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Harvey Gerst
New member
60,000+ views? Wow, it's nice to see that people are still finding this thread to be of some use.
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gordone
Well-known member
And this has been helping people for ~2.5 years!!! (since April '01).
You created a Monster Harvey!
You created a Monster Harvey!
Harvey Gerst said:
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Nd:Apricot Stu
New member
Difficulty with "reverberation radius"
Harvey,
This thread has been incredibly helpful. Write a book on it someday and make some money off this info!
Anyway, my question is about the concept of reverberation radius. Your PDF "Microphone" file mentions: "the larger the room and the less reverberant it is, the greater will be the reverberation radius.
The first part makes sense, large room, long path-length, larger radius. However, the reverberance (as I understand it) is only dependant on the attenuation from the walls, and how accoustically reflective they are...
So I guess I don't see how amplitude ties into radius.
Thanks for the help,
Chris
Harvey,
This thread has been incredibly helpful. Write a book on it someday and make some money off this info!
Anyway, my question is about the concept of reverberation radius. Your PDF "Microphone" file mentions: "the larger the room and the less reverberant it is, the greater will be the reverberation radius.
The first part makes sense, large room, long path-length, larger radius. However, the reverberance (as I understand it) is only dependant on the attenuation from the walls, and how accoustically reflective they are...
So I guess I don't see how amplitude ties into radius.
Thanks for the help,
Chris
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Harvey Gerst
New member
I don't remember writing that, but what happens is this:
If you have a less reverberant room, it means that some of the signal (that is normally reflected) is being absorbed. The absorbtion acts like a mechanical delay, further increasing the reverberation radius.
The absorbtion pretty much "tricks" the wave into thinking the room is larger than it really is, by slowing the wave down as it passes thru the absorbing stuff twice, once going in, and then coming back out.
It's similar to an acoustic lens for a tweeter; the boundry layer of air molecules at the lens surface is denser than the normal air.
The sound wave front comes off the tweeter basically flat, but the outer edges of the lens are wider, so the center goes straight ahead while the lens curves the wave front by progessively slowing part of it down thru the denser molecules.
This bends the wave and it then follows the new curve, spreading out wider than it would without the lens.
Same idea; going thru the denser absorbing material twice has the same effect - making the wave appear slower by delaying the sound, thereby increasing the apparent radius.
Does that make a little more sense now, Chris?
If you have a less reverberant room, it means that some of the signal (that is normally reflected) is being absorbed. The absorbtion acts like a mechanical delay, further increasing the reverberation radius.
The absorbtion pretty much "tricks" the wave into thinking the room is larger than it really is, by slowing the wave down as it passes thru the absorbing stuff twice, once going in, and then coming back out.
It's similar to an acoustic lens for a tweeter; the boundry layer of air molecules at the lens surface is denser than the normal air.
The sound wave front comes off the tweeter basically flat, but the outer edges of the lens are wider, so the center goes straight ahead while the lens curves the wave front by progessively slowing part of it down thru the denser molecules.
This bends the wave and it then follows the new curve, spreading out wider than it would without the lens.
Same idea; going thru the denser absorbing material twice has the same effect - making the wave appear slower by delaying the sound, thereby increasing the apparent radius.
Does that make a little more sense now, Chris?
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Nd:Apricot Stu
New member
Optical Analogies
Very clear, thanks. My background is in optics and electro-magnetics and I've been trying to draw analogies between acoustics and those fields. From what you explained, sound absorbing material is not just a bad reflector, but it includes change of media density, changing wave speed.
I had previously thought the optical analogy of a sound aborber was a "cloudy mirror", but from what you've described it's more like a cloudy mirror submersed in water.
Could you provide some other ideas about relationships between these fields? Although electro-magnetic waves and accoustic waves are probably very different in some ways (especially concerning polarization), I bet there are quite a few places where they similar (diffraction, transmission, absorption, reflection).
One curiousity is an analogy for non-linear optical materials. In the world of light, those materials have a "fast" and a "slow" axis, depending on the incident polarization. Is there an acoustic equivalent? I don't understand acoustic polarization (if there is such a thing) well enough to even guess at this one...
