Ever seen those 70´s singers with two mics taped up together and wondered.....

[alonso]

Well, those mics are taped parallel to each other, I suppose to get the vocal in stereo, but shouldn´t this positioning cause phase cancellation?

 

[Badger]

Thats the point, they are wired out of phase with each other to cancel, when you step up to the mic, you are closer to one than the other, so the one you are closer to wins out. But the drums, etc are hitting both mics at the same level, so that cancel out.

Its done to keep background noise and feedback from coming through the mic....

 

[alonso]

Thanks for the clever answer dude!!!!

 

[sjjohnston]

Well, it's clever. Whether it's right or not is another question. ... Can't say that I know, but I suspect it's could be the result of a kludgey "I had to do something in a hurry, and this was the easiest way to do it" process. Like they needed to input the vocals into two different boxes, and that was the easiest way to do it in the 15 minutes they had left before the show started.

 

[TexRoadkill]

We used to use two mics a lot for corporate shows. We only had one active at a time the other was just for backup. When some jerkoff CEO is paying $20k for a gig they get pretty pissed if the mic goes out on them.

 

[sjjohnston]

That makes sense.

Even if the CEO is a really nice guy.

 

[Badger]

I wasnt just guessing, this used to be a pretty coman trick, the Grateful dead used to do this for one......

Geez....You think I just make this shit up?

 

[Badger]

from http://www.dead.net/cavenweb/deadfile/newsletter19soundrap.html

A major improvement in the quality of the vocal sound is due to the use of differential microphones. Each singer has a perfectly matched pair of Bruel and Kjaer microphones hooked up out of phase, only one of which he sings into. Any sound which goes equally into both microphones is cancelled out when the two signals are added together. Therefore leakage of instruments and background noise into the vocal channel is minimized.

 

[barefoot]

"a perfectly matched pair of Bruel and Kjaer microphones"

Thems some spensive micryphones.

Definitely not a 15 min "duct tape" fix.

barfoot

 

[sjjohnston]

I don't know who wrote that page ... but I'm not following the setup at all.

If the two mics are next to each other (taped together or not), how could you possibly sing into only one of them?

If they're in different places, how are they supposed to cancel out anything?

If they're directional and facing in opposite directions, whoopee, they just invented a dual-diaphragm figure-8 pattern mic ... which doesn't cancel everything, it just has nice nulls on the sides.

 

[Harvey Gerst]

When I did that, one mic was to feed the pa or house system, while the other mic was the feed for TV, recording, or a remote radio broadcast.

 

[alonso]

Is it really necessary to have two separate mics to have two separate signals for two different places? Isn't it easier just to tell the PA guy to send a signal to the TV people? Or they just don't trust each other and they insist on having their own piece of the action?

 

[skippy]

The Greatful Dead used to do this (as Bdgr says), in the mid-70's Bag End/Wall Of Sound days anyway, to feed one mic to the mains and one mic minus the second mic to the monitors for stage-mix feedback control- done with transformer buck windings as I recall. Their monitor sound must have sucked hind tit, but that's another story, anyway. Despite that, Bag End used to use this application as a marketing tool right up through the late 70s. Of course, their market dried up at about the same time as the market for line arrays where one column was used for a single string on Lesh's basses dried up.

Which is actually a damned shame, because those Bag End line array speakers were actually very nice, cabinetwise, and *way* the hell ahead of their time: Meyer learned a lot from them... Good product, slightly warped application. I actually owned one of those 15" ported enclosures for a time in the late 70s as a bass cabinet (not one that was used by the Dead, of course- it was a pawnshop refugee). And with a good JBL 15" driver, it was _righteous_ with a fender Bassman 50 or small Ampeg driving it. Accurate for PA? No freakin' _way_, but righteous just the same. And capable of withstanding nuclear war (11-ply, 1.0" plywood, as I recall, and with interchangeable port ducts to tune the box to the parameters of the driver). Should never have sold it: it'd *still* be righteous on a Stick rig, and it'll still be here when the cockroaches have eaten the last of the Pop-Tarts.

Sort of like the Community Light and Sound Googa-Moogas (Yes, there *was* such a product afoot, and at the same time. Just like the Heil Sound Purple Horns.). But I digress...

More often, though, the two-mic-coincident technique was used for live recording where the artist required One Of These for his vocal sound, and the OB crew needed One Of Those for their vocal use. See also "avoidance of limiters" and "Daltrey never slept here..."

Wonder what ever became of Bag End? Harvey, heard anything of 'em?

