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Old 15th February 2020, 08:29 AM   #1041
mabat is offline mabat  Czech Republic
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Quote:
Originally Posted by Dave Zan View Post
The latest MEMS microphones have tiny ports, pretty decent specifications and cost only a few dollars each so well worth consideration.
I still have six Panasonics WM-61 so I will start with those.
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Old 15th February 2020, 09:05 AM   #1042
Dausend Acoustics is offline Dausend Acoustics  Germany
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You should also have a look into Makarskis PHD (Chpter 3):


http://publications.rwth-aachen.de/r...ki_Michael.pdf


There are some measurements, they used a 1mm probe and also measured with a reasonable termination (a small horn/wg). They method they are using gives very good simulation results.


You could also try a more easy method, described here in Jörg Panzers Paper with AKABAK (the succesor to ABEC3):
http://pub.dega-akustik.de/ICA2019/d...les/000394.pdf


But even without those advanced technics, when you use a modern type compression driver with very high to out of range break ups, with proper ABEC sims the results are already really good!



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Old 15th February 2020, 09:59 AM   #1043
mabat is offline mabat  Czech Republic
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Thanks, those are some comprehensive materials!

Quote:
But even without those advanced technics, when you use a modern type compression driver with very high to out of range break ups, with proper ABEC sims the results are already really good!
Yeah, I really don't expect making any real improvements. I'm just curious and also I desperately need to put my hands on something physical now - for too long I have been doing a purely abstract work.
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Old 15th February 2020, 03:06 PM   #1044
mabat is offline mabat  Czech Republic
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Originally Posted by gedlee View Post
... Just need to space the mic ports along the tube, probably in some random, certainly not equal, spacing. How many is up to you and your computational capacity.
Would this be OK?
(There are parts still missing in the drawing. This is only for the port spacing now.)

- Nah, now I see it's not very good. It's hard! I think I will really run a random generator and pick the one I like.
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Last edited by mabat; 15th February 2020 at 03:25 PM.
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Old 15th February 2020, 04:59 PM   #1045
pelanj is online now pelanj  Czech Republic
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How about using the Golomb rule so that no two distances are the same?

Last edited by pelanj; 15th February 2020 at 05:02 PM.
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Old 15th February 2020, 06:39 PM   #1046
gedlee is offline gedlee  United States
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Like 25, 36, 48, 61, 74, 88.

As to using gated measurements, I have always thought that should be possible, but honestly I don;t know anyone who has tried that.
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Old 15th February 2020, 07:39 PM   #1047
mabat is offline mabat  Czech Republic
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Questions, still -

1) What rotations (the angles) of the driver will be necessary?

2) How critical is the first port distance from the tube beginning? I'm asking because if shifted more down the tube it would easily allow for a free rotation of the whole mounting flange without a need to re-mount the driver. Otherwise the rotation will be not so effortless.

3) Is the closer spacing at the beginning intentional, i.e. would it be worse if reversed?
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Old 15th February 2020, 07:47 PM   #1048
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There can be issues with close locations because of near-field effects (which can cause numerical instability,) so moving further back is not a problem. Rotating the driver on the mount can add data and find non-axisymmetric modes. I'm not sure if my math has that possibility, but it's not a difficult extension.
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Old 15th February 2020, 07:52 PM   #1049
mabat is offline mabat  Czech Republic
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In PWT_modes.pdf you state "..., and the extension to a rotated driver is also quite straightforward.".
Well, it has been twenty years

OK, I'll move the ports a bit further. That will make it a lot easier.
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Last edited by mabat; 15th February 2020 at 07:56 PM.
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Old 16th February 2020, 05:10 AM   #1050
mabat is offline mabat  Czech Republic
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Originally Posted by gedlee View Post
As to using gated measurements, I have always thought that should be possible, but honestly I don;t know anyone who has tried that.
I thought that prof. Merhaut demonstrated that years ago but after I looked at his paper* again I see he in fact used short pulses as test signals (and then gated FFT). It was in 1985 so I wonder if it was because of the lack of todays techniques (MLSSA came in 1987, IIRC) or because it was so obvious to him that it would be wrong (but then I think he would mention that).

Is it really so different from making gated measurements of a speaker in a room?


* Impulse Measurement on Horn-Type Loudspeaker Drivers, Josef Merhaut (Vol. 34, pp. 245-254 [1986 April]); and more in Vol. 35, pp. 144-145
(Also in Loudspeakers anthology, Volume 4)
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