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radio shack mic mods.

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November 20, 2004 8:55:43 PM

Archived from groups: rec.audio.pro (More info?)

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

More about : radio shack mic mods

Anonymous
November 21, 2004 12:19:55 AM

Archived from groups: rec.audio.pro (More info?)

"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
November 21, 2004 12:19:56 AM

Archived from groups: rec.audio.pro (More info?)

<Mannr@uwaterloo.ca> wrote in message news:871xeokkok.fsf@uwaterloo.ca...
> "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.
Related resources
Anonymous
November 21, 2004 12:35:13 AM

Archived from groups: rec.audio.pro (More info?)

"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?
November 21, 2004 1:13:16 AM

Archived from groups: rec.audio.pro (More info?)

"Richard Crowley" <rcrowley7@xprt.net> wrote in message
news:10q0a8jdntj7970@corp.supernews.com...
> "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?
>
>
>

i have sputtered my gold-flash on a diaphragm but it's another
subject....sorry couldn't resist...IOW-obviously not. it's more like
homemade as in homemade pie with the ready-made crust.
Anonymous
November 21, 2004 11:58:06 AM

Archived from groups: rec.audio.pro (More info?)

"alan" <.@.> wrote in message news:cnosiv$mci$1@gnus01.u.washington.edu...
> 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
Anonymous
November 21, 2004 1:14:14 PM

Archived from groups: rec.audio.pro (More info?)

In article <cnosiv$mci$1@gnus01.u.washington.edu>, 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."
Anonymous
November 21, 2004 2:02:50 PM

Archived from groups: rec.audio.pro (More info?)

In article <cnosiv$mci$1@gnus01.u.washington.edu> .@. 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 (mrivers@d-and-d.com)
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 here: double-m-eleven-double-zero at yahoo
Anonymous
November 21, 2004 2:19:28 PM

Archived from groups: rec.audio.pro (More info?)

"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.
November 21, 2004 3:00:28 PM

Archived from groups: rec.audio.pro (More info?)

"Scott Dorsey" <kludge@panix.com> wrote in message
news:cnqbc6$rlg$1@panix1.panix.com...
> In article <cnosiv$mci$1@gnus01.u.washington.edu>, 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."

thanks.
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. im not really after an audio test
instrument.
-alan
November 21, 2004 3:01:39 PM

Archived from groups: rec.audio.pro (More info?)

"alan" <.@.> wrote in message news:y9idnRgCxZtObj3cRVn-tg@comcast.com...
>
> "Scott Dorsey" <kludge@panix.com> wrote in message
> news:cnqbc6$rlg$1@panix1.panix.com...
>> In article <cnosiv$mci$1@gnus01.u.washington.edu>, 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."
>
> thanks.
> 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. im not really
> after an audio test instrument.
> -alan
>
link: http://www.uneeda-audio.com/pzm/index.htm
Anonymous
November 21, 2004 11:22:38 PM

Archived from groups: rec.audio.pro (More info?)

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
Anonymous
November 21, 2004 11:28:56 PM

Archived from groups: rec.audio.pro (More info?)

In article <y9idnRgCxZtObj3cRVn-tg@comcast.com> .@. 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 (mrivers@d-and-d.com)
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 here: double-m-eleven-double-zero at yahoo
November 21, 2004 11:28:57 PM

Archived from groups: rec.audio.pro (More info?)

"Mike Rivers" <mrivers@d-and-d.com> wrote in message
news:znr1101075067k@trad...
>
> In article <y9idnRgCxZtObj3cRVn-tg@comcast.com> .@. 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 (mrivers@d-and-d.com)
> 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 here: 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...
Anonymous
November 22, 2004 2:35:56 AM

Archived from groups: rec.audio.pro (More info?)

"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.
Anonymous
November 22, 2004 2:17:32 PM

Archived from groups: rec.audio.pro (More info?)

In article <cnrpfq02rdv@enews3.newsguy.com> arcane@arcanemethods.com writes:

> 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.