Very clear, thanks. My background is in optics and electro-magnetics and I've been trying to draw analogies between acoustics and those fields. From what you explained, sound absorbing material is not just a bad reflector, but it includes change of media density, changing wave speed.
I had previously thought the optical analogy of a sound aborber was a "cloudy mirror", but from what you've described it's more like a cloudy mirror submersed in water.
Could you provide some other ideas about relationships between these fields? Although electro-magnetic waves and accoustic waves are probably very different in some ways (especially concerning polarization), I bet there are quite a few places where they similar (diffraction, transmission, absorption, reflection).
One curiousity is an analogy for non-linear optical materials. In the world of light, those materials have a "fast" and a "slow" axis, depending on the incident polarization. Is there an acoustic equivalent? I don't understand acoustic polarization (if there is such a thing) well enough to even guess at this one...
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Harvey Gerst
New member
Yeah, kinda, but I think things may get too heavy for this kinda thread.
When a flat front sound wave is forced thru a vertical slit (that is smaller than the wavelength), the sound is bent into a curved wave front in the horizontal axis, but not the vertical axis. It's kinda like polarization, but not exactly.
Light waves can be described as being made up of either particles or waves, depending on what you wanna do with the light, but sound waves stay pretty much waves from a physics standpoint.
And then you have the "quantum physics" angle when you hafta deal with someone like Dolly Parton; You can measure her, or listen to her music, but you can't do both at the same time.
When a flat front sound wave is forced thru a vertical slit (that is smaller than the wavelength), the sound is bent into a curved wave front in the horizontal axis, but not the vertical axis. It's kinda like polarization, but not exactly.
Light waves can be described as being made up of either particles or waves, depending on what you wanna do with the light, but sound waves stay pretty much waves from a physics standpoint.
And then you have the "quantum physics" angle when you hafta deal with someone like Dolly Parton; You can measure her, or listen to her music, but you can't do both at the same time.
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Nd:Apricot Stu
New member
Optics and
And who can forget the infamous "Dolly-Exclusion Principle". It so elegantly describes the nature of the pair.
Chris
Note to others on forum:
(even though I'm secretly a physics geek, please don't destroy my big black nerd glasses)
And who can forget the infamous "Dolly-Exclusion Principle". It so elegantly describes the nature of the pair.
Chris
Note to others on forum:
(even though I'm secretly a physics geek, please don't destroy my big black nerd glasses)
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virgoanmethod
New member
vox said:
Ditto.
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arcanemethods
New member
I have two papers that may be of interest to the physicist/EE with the maths to handle them. Except for the high frequency regions, they are pretty much definitive with respect to the models of single and dual diaphragm mics and can predict their performance and patterns over the full range of design choices. They are generalized to acoustic point sources so as to include a full treatment of proximity.
Is there a place where they could be uploaded for access by this group? They are too big, about 2.1 MB total, for attachment.
They are by Guy Torio who works (or once worked) for Shure. I have tried in numerous places including Shure to locate him for permission to post them and, while several people remember him, he seems to have disappeared.
I hope someday to find or work out a treatment of the high frequency performance but that is so complicated by diffraction effects and geometry of the capsule that it may remain empirical for some time to come.
Bob
Is there a place where they could be uploaded for access by this group? They are too big, about 2.1 MB total, for attachment.
They are by Guy Torio who works (or once worked) for Shure. I have tried in numerous places including Shure to locate him for permission to post them and, while several people remember him, he seems to have disappeared.
I hope someday to find or work out a treatment of the high frequency performance but that is so complicated by diffraction effects and geometry of the capsule that it may remain empirical for some time to come.
Bob
ausrock
Well-known member
Bob,
It may be an idea to visit the Tech Talk forum at http://www.recording.org/cgi-local/ubb/ultimatebb.cgi .........you may have to register (if you haven't been there already). There are guys there that host buckets loads of tech info on there own sites, some guys are working towards a DIY large diaphram capsule at the moment, and there is the Group DIY site which is seperate but linked in with Tech Talk.
It may be an idea to visit the Tech Talk forum at http://www.recording.org/cgi-local/ubb/ultimatebb.cgi .........you may have to register (if you haven't been there already). There are guys there that host buckets loads of tech info on there own sites, some guys are working towards a DIY large diaphram capsule at the moment, and there is the Group DIY site which is seperate but linked in with Tech Talk.
