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#1
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radio shack mic mods.
Hello out there, i reacently learned there is a mod for the radio shack
boundary mics that increases freq. response and less noise. has anyone tried this? what kind of results? i also saw a tape-op article on homemade mics-sounds like i need to hone my soldering skills! anyone else making home-made mics? thanks -alan |
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#2
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"alan" .@. writes:
Hello out there, i reacently learned there is a mod for the radio shack boundary mics that increases freq. response and less noise. has anyone tried this? what kind of results? i also saw a tape-op article on homemade mics-sounds like i need to hone my soldering skills! anyone else making home-made mics? thanks -alan Visit the Yahoo group, "micbuilders" (groups.yahoo.com). Richard |
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#3
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"alan" .@. writes:
Hello out there, i reacently learned there is a mod for the radio shack boundary mics that increases freq. response and less noise. has anyone tried this? what kind of results? i also saw a tape-op article on homemade mics-sounds like i need to hone my soldering skills! anyone else making home-made mics? thanks -alan Visit the Yahoo group, "micbuilders" (groups.yahoo.com). Richard |
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#4
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wrote in message ... "alan" .@. writes: Hello out there, i reacently learned there is a mod for the radio shack boundary mics that increases freq. response and less noise. has anyone tried this? what kind of results? i also saw a tape-op article on homemade mics-sounds like i need to hone my soldering skills! anyone else making home-made mics? thanks -alan Visit the Yahoo group, "micbuilders" (groups.yahoo.com). Richard will do, thanks. |
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#5
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wrote in message ... "alan" .@. writes: Hello out there, i reacently learned there is a mod for the radio shack boundary mics that increases freq. response and less noise. has anyone tried this? what kind of results? i also saw a tape-op article on homemade mics-sounds like i need to hone my soldering skills! anyone else making home-made mics? thanks -alan Visit the Yahoo group, "micbuilders" (groups.yahoo.com). Richard will do, thanks. |
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#6
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"alan" .@. wrote ...
Hello out there, i reacently learned there is a mod for the radio shack boundary mics that increases freq. response and less noise. has anyone tried this? what kind of results? Conventional search methods will turn them up. However, last time I checked, they were all for models that are not sold by RS anymore. i also saw a tape-op article on homemade mics-sounds like i need to hone my soldering skills! anyone else making home-made mics? thanks Define "homemade". Do you have a high-vacuum chamber to sputter your own gold flash on your homemade diaphragms? |
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#7
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"alan" .@. wrote ...
Hello out there, i reacently learned there is a mod for the radio shack boundary mics that increases freq. response and less noise. has anyone tried this? what kind of results? Conventional search methods will turn them up. However, last time I checked, they were all for models that are not sold by RS anymore. i also saw a tape-op article on homemade mics-sounds like i need to hone my soldering skills! anyone else making home-made mics? thanks Define "homemade". Do you have a high-vacuum chamber to sputter your own gold flash on your homemade diaphragms? |
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#8
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"alan" .@. wrote in message ... Hello out there, i reacently learned there is a mod for the radio shack boundary mics that increases freq. response and less noise. has anyone tried this? what kind of results? i also saw a tape-op article on homemade mics-sounds like i need to hone my soldering skills! anyone else making home-made mics? thanks -alan There should be multiple plans and instructions for modification of PZMs on Harvey Gerst's site... http://www.itrstudio.com/pzm.txt Here's a site that with diagrams that converts the mic to total phantom power... http://www.jdbsound.com/art/art520.html -- David Morgan (MAMS) http://www.m-a-m-s.com Morgan Audio Media Service Dallas, Texas (214) 662-9901 _______________________________________ http://www.artisan-recordingstudio.com |
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#9
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"alan" .@. wrote in message ... Hello out there, i reacently learned there is a mod for the radio shack boundary mics that increases freq. response and less noise. has anyone tried this? what kind of results? i also saw a tape-op article on homemade mics-sounds like i need to hone my soldering skills! anyone else making home-made mics? thanks -alan There should be multiple plans and instructions for modification of PZMs on Harvey Gerst's site... http://www.itrstudio.com/pzm.txt Here's a site that with diagrams that converts the mic to total phantom power... http://www.jdbsound.com/art/art520.html -- David Morgan (MAMS) http://www.m-a-m-s.com Morgan Audio Media Service Dallas, Texas (214) 662-9901 _______________________________________ http://www.artisan-recordingstudio.com |
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#10
