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Gear / Technical Help => Microphones & Setup => Topic started by: jerryfreak on September 08, 2007, 12:45:17 AM
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is it possible to mount these mics in a way that would attenuate some sound from the rear?
I've been pleased with the results outdoors, but indoors, id like to find a way to attenuate room reflections.
I'm thinking what if the mic was mounted one one side of a sound-absorbing foam baffle?
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j-disc or schneider disc :) or try healy omni mehtod
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i should add that it ideally would be low-pro (think in a hat)
j-disc or schneider disc :) or try healy omni mehtod
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jerryfreak, there's a problem with this in terms of basic physics. The range of audible frequencies has a 1000:1 range of wavelengths because of the familiar 20 - 20,000 Hz business. But to block a sound wave, an object needs to be at least half the wavelength of that wave. So unfortunately, any baffle, etc., that you might practically use could only be effective at high frequencies.
If you used a baffle six inches in diameter, for example, the waves for any sound beneath about 1100 Hz would simply flow around it, and so forth. That might sharpen the localization in your stereo recordings and it's a worthwhile experiment for its own sake, but it won't turn your omnis into some other directional pattern.
There is currently a product being marketed by a Chinese microphone manufacturer which claims to absorb the sound waves from behind a directional microphone. But the product is just a curved piece of metal a few inches across, lined with sound-absorbing foam. That might have an effect above, say, 2 kHz, but certainly not below.
The way most cardioid microphones work nowadays is that they have a front and a rear sound inlet, with an acoustical delay line in the rear inlet, arranged so that sound arriving from the front is reinforced while sound arriving from the rear is canceled. But it's actually more complicated than that, because the entire internal architecture of the capsule (the internal volume of air) has to optimized for that purpose, and the membrane tension has to be set right for it (lower than with an omni), or else the frequency response will be all wrong.
In other words there's no real hope of transforming an omni into a usable directional microphone, unless the capsule was designed in advance to make this transformation itself, i.e. unless it was designed and built to be a two-pattern switchable microphone.
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thanks,
excellent post!
just have to get closer to the sound source to minimize incident reflections i suppose
jerryfreak, there's a problem with this in terms of basic physics. Sound across the range of audible frequencies has a 1000:1 range of wavelengths (which goes along with the 20 - 20,000 Hz business). And in order to block a sound wave to any real extent, the size of an object needs to be at least half the wavelength of that wave.
So unfortunately, any baffle, etc., that you might practically use could only be effective at high frequencies. If you used a baffle six inches in diameter, for example, the waves for any sound beneath about 1100 Hz would simply flow around it, and so forth.
There is currently a product being marketed by a Chinese microphone manufacturer which claims to absorb the sound waves from behind a directional microphone. But the product is just a curved piece of metal a few inches across, lined with sound-absorbing foam. That might have a slight effect at, say, 1 kHz and above, but certainly not at 500 Hz or below.
The way most cardioid microphones work nowadays is that they have a front and a rear sound inlet, with an acoustical delay line in the rear inlet, arranged so that sound arriving from the front is reinforced and sound arriving from the rear is canceled. But it's actually more complicated than that because the entire internal architecture of the capsule (the internal volume of air) has to optimized for that purpose and the membrane tension has to be set right for it (lower than with an omni), or else the frequency response will be all wrong.
In other words, there's no real hope of transforming an omni into a usable directional microphone, unless the "omni" was designed in advance to make this transformation itself, i.e. unless it was designed and built to be a two-pattern switchable microphone.
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is it possible to mount these mics in a way that would attenuate some sound from the rear?
I've been pleased with the results outdoors, but indoors, id like to find a way to attenuate room reflections.
I'm thinking what if the mic was mounted one one side of a sound-absorbing foam baffle?
Put it at the focal point of a parabolic reflector - it will then be very directional. ;D
You could also hang duvets to change the room acoustics.
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Seems interesting, Moke.
I am going to mount stereo omni in a club permanantly. In what looks to be pretty sweet placement (12' from stage, DFC) there is a mirror ball. I am wondering:
a) if i can do HRTF effect (1-2" from ball) and
b) about a baffle to give crowd noise rejection
Any thoughts from the group?
Thanks
Joe
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is it possible to mount these mics in a way that would attenuate some sound from the rear?
I've been pleased with the results outdoors, but indoors, id like to find a way to attenuate room reflections.
I'm thinking what if the mic was mounted one one side of a sound-absorbing foam baffle?
Low profile on-body mounting in the collar-bone area of the chest will diminish rear sounds nicely. However, in this area, whatever's in front of you should be considered as also blocking (some) line-of-sight with the pickup sounds.
Seems interesting, Moke.
I am going to mount stereo omni in a club permanently. In what looks to be pretty sweet placement (12' from stage, DFC) there is a mirror ball. I am wondering:
a) if i can do HRTF effect (1-2" from ball) and
b) about a baffle to give crowd noise rejection
Any thoughts from the group?
Thanks
Joe
HRTF baffling is a totally absorptive at all audio frequencies (complete opposite of mirror ball reflective) surface.
True HRTF acoustic baffle suitable for permanent mounting with top/bottom mic threads and may be used with various small omni pickups is available from my company. Suggest mounting baffle at least 3' distance from the mirror ball and other large hard reflective surfaces
(http://www.sonicstudios.com/lgbmws1.jpg)
See this at: www.sonicstudios.com/access.htm#liteguy (http://www.sonicstudios.com/access.htm#liteguy) and www.sonicstudios.com/liteguy.htm (http://www.sonicstudios.com/liteguy.htm)
Music live session/performance recordings using true HRTF baffling at: www.sonicstudios.com/mp3_2slp.htm (http://www.sonicstudios.com/mp3_2slp.htm)
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guysonic, the idea that a small baffle could absorb, or reflect, or do anything whatsoever across the entire range of sound frequencies is contrary to elementary physics. Whoever is making this claim doesn't know (or doesn't care) what the f**k he's talking about.
This isn't even remotely controversial; it's just plain wrong at the "how much is 2 times 2" level. Low frequencies = wavelengths way, way larger than the baffle = they just flow around it and aren't affected by it, like a tyrannosaurus being "attacked" by two baby gnats.
Fortunately, the effectiveness of "dummy head"-style recording doesn't actually rely on this absurd claim.
--best regards
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guysonic, the idea that a small baffle could absorb, or reflect, or do anything whatsoever across the entire range of sound frequencies is contrary to elementary physics. Whoever is making this claim doesn't know (or doesn't care) what the f**k he's talking about.
This isn't even remotely controversial; it's just plain wrong at the "how much is 2 times 2" level. Low frequencies = wavelengths way, way larger than the baffle = they just flow around it and aren't affected by it, like a tyrannosaurus being "attacked" by two baby gnats.
Fortunately, the effectiveness of "dummy head"-style recording doesn't actually rely on this absurd claim.
--best regards
The truth is water based flesh DOES have this unique absorption property. My GUY and LiteGUY baffle virtually replicates this as there is very little difference from person wearing or GUY/LiteGUY baffle recordings as is proven by the hundreds of sample recordings done over a 22 year period.
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post samples, please. i'm interested.
thanks
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post samples, please. i'm interested.
thanks
The hundreds of sample (musical) recordings are linked on the already posted page www.sonicstudios.com/mp3_2slp.htm (http://www.sonicstudios.com/mp3_2slp.htm)
Natural sounds, and ambient/compositional type HRTF recordings found on page: www.sonicstudios.com/mp3.htm (http://www.sonicstudios.com/mp3.htm)