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MichaelAlan
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 Posted: Thu Mar 15, 2012 2:00 pm Post subject: Ribbon mics and air...particles.... |
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I recently read that the element in a ribbon mic responds to the velocity of air particles, not the air pressure like a dynamic... this is a little confusing to me. Anyone know exactly how this works and what it means as far as the sound of a ribbon? Been wanting to get one for a looooong time...
Edit: Sorry... this shoulda been in the equipment forum 
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dubold
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jhharvest
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| Posted: Fri Mar 16, 2012 8:27 am Post subject: Re: Ribbon mics and air...particles.... |
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| dubold wrote: | | where'd you read that? |
The concept is mentioned for example here.
I'll try to explain it: Sound waves are minute changes in air pressure. Our ears and omni microphones work by detecting these changes in the air pressure. A ribbon microphone, however, due to its open design can not detect changes in pressure as such. Instead it detects the movement of the air particles as they are pushed along by the pressure wave.
Omni microphone is like a gum bubble which you can blow up or deflate, depending on how much pressure you exert on it with your lungs. Ribbon mic is like a sheet of paper which you can push or pull by blowing and sucking. |
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blungo2
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| Posted: Fri Mar 16, 2012 8:37 am Post subject: Re: Ribbon mics and air...particles.... |
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i think you guys are crazy. AFAIK air pressure IS the movement of air particles, or the force they exert.
Ribbons (and all mics other than omnis) just sense the difference in air pressure rather than the overall pressure as explained in the gum analogy above. |
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Gregg Juke
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| Posted: Fri Mar 16, 2012 9:45 am Post subject: Re: Ribbon mics and air...particles.... |
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I'm no physicist, but it sounds like semantics to me.
GJ |
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dubold
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| Posted: Fri Mar 16, 2012 11:18 am Post subject: Re: Ribbon mics and air...particles.... |
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| jhharvest wrote: | | dubold wrote: | | where'd you read that? |
The concept is mentioned for example here.
I'll try to explain it: Sound waves are minute changes in air pressure. Our ears and omni microphones work by detecting these changes in the air pressure. A ribbon microphone, however, due to its open design can not detect changes in pressure as such. Instead it detects the movement of the air particles as they are pushed along by the pressure wave.
Omni microphone is like a gum bubble which you can blow up or deflate, depending on how much pressure you exert on it with your lungs. Ribbon mic is like a sheet of paper which you can push or pull by blowing and sucking. |
That's an interesting description of how a ribbon mic works, mechanically, but what's it got to do with air particles?
I've only ever heard "air particles" used to describe particulate matter in the air; if the ribbon mic is only responding to particles coming in from the front, how does the ribbon move back "toward" the sound source? tensile strength of the ribbon makes it rebound?
Or is the ribbon moving in the compression and rarefaction of a sound wave, just like a dynamic or condenser mic?
The only thing I can find referring to "air particles" and sound is the wikipedia entry on particle velocity,
which is why I asked MichaelAlan where they read this...
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jhharvest
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| Posted: Fri Mar 16, 2012 11:47 am Post subject: Re: Ribbon mics and air...particles.... |
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| dubold wrote: | | I've only ever heard "air particles" used to describe particulate matter in the air; if the ribbon mic is only responding to particles coming in from the front, how does the ribbon move back "toward" the sound source? tensile strength of the ribbon makes it rebound? |
I think the idea of the "air particles" is just another name for the air molecules. I have no idea where it's come from.
The other name for "air velocity microphone" is "pressure gradient" microphone. When there is a lower pressure on the front of the microphone this will actually pull the "air particles" towards the back of the element as they move in to equalise the pressure difference. |
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qued
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| Posted: Fri Mar 16, 2012 1:00 pm Post subject: Re: Ribbon mics and air...particles.... |
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| I think it can also influence the sound of a mic too. Close to low frequency sound sources, air gets moved around in addition to what is caused by the sound waves alone. Picture ripples in a bathtub comared to sloshing around the whole tub. I'm guessing sensitivity to this low frequency air motion is what creates a proximity effect for many mics. |
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MichaelAlan
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| Posted: Fri Mar 16, 2012 3:02 pm Post subject: Re: Ribbon mics and air...particles.... |
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As someone else said previously, wouldn't you detect air pressure by sensing the air particles that hit something...
I had just never heard this before and I couldn't make sense of it. Sounds like no one else can either so it's probably not worth spending effort trying to figure out....
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Matt C.
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| Posted: Fri Mar 16, 2012 3:31 pm Post subject: Re: Ribbon mics and air...particles.... |
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| do a google search for "microphones methods of operation and type examples". it's a paper written by some people at Neumann, I think. The first chunk explains this very well. |
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The Scum
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| Posted: Fri Mar 16, 2012 6:13 pm Post subject: Re: Ribbon mics and air...particles.... |
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Like this one here:
www.neumann.com/download.php?download=docu0002.PDF
It makes a pretty reasonable distinction:
Velocity Transducers output a voltage that is proportional to the speed of motion of the diaphragm. If the diaphragm is not moving, there's no voltage generated.
-as opposed to-
Displacement Transducers output a voltage proportional to the displacement of the diaphragm. The location of the diaphragm is represented as a voltage.
Pressure vs Pressure Gradient elements are a different taxonomical differentiation.
From a static physical viewpoint, air pressure and air velocity are analogous to Voltage and current. Pressure/Voltage is potential energy (stored and looking for release). Motion/velocity/current is kinetic energy.
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jhharvest
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| Posted: Sat Mar 17, 2012 1:35 am Post subject: Re: Ribbon mics and air...particles.... |
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But the op was asking about "air velocity" microphones. The reason why I brought up the pressure gradient in the first place was because the pressure difference (or gradient) is linked to the air particle velocity.
Or, as it is explained in the same document:
| Quote: | Since every pressure difference occurring in the sound field immediately
gives rise to a sound particle velocity in the direction of this pressure differ-
ence or gradient, the voltage output of pressure gradient microphones is
always proportional to the sound particle velocity.
Sometimes, these microphones are also referred to as “velocity micro-
phones”. However, it would be preferable to confine this term to micro-
phones with compliant diaphragms, i.e. possessing little acoustic impedance,
and thus largely following the movement of the air particles. |
'Compliant diaphragms', e.g. ribbon mics where the ribbon can move very freely. |
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MichaelAlan
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| Posted: Sat Mar 17, 2012 1:53 pm Post subject: Re: Ribbon mics and air...particles.... |
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I seriously thought this would be a cut n dry thing... oops.
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dubold
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dubold
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| Posted: Sun Mar 18, 2012 9:15 am Post subject: Re: Ribbon mics and air...particles.... |
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| The Scum wrote: | Like this one here:
www.neumann.com/download.php?download=docu0002.PDF
It makes a pretty reasonable distinction:
Velocity Transducers output a voltage that is proportional to the speed of motion of the diaphragm. If the diaphragm is not moving, there's no voltage generated.
-as opposed to-
Displacement Transducers output a voltage proportional to the displacement of the diaphragm. The location of the diaphragm is represented as a voltage.
Pressure vs Pressure Gradient elements are a different taxonomical differentiation.
From a static physical viewpoint, air pressure and air velocity are analogous to Voltage and current. Pressure/Voltage is potential energy (stored and looking for release). Motion/velocity/current is kinetic energy. |
alright, now that makes sense to me.
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