Topic: Mounting mics (CA-14s) on a flat surface?

[BradM]

I'm thinking of trying my CA-14s (cardioid) at a pub which doesn't really have a good place to set up a stand, but it does have a bulkhead running across the width of the bar, parallel to the front of the stage. My plan is to masking-tape some bits of cardboard to the bulkhead and clip the mics to it, but I'm concerned that there might be an issue with having them so close (within 1") to a flat surface rather than having them out in mid-air all on their own. Am I right to be concerned?

Thanks,
Brad

[ScoobieKW]

What you are talking about is called boundary micing. Works best with omni capsules.

Instead of cardboard, try something absorbent, mousepad or towel between the wood and the mic.

(edit) I see that you have cardioids. In this case, I'd McGuyver a bracket. Something you can gaff tape to the bulkhead that allows your mics to point forward towards the stage, the lack of space behind the mic works to your advantage as the sound reflections from the bulkhead will arrive almost simultaneously to the direct sound. This combats the slapback echo many smaller clubs have.

Would love to hear how it turns out.

[to_taper]

Can you please add a little more detail to your suggestion? Pease pardon my ignorane, but I don't know what it means to mcguyver a bracket.

Thanks,

John

[ScoobieKW]

McGuyver was an american tv character who could improvise anything with the contents of his pocket and a swiss army knife.

So I'd grab the cardboard and some tape, and see what I could cobble together. The key is making sure your mics are pointed at the music source with an angle for stereo separation. DIN, XY, ORTF depending on placement.

[to_taper]

Thanks. I obviously didn't watch enough TV.

[Gutbucket]

Probably more that you want to know but here you go-

As a general rule you want to place mics so as to eliminate reflections off nearby surfaces.  You can do that in several ways- the most obvious is placing them far away from all reflecting surfaces.  Other choices are using the directivity of the mic to reduce pickup of reflections by orienting the microphone so its direction of minimum sensitivity points toward the direction of the reflection.  For a cardioid pattern mic that minimal sensitivity direction is directly to the rear of the mic.  A third option is placing them very, very close to the surface, preferably flush with it.  That’s the boundary-mounting thing which is less complicated to do with omnis and difficult with directional mics which need the vents on the rear side of their diaphragm to be unobscured for correct operation.
 
The best bet for cardioids is getting them far enough away from other stuff so they work right.  Your best bet in this situation may be affixing a wire or rod or something to the bulkhead (coat hanger wire might work) so the mics are mounted a foot or two above it in open air.  Direct reflections off the bulkhead surface should be mostly directed forward, not up.  You could also make the support arm project forward from the bulkhead and rely on the rear rejection of the mics.  In that case, farther away is better, if you can’t get them very far, then using more spacing between mics to allow less angle between them so their low sensitivity region points directly towards the surface behind might help, but you will need some ‘breathing space’ for the vents and cardioid pattern to work correctly.

Omnis are more applicable to mounting directly to a surface (boundary mounting) and might actually be a better choice in this case if you have a pair.  When placed directly on the surface they will no longer be omni-directional, but hemispherical, with the pattern extending perpendicularly from the surface- which behaves sort of like a cardioid pickup pattern facing away from the wall.  Besides being easy to mount that way (space them apart and gaff tape them to the wall), there are other advantages which boundary mounting provides. If you have omnis, try it.  This situation sounds like a perfect one for it.

If your bulkhead is wall-like with a flat top edge and a square corner edge between the front and top surfaces, you may be able to mount your cardioid mics in a spaced A-B configuration (the typical omni configuration- spaced apart but pointing directly forward) by gaff taping them directly to the top edge so that the front face of the capsule is effectively flush with the front of the bulkhead, yet the vents in the mic body are still open and unblocked- they would only be blocked along the tangential line were the capsule contacts the top surface.  You’d need to be careful not to block them with the tape.  That will semi-boundary-mount them and avoid delayed reflections off the surface by getting them as close to the surface as possible, and point them in the right direction.  It has a decent chance of working in this case because of the edge mounting situation.. Can't guarantee it will work but should be easy to do and worth a try.  Closer together with a bit of angle might work too as long as the face of the capsules is pretty much flush with the front of the bulkhead.

Cardioids can not be boundary mounted to the center of a surface so their pattern extends perpendicular to it like omnis, but small ones can sometimes be successfully attached to a surface so they point across it.  Instead of the hemispherical pattern a boundary mounted omni would have, that creates a half-cardioid shape favoring the direction in which the mic is pointing.  Some directional boundary mounted directional mics from AT and Crown work that way but they are specially designed to do so.  But that wouldn’t work in this case because the half-cardioid pattern would be pointing 90 degrees away from the stage.

