Topic: baffle questions

[dmaster]

So, I'm not sure if this has ever been discussed or considered or anything, but I'm wondering how to perhaps "optimize" omni mics in a small-venue club setting where crowd noise may be a signficant problem. 

I seem to be able to tape an above-average number of rock bands that allow taping lately (and plenty of them are nice if you just ask), but almost all of the shows I see are in small venues where the crowd noise is significant, and often times I'm stuck in a specific spot if I'm clamping or using a stand.   It's getting to the point that I seriously am frustrated with a lot of my recordings when two people get together and start talking near my stand and they're louder than the music but I can't manage to shut them up. 

I'd like to in some way "isolate" the mics, so that they pick up more sound of the band, than the sounds "below" them.   Understandably with omni's this is not the "natural" setup, but my mics are DPA 4061's until I get a lot more money to buy a set of open cards and a preamp.   It's probably not going to happen any time soon, so I'd like to try and maximize the results of the mics I have, rather than hear suggestions on "you should be using cardioid mics if you want to avoid the crowd noise". 

Now, with all that out of the way, has anyone even attempted to baffle or otherwise "directionalize" omni mics by in some way reducing the sound coming from a particular direction?    With miniature mics the size of the DPA's, is there any sort of suggestion on the size of such a contraption?    Ideally, I'd like to  (assuming this makes any sense to anyone but me) reduce the volume of the sounds coming from below and behind the mic stand, but let everything above and in front come in loud and clear.    Essentially turning the 360 degree pattern of an omni mic, into something more of a 180 degree but not entirely blocking out the sound altogether. 

I'm using a j-disc right now, and I definitely notice a distinct sound difference.  Would the same sort of baffle underneath the mics cause a similar sort of restriction of sound?     My half-assed idea at the moment is to chop a tennis ball in half, fill it with foam and mount the mics on the tennis balls, and attach the tennis balls to the j-disc.    I'm thinking unfortinately that this may be too insignificant of a barrier to noise. 

Am i wasting my time here, or is this worth perhaps messing around with some materials and seeing if I can get any significant results? 

[RebelRebel]

a number of different manufacturers (schoeps has the Ka40 and 50) make spherical isolation units that serve to give omnidirectionals more directionality and focus. sounds like what you are trying to accomplish.  It wont turn an omni into a "true" cardiod, but will serve to provide more directivity of high frequencies, and also will provide greater clarity in diffuse field miking situations. The great thing with the sphere mounts is that all of the great low end extension is preserved, so one gets the LF of omnis, but the directionality of cardiods.

So, I'm not sure if this has ever been discussed or considered or anything, but I'm wondering how to perhaps "optimize" omni mics in a small-venue club setting where crowd noise may be a signficant problem. 

I seem to be able to tape an above-average number of rock bands that allow taping lately (and plenty of them are nice if you just ask), but almost all of the shows I see are in small venues where the crowd noise is significant, and often times I'm stuck in a specific spot if I'm clamping or using a stand.   It's getting to the point that I seriously am frustrated with a lot of my recordings when two people get together and start talking near my stand and they're louder than the music but I can't manage to shut them up. 

I'd like to in some way "isolate" the mics, so that they pick up more sound of the band, than the sounds "below" them.   Understandably with omni's this is not the "natural" setup, but my mics are DPA 4061's until I get a lot more money to buy a set of open cards and a preamp.   It's probably not going to happen any time soon, so I'd like to try and maximize the results of the mics I have, rather than hear suggestions on "you should be using cardioid mics if you want to avoid the crowd noise". 

Now, with all that out of the way, has anyone even attempted to baffle or otherwise "directionalize" omni mics by in some way reducing the sound coming from a particular direction?    With miniature mics the size of the DPA's, is there any sort of suggestion on the size of such a contraption?    Ideally, I'd like to  (assuming this makes any sense to anyone but me) reduce the volume of the sounds coming from below and behind the mic stand, but let everything above and in front come in loud and clear.    Essentially turning the 360 degree pattern of an omni mic, into something more of a 180 degree but not entirely blocking out the sound altogether. 