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In article , alan .@. wrote:
Hello out there, i reacently learned there is a mod for the radio shack boundary mics that increases freq. response and less noise. has anyone tried this? what kind of results? i also saw a tape-op article on homemade mics-sounds like i need to hone my soldering skills! anyone else making home-made mics? thanks This is Phil Rastoczny's mod, which was posted here originally in 1983. It was for the original Radio Shack PZMs, which were OEM'ed by Crown and weren't all that bad. A few years ago, Radio Shack discontinued them in favor of the junky boundary mikes they are selling now, which are not worth modifying. The tape-op article uses now-discontinued Panasonic capsules. It's not bad although the RF noise rejection isn't so hot. I don't know where you would get capsules for it. I did an article in Recording magazine about how various electret mikes work inside, with a bunch of different schematics of working designs. That was a couple years ago, though. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
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#11
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In article , alan .@. wrote:
Hello out there, i reacently learned there is a mod for the radio shack boundary mics that increases freq. response and less noise. has anyone tried this? what kind of results? i also saw a tape-op article on homemade mics-sounds like i need to hone my soldering skills! anyone else making home-made mics? thanks This is Phil Rastoczny's mod, which was posted here originally in 1983. It was for the original Radio Shack PZMs, which were OEM'ed by Crown and weren't all that bad. A few years ago, Radio Shack discontinued them in favor of the junky boundary mikes they are selling now, which are not worth modifying. The tape-op article uses now-discontinued Panasonic capsules. It's not bad although the RF noise rejection isn't so hot. I don't know where you would get capsules for it. I did an article in Recording magazine about how various electret mikes work inside, with a bunch of different schematics of working designs. That was a couple years ago, though. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
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#12
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In article .@. writes: Hello out there, i reacently learned there is a mod for the radio shack boundary mics that increases freq. response and less noise. has anyone tried this? Unless there's something recent, the Radio Shack PZM (really made by Crown) mics for which modifications were floating around were very different than what you can buy today. So the first step is finding one of the older mics. The simplest modification is cutting off the 1/4" phone plug and replacing it with an XLR so you have a balanced output. (it's a two-conductor shielded cable). The next modification (or the first modification if you do it first) is to replace the AA battery with two 6V photo batteries. There's also at least one modification that removes the transformer. These days, I suspect that anything beyond the battery and connector wouldn't be worth the effort. -- I'm really Mike Rivers ) However, until the spam goes away or Hell freezes over, lots of IP addresses are blocked from this system. If you e-mail me and it bounces, use your secret decoder ring and reach me he double-m-eleven-double-zero at yahoo |
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#13
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In article .@. writes: Hello out there, i reacently learned there is a mod for the radio shack boundary mics that increases freq. response and less noise. has anyone tried this? Unless there's something recent, the Radio Shack PZM (really made by Crown) mics for which modifications were floating around were very different than what you can buy today. So the first step is finding one of the older mics. The simplest modification is cutting off the 1/4" phone plug and replacing it with an XLR so you have a balanced output. (it's a two-conductor shielded cable). The next modification (or the first modification if you do it first) is to replace the AA battery with two 6V photo batteries. There's also at least one modification that removes the transformer. These days, I suspect that anything beyond the battery and connector wouldn't be worth the effort. -- I'm really Mike Rivers ) However, until the spam goes away or Hell freezes over, lots of IP addresses are blocked from this system. If you e-mail me and it bounces, use your secret decoder ring and reach me he double-m-eleven-double-zero at yahoo |
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#14
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"Mike Rivers" wrote ...
Unless there's something recent, the Radio Shack PZM (really made by Crown) mics for which modifications were floating around were very different than what you can buy today. So the first step is finding one of the older mics. The simplest modification is cutting off the 1/4" phone plug and replacing it with an XLR so you have a balanced output. (it's a two-conductor shielded cable). The next modification (or the first modification if you do it first) is to replace the AA battery with two 6V photo batteries. There's also at least one modification that removes the transformer. The current ones don't even have a transformer. They do, however, have a transformer-size/shape inductor. (Inside the microphone "head") These days, I suspect that anything beyond the battery and connector wouldn't be worth the effort. |
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#15
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"Mike Rivers" wrote ...