[ScoobieKW]

What he said.

[to_taper]

Extremely helpful for a new CA-14 owner.

Many thanks,

John

[Gutbucket]

Glad to help, & welcome to the club, John.

[Church-Audio]

Probably more that you want to know but here you go-

As a general rule you want to place mics so as to eliminate reflections off nearby surfaces.  You can do that in several ways- the most obvious is placing them far away from all reflecting surfaces.  Other choices are using the directivity of the mic to reduce pickup of reflections by orienting the microphone so its direction of minimum sensitivity points toward the direction of the reflection.  For a cardioid pattern mic that minimal sensitivity direction is directly to the rear of the mic.  A third option is placing them very, very close to the surface, preferably flush with it.  That’s the boundary-mounting thing which is less complicated to do with omnis and difficult with directional mics which need the vents on the rear side of their diaphragm to be unobscured for correct operation.
 
The best bet for cardioids is getting them far enough away from other stuff so they work right.  Your best bet in this situation may be affixing a wire or rod or something to the bulkhead (coat hanger wire might work) so the mics are mounted a foot or two above it in open air.  Direct reflections off the bulkhead surface should be mostly directed forward, not up.  You could also make the support arm project forward from the bulkhead and rely on the rear rejection of the mics.  In that case, farther away is better, if you can’t get them very far, then using more spacing between mics to allow less angle between them so their low sensitivity region points directly towards the surface behind might help, but you will need some ‘breathing space’ for the vents and cardioid pattern to work correctly.

Omnis are more applicable to mounting directly to a surface (boundary mounting) and might actually be a better choice in this case if you have a pair.  When placed directly on the surface they will no longer be omni-directional, but hemispherical, with the pattern extending perpendicularly from the surface- which behaves sort of like a cardioid pickup pattern facing away from the wall.  Besides being easy to mount that way (space them apart and gaff tape them to the wall), there are other advantages which boundary mounting provides. If you have omnis, try it.  This situation sounds like a perfect one for it.

If your bulkhead is wall-like with a flat top edge and a square corner edge between the front and top surfaces, you may be able to mount your cardioid mics in a spaced A-B configuration (the typical omni configuration- spaced apart but pointing directly forward) by gaff taping them directly to the top edge so that the front face of the capsule is effectively flush with the front of the bulkhead, yet the vents in the mic body are still open and unblocked- they would only be blocked along the tangential line were the capsule contacts the top surface.  You’d need to be careful not to block them with the tape.  That will semi-boundary-mount them and avoid delayed reflections off the surface by getting them as close to the surface as possible, and point them in the right direction.  It has a decent chance of working in this case because of the edge mounting situation.. Can't guarantee it will work but should be easy to do and worth a try.  Closer together with a bit of angle might work too as long as the face of the capsules is pretty much flush with the front of the bulkhead.

Cardioids can not be boundary mounted to the center of a surface so their pattern extends perpendicular to it like omnis, but small ones can sometimes be successfully attached to a surface so they point across it.  Instead of the hemispherical pattern a boundary mounted omni would have, that creates a half-cardioid shape favoring the direction in which the mic is pointing.  Some directional boundary mounted directional mics from AT and Crown work that way but they are specially designed to do so.  But that wouldn’t work in this case because the half-cardioid pattern would be pointing 90 degrees away from the stage.

Shure SM91 BETA 91 Phase coherent cardioid mic works on this principle quite nicely but it is not a very flat sounding mic.

[Gutbucket]

Phase coherent cardioid

That's the term I was trying to remember!  Couldn't remember what it was called.

Thanks Chris.. and appologies for the suggestion of attaching your mics with gaffer tape! 

[Church-Audio]

Phase coherent cardioid

That's the term I was trying to remember!  Couldn't remember what it was called.

Thanks Chris.. and appologies for the suggestion of attaching your mics with gaffer tape! 

lol no problem. The Shure sm91 simply uses a brass strap to strap the capsule down to the surface. It does not have any shock mount instead relying on rubber feet and a super heavy metal plate to reduce vibrations into the capsule. The capsule it self is around $120 each to replace and when not mounted on the metal plate actually sounds quite nice. Its a three wire goldplated diaphram capsule 10 mm or 12 mm I cant remember the exact size.