Another argument about a word, eh? Strike "very" and we'll just say
they're different. How's an SM57 different from an RE11? They're just
different - they both work on the same principle, but they have
different elements and are mounted in different cases, and they just
sound different. Some people would say "very different," some would
just say "different," and others wouldn't care even if they recognized
the difference.

The new Radio Shack boundary mics compared to the original ones look
different, they have different capsules, they have different
electronics. They have flat plates, they pick up sound in roughly a
hemispherical pattern, and they use a battery for power, so yeah, I
guess they're not so different after all.

The point is that the old Radio Shack PZM was actually a fairly useful
mic for things that you'd use a PZM for (which is far from
"everything"). The new ones have zero reputation around here so I see
no reason to recommend using them, or even modifying them. But there's
no reason why someone shouldn't experiment if he has the time, the
money, and most important, the means to evaluate the effect of the
modification.

> 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 sounds to me like they're questioning the
validity of Ed Long's original work in designing this microphone
configuration. 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.

> 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.


--
I'm really Mike Rivers (mrivers@d-and-d.com)
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 here: double-m-eleven-double-zero at yahoo
Anonymous
November 22, 2004 2:56:46 PM

Archived from groups: rec.audio.pro (More info?)

Bob Cain <arcane@arcanemethods.com> 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."
November 22, 2004 3:40:33 PM

Archived from groups: rec.audio.pro (More info?)

"Mike Rivers" <mrivers@d-and-d.com> wrote in message
news:znr1101129030k@trad...
>
> In article <cnrpfq02rdv@enews3.newsguy.com> arcane@arcanemethods.com
> writes:
>
>> 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.
>
> Another argument about a word, eh? Strike "very" and we'll just say
> they're different. How's an SM57 different from an RE11? They're just
> different - they both work on the same principle, but they have
> different elements and are mounted in different cases, and they just
> sound different. Some people would say "very different," some would
> just say "different," and others wouldn't care even if they recognized
> the difference.
>
> The new Radio Shack boundary mics compared to the original ones look
> different, they have different capsules, they have different
> electronics. They have flat plates, they pick up sound in roughly a
> hemispherical pattern, and they use a battery for power, so yeah, I
> guess they're not so different after all.
>
> The point is that the old Radio Shack PZM was actually a fairly useful
> mic for things that you'd use a PZM for (which is far from
> "everything"). The new ones have zero reputation around here so I see
> no reason to recommend using them, or even modifying them. But there's
> no reason why someone shouldn't experiment if he has the time, the
> money, and most important, the means to evaluate the effect of the
> modification.
>
>> 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 sounds to me like they're questioning the
> validity of Ed Long's original work in designing this microphone
> configuration. 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.
>
>> 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.
>
>
> --
> I'm really Mike Rivers (mrivers@d-and-d.com)

Actually it would be fun to try, but you are correct. i know there are no
perfect solutions, but im just trying to save some dough, and thought i'd
stumbled onto something.
-alan
November 22, 2004 7:43:13 PM

Archived from groups: rec.audio.pro (More info?)

"Scott Dorsey" <kludge@panix.com> wrote in message
news:cnt5oe$r19$1@panix2.panix.com...
> Bob Cain <arcane@arcanemethods.com> 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."

i called Rick, the fellow selling a kit for the mod and he explained to me
the difference between the mic elements and the surfaces. i also told him
about this conversation and he said he doesnt like the newsgroups because
the signal to noise ratio is too high! lol.
i bought the kit so that i can try it for fun, it's not too expensive. i'll
compare the before and after by miking something weird like a didgeridoo or
something with lots of harmonics or maybe just a sweeping sine wave and post
the results.
-alan
Anonymous
November 23, 2004 12:33:05 AM

Archived from groups: rec.audio.pro (More info?)

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
Anonymous
November 23, 2004 12:46:08 AM

Archived from groups: rec.audio.pro (More info?)