Unless there's something recent, the Radio Shack PZM (really made by Crown) mics for which modifications were floating around were very different than what you can buy today. So the first step is finding one of the older mics. The simplest modification is cutting off the 1/4" phone plug and replacing it with an XLR so you have a balanced output. (it's a two-conductor shielded cable). The next modification (or the first modification if you do it first) is to replace the AA battery with two 6V photo batteries. There's also at least one modification that removes the transformer. The current ones don't even have a transformer. They do, however, have a transformer-size/shape inductor. (Inside the microphone "head") These days, I suspect that anything beyond the battery and connector wouldn't be worth the effort. |
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#16
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In article .@. writes: i have found an article by Rick Chinn that mentions the newer 330-3022, and they sell a PCB to convert it for phantom power. even with the junky mics, if this $30 mod would increase freq response and noise rejection...might be good for classrooms and/or audiences. I wouldn't spend the $30 on the mod. You won't change the pattern (noise rejection) and you might clean up the low frequency response, but you don't need that for classroom and audience recording. If the modification gave you higher output for a given sound level, that might help but that depends on what you're connecting it to. -- I'm really Mike Rivers ) However, until the spam goes away or Hell freezes over, lots of IP addresses are blocked from this system. If you e-mail me and it bounces, use your secret decoder ring and reach me he double-m-eleven-double-zero at yahoo |
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#17
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In article .@. writes: i have found an article by Rick Chinn that mentions the newer 330-3022, and they sell a PCB to convert it for phantom power. even with the junky mics, if this $30 mod would increase freq response and noise rejection...might be good for classrooms and/or audiences. I wouldn't spend the $30 on the mod. You won't change the pattern (noise rejection) and you might clean up the low frequency response, but you don't need that for classroom and audience recording. If the modification gave you higher output for a given sound level, that might help but that depends on what you're connecting it to. -- I'm really Mike Rivers ) However, until the spam goes away or Hell freezes over, lots of IP addresses are blocked from this system. If you e-mail me and it bounces, use your secret decoder ring and reach me he double-m-eleven-double-zero at yahoo |
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#18
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"Mike Rivers" wrote in message
news:znr1101075067k@trad... In article .@. writes: i have found an article by Rick Chinn that mentions the newer 330-3022, and they sell a PCB to convert it for phantom power. even with the junky mics, if this $30 mod would increase freq response and noise rejection...might be good for classrooms and/or audiences. I wouldn't spend the $30 on the mod. You won't change the pattern (noise rejection) and you might clean up the low frequency response, but you don't need that for classroom and audience recording. If the modification gave you higher output for a given sound level, that might help but that depends on what you're connecting it to. -- I'm really Mike Rivers ) However, until the spam goes away or Hell freezes over, lots of IP addresses are blocked from this system. If you e-mail me and it bounces, use your secret decoder ring and reach me he double-m-eleven-double-zero at yahoo true, and they will be useful anyway. i'm going to give them a call and see what they say. hey thanks for the input! i'll look for those older ones... |
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#19
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"Mike Rivers" wrote in message
news:znr1101075067k@trad... In article .@. writes: i have found an article by Rick Chinn that mentions the newer 330-3022, and they sell a PCB to convert it for phantom power. even with the junky mics, if this $30 mod would increase freq response and noise rejection...might be good for classrooms and/or audiences. I wouldn't spend the $30 on the mod. You won't change the pattern (noise rejection) and you might clean up the low frequency response, but you don't need that for classroom and audience recording. If the modification gave you higher output for a given sound level, that might help but that depends on what you're connecting it to. -- I'm really Mike Rivers ) However, until the spam goes away or Hell freezes over, lots of IP addresses are blocked from this system. If you e-mail me and it bounces, use your secret decoder ring and reach me he double-m-eleven-double-zero at yahoo true, and they will be useful anyway. i'm going to give them a call and see what they say. hey thanks for the input! i'll look for those older ones... |
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#20