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arcanemethods
New member
ausrock said:Bob,
It may be an idea to visit the Tech Talk forum at http://www.recording.org/cgi-local/ubb/ultimatebb.cgi
Thanks, Ausrock. I found a home for them with one of their members. See:
http://vacuumbrain.com/TA/Microphone/single_diaphragm_paper.pdf
and:
http://vacuumbrain.com/TA/Microphone/dual_diaphragm_paper.pdf
They are 20 some pages each. Enjoy, and I look forward to any discussion.
Bob
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Capt Dunsel
New member
I'm only on page 6 of the thread, but I had to come here and post this:
As someone who is just starting out in the wonderful world of recording, this thread is the best thing since sliced bread! I had no idea of the intricacies of micing, and what I've learned so far would have taken YEARS to learn on my own.
Thank you Harvey and all you others for helping us "young 'uns" learn to spread our wings and fly!
As someone who is just starting out in the wonderful world of recording, this thread is the best thing since sliced bread! I had no idea of the intricacies of micing, and what I've learned so far would have taken YEARS to learn on my own.
Thank you Harvey and all you others for helping us "young 'uns" learn to spread our wings and fly!
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OPunWide
New member
There is a relatively new website that allows browsing and searching of microphone specs.
It's called Microphone Data. http://www.microphone-data.com/
It requires registration to get in, but appears to have a lot of info.
It might be a good idea to review this thread's section on Mic Specs (archived here) before taking the data too seriously.
It's called Microphone Data. http://www.microphone-data.com/
It requires registration to get in, but appears to have a lot of info.
It might be a good idea to review this thread's section on Mic Specs (archived here) before taking the data too seriously.
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MauiDino
New member
Amazing thread folks.. and thanks Harvey.
I've just purchased some mics for home recording and went searching out topics about patterns and usage of various mics. I landed in the right spot here!
Big Mahalo to all...
I've just purchased some mics for home recording and went searching out topics about patterns and usage of various mics. I landed in the right spot here!
Big Mahalo to all...
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Harvey Gerst
New member
Gee, and things were going so well here.
Buck62
噛んでくれ
Re: FREE GEAR $1000 Dollars of sE Gear
Reported... and hopefully it will be gone soon.
Reported... and hopefully it will be gone soon.
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jarick
New member
If I can contribute a bit...
I've spent the last week or so mulling over stereo recording techniques (my main instrument is the drums, and i've always had difficulty with overhead mic'ing), and I've found a whole bunch of useful information I'd like to share.
https://www.neumann.com/infopool/download.php?Datei=lect0026.PDF
Here is Neumann himself describing stereo recording and playback. Good information on how we perceive and localize stereo sounds.
http://www.tape.com/Bartlett_Articles/stereo_microphone_techniques.html
There is a great description (along with diagrams) of all the main stereo mic'ing techniques here, along with the pro's and con's of each.
http://www.microphone-data.com/pdfs/Stereo zoom.pdf
Here is a wonderful (although a bit theory-heavy) exploration of "stereophonic zoom" which is near-coincident mic'ing techniques. It goes into the differences between patterns and frequency response, as well as translation to loudspeaker systems.
http://www.josephson.com/tn5.html
All about the optimum stereo signal (OSS) technique and the Jecklin disc. Very good little article.
Now I've read through the post (and, like many people, made my own Word document with summaries and pictures), but this is some wonderful reading about the theory behind stereo mic'ing. Now I just need to get some C4's, a stereo bar, and a jecklin disc and put it all to work!
By the way, Harvey, thanks for sharing your knowledge. One question, though, when you were talking about X/Y mic'ing, you mentioned that omni's could be used (albeit with less stereo separation). From what I've read, it looks like X/Y mic'ing relies on level difference caused by microphone directionality, and, because omni's do not have that characteristic, they would be either almost completely in or out of phase and not give a stereo image. Was that a typo on your part, or is there something more at work?
