Grateful Dead Music Forum

A place to talk about the music of the Grateful Dead 

Chat about Equipment Info
 #142647  by Jon S.
 Thu Nov 06, 2014 7:17 am
My basement practice space is configured as such that feedback is sometimes an issue using my small powered mixer through passive speakers. Folks with 31 band EQ or on-board anti-feedback filters wouldn't care but FWIW, I just realized I own a Whirlwind Combiner. Here's an excerpt from the brief manual:
Note: The IMP COMBINER uses transformer coupling to combine two microphones into one. ...

Female XLR input jacks for connection of low impedance balanced signals such as that from microphones.

A male XLR jack that outputs a balanced, low impedance (150 Ohms) signal for connection to balanced, low-Z equipment (mixing console, workstation, etc.)

A switch that reverses pins 2 and 3 on the female XLR jack labeled INPUT 2, thus reversing the polarity between inputs. Use for correcting opposite polarity inputs or for purposely throwing the two inputs out of phase to reject feedback and extraneous noise. Or use in situations where two microphone diaphragms must move 180 degrees out of phase to properly pick up an audio signal (example: miking drums with a mic above and below each drum.)
WTF, I'll try it at band practice Sunday and see what gives.

Curious, though - anyone else, in the 2nd decade of the 21st century, employing this trick?
 #142649  by Rusty the Scoob
 Thu Nov 06, 2014 8:41 am
Sombody with better tech knowledge than me please correct me if I'm wrong, but isn't that exactly the setup that they used with the Wall of Sound? And it helped eliminate feedback but didn't sound particularly good.

 #142650  by TI4-1009
 Thu Nov 06, 2014 9:04 am
Just like two pickups or coils (or speakers) out of phase, shouldn't that change the sound? If you have the two opposite sine waves, both constantly changing, you should be cancelling out a constantly shifting set of frequencies. Right? It might do what you're after, but it may also sound different. Which may still be OK- for a basement practice room.
 #142652  by zambiland
 Thu Nov 06, 2014 10:20 am
I suppose you could try it. There are a number of issues with doing it in a small room, because the nature of the reflections are such that they are going to have more variability in terms of what hits one capsule and not the other. On their stage, the mics were far from any reflective surfaces, which won't be the case in a basement.

One thing to keep in mind is that they used omni capsules, not standard cardioid capsules.

But what the hell, why not try it? It's also possible that throwing a single mic out of polarity might even improve feedback issues.
 #142653  by tatittle
 Thu Nov 06, 2014 11:18 am
Come to think of it their mic's from WOS era did sound akin to the 2/4 RWRP humcancel quack Strat positions somewhat. I hadn't thought about that before.
 #142656  by Jon S.
 Thu Nov 06, 2014 12:24 pm
The Strat PUPs example seems inappropos to me because in that case the strings are always vibrating over both PUPs whereas in the microphone case the vocals are always though just the one of the two mics.
 #152049  by pablomago
 Sat May 07, 2016 4:04 pm
Crown made a dual diaphragm condenser mic the CM-310. I have one and I like to use it on singing drummers to keep the drum kit out of the vocal mic. You have to be right on it, but it works well and sounds good. They turn up on ebay from time to time and usually for not a lot more then a BETA 58. Sometimes less. And they look better then two mics. :-)

I also use a Crown CM-200 another good condenser vocal mic that are a good deal. Harmon owns Crown and has discontinued all of the Crown mics other then the headset mics and PZM's. Since Harmon also owns AKG, there's no need for two competing microphone lines. Snag 'em while you can.