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Mike Rivers wrote: Unless there's something recent, the Radio Shack PZM (really made by Crown) mics for which modifications were floating around were very different than what you can buy today. So the first step is finding one of the older mics. How were they very different, Mike? The things are so dirt simple that it's hard to see where there is any room for difference. BTW, a member of the micbuilders yahoo newsgroup posted links to some recent research showing that all the PZM mode does is screw up the frequency response compared to a surface mounted small omni without a baffle or gap. Directional performance is the same, a hemisphere. I think for a boundry application it would be hard to beat a Knowles FG-3329, which is a omni in a stainless steel cylinder .1 inches long and .1 inches in diameter, mounted flush with the surface of a thin nick five or six inches in diameter off a large radius dome. That capsule is three wire which allows for source follower operation and low distortion and has better noise and frequency response specs than any of the Panasonics. It isn't as cheap, though. Thirty dollars or so leaded from DigiKey. Don't even think about attaching leads to the cheaper non-leaded versions yourself without a micro-waldo. A very good tech friend fried three of them attempting it for me and the fourth had an intermittant connection. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
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#21
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Mike Rivers wrote: Unless there's something recent, the Radio Shack PZM (really made by Crown) mics for which modifications were floating around were very different than what you can buy today. So the first step is finding one of the older mics. How were they very different, Mike? The things are so dirt simple that it's hard to see where there is any room for difference. BTW, a member of the micbuilders yahoo newsgroup posted links to some recent research showing that all the PZM mode does is screw up the frequency response compared to a surface mounted small omni without a baffle or gap. Directional performance is the same, a hemisphere. I think for a boundry application it would be hard to beat a Knowles FG-3329, which is a omni in a stainless steel cylinder .1 inches long and .1 inches in diameter, mounted flush with the surface of a thin nick five or six inches in diameter off a large radius dome. That capsule is three wire which allows for source follower operation and low distortion and has better noise and frequency response specs than any of the Panasonics. It isn't as cheap, though. Thirty dollars or so leaded from DigiKey. Don't even think about attaching leads to the cheaper non-leaded versions yourself without a micro-waldo. A very good tech friend fried three of them attempting it for me and the fourth had an intermittant connection. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
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#22
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"Bob Cain" wrote ...
Mike Rivers wrote: Unless there's something recent, the Radio Shack PZM (really made by Crown) mics for which modifications were floating around were very different than what you can buy today. So the first step is finding one of the older mics. How were they very different, Mike? The things are so dirt simple that it's hard to see where there is any room for difference. Completely different mechanically. Capsule is not parallel to the surface (likely circumventing Crown's patent?) Completely different in every way. Likely uses different (and cheaper) electret capsules, etc. etc. Completely different circuit also. Uses a small (3/4-inch cube) inductor in lieu of a load resistor, etc. BTW, a member of the micbuilders yahoo newsgroup posted links to some recent research showing that all the PZM mode does is screw up the frequency response compared to a surface mounted small omni without a baffle or gap. Directional performance is the same, a hemisphere. PZM was a solution looking for a problem. Certainly there were *some* situations where PZM was the perfect solution, but the vast majority of the applications I saw (and heard described) ranged from inappropriate to ridiculous. 4-ft square sheets of clear plastic flown over the audience just to provide an adequate baffle for a PZM? At an outdoor venue even. |
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#23
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"Bob Cain" wrote ...
Mike Rivers wrote: Unless there's something recent, the Radio Shack PZM (really made by Crown) mics for which modifications were floating around were very different than what you can buy today. So the first step is finding one of the older mics. How were they very different, Mike? The things are so dirt simple that it's hard to see where there is any room for difference. Completely different mechanically. Capsule is not parallel to the surface (likely circumventing Crown's patent?) Completely different in every way. Likely uses different (and cheaper) electret capsules, etc. etc. Completely different circuit also. Uses a small (3/4-inch cube) inductor in lieu of a load resistor, etc. BTW, a member of the micbuilders yahoo newsgroup posted links to some recent research showing that all the PZM mode does is screw up the frequency response compared to a surface mounted small omni without a baffle or gap. Directional performance is the same, a hemisphere. PZM was a solution looking for a problem. Certainly there were *some* situations where PZM was the perfect solution, but the vast majority of the applications I saw (and heard described) ranged from inappropriate to ridiculous. 4-ft square sheets of clear plastic flown over the audience just to provide an adequate baffle for a PZM? At an outdoor venue even. |
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#24
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#26
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Bob Cain wrote:
