Topic: Recording Hypothetical.

[tonebloke]

This question didn't seem to fit into any particular section of the board (I could be wrong).

I'm currently running a R09-HR with CA-11's and a battery box. What I want to ask is:

If I had set of Cardoid's AND Omni's and piggybacked both to the imput - with the cardoids facing forward towards the stage and the omni's facing out at 90-120 degrees from the stage (towards the side of the venue) would the picking up of the audio 1. work in synch and 2. come out as a decent recording?


What brought this up? At work today I just happened to have a "stare" moment at a multi point power board and my CA-11's popped into my mind and then wondered whether plugging in two sets of mics would work.

Remember this is just hypothetical. 

[hummat]

I think there would be a big possibility of unrepairable phase issues.

-j

[page]

I think there would be a big possibility of unrepairable phase issues.

Bingo.
Sometimes phasing/comb filters work to complement a sound, but most of the time (IMHO) they don't when mixing multiple mic sources. ymmv.

[Gutbucket]

Phase interaction issues potentially become problematic if the mics are moved apart from each other and the four mics are all in different places, but there shouldn't be phase problems if the mics on each side are positioned coincident with each other.  Of course that doesn't stop a lot of people around here from doing just that, but they are powering the mics correctly and either recording all four channels separately, or combining them after the preamp.

The practical problem is electrical.  The mics are likely to interact with each other and the input stage of the recorder or preamp in problematic ways if combined at mic level.  They may not be powered properly, their performance may suffer dramatically, the load on the input stage of the recorder becomes unpredictable, and the mix between them is likely to not be what you're hoping for.  If you want to do this the channels could be combined at line level (after the mic preamp), or the four channels recorded individually and mixed latter which gives you the most flexibility in controlling the mix between the two.

If done correctly, combining a coincident omni and a cardioid mic modifies the overall pickup pattern (polar pattern) to something between that of the two individual mics. If the mics are of equal sensitivity and are combined in equal amounts, you end up with a wide cardioid pattern that is halfway between a cardioid and omni in shape, pointed in the direction of the cardioid.  That's exactly how large diaphragm mics with electrically switchable patterns work.  They electrically combine two back to back cardioid elements in the mic itself, mixed together in various ratios and with the appropriate polarity to create resulting patterns that range from omni to cardioid to figure 8 or patterns in between.

[tonebloke]

Phase interaction issues potentially become problematic if the mics are moved apart from each other and the four mics are all in different places, but there shouldn't be phase problems if the mics on each side are positioned coincident with each other.  Of course that doesn't stop a lot of people around here from doing just that, but they are powering the mics correctly and either recording all four channels separately, or combining them after the preamp.

The practical problem is electrical.  The mics are likely to interact with each other and the input stage of the recorder or preamp in problematic ways if combined at mic level.  They may not be powered properly, their performance may suffer dramatically, the load on the input stage of the recorder becomes unpredictable, and the mix between them is likely to not be what you're hoping for.  If you want to do this the channels could be combined at line level (after the mic preamp), or the four channels recorded individually and mixed latter which gives you the most flexibility in controlling the mix between the two.

If done correctly, combining a coincident omni and a cardioid mic modifies the overall pickup pattern (polar pattern) to something between that of the two individual mics. If the mics are of equal sensitivity and are combined in equal amounts, you end up with a wide cardioid pattern that is halfway between a cardioid and omni in shape, pointed in the direction of the cardioid.  That's exactly how large diaphragm mics with electrically switchable patterns work.  They electrically combine two back to back cardioid elements in the mic itself, mixed together in various ratios and with the appropriate polarity to create resulting patterns that range from omni to cardioid to figure 8 or patterns in between.

Thanks for your thoughts guys. I was only wondering.

Gutbucket:
I appreciate your answer but most if it doesn't compute in my head. Are you saying it is possible? The way I read your reply is if I put an card AND omni  side by side (as in - taped together) on either side of me it may work but 1. there is no guarantee and 2. if it did the interaction of the dual imput wouldn't necessarily "mesh".

Thanks.

[Gutbucket]

Short and long of it is that I wouldn't do it unless you plug each mic into a seperate input circuit.  If both mics are Church Audios you have a better chance of making it work with a single input if you are really set on doing this, and I suggest you ask Chris Church about the interaction and load they place on the recorder input and powering.

If you plug the mics into seperate preamps before combining their outputs, then placing the mics as close together as possible helps reduces phase cancellations between them, which is only becomes important if you are mixing those two channels together.  The reasons for mixing them could be to change the overall frequency response or the directional pickup pattern of the combined microphones on that side.

[tonebloke]

Thanks Gb. As in the header - Recording Hypothetical. It all seems a bit too hard so I won't even try; but it would be an interesting experiment though.

Much thanks for your imput.

[Gutbucket]

I was looking for something easier to mess with, but found an excel spreadsheet on-line which plots the resulting pickup pattern derived from combining omni and figure-8 components in various ratios.  This shows what is going on hypothetically, assuming the microphones were arranged perfectly coincident, are equally sensitive, and behave ideally.  The spreadsheet starts with the two most basic patterns, omni & figure-8, from which all other patterns are derived by combining those two in various ratios.  A cardioid pattern is the result of combining omni & figure-8 components with a 50/50 ratio.

For your example of combining a cardioid and omni, the cardioid alone is made up of 50% omni and 50% figure-8 components.  When that is combined with another omni, the omni component is doubled and the figure 8 halved.  If you enter .75 for the omni and .25 for the figure-8 in the ratio cells in the upper left you'll see that the result is a sub-cardioid pattern which is halfway between a cardioid and omni.

Heres a link to the spreadsheet you care to play around with it-
http://100db.com/download/polar.htm