 

[Harvey Gerst]

Is it really necessary to have two separate mics to have two separate signals for two different places? Isn't it easier just to tell the PA guy to send a signal to the TV people? Or they just don't trust each other and they insist on having their own piece of the action?

Unless I know the guy running the house system, no thanks, I don't want him deciding what I will or won't get. Plus he's mixing for that room, and that's different from what I might want to get.

 

[Badger]

I don't know who wrote that page ... but I'm not following the setup at all.

If the two mics are next to each other (taped together or not), how could you possibly sing into only one of them?

If they're in different places, how are they supposed to cancel out anything?

If they're directional and facing in opposite directions, whoopee, they just invented a dual-diaphragm figure-8 pattern mic ... which doesn't cancel everything, it just has nice nulls on the sides.

Your not singing into only one of them, just more into one of them than the other, so it has a stronger signal, and therefore doesnt get canceled out. back off a foot or so, and you are hitting both of them the same.

 

[Light]

Bdgr is right. I had a teacher in college who was a tech for the company who supplied the cluster they used for keyboards. The first day he worked on the show, he asked the engineer how the line array stuff worked. When he was told, he didn't believe it. The engineer gave him a dB meter, and told him to walk away from the stage while some music was playing. My teacher started at the front edge of the stage, and walked away, watching the meter. The volume would fluctuate by less than 3 dB, total, all the way to the back of the arena. The problems with the “Wall of Sound” were the balcony got almost no low end, and it was ridiculously expensive and time consuming to set-up and move. They stopped using the "wall" the first day of the energy crisis.

There monitor system was the front of house system. Every thing was right behind them, so they heard everything through the FOH speakers. The mics were wired with reversed polarity so they would cancel anything which hit both mics. You pick one mic (it does not matter which one) and eat the mic as you sing. It works great. If you don't believe it, try it. Take a couple of 57s and hold them next to one another, sing into one, and eat the mic. By the time you are 1 inch away from the mic, you voice is canceled out, but if your lips are touching the mic, it comes through clearly.

One last comment on line arrays. There are a lot of different speaker manufactures coming out with line arrays these days. Even Meyer is making a line array now, and for a few years they were trying to fend off the current trend towards line arrays for event PA systems. The problem is this. They are NOT line arrays. When the V-DOSC system came out, it was designed and spec'ed to be hung in a straight line, perfectly vertical. This is a line array. But pretty much the first time anyone tried to use it, they found that they could not hang the arrays straight and get sufficient coverage of the front rows. The fix they found was to arc the bottom of the array. The only thing is, as soon as you arc the array, the coupling which was taking place when it was vertical ceases to take place, and you start to get some serious comb filtering. The other problem with line arrays is that they, by there very nature, narrow the width of the dispersion from the cabinets. In an array, a cabinet which has a 90 degree dispersion is reduced to about 70 degrees, or there abouts. On top of all of that, I (personally) find the modern line arrays to sound really inconsistent and flat. Give me clusters, any day.

Light

"Cowards can never be moral."
M.K. Gandhi

 

[sjoko2]

Harveys answer is the only right one........ thank god for the day someone invented good splits.

 

[barefoot]

If the mics are omni's they would have a figure 8 pattern only in the low frequencies. It would turn into a complex frequency dependent lobing pattern as the wavelengths approach then get smaller than the mic separation. There would always be a null down the center, but not much side cancellation. Cardioids would only fair slightly better.

The way I could see this work is if you used supercardioids placed a few inches apart. This way you could sing into just one, the other would be isolated from your voice, and the directionality of both mics points in the direction of the null. Now, my experience with microphones is pretty much limited to test mics used for loudspeaker design and acoustic measurements. So, I don't know if supercardioids are practical for singing purposes, but this would work theoretically, if not practically.

barefoot

 

[The Byre]

And the answer is . . .

that we used to be able to take some of the signal for recording and video off the main mix or a sub-group. But things like lead singers were critical, so a separate mic was used. TRhis was because there was no such thing often as a splitter box.

Sometimes everything was double mic'ed. Don't forget, the PA and the film company were not the same and used different types of equipment!

 

[sjoko2]

Re: And the answer is . . .

that we used to be able to take some of the signal for recording and video off the main mix or a sub-group. But things like lead singers were critical, so a separate mic was used. TRhis was because there was no such thing often as a splitter box.

Sometimes everything was double mic'ed. Don't forget, the PA and the film company were not the same and used different types of equipment!

correct, apart from that they used film, as video had not been invented