Mike Rivers wrote: Unless there's something recent, the Radio Shack PZM (really made by Crown) mics for which modifications were floating around were very different than what you can buy today. So the first step is finding one of the older mics. How were they very different, Mike? The things are so dirt simple that it's hard to see where there is any room for difference. The capsule design is very different, and it's positioned differently against the backplate. The capsule used in the earlier Crown-made one was very different than the one used in the current one. I think for a boundry application it would be hard to beat a Knowles FG-3329, which is a omni in a stainless steel cylinder .1 inches long and .1 inches in diameter, mounted flush with the surface of a thin nick five or six inches in diameter off a large radius dome. That capsule is three wire which allows for source follower operation and low distortion and has better noise and frequency response specs than any of the Panasonics. It isn't as cheap, though. Thirty dollars or so leaded from DigiKey. Don't even think about attaching leads to the cheaper non-leaded versions yourself without a micro-waldo. A very good tech friend fried three of them attempting it for me and the fourth had an intermittant connection. The problem is that if you put a clean and flat omni against a boundary, you get a rising top octave. You might be better off with a microphone that has a deliberately rolled-off top end. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
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#27
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Bob Cain wrote:
Mike Rivers wrote: Unless there's something recent, the Radio Shack PZM (really made by Crown) mics for which modifications were floating around were very different than what you can buy today. So the first step is finding one of the older mics. How were they very different, Mike? The things are so dirt simple that it's hard to see where there is any room for difference. The capsule design is very different, and it's positioned differently against the backplate. The capsule used in the earlier Crown-made one was very different than the one used in the current one. I think for a boundry application it would be hard to beat a Knowles FG-3329, which is a omni in a stainless steel cylinder .1 inches long and .1 inches in diameter, mounted flush with the surface of a thin nick five or six inches in diameter off a large radius dome. That capsule is three wire which allows for source follower operation and low distortion and has better noise and frequency response specs than any of the Panasonics. It isn't as cheap, though. Thirty dollars or so leaded from DigiKey. Don't even think about attaching leads to the cheaper non-leaded versions yourself without a micro-waldo. A very good tech friend fried three of them attempting it for me and the fourth had an intermittant connection. The problem is that if you put a clean and flat omni against a boundary, you get a rising top octave. You might be better off with a microphone that has a deliberately rolled-off top end. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
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#28
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#29
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#30
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Mike Rivers wrote: BTW, a member of the micbuilders yahoo newsgroup posted links to some recent research showing that all the PZM mode does is screw up the frequency response compared to a surface mounted small omni without a baffle or gap. Directional performance is the same, a hemisphere. Anyone can post a link. ??? Have they experimented with this and posted any real life experience? It was Eric Benjamin, you may have heard of him, and it was published measurement data, not measurements he did himself. It sounds to me like they're questioning the validity of Ed Long's original work in designing this microphone configuration. Precisely. Do you happen to have a link to his acousitcal analysis of the configuration? Everything I've seen is hand waving with little solid technical substance. Boundary mics have been made with a flush-mounted omni capsule looking up through a plate for quite a while. Generally they're used in installed sound applications like conference rooms. What we know as a "PZM" is sometimes used in those applications, but more often they're found in portable applications. The two concepts may be interchangeable in the lab, but not necessarily in practice. It boils down to a different shaped orfice and at the wavelengths where that difference should manifest, we ain't hearing much of anything. That's why I'd like to see Long's analysis (assuming it is more than verbage and drawings.) It's really hard to see what differing effect the configuration would have, relative to a flush mount, on anything but the highest frequencies and what it might do there doesn't seem that it would be anything good. What screws up the response relative to flush mount in practice is the diffraction due to the cantilever that holds things above the gap. The dimensions of that are such that the effects reach down a ways. I think for a boundry application it would be hard to beat a Knowles FG-3329, which is a omni in a stainless steel cylinder .1 inches long and .1 inches in diameter, mounted flush with the surface of a thin nick five or six inches in diameter off a large radius dome. Hey, the guy didn't ask about building his own microphone, he asked about modifying a microphone that he could buy off the shelf. I doubt that he has the facilities to build what you're describing, though it certainly sounds like an interesting experiment for someone who's as interested in building microphones as using them. Yeah, that was the spirit in which it was offered although making such a thing doesn't amount to much more work than modifying an existing widget. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
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#31