I'm using a j-disc right now, and I definitely notice a distinct sound difference.  Would the same sort of baffle underneath the mics cause a similar sort of restriction of sound?     My half-assed idea at the moment is to chop a tennis ball in half, fill it with foam and mount the mics on the tennis balls, and attach the tennis balls to the j-disc.    I'm thinking unfortinately that this may be too insignificant of a barrier to noise. 

Am i wasting my time here, or is this worth perhaps messing around with some materials and seeing if I can get any significant results? 

[Gutbucket]

One way of effecively 'directionalizing' your 4061's is to use them as boundry layer mics.  Crown is generally credited with developing this technique with their PZM mics, although many manufacturers offer 'boundry layer' condensers now.  In fact DPA sells little boundry layer mounts specifically for the 4061's. 

They all work by placing the capsule very close to a surface, so close that comb filtering effects from relections off the surface are driven up into the ultrasonic range.  The sound pressure level at the mic is increased for sound sources perpendicular to the boundry.  The SPL of such sources is doubled at the mic.  So the sensitivity of the mic (and s/n ratio) is increased by 6db for direct sources, but incoherent sources (reverberation off axis) is increased by only 3db.  Sources behind the boundry are much more attenuated due to the baffle effect. 

The typical applications for boundry mics are placement on the back wall, stage floor, attached to the lid of a piano, conference tables, etc.  The main drawback for our applications is that you need to mount the mics on a large surface.  The larger the surface the lower the 6db reinforcement cutoff. An infinite boundry would have a flat requency response increase.  This is often not very convenient for section or club taping since you'd ideally be mounting large flat surfaces for your mics.  It's been done and great results can be had by mounting omni mics flush to the surface of two pieces of hinged plexiglass.  The hinge allows the recording angle to be changed, and the plexiglass is at least transparent.  This becomes similar to a jeckiln disk in some ways, except the mics are flush, the surface is hard and smooth instead of fuzzy and the surfaces  are larger and angled toward the source.  I'm going to try taping my 4060 mics to the mirrored back wall of a local venue, were the sound board is up against the back wall and the tape section directly in front.  Mounting the mics this way sould actually make the omni characteristics work better in this small club by increasing the direct/reverberant ratio and eliminating the bounce back from the highly reflective back wall (or rather, using it to advantage).  I'll try a simple spaced A/B pair first, then maybe get a little more complex, like placing them much closer together and putting a jecklin baffle in between them.

Take a look at this document from Crown: http://www.crownaudio.com/pdf/mics/127089.pdf

It explains how to use their PZM mics and shows all kinds of boundry setups that you can build if you can get away with mounting something like them!  At the very least it's a great way to understand the concepts.  Illustrated are simple V-shaped boundries, complex W-shaped, pyramid shaped and other crazy forms that increase the direct sound by 18db in some cases.  It also goes into detail about how and why the boundry method works with lots of technical detail about frequency response and polar characteristics.

The sperical isolation units Teddy mentions are actually a subset of this boundry techique.  They act primarily on the higher freqency range because of the limited surface area of the sphere.  Increasing the size of the sphere lowers the effective frequency where the increased directionality and focus taper off towards the standard response of the mic.  Smaller spheres create a rising high frequency response that can be helpful in the diffuse field.  They are buit in to the Neuman M150 that the Decca tree setup was built around.

Interesting ideas, this stuff.  Hope this helps more than confuses!

[RebelRebel]

too bad that crown's mics sound like garbage.   

One way of effecively 'directionalizing' your 4061's is to use them as boundry layer mics.  Crown is generally credited with developing this technique with their PZM mics, although many manufacturers offer 'boundry layer' condensers now.  In fact DPA sells little boundry layer mounts specifically for the 4061's. 

They all work by placing the capsule very close to a surface, so close that comb filtering effects from relections off the surface are driven up into the ultrasonic range.  The sound pressure level at the mic is increased for sound sources perpendicular to the boundry.  The SPL of such sources is doubled at the mic.  So the sensitivity of the mic (and s/n ratio) is increased by 6db for direct sources, but incoherent sources (reverberation off axis) is increased by only 3db.  Sources behind the boundry are much more attenuated due to the baffle effect. 

