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kick drum microphone phase shifting
Posted: Wed Nov 14, 2007 9:59 pm
by marx
hi, i want to make a small mic phase shifting device for kick drum but i cant find schematics or some theory on the web. is there way to make something like that? thanks
Posted: Fri Nov 23, 2007 1:26 pm
by EK Sound
To flip the "phase" or polarity of a mic line, simply reverse pins 2 and 3 on the XLR connector. If you are handy with a soldering iron, you could build a box with a DPDT toggle switch to do exactly that (see the attached pic for the wiring on the back of the switch). The sheild line (pin 1) would be connected straight through. Any decent DPDT toggle (with NO center OFF position) will work. Be sure NOT to switch the phase/polarity with condenser mics "live" to the monitors... there might be a big BANG.
Dave.
Posted: Sat Mar 01, 2008 4:03 am
by Studio A
OK, now what if you want to variably adjust the phase? Not just 180 degrees.
Posted: Tue Mar 04, 2008 8:23 am
by EK Sound
Delay...
For example, it takes 16mSec to complete one full cycle at 60Hz. If you wanted 45 degrees of phase shift at 60Hz, you would use a delay time of 2mSec. Of course that same 2mSec delay time would produce 22.5 degrees of phase shift at 30Hz, and 90 Degrees of phase shift at 120Hz.
There is no way to partially shift the phase of all frequencies at the same time by an equal amount.
Dave.
Posted: Tue Mar 04, 2008 10:05 am
by Studio A
Interesting...thanks.
So assuming the multi mic phasing is due to direct sound and not reflections. Can we measure the distances from the source to the mics, find the difference and determine the exact amount of delay to align the signals?
Posted: Wed Mar 05, 2008 12:28 am
by MMazurek
Posted: Wed Mar 05, 2008 1:39 am
by EK Sound
The problem is with multiple mics and sources like a drum kit. Lets take the snare mic... if you time/phase align all the other mics to the snare mic, the kick mic (as an example) will be out of line with the tom mics because the distance between mics is not constant... there is no way to "perfectly align" *all* the drum mics. This is why some of the best drum sounds have been obtained with only one or two mics. Pick your battles... only mess with phase on the worst offender. Careful choice and placement of the mics will minimize leakage and phase problems.
Dave.