Scott Dorsey wrote:
> Bob Cain <arcane@arcanemethods.com> 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
Anonymous
November 23, 2004 12:32:55 PM

Archived from groups: rec.audio.pro (More info?)

Bob Cain <arcane@arcanemethods.com> wrote:
>Scott Dorsey wrote:
>> Bob Cain <arcane@arcanemethods.com> 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."
Anonymous
November 23, 2004 6:36:02 PM

Archived from groups: rec.audio.pro (More info?)

Mike Rivers wrote:
> In article <cnuhvm0ujr@enews2.newsguy.com> arcane@arcanemethods.com 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 bullshit.


> 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
Anonymous
November 24, 2004 8:06:33 AM

Archived from groups: rec.audio.pro (More info?)

On Tue, 23 Nov 2004 15:36:02 -0800, Bob Cain
<arcane@arcanemethods.com> 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
Anonymous
November 24, 2004 8:06:34 AM

Archived from groups: rec.audio.pro (More info?)

Chris Hornbeck wrote:

> Is there any factor-of-two difference in the two arguments,
> or have I just been watching too many French movies lately?

Not a difference. You get it either way.


Bob
--

"Things should be described as simply as possible, but no
simpler."

A. Einstein
November 24, 2004 1:55:07 PM

Archived from groups: rec.audio.pro (More info?)

In article <co0hh202cmm@enews4.newsguy.com>, arcane@arcanemethods.com
says...
> 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.

Forgive my ignorance, but isn't the point of it being that
very little direct sound enters the capsule at all? Isn't that
why it's inside that arm? All the sound it hears is a reflection
from the boundary, correct? I know some small amount will actually
come in, but it should be miniscule compared to the reflected sound.
I have two of them that I've modified back-to-back on a sheet of
plexiglass; I use them for drum overheads, and they are clean and
detailed. A check with my software reveals a bit of top-octave
rise, but not a lot, and it's pretty smooth (about 4dB by the top
of its range, around 20KHz).
---Michael (of APP)...
Anonymous
November 24, 2004 7:23:15 PM

Archived from groups: rec.audio.pro (More info?)

Bob Cain 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.

Here's more information on that:


The Acoustical Behavior of Pressure-Responding microphones
Positioned on Rigid Boundaries - a Review and Critique

Stanley P. Lipshitz and John Vanderkooy

AES Preprint 1796 (1981 May)

Abstract
Pressure-responding microphones have occasionally been
placed on rigid boundaries for recording purposes, and
indeed there is merit in this idea. A new type of
microphone, called the "pressure zone microphone", has
recently been introduced for this purpose. This microphone
obscures the diaphragm from receiving any direct sound by
pointing it towards the rigid boundary, in the mistaken
belief that, were it pointing forwards, it would display the
on-axis high-frequency rise characteristic of such
microphones when used free-field. It is shown that this is
not true, and that, for a given capsule size, the frequency
and polar responses are significantly degraded by obscuring
the diaphragm. Conversely, for a given frequency and polar
response tolerance, a larger diaphragm, giving lower
self-noise, could be used for a non-occluded design. We
present both experimental data and a theoretical model to
verify our contentions.

Conclusion:
A small (less than 0.5 in diameter) pressure-calibrated
microphone mounted flush with a large rigid boundary
exhibits almost perfect frequency and polar responses over
the entire audio band. Placing an obstruction between its
diaphragm and the incident sound degrades both aspects of
performance. In order to regain acceptable performance, such
an obscured microphone must resort to a substantially
smaller diaphragm size with the attendant deterioration in
its self-noise.

--

"Things should be described as simply as possible, but no
simpler."

A. Einstein
Anonymous
November 25, 2004 8:41:57 PM

Archived from groups: rec.audio.pro (More info?)