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Mike Rivers wrote: BTW, a member of the micbuilders yahoo newsgroup posted links to some recent research showing that all the PZM mode does is screw up the frequency response compared to a surface mounted small omni without a baffle or gap. Directional performance is the same, a hemisphere. Anyone can post a link. ??? Have they experimented with this and posted any real life experience? It was Eric Benjamin, you may have heard of him, and it was published measurement data, not measurements he did himself. It sounds to me like they're questioning the validity of Ed Long's original work in designing this microphone configuration. Precisely. Do you happen to have a link to his acousitcal analysis of the configuration? Everything I've seen is hand waving with little solid technical substance. Boundary mics have been made with a flush-mounted omni capsule looking up through a plate for quite a while. Generally they're used in installed sound applications like conference rooms. What we know as a "PZM" is sometimes used in those applications, but more often they're found in portable applications. The two concepts may be interchangeable in the lab, but not necessarily in practice. It boils down to a different shaped orfice and at the wavelengths where that difference should manifest, we ain't hearing much of anything. That's why I'd like to see Long's analysis (assuming it is more than verbage and drawings.) It's really hard to see what differing effect the configuration would have, relative to a flush mount, on anything but the highest frequencies and what it might do there doesn't seem that it would be anything good. What screws up the response relative to flush mount in practice is the diffraction due to the cantilever that holds things above the gap. The dimensions of that are such that the effects reach down a ways. I think for a boundry application it would be hard to beat a Knowles FG-3329, which is a omni in a stainless steel cylinder .1 inches long and .1 inches in diameter, mounted flush with the surface of a thin nick five or six inches in diameter off a large radius dome. Hey, the guy didn't ask about building his own microphone, he asked about modifying a microphone that he could buy off the shelf. I doubt that he has the facilities to build what you're describing, though it certainly sounds like an interesting experiment for someone who's as interested in building microphones as using them. Yeah, that was the spirit in which it was offered although making such a thing doesn't amount to much more work than modifying an existing widget. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
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#32
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Scott Dorsey wrote: Bob Cain wrote: How were they very different, Mike? The things are so dirt simple that it's hard to see where there is any room for difference. The capsule design is very different, Hmmm, I had one of the old ones years ago and it had a 1/4" aluminum can electret in it which I'm pretty sure is the same as the current model. At about $.35 in OEM quantities it's pretty difficult to understand why they'd have substituted something inferior to the WM60A which I've seen reported as the original capsule. Don't they both hold the capsule in a similar cantilever over a flat plate with the same gap? The problem is that if you put a clean and flat omni against a boundary, you get a rising top octave. Why is that? What happens at a reflective surface isn't frequency dependant. It should be no different than having it in free space between two identical rooms with identical contents and sources in them (thus the 6 dB increase in sensitivity.) Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
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#33
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Scott Dorsey wrote: Bob Cain wrote: How were they very different, Mike? The things are so dirt simple that it's hard to see where there is any room for difference. The capsule design is very different, Hmmm, I had one of the old ones years ago and it had a 1/4" aluminum can electret in it which I'm pretty sure is the same as the current model. At about $.35 in OEM quantities it's pretty difficult to understand why they'd have substituted something inferior to the WM60A which I've seen reported as the original capsule. Don't they both hold the capsule in a similar cantilever over a flat plate with the same gap? The problem is that if you put a clean and flat omni against a boundary, you get a rising top octave. Why is that? What happens at a reflective surface isn't frequency dependant. It should be no different than having it in free space between two identical rooms with identical contents and sources in them (thus the 6 dB increase in sensitivity.) Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
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#34
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#36
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Bob Cain wrote:
Scott Dorsey wrote: Bob Cain wrote: How were they very different, Mike? The things are so dirt simple that it's hard to see where there is any room for difference. The capsule design is very different, Hmmm, I had one of the old ones years ago and it had a 1/4" aluminum can electret in it which I'm pretty sure is the same as the current model. At about $.35 in OEM quantities it's pretty difficult to understand why they'd have substituted something inferior to the WM60A which I've seen reported as the original capsule. Try measuring the frequency response. The original capsule is not anything like the WM60A. The WM60A has a resonant chamber built in front of the diaphragm to hold the high end up above the resonant point of the diaphragm. The capsule that Crown uses does not have this, and since the resonant point is fairly low, it has a very low dropoff of the top end. This is combined with the top end rise from the boundary effect to give a reasonably flat response on the whole combined system. Don't they both hold the capsule in a similar cantilever over a flat plate with the same gap? No, the new one in fact mounts the capsule with the diaphragm perpendicular to the boundary. The problem is that if you put a clean and flat omni against a boundary, you get a rising top octave. Why is that? What happens at a reflective surface isn't frequency dependant. It should be no different than having it in free space between two identical rooms with identical contents and sources in them (thus the 6 dB increase in sensitivity.) Think of it as a comb filtering effect. I can probably dig up the white paper from Crown around here somewhere if you want to see it, though. The top octave rise is part of what makes the whole thing work. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
