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Old 3rd May 2012, 01:51 AM   #1
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Default Mic Housing source

Would anyone happen to know of a source for empty zoom mic housings, or cheap ones that can be stripped? I would consider fabricating them except there are almost no resources except for the patents. Perusing those is most arduous.

They need to have front and back ports for NC electret capsules, and be a short as possible for a max. range of 25ft. The cheapest and shortest mic I found in this class is the rubbish Vivitar MIC-403.

Any leads will be greatly appreciated.
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Old 3rd May 2012, 02:41 PM   #2
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By zoom do you mean variable unidirectional pattern? I know of none, but for the RCA MI-10006A rifle microphone. Maybe a mic capsule, facing a parabolic dish, could do a zoom function if you change the capsule's distance to the sweet spot.
The reason you can not buy a body only for a unidirectional mic is that the capsule and the body are a "system", one useless without the other. Microphone capsule design is basic engineering, marrying to a body is art and craft, data well guarded by the manufacturer. E
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Old 3rd May 2012, 03:57 PM   #3
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It appears the term "zoom" is used for unidirectional capture of sound at more than usual distances. They usually have long tubes with ports for passive background noise cancellation using the NC capsule with back ports. Most have a "boost" switch which increases gain electronically. They are a standard external accessory for camcorders (internal mics are usually rubbish), and necessary in many recording and sound reinforcement situations.

I have not seen a "variable pattern" design, although I guess since the effective pattern is determined by the tube dimensions and the exact location of the capsule therein, those are the determining factors. I did see one with a removable extension, but at any rate, the final arrangement has fixed attributes. I have never seen a design similar to the "goose feathers" of a jet turbine exhaust nozzle; probably since as the sound source gets farther away, the frontal diameter of the tube offers less refraction (capturing more of the wave), and at the same time, the operation of the noise-cancelling element decreases, due to the angle of incidence being more at a right angle to the plane of the membrane.

I agree. Obtaining internal, corporate mic design notes from, say Sure, would be like trying to get the sourcecode of Watson from IBM. Okay, that is what I was afraid of. I read a couple of patents and managed to extrapolate a tip or two. The Handbook for Sound Engineers, as well as good old sound physics fundamentals seem to be the places for me to dwell for awhile. From there, as you declared, it amounts to artistic design, rather than a simple "nut-and-bolt" construction process.

The Vivitar will be disected and scrutinized as soon as it arrives. I had bown out a PC sound card input circuit with this mic running on boost. However, it could also have been caused by an ALSA beta driver. Many Linux users were complaining about poor mic gain..... Software can blow hardware.

Thank you much for your input.
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Old 3rd May 2012, 04:17 PM   #4
cbdb is offline cbdb  Canada
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They are usually called shotgun mics, and yes its all about the slots in the housing cancelling the sound that comes in at an angle (not the angle of the membrane, or omni mics wouldnt work). And used extensively in movie/tv production. Heres a past thread:How does one build a shotgun microphone?
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Old 3rd May 2012, 04:58 PM   #5
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Thank you for the correction. Shotgun is the correct term, where "zoom" seems more of a colloquialism or a buzz-word. Shotgun describes the basic pattern (cardioid, super-, hyper-) and zoom impies it has an extended pickup range in space.

All the considerations of mic design along with the DSP my app needs is overloading my circuits. I almost blew a fuse envisioning digipot gain/mix control of the array alone. I am pursuing mechanical means to reduce control complexity and maximize performance. I was tempted to acquire a used auto-mixer and adapt it to my app.

Last edited by ITPhoenix; 3rd May 2012 at 05:11 PM. Reason: spelling error
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Old 3rd May 2012, 05:26 PM   #6
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ITP: if you would tell us what your ap is maybee someone here could suggest alternate ways. E
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Old 3rd May 2012, 06:00 PM   #7
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Yes, thanks for reminding me. A general overview, a basic block diagram, and some specs would be expedient. Until then, I have:

Array of mics able to capture speech in a 360 deg. circle at min. distance of 2ft. & max. distance of 25ft.

Single channel, mono output to PC sound card for speech recognition.

Individual, automatic gain by DSP to prevent clipping or low input signal, and for backround noise attenuation.

An additional, less time-constrained, streaming output of all mics through USB for diarization and natural language processing on PC.

Noise cancelling, electret capsules for elements.

A second set of elements is permitted if cost-effective.

Maximum diameter of array =<6 in.

Last edited by ITPhoenix; 3rd May 2012 at 06:01 PM. Reason: grammar
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