The typical applications for boundry mics are placement on the back wall, stage floor, attached to the lid of a piano, conference tables, etc.  The main drawback for our applications is that you need to mount the mics on a large surface.  The larger the surface the lower the 6db reinforcement cutoff. An infinite boundry would have a flat requency response increase.  This is often not very convenient for section or club taping since you'd ideally be mounting large flat surfaces for your mics.  It's been done and great results can be had by mounting omni mics flush to the surface of two pieces of hinged plexiglass.  The hinge allows the recording angle to be changed, and the plexiglass is at least transparent.  This becomes similar to a jeckiln disk in some ways, except the mics are flush, the surface is hard and smooth instead of fuzzy and the surfaces  are larger and angled toward the source.  I'm going to try taping my 4060 mics to the mirrored back wall of a local venue, were the sound board is up against the back wall and the tape section directly in front.  Mounting the mics this way sould actually make the omni characteristics work better in this small club by increasing the direct/reverberant ratio and eliminating the bounce back from the highly reflective back wall (or rather, using it to advantage).  I'll try a simple spaced A/B pair first, then maybe get a little more complex, like placing them much closer together and putting a jecklin baffle in between them.

Take a look at this document from Crown: http://www.crownaudio.com/pdf/mics/127089.pdf

It explains how to use their PZM mics and shows all kinds of boundry setups that you can build if you can get away with mounting something like them!  At the very least it's a great way to understand the concepts.  Illustrated are simple V-shaped boundries, complex W-shaped, pyramid shaped and other crazy forms that increase the direct sound by 18db in some cases.  It also goes into detail about how and why the boundry method works with lots of technical detail about frequency response and polar characteristics.

The sperical isolation units Teddy mentions are actually a subset of this boundry techique.  They act primarily on the higher freqency range because of the limited surface area of the sphere.  Increasing the size of the sphere lowers the effective frequency where the increased directionality and focus taper off towards the standard response of the mic.  Smaller spheres create a rising high frequency response that can be helpful in the diffuse field.  They are buit in to the Neuman M150 that the Decca tree setup was built around.

Interesting ideas, this stuff.  Hope this helps more than confuses!

[Gutbucket]

Good reason to use the DPA's instead!    Never tried any Crown mics, myself.

[Gutbucket]

Sounds like SparkE! is doing something like what you're talking about check out:
http://taperssection.com/index.php?topic=60802.60 page 5. He mentions reducing the noise behind the mics with his angled pseudo jecklin baffle.

[BayTaynt3d]

Sounds to me if this is your primary taping environment that you should seriously consider getting a set of cards, if not hypers.

[dmaster]

Sounds to me if this is your primary taping environment that you should seriously consider getting a set of cards, if not hypers.

I completely agree and I'm going to in the future.   However, I don't have the cash to drop on new mics and a preamp at the moment.   I can however take stuff that would be garbage from work and hack it into something useable if necessary to make the most out of what I have until I get a spare chunk of change.    

I think I'm gonna try and experiment with some stuff in the near future and see what I can get out of it.   No matter what I do, it can hardly be as bad as a few of my recent recordings, so I'm pretty optimistic if I can make anything at all happen. 

[RebelRebel]

or just record acoustic music in halls made for concerts, and you wont have that problem.

Sounds to me if this is your primary taping environment that you should seriously consider getting a set of cards, if not hypers.

I completely agree and I'm going to in the future.   However, I don't have the cash to drop on new mics and a preamp at the moment.   I can however take stuff that would be garbage from work and hack it into something useable if necessary to make the most out of what I have until I get a spare chunk of change.    

I think I'm gonna try and experiment with some stuff in the near future and see what I can get out of it.   No matter what I do, it can hardly be as bad as a few of my recent recordings, so I'm pretty optimistic if I can make anything at all happen.