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Bob Cain wrote:
Scott Dorsey wrote: Bob Cain wrote: How were they very different, Mike? The things are so dirt simple that it's hard to see where there is any room for difference. The capsule design is very different, Hmmm, I had one of the old ones years ago and it had a 1/4" aluminum can electret in it which I'm pretty sure is the same as the current model. At about $.35 in OEM quantities it's pretty difficult to understand why they'd have substituted something inferior to the WM60A which I've seen reported as the original capsule. Try measuring the frequency response. The original capsule is not anything like the WM60A. The WM60A has a resonant chamber built in front of the diaphragm to hold the high end up above the resonant point of the diaphragm. The capsule that Crown uses does not have this, and since the resonant point is fairly low, it has a very low dropoff of the top end. This is combined with the top end rise from the boundary effect to give a reasonably flat response on the whole combined system. Don't they both hold the capsule in a similar cantilever over a flat plate with the same gap? No, the new one in fact mounts the capsule with the diaphragm perpendicular to the boundary. The problem is that if you put a clean and flat omni against a boundary, you get a rising top octave. Why is that? What happens at a reflective surface isn't frequency dependant. It should be no different than having it in free space between two identical rooms with identical contents and sources in them (thus the 6 dB increase in sensitivity.) Think of it as a comb filtering effect. I can probably dig up the white paper from Crown around here somewhere if you want to see it, though. The top octave rise is part of what makes the whole thing work. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
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#38
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Mike Rivers wrote: In article writes: It was Eric Benjamin, you may have heard of him, and it was published measurement data, not measurements he did himself. Yes, I know Eric Benjamin (the one at Dolby). But I forgot why you brought this up. Because he was the one that reported this testing of the PZM which found it wanting in comparison to a simpler omni. I mentioned his name because if you know him you know that he rarely, never in my experience, reports anything that diverges from fact. I also know him personally and know that his nature admits no bull****. No. They didn't have links back then. I'm sure the PZM was developed experimentally with some analysis to show that the principle works. I doubt there was any sort of optimization analysis. Someone who worked with him at the time that he was hand-building PZMs said that he used a dollar bill as a gage to set the spacing of the capsule off the boundary plate. Not very scientific, but reasonably repeatable. Or maybe it was his first dollar. How about Cain's analysis? You'te pretty good at that sort of thing. Here's where my doubt about all this happens. There is no difference at all between a PZM on a wall and two summed capsules on cantilevers in free space facing each other with twice the gap between them and where the room on one side of the pair is a mirror image of what's on the other side. I can't see how the PZM configuration offers anything positive compared to a single omni at that position. The fact that sound approaching the PZM at any angle other than perpindicular reaches the opening at the center of the capsule with a variety of delays only implies combing at the highest frequencies. The cantilever itself introduces diffraction and angular variations that reach lower. Absolutely no benefit from this configuration is apparent to me in theory. What screws up the response relative to flush mount in practice is the diffraction due to the cantilever that holds things above the gap. The dimensions of that are such that the effects reach down a ways. I'm sure that Crown has frequency response and polar plots. Have you looked there? I've learned, as I think you have too, not to pay much attention to manufacturer's plots. The design was from the days when they didn't have a lot of graphic artists so what you can find, if you can find old data, is likely to be close to what you get. Maybe someone with a well indexed library of audio magazines going back to the '70s can find a good review of an early generation PZM - maybe a Studio Sound issue. I might even have one myself. It really isn't a review I'd like to see but some theoretical acoustical analysis that defines the difference and the benefits quantitatively. The principle of the PZM (as it was explained to me by Farrell Becker, an associate of Ed Long's at the time, back stage at Wolf Trap) is that the path length from the source to the capsule is independent of the distance between the source and the microphone. The same is truer with an omni having a small orfice at the same postion. Since everything that gets to the capsule (theoretically) is reflected off the boundary plate, everything travels through the same path which is much shorter than the shortest wavelength supported by the microphone. So there is no phase cancellation at certain frequencies due to the path length. The idea was to make a microphone with flat frequency response, at least down to the lowest frequency that could bounce off the boundary plate. This is the hand waving (not yours, I know) that really makes no acoustical sense. Reflection from the plate or a wall on which it is mounted just gives rise to a virtual source on the other side which is summed with the real source at the capsule itself. Imagine the wall as a mirror and you'll see what the mic hears. I'm sure those worked fine for the person who wrote the article, and it makes good copy. That's what I think. It was a cute marketing ploy, an intruiging looking widget with no substantial real difference that isn't of a somewhat negative nature. