually, go here.

http://www.zaphaudio.com/setup.html

Scroll down to measurements and infinite baffle. It IS a piece of 4x8, with bracing and whatnot.

[weinstro]

why not just ask him?

Mr. Krutke discourages direct contact, in an effort to protect his time, which I can certainly respect, and occasionally admire as I have multiple time demands as well.

If he wants to respond, he will. Otherwise, I'm hoping someone else has a recollection.

[weinstro]

Actually, go here.

http://www.zaphaudio.com/setup.html

Scroll down to measurements and infinite baffle. It IS a piece of 4x8, with bracing and whatnot.

Ok, there is a bit more detail here. I understand that the tweeter measurement distance is 4", presumably for both frequency response and HD.

For the woofer, it looks like two measurements which are spliced. One is at 0.25", while the other is "it depends". Now, would the 0.25" distance be ~>600 Hz, or ~<600 Hz? The 600 Hz figure is listed on the measurement details for the 5.5" drivers.

Regards,

Rob

[johnnyrichards]

Ok, there is a bit more detail here. I understand that the tweeter measurement distance is 4", presumably for both frequency response and HD.

For the woofer, it looks like two measurements which are spliced. One is at 0.25", while the other is "it depends". Now, would the 0.25" distance be ~>600 Hz, or ~<600 Hz? The 600 Hz figure is listed on the measurement details for the 5.5" drivers.

Regards,

Rob

Less than. Close micing is for low frequency measurements... There is some science behind that, but it is beyond me.

[evilskillit]

Well I think very close, like less than an inch or couple of inches from the dustcap is the only way to capture LF without getting room interaction since the waves are so large... ?

[r-carpenter]

Fr of the tweeter is measured on axis 1 meter at 2.83v Zaph mentions that he gets as close as 4 inches without an affect on FR.
FR of the woofer is measured twice: near field (mice close to the dust cap for low frequency data acquisition) and far field at 1 meter for high frequency.
I think that's what Zaph is doing.
Is your question related to an absolute FR level?

[weinstro]

Fr of the tweeter is measured on axis 1 meter at 2.83v Zaph mentions that he gets as close as 4 inches without an affect on FR.
FR of the woofer is measured twice: near field (mice close to the dust cap for low frequency data acquisition) and far field at 1 meter for high frequency.
I think that's what Zaph is doing.
Is your question related to an absolute FR level?

Not yet. I'm attempting to use the FRD toolset (and PCD, too) to walk through the design in order to validate the steps. This is a self-learning exercise.

The basic approach seems to be:
• Enter measured test data
• remove effects of test baffle
• add effects of target baffle and enclosure
• normalize, extract phase, model crossovers

What I have is traced FR data, and some baffle diffraction models. But, the effect of the baffle is impacted somewhat by the measurement distance. So, some knowledge of the distance would be helpful.

Regards,

Rob