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In footage from concerts in the 1970's +/- I've notice that they often had pairs of microphones taped together, e.g. these:
It seems like it was somewhat "standard practice" at one time; why did the engineers set up the microphones in this manner back in the day?
In these pictures it's likely that one mic is for the PA and the other mic is for recording. Either they didn't have mic splitters or they didn't trust them! This was a very common way of doing things in the 70s.
The Grateful Dead are known to use two mics as a noise cancelling technique. The output of the two mics is combined with equal levels but opposite polarity.
In this arrangement two omnidirectional mics are set up so that one is a few inches further from the wanted sound source than the other. That's quite a different physical arrangement to the one in your photos.
The signals from the two mics contain almost identical levels of background noise, but one has a louder version of the vocal than the other. By combining the two, with reversed phase, (background noise minus background noise = silence), (vocal from closer mic minus vocal from further mic = audible vocal). There is some phasing-related distortion on the vocal, but in a live setting it's too subtle to matter.
Of course this doesn't only apply to vocals - it could work for any sound source. Indeed it may be more suited to acoustic instruments, because it's reasonably easy to shove your mouth right up to a unidirectional mic -- it's less easy with certain instruments.
Most bands don't need this because they play on a reasonably quiet stage, with the PA speakers in front of them. The Grateful Dead play in front of a loud backline, so they need tricks like this to deal with background sound.
I can't find any photographs of the Grateful Dead employing this technique - so it's possible they only use(d) it in certain circumstances. All the photos I've found show them in the 70s, with one mic for PA and one for recording.
Source: http://www.soundonsound.com/sos/jul10/articles/qa0710_4.htm
Different microphones do have different characteristics, and it's certainly possible to fine-tune the sound by combining signals from more than one mic - perhaps running each one through a different effects chain.
However this is something you'd be more likely to do in a studio than in a live setting.
I have seen footage of Bryan Ferry performing with two handheld mics, deliberately moving one or the other closer to his mouth, to achieve a stereo pan.
During Live Aid, Bryan Ferry was apparently using two mics for musical effect. In fact, one was broken:
"And then my microphone wasn't working, which for a singer is a bit of a handicap. A roadie ran on with another mic so then I was holding two mics taped together and I wasn't really sure which one to sing into. It was a great day though."
Source: http://www.theguardian.com/music/2004/oct/17/popandrock5
It was for noise canceling not recording. The Mics are out of phase so no feed back. this is the time when they used there own PA called " wall of sound" only used for one year. all the speakers were placed behind the Dead so in order to prevent ,what we all know happens when you put a mic in front of the speaker, feedback bear made a mic that was out of phase to mic the feedback and cancel it out making silence. Neat idea but it made jerry and bobby sound like they were holding there nose closed while singing. some dead heads refer to the sound when they saw them live amazing but jerry sounded like he had a cold. Naisly
Used for live recording before modern technology allowed easy splitting of individual chanels. Extra mikes to multi track recorder allowed an uncomplicated method to grab each sound source without having to disturb or modify the PA FOH mixer channels.
The chap wearing the Fox's head is Peter Gabriel, and I would go so far as to say the image is either a photograph or a film still from Genesis' concert held at the Bataclan in Paris on the 10th of January 1973. This concert was partly filmed to be shown on French TV, so it stands to reason that one microphone fed the house PA system (or Genesis' own) and the other was fed to tape for the benefit of the broadcast. The footage can be viewed on Youtube.
As a footnote to the other image (Bob Weir and Donna Godchaux of the Grateful Dead), you can see some of the Dead's Wall-of-Sound PA system in the background of the photo. However the microphones aren't the Alembic-designed units seen in The Grateful Dead Movie, but an earlier setup with (what looks like) off-the-shelf microphones setup for the same purpose.
In those days, the PA system was tuned to what the house sound and the band wanted, and film makers of the day were not an integral part of the gig. Soundboards of that time were not set up to be tapped into in that way back in those days, and were not trusted to deliver the sound that the film maker wanted. It was deemed simpler for the film sound to have its own microphones, rather than risk messing up the gig sound, which was what the band was being paid for. Lots of extra cabling and equipment needed, but parallel systems were a comfort zone for the acts of the time. Another factor of the time was 4 channel audio, which was also new, and separate microphone systems for recording that way was needed, which also required a parallel system for recording. Rock acts were fairly easy to record in quad, but what sounded good for the PA and what was needed for a multi-track master recording were not always the same. Splitters of the time were not simple affairs in those days, as integrated circuits that we take for granted now did not exist in those days, and the ones that did exist were expensive and not trusted by sound engineers until years later because of hum problems.
This microphone technique is referred to as "Point Source" miking. The idea is to wire the microphones out of phase with each other to cancel the signal that is being picked up by both microphones to hopefully limit feedback and background noise. Then when the performer would sing into only one microphone, the signal would not be effectively cancelled and could be mixed and amplified. This idea was considered theoretically brilliant and was published in numerous audio magazines and picked up by just about anyone who was building a sound system back then. The Grateful Dead system was probably the most talked about at the time. At the time that this practice was attempted, stage set-up often utilized high power Marshall stacks and monitors were in rudimentary stages of development. Soon enough instruments were miked and mixed into the out front and monitor systems eliminating the requirement for the brute power of the large amps, the behind the band speaker stacks,(terrible idea) was replaced by floor monitors and side fill, and later, in ear monitors mixed specifically for the performers taste and requirements. Also, it seems that in order to really be effective in point source technique, the microphones should be carefully matched up in their frequency response, something that was largely ignored in the world of rock and roll. After all the rock and roll stage has never really been a precise lab setting to fine tune such ideas. The basic laws of physics came into play and the latest magical notion was abandoned and replaced by other ideas.
I have seen the 2 Microphones taped together in many 1970 Films/early videos. 1 thought I had was that the early sound systems did not have enough POWER per channel to carry good strong vocals, and that is why some singers were using 2 Microphones, 1 in 1 channel and a 2nd in another channel on the Board for more POWER.
If you look closely at the photos you refer to and you know how sound systems are wired there is only one correct answer to this question.think about how many cables exit these pairs of mics if you can find a photo with more than one cable on any pair I will be very surprised how do you send one output to two different destinations ? Y them witch will totally defeat the Y which is converting the two mics to one cable in the first place it’s true this was done before the days of isolated splits but has nothing to do with recording or foh and monitors the two mics are wired out of phase there for canceling feedback or any other unwanted signal pay close attention you will see only one of the two mics is being sung or spoken into they are set up for noise cancelation.
I hadn't really noticed this but I'm guessing it was probably used to create a stereo effect to make the vocals a bit richer. I don't think it is really necessary anyway which might explain why it was abandoned. It's also hard for the singer to move away from the mic stand.
