all my rowdy friends are over here...
 
I understand close micing, in principle and room micing in principle and I understand about getting phase problems from having two close mics but having one maybe a foot farther away than the other.
 
However I do not understand doing close micing and room micing and not having a problem. I could be totally in left field but I think that I read somewhere that once you get a certain distance away... that the delay is no longer an issue. It doesn't make sense to me so I thought I'd ask.
 
Also using a close mic on an acoustic guitar and a vocal mic. I suppose good unidirectional mics would be a great helps there and an omni for a room mic.... but I really don't know... so what do you think?
 
Most of my mics are condensers, except I have a cheap ADK and an SM-57.. next mic on my list is an SM7b (price is a consideration), unless someone has a better idea and I am very much open to suggestions. I want the SM7b for vocals and expecially for harmonies to keep from building up badness by using the same condenser too many times. I guess the SM-57 would work for backup vocals....
 
Anyway, before I ramble too long... what about the close/room thing? Is there a formula for distances?
 
Thanks!
 
J
 
 

Phase is not a problem when the microphones are far apart (relative to what's being miked) because the room sound is diffuse. A given frequency might still arrive at the room mic at a phase angle that causes destructive/constructive interference (comb filtering), but there will also be dozens of reflections of the same frequency arriving at various intervals and causing various amounts of both destructive and constructive interference.

The only formula I know of is a rough rule-of-thumb for determining the minimum distance between microphones: the microphones should be at least 3x further apart than the closest distance to the source. So if your mic is an inch from the snare drum, the room mic should be at least 3 inches away! :)

[*Caution!*  Amateur content below - use at your own risk! LOL.]

If you think you might have some phase issues (maybe the room mic sounds like there's a blanket over it), then flip the phase on that channel and see if the volume spikes up.  If it does, then you can decide whether it sounds good to simply leave it that way, or you can move the mic and try the test again.

In addition to managing distance you can manage the levels.

The effects of comb filtering (phase cancellation etc) are greatest when the the two sources are mixed together at similar levels.

If you keep one track 6dB lower than  the other it will be hard to hear phase issues as unnatural artifacts you'll just get a blend effect.


You can use the close mic for tone and blend the room mic in to add fullness... just don't get the two tracks at nearly same level.


An interesting corollary is that placing the mics at different distance as Dave suggests also has the effect of inherently managing the sound levels.

If the far mic is 3x as far from the source as the close mic then the SPL at the far mics is already about 6dB lower than the near mic and you can set both input trims on the pre amps the same and just sum the the two tracks and find you are getting a nice blend with minimal phase problems. It just works... and then you can tweak for the effect you really want. 


best regards,
mike

Wow. Thanks a lot guys. I understand, it makes good sense! It also helps me to understand both the importance of a good sounding room and how to utilize that good sounding room. It makes sense to have a room with good acoustics or an "alive room" for tracking and a dead or flat room for mixing... things I have been aware of but have not quite understood.
It makes sense to me now why I shoud have a sound source where I intend to play and then walk around the room to see where it sounds best and try placing the room mic there. Something Danny said in another thread too about having your speaker in a guitar cabinet at or at least closer to ear level instead of on the floor. I have always liked the tone of a tweed Champ sitting on the kitchen counter. It really does make a difference. I'm nt going to try that with a 4x12 though, laff. The tilt back legs on my CVR (Vibrolux) really make a difference to my ears when I use them. I guess I am thinking out loud about a few things but they are coming together. I learn so much here and one of the biggest things I learn is how much I don't know.
It is great to have people who know so much be so willing to share knowledge, it really helps me at least to have more confidence, and I appreciate it.

Thank you!
Julien