"Bob Cain" <arcane@arcanemethods.com> wrote in message
news:co38lh01ho7@enews3.newsguy.com...
>
>
> Bob Cain 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.
>
> Here's more information on that:
>
>
> The Acoustical Behavior of Pressure-Responding microphones
> Positioned on Rigid Boundaries - a Review and Critique
>
> Stanley P. Lipshitz and John Vanderkooy
>
> AES Preprint 1796 (1981 May)
>
> Abstract
> Pressure-responding microphones have occasionally been
> placed on rigid boundaries for recording purposes, and
> indeed there is merit in this idea. A new type of
> microphone, called the "pressure zone microphone", has
> recently been introduced for this purpose. This microphone
> obscures the diaphragm from receiving any direct sound by
> pointing it towards the rigid boundary, in the mistaken
> belief that, were it pointing forwards, it would display the
> on-axis high-frequency rise characteristic of such
> microphones when used free-field. It is shown that this is
> not true, and that, for a given capsule size, the frequency
> and polar responses are significantly degraded by obscuring
> the diaphragm. Conversely, for a given frequency and polar
> response tolerance, a larger diaphragm, giving lower
> self-noise, could be used for a non-occluded design. We
> present both experimental data and a theoretical model to
> verify our contentions.
>
> Conclusion:
> A small (less than 0.5 in diameter) pressure-calibrated
> microphone mounted flush with a large rigid boundary
> exhibits almost perfect frequency and polar responses over
> the entire audio band. Placing an obstruction between its
> diaphragm and the incident sound degrades both aspects of
> performance. In order to regain acceptable performance, such
> an obscured microphone must resort to a substantially
> smaller diaphragm size with the attendant deterioration in
> its self-noise.

All of this is true. The diameter of an RS PZM is closer to 1/4",
and the self noise is indeed higher. But much of the increased self
noise is reduced by the 6db increase in sensitivity due to the
pressure zone.

Norm Strong
Anonymous
November 25, 2004 8:41:58 PM

Archived from groups: rec.audio.pro (More info?)

normanstrong wrote:

> All of this is true. The diameter of an RS PZM is closer to 1/4",
> and the self noise is indeed higher. But much of the increased self
> noise is reduced by the 6db increase in sensitivity due to the
> pressure zone.

Norm, that is due to being at the boundry rather than being
"pressure zone". A surface mounted omni will give the same
sensitivity increase without interfering with the response
or directivity.


Bob
--

"Things should be described as simply as possible, but no
simpler."

A. Einstein
Anonymous
November 27, 2004 2:34:43 AM

Archived from groups: rec.audio.pro (More info?)

Bob Cain <arcane@arcanemethods.com> wrote:

> I can't see how the PZM configuration offers anything positive
> compared to a single omni at that position.

I'll give you 3 reasons :

1) They are hemispherical, not omni, which may be the desired pattern.

2) They are low profile. You can place them on a conference table and
they won't be in the sight of anyone.

3) The timber (color of the sound, tone, whatever you want to call it)
of the sound is constant whatever the distance of the source.

I frequently use PZMs on the lip of the stage when videotaping theater
performances. The mics are invisible from the public perpective and
will provide a perfect balance between on-stage and audience sound. The
fact the sound is constant (in timber, not volume!) whether the
comedians are close or far from the mics is an outstanding and desirable
characteristic for this application. You just need to ride the faders
and/or use an AGC or compressor.

PS : I kinda work at the bottom of the chain, quality-wise, so YMMV! :) 

PS2 : Placing them on a soft but thin material is usefull to isolate
them from the surface they are on, to avoid floor noise.

Regards,
--
Eric (Dero) Desrochers
http://homepage.mac.com/dero72

Hiroshima 45, Tchernobyl 86, Windows 95
December 5, 2004 3:58:56 PM

Archived from groups: rec.audio.pro (More info?)

"alan" <.@.> wrote in message news:p fadne4FuYQq0z_cRVn-qw@comcast.com...
>
-snip-

wow that mic is a POS! not even worth doing tests on. i took it back to RS.
i would have liked to do more with it but got busy with less important
things :)  hey thanks everyone for your expert input *bow-grovel-grovel*
-OP alan
!