free field vs diffuse field omnis

[noetic]

hi all. nice to find this forum and participate. appreciate the overt reminder that ignorance and stupidity aren't identical.

my basic understanding is:

free field: flat freq. response, better suited for close miking.
diffuse field: (slightly) exaggerated high end, better suited for distance miking..

is that a fairly accurate summary?

if you could have only one omni to cover both close miking and overhead/room mic duties, which type would you probably prefer (acknowledging that there's likely to be significant tonal variety among omnis of the same type)?

also, if not labelled one or the other, is an omni more likely to be free field or diffuse?

thanks in advance for straightening me out,

noetic

[seaneldon]

Free-field is when the direct sound "outweighs" the reverb/ambiance of the recording space, ie. closer to the source. You enter the diffuse-field when you get the mic back far enough so the ambiance "outweighs" the direct sound.

Some mic manufacturers do make different versions of the same omnis for one application vs. the other. I personally prefer to have an omni that's flatter in frequency response, but then again I ain't doing classical recordings in huge halls so my needs are different from most people agonizing over pressure transducers...

[noetic]

hey sean, thanks for that.

looking at the freq plots for the avensons and the gefell m920s, it looks like the avensons are pretty flat while the gefells are optimized for diffuse field placement.

has that been your experience in working with them?

[seaneldon]

I've no experience with the M920's...do you have that model number correct? I know of the M930/940/950 which are large diaphragms and directional, and the M296 which is a small nickel diaphragm omni.

The Avensons are electret mics a la Earthworks...indeed they are flatter in frequency response and do appear "darker" when you pull them back. They are a little noisy (all electrets are) though quieter than the Earthworks stuff...but in quieter/more dynamic classical situations you'd probably have too much noise. I have put them in an equilateral triangle with the kick drum, on the floor, about 15 feet away with great success. They work fine with any moderate SPL recording.

[noetic]

yup, i botched the model number; i meant the m296. thanks for the insight. i'm pretty sure now i'm looking for flat omnis.

[Sweet.]

Sean, in your experiences, how do you like the STOs in a rock style recording, either as room mics, overheads, maybe even guitars?

I've been wanting a set of omnis up in my room, and I figured I'd pick up a set from Brad here in town if I heard good things.

[seaneldon]

The STO2's do fine for rock'n'roll where noisefloor is typically defeated by louder signals. As I said before I've used them on the floor as room mics for the drums quite a few times and have been pleased with the results. Their sound is quite "pure". Not an M296 by any stretch of the imagination but a great tool anyway.

I typically use directional microphones for overheads as I'm trying to knock down some bleed from the rest of the band, and because they're a little more forgiving in the stereo image department than omni mics are. If you have a pair of omnis over the drums and one of them is a just a little too close/far/left/right/whatever the center image can get pulled off to one side very easily. This doesn't happen as much with cardioid/figure-of-eight. The STO2's are good on acoustic guitars if the guitar itself is a good guitar. It won't make a small sounding guitar any "larger" the way an RCA 77DX or U47 does, for instance.

Give Brad a call and see if he'll let you try 'em out. If not, I know of at least one shop that does bthead