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
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Mike Rivers wrote: In article writes: It was Eric Benjamin, you may have heard of him, and it was published measurement data, not measurements he did himself. Yes, I know Eric Benjamin (the one at Dolby). But I forgot why you brought this up. Because he was the one that reported this testing of the PZM which found it wanting in comparison to a simpler omni. I mentioned his name because if you know him you know that he rarely, never in my experience, reports anything that diverges from fact. I also know him personally and know that his nature admits no bull****. No. They didn't have links back then. I'm sure the PZM was developed experimentally with some analysis to show that the principle works. I doubt there was any sort of optimization analysis. Someone who worked with him at the time that he was hand-building PZMs said that he used a dollar bill as a gage to set the spacing of the capsule off the boundary plate. Not very scientific, but reasonably repeatable. Or maybe it was his first dollar. How about Cain's analysis? You'te pretty good at that sort of thing. Here's where my doubt about all this happens. There is no difference at all between a PZM on a wall and two summed capsules on cantilevers in free space facing each other with twice the gap between them and where the room on one side of the pair is a mirror image of what's on the other side. I can't see how the PZM configuration offers anything positive compared to a single omni at that position. The fact that sound approaching the PZM at any angle other than perpindicular reaches the opening at the center of the capsule with a variety of delays only implies combing at the highest frequencies. The cantilever itself introduces diffraction and angular variations that reach lower. Absolutely no benefit from this configuration is apparent to me in theory. What screws up the response relative to flush mount in practice is the diffraction due to the cantilever that holds things above the gap. The dimensions of that are such that the effects reach down a ways. I'm sure that Crown has frequency response and polar plots. Have you looked there? I've learned, as I think you have too, not to pay much attention to manufacturer's plots. The design was from the days when they didn't have a lot of graphic artists so what you can find, if you can find old data, is likely to be close to what you get. Maybe someone with a well indexed library of audio magazines going back to the '70s can find a good review of an early generation PZM - maybe a Studio Sound issue. I might even have one myself. It really isn't a review I'd like to see but some theoretical acoustical analysis that defines the difference and the benefits quantitatively. The principle of the PZM (as it was explained to me by Farrell Becker, an associate of Ed Long's at the time, back stage at Wolf Trap) is that the path length from the source to the capsule is independent of the distance between the source and the microphone. The same is truer with an omni having a small orfice at the same postion. Since everything that gets to the capsule (theoretically) is reflected off the boundary plate, everything travels through the same path which is much shorter than the shortest wavelength supported by the microphone. So there is no phase cancellation at certain frequencies due to the path length. The idea was to make a microphone with flat frequency response, at least down to the lowest frequency that could bounce off the boundary plate. This is the hand waving (not yours, I know) that really makes no acoustical sense. Reflection from the plate or a wall on which it is mounted just gives rise to a virtual source on the other side which is summed with the real source at the capsule itself. Imagine the wall as a mirror and you'll see what the mic hears. I'm sure those worked fine for the person who wrote the article, and it makes good copy. That's what I think. It was a cute marketing ploy, an intruiging looking widget with no substantial real difference that isn't of a somewhat negative nature. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
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On Tue, 23 Nov 2004 15:36:02 -0800, Bob Cain
wrote: Mike Rivers wrote: path length. The idea was to make a microphone with flat frequency response, at least down to the lowest frequency that could bounce off the boundary plate. This is the hand waving (not yours, I know) that really makes no acoustical sense. Reflection from the plate or a wall on which it is mounted just gives rise to a virtual source on the other side which is summed with the real source at the capsule itself. Imagine the wall as a mirror and you'll see what the mic hears. Is there any factor-of-two difference in the two arguments, or have I just been watching too many French movies lately? Bonjour, Chris Hornbeck |
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