Polar Response Measurement Jig ideas?

bikinpunk · 31st March 2011, 12:31 AM

I'm going to build a jig of some sort - that could be as simple as tape on the floor or as complicated as a swivel setup - to take polars at various angles from 0 to 90 degrees, with (15* intervals). I'm trying to stay simple and one constraint is that the setup not cause reflections.

In my case, I need something that would allow me to move the mic around the wall I've built.

I've considered doing something that uses a swivel at the base of the IEC baffle I've built, attach it to the mic stand and simply move the mic stand in a circular pattern. I'd like to take it a step further, though, and make it adjustable in distance from the baffle/driver being tested for various reasons.

I was wondering if anyone here might have some suggestions and/or pictures of what their polar jigs look like that could help me get my blue sky imagination going. A trip to Lowe's always helps kick my brain in to gear, but it also kicks my wallet up about 5 notches too high.

Here's what the baffle looks like:

Note, the above isn't completely final. I still have to determine final bracing. It's up just to get an idea of what else needs to be done. FWIW, since I took the picture above, I've added absorption panels to the ceiling. So far, I've got a flat impulse response on-axis out to 12ms.

Thanks,
Erin

bikinpunk · 31st March 2011, 03:17 AM

I'm sorry; it has been brought to my attention that what I'm calling polar response is not what I'm after. I'm simply after various degrees of off-axis response. Sorry for the mix up, guys.

mickeymoose · 2nd April 2011, 02:15 AM

If you are trying to measure frequency response, not even MLS can get you there with your setup. Room (walls, ceiling, floor) reflections will interfere and make any measured result non-repeatable and therefore invalid. The board dimensions are far smaller than the ideal "infinite baffle" (1/4 wavelength). The mic should be at all times 1 meter from the sound source (that is not the front of the speaker but somewhere behind the dustcap).
The best I could do, on a limited budged, was to dig a big hole, speaker flush to ground, mounted on a sheet of MDF, facing up and the mic suspended from above.
Make sure it is not windy or raining that day!
E

31st March 2011, 12:31 AM	#1
bikinpunk diyAudio Member Join Date: Jan 2009 Location: Decatur, Al	Polar Response Measurement Jig ideas? I'm going to build a jig of some sort - that could be as simple as tape on the floor or as complicated as a swivel setup - to take polars at various angles from 0 to 90 degrees, with (15* intervals). I'm trying to stay simple and one constraint is that the setup not cause reflections. In my case, I need something that would allow me to move the mic around the wall I've built. I've considered doing something that uses a swivel at the base of the IEC baffle I've built, attach it to the mic stand and simply move the mic stand in a circular pattern. I'd like to take it a step further, though, and make it adjustable in distance from the baffle/driver being tested for various reasons. I was wondering if anyone here might have some suggestions and/or pictures of what their polar jigs look like that could help me get my blue sky imagination going. A trip to Lowe's always helps kick my brain in to gear, but it also kicks my wallet up about 5 notches too high. Here's what the baffle looks like: Note, the above isn't completely final. I still have to determine final bracing. It's up just to get an idea of what else needs to be done. FWIW, since I took the picture above, I've added absorption panels to the ceiling. So far, I've got a flat impulse response on-axis out to 12ms. Thanks, Erin

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31st March 2011, 03:17 AM	#2
bikinpunk diyAudio Member Join Date: Jan 2009 Location: Decatur, Al	I'm sorry; it has been brought to my attention that what I'm calling polar response is not what I'm after. I'm simply after various degrees of off-axis response. Sorry for the mix up, guys.

2nd April 2011, 02:15 AM	#3
mickeymoose diyAudio Member Join Date: Nov 2008	If you are trying to measure frequency response, not even MLS can get you there with your setup. Room (walls, ceiling, floor) reflections will interfere and make any measured result non-repeatable and therefore invalid. The board dimensions are far smaller than the ideal "infinite baffle" (1/4 wavelength). The mic should be at all times 1 meter from the sound source (that is not the front of the speaker but somewhere behind the dustcap). The best I could do, on a limited budged, was to dig a big hole, speaker flush to ground, mounted on a sheet of MDF, facing up and the mic suspended from above. Make sure it is not windy or raining that day! E

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