Mic cage designs for acoustics

[shaund]

Hi all - an idea I've been toying with is whether or not you could 3d print acoustically useful inserts for the inside of a mic cage. I'm thinking something that would cause diffusion in the 7k range (might, for example, smooth out some sibilance if it was caused by acoustical resonance within the cage - not sure that's really a thing.) 7k is about 1.9" in terms of wavelength size; you would have to build a diffuser (probably 2d like a mini skyline, though never seen that done) that has a max depth of about 1/2" to address the quarter wavelength of 7k.

 

Also, maybe a 1/2" of absorption on either side would change the sound in the sibilance region? I'll attach a drawing I made the other day by way of visual explanation. (Scale is wrong - if that's a 1" capsule, then the diffusion marked in blue is not deep enough.)

 

Anyhow - the idea kind of reminds me of Josephson's metal foam grill on the C715.

 

Think something like this would work? If it wouldn't be audible, anybody have theoretical grill designs / basket designs that you think WOULD affect the sound of the capsule?

 

[Dr Mike Metlay]

If you can 3D print one and mess around with it, why not? But anyone who's worked with the insides of mics can tell you that pretty much everything inside the headbasket matters to the capsule, for good or ill. That foamed-metal grille on the Josephson mics is sturdy enough so the mic doesn't need a headbasket frame, so there aren't any acoustic shadows against the capsule. Which was sort of the point - the foam bubbles are random in placement and size, which results in a very transparent cover for the capsule that is nevertheless very sturdy.

 

Resonances within mic enclosures are very much a thing, and most capsule designs are tweaked so that the big resonances promote frequencies that the designers want to boost. That's one of many reasons overseas pirates imitate the size and shape of Neumann bodies and headbaskets so closely.

 

I'm pretty sure Matt can weigh in with more real data and correct me if I've said something way off base.

 

mike

 

[matthew mcglynn]

Everything Mike said is true, in my experience. I can add that I've seen mics whose circuits are changed to account for acoustic EQ effects of the grille. Great microphones are truly the result of great design, where the capsule and circuit and enclosure all work together to create the desired sound.

 

My personal sense is that the microphone would have to be as big as a football to give you enough space to have even a miniature version of a quadratic residue diffusor ( ) inside the grille. Sure, you could print something smaller, but would it be effective at a frequency you can actually hear?

 

Regarding the piece hovering over the capsule, I think you'd be better off with a piece of metal mesh, so as to minimize the reflection rather than scatter it back into the capsule. That is, let the sound escape rather than trying to control how it bounces.

 

Al those reasons explain why I have not already done the very experiment you propose. I've considered it. We've sketched capsule mounts with grooves in them. We've covered the deck plate with various foam layers and arbitrarily sized chunks. We haven't found anything that is both practical to make, and effective. There are other factors that are easier to control that often have a bigger effect. YMMV, though, so if you get some results, please share.

 

On a related note, I hired a drywall guy a couple years ago when I was building my studio. He told me that a former client had asked him to put a really thick coating of mud on the walls, with a lot of variation in depth, in order to act like a full room-sized diffusor. It seemed like a really cool idea. But in practice, drywall mud that varies in depth more than about 1/4'' is going to look awful, be a nightmare to paint and to keep clean, and possibly won't be structurally sound (e.g. big chunks might cleave off if you knock into the wall). And its effective diffusion frequency is about 28kHz -- quite a bit higher than useful.

 

 

[shaund]

Hey Matt - very interesting that you've already experimented with sounds absorption and diffusions in the cage. In terms of frequencies you can address with absorption, 1/4 wavelength of 3.5Khz is about 1". Given this, if you simply took a "long" cage and added 1" of OC703 to the top and bottom, seems like you would dampen resonance of the mic cage from 3.4k up quite a bit. Of course, it's taking up a lot of real estate in the cage (1" for absorption at the top, whatever the gap is to the capsule, the capsule diameter, more airspace, 1" at the bottom).

 

In terms of the the size needed for diffusion, I think you can scale it down using something like www.subwoofer-builder.com/qrdude.htm (that's what I've used in the past.) If you change the well width lower than the minimum recommended, I don't think it works as well... but it still works somewhat. I was thinking of 3d printing the output of a QRDude schematic, essentially.

 

What mic cage absorption / diffusion experiments have you done, and did you hear anything? If you were going to try something else in the future, what would it be? (ie. what areas of research in physical mic cage design do you think are interesting to pursue?)