Rational Acoustics



Desmond Lee
October 11th, 2018, 07:57 PM
Hi everyone, my apologies if this has been post before.
Saw some photos on facebook recently about someone place their measurement mic in a way I haven't seen before, and is beyond my knowledge of the reason doing so.
Two microphones, pointing tip to tip of each other. Kind of like X-Y microphone technique, and I guest one of the mic was being used as reference.
Anyone care to elaborate such measurement technique?
Here attached photos of such measurement mic placement.
Thanks in advance.
Des
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fedele
October 12th, 2018, 02:56 AM
Hi everyone, my apologies if this has been post before.
Saw some photos on facebook recently about someone place their measurement mic in a way I haven't seen before, and is beyond my knowledge of the reason doing so.
Two microphones, pointing tip to tip of each other. Kind of like X-Y microphone technique, and I guest one of the mic was being used as reference.
Anyone care to elaborate such measurement technique?
Here attached photos of such measurement mic placement.
Thanks in advance.
Des
1007

1008

In the second image, but probably also in the first, the are comparing the microphones. It is necessary to try to place the microphones at the same distance from the source, as much as possible, making two measurements in the closest possible position. That's why they are placed in that way: at that distance from the source, the differences are negligible compared to the specific application (live tuning)

Desmond Lee
October 12th, 2018, 09:24 AM
So that's just for comparing the mics when doing multiple mic measurements?

Chris Tsanjoures
November 5th, 2018, 01:51 PM
This type of measurement is simple a mic comparison, often reffered to as the substitution, or pressure calibration (refer to IEC 61094-5 for more info).

As a general application this is often done to compare one mic to another and see how much, or how little, they deviate for informational purposes or to create calibration files. Configuration wise, you set the microphone you want as your 'baseline', or standard to compare to, as your reference. The other microphone would be the measurement input of a transfer function. The resultant measurement will be how different, or not, the measurement is from the reference.

In the attached image, there is a mic comparison of an Earthworks S30 to an iSEMcon 7150 microphone. Smoothing is 1/3 octave.

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gluis
May 30th, 2019, 12:01 PM
Hi everyone, my apologies if this has been post before.
Saw some photos on facebook recently about someone place their measurement mic in a way I haven't seen before, and is beyond my knowledge of the reason doing so.
Two microphones, pointing tip to tip of each other. Kind of like X-Y microphone technique, and I guest one of the mic was being used as reference.
Anyone care to elaborate such measurement technique?
Here attached photos of such measurement mic placement.
Thanks in advance.
Des
1007

1008

I'm not so sure that this was made to compare both mics, as in my opinion if you want to do that, they also should be pointing more or less in the same direction. Remember that even being omni mics, they definitely will have some directionality on HF because of diaphragm size. It seems to me that they might either be calibrating them to show the same SPL, or using one for the left side and one for the right side of the PA (one side and one mic at a time of course). This way you have your mic pointing at the side you want to measure and not be affected for the HF directionality mentioned above. Still, I can think of many situations to better use 2 microphones to measure :-).

The second picture makes me believe the first option should be the correct one as the rightmost mic in the pic is attached to a wireless transmitter, so the probably wanted to have both showing the same SPL, and they were calibrating them at the time of the pic was taken. It makes no sense to have a wireless transmitter on a mic that will stay there. Or maybe they were actually comparing mics FR, but they were doing it the wrong way LOL. If that was the case I would rather use a much shallower angle between mics to have them pointed closer to the same direction.

Chris Tsanjoures
May 30th, 2019, 08:54 PM
This measurement was done on a site, in the real world, and not in a laboratory. The HF directionality that you are pointing out would not amount too much of anything, often time less than 3dB above 10kHz, where the PA system is most likely already rolling, or rolled off.

At those frequencies, if you don't like the HF response, just move your mic 30cm and get a different one.

I'm sure this was done to compare the RF to the wire. In this case, the only things in the HF that would matter would be large areas of bad behavior. I'd be more interested in what, if any, HPF there is on the RF.

gluis
June 2nd, 2019, 01:07 AM
This measurement was done on a site, in the real world, and not in a laboratory. The HF directionality that you are pointing out would not amount too much of anything, often time less than 3dB above 10kHz, where the PA system is most likely already rolling, or rolled off.

At those frequencies, if you don't like the HF response, just move your mic 30cm and get a different one.

I'm sure this was done to compare the RF to the wire. In this case, the only things in the HF that would matter would be large areas of bad behavior. I'd be more interested in what, if any, HPF there is on the RF.

Agreed. And you might had been there so probably you know as a fact what were they doing :-). Still, in my opinion, a gig is not the place to compare your microphones. Unless you are matching levels, I rather do it in the shop. As you noted, you'll not be getting full frequency response on HF, which is where you'll find most differences in high quality ones. And as good practice and to get accustomed to do it properly (again, in my opinion) is better to have them pointed closer to the same direction (kind of a shallow angle coincident pair perhaps?).

Of course they might had dropped one and were checking overall condition, or where in fact just calibrating them for the same level. BTW I'm referring to the wired pair. You are right on the WL vs wired compare.