Ive often wondered this and seeing an add for "the best of Free" compilation the other day reminded me- why in old concert footage (usually 60s or early 70s) do you see 2 microphones in front of the vocalist. i.e. both on the same stand gaffa taped together?

Ive seen it quite often and I cant think of any good reason for it.

Any thoughts?

Cheers

SC

Hi, possibly split feed, one to PA one to recording console or broadcast?......or FOH and monitor feed? Dave

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My head hurts!

It may be complete rubbish, but I'd always heard it was to eliminate feedback and drum/amp noise going into the mike, one mike is phase/polarity reversed.The Singer only sings into one but all other noise going into both is canceled, like a humbucking pickup.

As I say maybe rubbish.

Regards, Andrew

Edited by ASG (29/04/10 06:26 PM)

Usually for FOH and a recording truck.

Hugh

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Technical Editor, Sound On Sound

I seem to remember an article in Performing musician about the Grateful Dead usingn 2 mics for noise cancelling. And there's a brief reference to the technique here

But generally I'd have thought broadcast and record via separate mics.

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I've never liked a solo violin, you need at least five for a proper fire.

Usually the PA and recording rigs were separate at this time - really good splitters and decent FOH mics had to wait until mid-70s or so - and in the 80s, when I was doing this sort of thing, scepticism was sometimes rife about the effect of our splitters on the hum level in the PA rig. The number of times we pulled the barrels out and watched the roadies' faces fall as they realised they couldn't blame us...OK, smug mode, but it got a bit wearing after a while!

The two mic noise cancelling idea is well known and very common in many sound applications -- most notably aircraft comms headsets -- but rarely these days in live sound / PA.

The idea is to have two microphones spaced a short distance apart (something between 1 and 2 inches usually) in front of the mouth (or whatever the sound source is). Both mics should be able to hear the sound source directly -- so if they are cardioids they both need to face the sound source, although this is more usually done with omni mics in general practice.

The ambient noise, being inherently diffuse sound will be captured equally in level by both mics -- their near spacing will make no significant difference to the ambient sound level they capture.

The wanted sound must be very muich in the nearfield of both mics, but provided the front mic is very close, the inverse square law of sound energy dispersion means that the slightly more distant mic will receive significantly less energy of the close sound source than the front mic.

This is also why omni mics are preferred -- because otherwise one mic would have a stronger bass response because of the proximity effect.

By combining the outputs of both mics at equal gains but in opposite polarities, the similar level of ambient noise from each will cancel to a very large degree, whereas the significantly different levels of the wanted close sound will hardly cancel at all.

There will be a slight level reduction of wanted sound in comparison to using the close mic on its own, but given the 30dB+ of ambient noise reduction this is a loss well worth suffering when working in very noisy conditions.

The physical spacing between the two mics will affect the frquency response of the wanted close sound because of the inherent comb filtering such an arrangement creates, but if the distance is only an inch or so the first comb notch will be well above any significant important component of the human voice.

..but to return the the original question, this noise cancelling technique really requires two identical mics spaced a precise distance apart. Most of those festival photos show dissimilar mics mounted with their capsulesmore or less coincident -- which lends weight to the suggestion that they were for separate recording and PA feeds, rather than exotic noise cancelling techniques.

Such techniques were required for the Grateful Dead because of the unconventional PA arrangaments they used to employ. I blame John Meyer

Hugh

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Technical Editor, Sound On Sound

60's & 70's eh?.....technique is very much alive & kicking today.
http://www.jimnicholsufo.com/wp-content/uploads/2009/09/obama-news-confere nce.jpg

Gordon Brown prefers tie-clips.....very dangerous!!!

I don't do any live work but I'd been thinking about split feed situation for Woodstock work. I've been wondering for todays presidential lectern situation whether the practice is maintained for same reasons or as a spare for failsafe option.

Quote Matt H:

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I've been wondering for todays presidential lectern situation whether the practice is maintained for same reasons or as a spare for failsafe option.

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It's a failsafe main and backup arrangement -- standard broadcast practice for 'grade 1' events. You'll have noticed that the party leaders and DD were all wearing double tie-clip mics during the debate last night.

The US presidential lecturn used to be fitted with Shure SM57s under posh foam windshields! Don't know if it still is... but opting or passive mics rathen than mics that required phantom power was a practical decision to minimise the chances of losing the output in a fault situation.

Hugh

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Technical Editor, Sound On Sound

Right-o' Hugh thanks for confirming broadcasters procedures. Those are indeed snazzy looking windshields. I' had read somewhere that 57's have been favoured choice on the lecturn for about 30 years now.
I caught Question Time instead & still can't help feeling that a boom op's life is not an easy one.

Quote Hugh Robjohns:

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Quote Matt H:

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I've been wondering for todays presidential lectern situation whether the practice is maintained for same reasons or as a spare for failsafe option.

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It's a failsafe main and backup arrangement -- standard broadcast practice for 'grade 1' events. You'll have noticed that the party leaders and DD were all wearing double tie-clip mics during the debate last night.

The US presidential lecturn used to be fitted with Shure SM57s under posh foam windshields! Don't know if it still is... but opting or passive mics rathen than mics that required phantom power was a practical decision to minimise the chances of losing the output in a fault situation.

Hugh

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The first UK debate was hosted by ITV, 2 lecturn mics,2 lavaliers per candidate and they still missed the opening statement...

Next time it was SKY,again 4 mics each and GB continually hitting his podium mics.

Eventually BBC's turn, they got it right,the Question Time lot.

As for the US lecturn thingy Ive always thought the SM58 the last thing to use, always poppping,or windblasting and needing to be used close only,otherwise disapearing.
Sennheiser 441 much superior.
The lecturn feeds distribution amps for the many news crews, I once narrowly missed a bollocking when we turned up late at the Clinton/Lewinski inquiry and I pinned a Tram dracula clip and radio tx on to one SM58.
The mob journos said I got away with it cos we were BBC 2...
(I had checked nobody was on my frequency..)
Also got told off for running into the White House,again late, fun to see all the crews lined up with their tanned ,big hair presenters,standing on boxes next to one another.
All lit with a 2k and reflectors,sometimes 30-40 crews and 'talent'...
All doing their pieces at the same time with the White House in BG but straining to hear what CNN said.
The beeb had a top floor hotel suite that overlooked the White House
and enables PTC with the W house in BG.
Our cameraman was out on the roof with a very long lens on his Arriflex SR, I looked at the WH roof and saw Secret Service men snipers taking a bead on Steve,they could have thought he had sniper weapon,he came in smartish.

Back to the original post,very common to strap anothe mic on to a PA mike.
ECM 50 particularly good,unobtrusive ,could be hidden in a foam gag and sounded better than many PA mics.



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I am the Walrus.

ROLO! I don't think I've ever seen so many words in one of your posts!

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http://www.loverslanestudios.co.uk