- Jarick
I've spent the last week or so mulling over stereo recording techniques (my main instrument is the drums, and i've always had difficulty with overhead mic'ing), and I've found a whole bunch of useful information I'd like to share.
https://www.neumann.com/infopool/download.php?Datei=lect0026.PDF
Here is Neumann himself describing stereo recording and playback. Good information on how we perceive and localize stereo sounds.
http://www.tape.com/Bartlett_Articles/stereo_microphone_techniques.html
There is a great description (along with diagrams) of all the main stereo mic'ing techniques here, along with the pro's and con's of each.
http://www.microphone-data.com/pdfs/Stereo zoom.pdf
Here is a wonderful (although a bit theory-heavy) exploration of "stereophonic zoom" which is near-coincident mic'ing techniques. It goes into the differences between patterns and frequency response, as well as translation to loudspeaker systems.
http://www.josephson.com/tn5.html
All about the optimum stereo signal (OSS) technique and the Jecklin disc. Very good little article.
Now I've read through the post (and, like many people, made my own Word document with summaries and pictures), but this is some wonderful reading about the theory behind stereo mic'ing. Now I just need to get some C4's, a stereo bar, and a jecklin disc and put it all to work!
By the way, Harvey, thanks for sharing your knowledge. One question, though, when you were talking about X/Y mic'ing, you mentioned that omni's could be used (albeit with less stereo separation). From what I've read, it looks like X/Y mic'ing relies on level difference caused by microphone directionality, and, because omni's do not have that characteristic, they would be either almost completely in or out of phase and not give a stereo image. Was that a typo on your part, or is there something more at work?
- Jarick
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Harvey Gerst
New member
Re: If I can contribute a bit...
It's a far more subtle approach to overheads, but it's worth a try when everything else ain't doing it. I didn't want to leave people with the impression that stereo omnis must ALWAYS be used wide spaced, or with a Jecklin disc.
And stuff like this is the purpose of the thread. The rule is that omnis are not directional. But, many difuse field omnis do exhibit a high frequency rise on axis, so they are "kinda" directional at high frequencies. That's when you can "bend" the rules by pointing an omni straight at something.
Once you know the rules, you can "break" them more intelligently.
No, it's not a typo. Omnis tend to be somewhat directional at high frequencies. This can be an advantage where you want the attack of the cymbals to be distinct and directional, without giving much directional information about the toms, kick, or snare. Combined with the close mics, it can sometimes be useful for some situations. That's why I mentioned it, although I usually use wide spaced omnis or cardioids.jarick said:
It's a far more subtle approach to overheads, but it's worth a try when everything else ain't doing it. I didn't want to leave people with the impression that stereo omnis must ALWAYS be used wide spaced, or with a Jecklin disc.
And stuff like this is the purpose of the thread. The rule is that omnis are not directional. But, many difuse field omnis do exhibit a high frequency rise on axis, so they are "kinda" directional at high frequencies. That's when you can "bend" the rules by pointing an omni straight at something.
Once you know the rules, you can "break" them more intelligently.
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jarick
New member
Neat. Now I've got even more stuff to try out! I suppose looking at the directivity curves of most REAL omni mics shows that a bit. That may actually be quite a bit more useful on acoustic guitar, or something else that doesn't need such wide stereo separation.
Thanks again!
- Jarick
Thanks again!
- Jarick
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arcanemethods
New member
I posted this yesterday in the ECM8000 thread but would like folks following this one to think about it too.
Something struck me recently that you guys might think about trying: if the FET used in a capsule has lithographic symmetery between the source and drain at the IC level, which is not altogether uncommon with FET's, then the 2-wire linkwitz modified capsule is _identical_ to the original capsule with the leads swapped.
A quick experiment done by one of the guys on the micbuilders Yahoo email list shows that the gain is nearly the same both ways with the same load resistor. The gain in common source mode was a good deal higher.
To the extent that this symmetry holds, a two wire capsule can be put in source follower mode just by reversing it in the circuit it comes with.
Bob
Something struck me recently that you guys might think about trying: if the FET used in a capsule has lithographic symmetery between the source and drain at the IC level, which is not altogether uncommon with FET's, then the 2-wire linkwitz modified capsule is _identical_ to the original capsule with the leads swapped.
A quick experiment done by one of the guys on the micbuilders Yahoo email list shows that the gain is nearly the same both ways with the same load resistor. The gain in common source mode was a good deal higher.
To the extent that this symmetry holds, a two wire capsule can be put in source follower mode just by reversing it in the circuit it comes with.
Bob
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