String Quartet with a PZM

[JustAnotherUser]

So, the Audubon 4tet is completing their Beethoven cycle, and I'm recording the concert. I want to try something new, for once. I will, of course, use a stereo technique I'm familiar with, but I want to set this up for fun. So... is it possible to create a boundary mic by just placing an omni on the floor of the stage. Anybody tried this? I'm thinking a spaced pair, but if something else will work better... I've got a couple different omnis available to me. If any of them would work, will the true omni be better than a variable pattern mic with an omni mode? I'm asking because I don't have a PZM at my disposal but want to try a boundary mic setup, anyway.

Just looking for advice and seeking the experience of those wiser than I.

Thanks

[JustAnotherUser]

To be a little more specific, how would you use a KSM44 or a KM184 as a boundary mic, or could you even do it?

[pkautzsch]

It *is* technically possible. I guess it's better to use a pressure mic if you want omni, but I've also used cardioids. Basically it's taping them to the floor and making sure nobody steps on them.
KM184 will give you a very nice cello sound if placed about 3ft in front of the cello. Violins and viola sound a bit uncommon, though.
If you don't have the audience problem, and a reflective ceiling, you can place them quite a bit farther out than you'd place a "standard" main pair, and they will sound quite nice. And it seems PZMs give less spread, so you can space them wider.

[Uncle Russ]

As I understand PZM construction, the capsule face is a specific fixed distance from a reflective surface, whether a floor, a Plexigas plate, or something else. If that is correct, then taping a cardioid mic to the floor might pick up some reflected sound but also would pick up direct sound. Hence, the result would not be a true pressure zone mic.

Right or wrong? And, in practice, does it matter? (I would think it should.) And please explain in simple English; I'm not a physicist.

[fifthcircle]

I've done this accidently- left a DPA 4006 on the floor during a sound check while I was switching mics out. Sounded pretty good- similar pickup to a traditional PZM, but with a MUCH better sound. I would imagine that doing the same with a cardiod mic would give you something similar to a PCC-160 or a CUB-1. A directional floor mount mic.

I've used CUB-1's in recordings before with mixed results. Definitely prefer it to a PCC-160, but the pickup is a bit strange sometimes. After all, you're basically picking up the floor reflections with a bit more direct sound. Sometimes it is ok, but much of the time, it really is lacking (especially I find with string instruments). It is passable with cello, but not a huge fan otherwise.

--Ben

[Don S]

Originally Posted by fifthcircle

I've done this accidently- left a DPA 4006 on the floor during a sound check while I was switching mics out. Sounded pretty good-.

Definitely prefer it to a PCC-160, but the pickup is a bit strange sometimes.
--Ben

I've been recording in very old theaters where I had to put omnis on "desk" stands on the lip of the stage and the mains about 30 feet back. When time aligned, they sounded just fine. Since there was low end with presence, it was a good solution.
I had a chance to carefully listen to the PCC160. It has LOTS of self noise! I was very surprised. A cheap Octava had much better S/N ratio.

[pkautzsch]

Originally Posted by Uncle Russ

As I understand PZM construction, the capsule face is a specific fixed distance from a reflective surface, whether a floor, a Plexigas plate, or something else. If that is correct, then taping a cardioid mic to the floor might pick up some reflected sound but also would pick up direct sound. Hence, the result would not be a true pressure zone mic.

Right or wrong? And, in practice, does it matter? (I would think it should.) And please explain in simple English; I'm not a physicist.

The theory behind all approaches to mics placed on surfaces is that in close proximity to a reflective surface you get 6 dB higher SPL level, and reflected sound doesn't have less treble than direct sound. The few centimeters in front of the surface are called "pressure zone" - so basically all you have to do is place your mic in this pressure zone.
To do so you could either
a. simply tape a mic to the surface. This is the ad-hoc solution, and it's basically what Sennheiser do with their E 901 bass drum mic (except that they don't simply tape it, but put it into a housing). It's the only way to make directional surface mics.
b. put up the mic in a way it faces the surface, and has a little gap between surface and diaphragm. That's what Crown basically do. This will pick up mostly reflected sound, plus a little direct sound "bent" around the mic body (mainly treble - wavelengths about as long as mic diameter)
c. put the diaphragm into the surface. That's what Schoeps and Neumann do.

The larger the surface, the lower the frequencies affected by pressure zone effect.
If you only use a small "surface" around the diaphragm, you're going towards the Neumann M 50 principle (which used plexiglas balls - DPA has a similar thing called APE "acoustic pressure equalizer" to use with their 4006 omnis).

[JustAnotherUser]

So taping a mic to a surface (like a stage) will not affect its frequency response?