Why multiple microphones for PA? - Page 1
Forum section: electronics / general

author: Circlotron
author_rank: Super Contributor
timestamp: January 02, 2018, 01:05:51 am
content: Sometimes you see someone addressing a crowd with a PA system and there is not just one (or two for stereo) but a whole series of microphones. And I don't mean all different ones where each and every news service has one jammed in place, but more like in the picture. Is it like a column of loudspeakers where there is good lateral dispersion but little in the vertical plane, but in this case good vertical pickup but less lateral? Or is it just that the speaker's words are so valuable that it takes many microphones to do them justice?Just like so many sycophants hanging around scribbling down gems of wisdom?

author: NiHaoMike
author_rank: Super Contributor
timestamp: January 02, 2018, 01:41:39 am
content: Phased array for better noise cancellation. Similar to what's used in the Amazon Echo.

author: David Hess
author_rank: Super Contributor
timestamp: January 02, 2018, 01:59:28 am
content: Even if they are not used noise reduction, often more than one microphone is installed for redundancy or separate services. If a microphone fails, it is really embarrassing to have to conduct diagnostics and repairs interrupting the event.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: January 02, 2018, 03:39:09 am
content: I think (warning: unsupported musings and opinion follow) it's a skeuomorph. In the early days of TV speeches, you'd see microphones piled up in front of the speaker, each mic carrying the logo of a broadcasting/news outfit. Of course, each reporter would only use the equipment of his/her channel.So the image of important leaders with piles of microphones and wires became ingrained. After all, they're important people. It's all symbolism. Why do they drive in huge cars in a cavalcade with motorcycle escorts?Why would you need noise-cancelling in North Korean parliament? One cough can send your whole family to the camps.I suppose he'd just feel silly with just one microphone. That's for pop singers.Do you see how important he is?

author: floobydust
author_rank: Super Contributor
timestamp: January 02, 2018, 03:50:05 am
content: I know it's very difficult to tie into a single mic preamp and mixer when you have dozens of people wanting a feed. One shorted cable and multiple news feeds get taken out.Some people move around a lot, turn their head during their speech, multiple mics might help with that.Or is this to make a fat, wide presenter look slimmer?

author: ajb
author_rank: Super Contributor
timestamp: January 02, 2018, 04:34:35 am
content: I think Alex has it, given the individual in the photograph. Kudos for the word skeuomorph, but I suspect in this case "cargo cult" might be a better fitIf you look at photos of other world leaders (or other heads of state, anyway) behind lecterns, there's only one or two mics visible, or rarely you still see a larger group of broadcaster-branded mics. Sometimes two are spread apart for better coverage of head-turners or swayers, but often they're right next to each other just for redundancy. (Hopefully anyone in such a position has long ago learned how to talk into a mic!) There's not really any point in capturing a single speaker in stereo, but you might want to capture at more than one gain level for better dynamic range and insurance against clipping--although I'm not sure that this would ever require more than one mic.Quote from: floobydust on January 02, 2018, 03:50:05 amThat's what distribution amps are for!

author: hermit
author_rank: Frequent Contributor
timestamp: January 02, 2018, 05:17:04 am
content: Quote from: NiHaoMike on January 02, 2018, 01:41:39 amStill seems pretty noisy to me.In that vein though, can you take out a 'hit' on someone's thumbs or do they just still do kneecaps?

author: Cyberdragon
author_rank: Super Contributor
timestamp: January 02, 2018, 05:36:56 am
content: They've been using this technique for a long time it seems.

author: Brumby
author_rank: Unknown
timestamp: January 02, 2018, 11:59:43 am
content: Quote from: floobydust on January 02, 2018, 03:50:05 amNO, NO, NO, NO, NO ..... !!!Been there, done that. It does not work. Unless you have some sort of dynamic phase correcting circuitry, the phase interference from two or more microphones will drive you nuts.Some years ago I tried a few options trying to chase a minister in a pulpit, including multiple microphones. The results were not good - especially when selected services were to be recorded and broadcast on an FM radio station. My recommended solution was a head mic - but the minister was somewhat old-fashioned and was aghast at the idea. The final solution was a carefully adjusted compressor/limiter with one channel dedicated to this mic.

author: ciccio
author_rank: Frequent Contributor
timestamp: January 02, 2018, 01:23:52 pm
content: Brumby is true : it does not work. It is a waste of microphones, cables, connectors and mixer's channels.If you want continuity against a microphone failure you can use two microphones, but you must be cautious: the two must be well selected for : sensitivity, frequency response, polar directivity, and the distance between the two mics must be fixed, better with a bar connecting the top of the goosenecks. In this way the comb-filter ecffect is predictable, and may be compensated in some way. There are better solutions.I see that in the German Parliament (Bundestag) the speaker's table is equipped wth a couple of fixed microphones that seem a kind of an array (see attached photo).Does anybody have some informations about the make - model of these?Regarding multiple mics: many years ago some of my customer (pop singers) asked for two different microhones taped toghether, one wired out-of-phase, connected to two channels of the mixer with different EQ settings. By moving the couple of mics in front of their mouth they could get interesting phase-shift effects...

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: January 02, 2018, 01:27:57 pm
content: Quote from: Cyberdragon on January 02, 2018, 05:36:56 amI wonder if it goes back to the radio days, people giving speeches would have tons of big microphones in front of them and that's the pictures that would be in the newspapers. Then it had to be continued for TV.It's now part of the symbolic language used in media.

author: David Hess
author_rank: Super Contributor
timestamp: January 02, 2018, 03:00:10 pm
content: Quote from: Alex Eisenhut on January 02, 2018, 03:39:09 amThat still happens where there is no existing distribution system for the news agencies to plug into; each one demands their own microphone. For fixed venues this was eventually seen as silly so a small number of redundant microphones are used with a distribution system for the media to plug into and I expect that is what we are seeing in the original photograph although 7 seems excessive. Maybe they are using noise cancelling; it would be easy enough to do with a linear array. Microphones are notoriously unreliable.

author: Brumby
author_rank: Unknown
timestamp: January 02, 2018, 11:10:00 pm
content: Quote from: Brumby on January 02, 2018, 11:59:43 amHaving slept on this, there is an approach that might work - and that is having an array of microphones that are gated, so that there is exactly one active at any point in time. Gating would be volume controlled and the switching process would need to be silent.Just a thought (not a recommendation).

author: Brumby
author_rank: Unknown
timestamp: January 02, 2018, 11:12:15 pm
content: Quote from: Brumby on January 02, 2018, 11:59:43 amHaving slept on this, there is an approach that might work - and that is having an array of microphones that are gated, so that there is exactly one active at any point in time. Gating would be volume controlled and the switching process would need to be silent.Just a thought (not a recommendation).

author: Electro Detective
author_rank: Super Contributor
timestamp: January 03, 2018, 10:20:34 am
content: Mr. Brumby testing a doubling effect ?In a 'PA' public address system application, if you can't get awesome gain before feedback with one well selected microphone (and an identical backup/s next to it), with some manual fader riding and compressor limiter and equaliser to keep unforeseen nasties in check,then it's job you shouldn't be attemptingunless suckered to do it for freesex or roadietard prestigeIf ratass rude reporters and snobby TV crews with pushy bossy boots no life producers want a free ride off your multi channel isolated distribution amp after all the work setting it up (and cash blown to buy it),then they can PAY for a balanced line (aka HIRE/RENT fee etc)or run around themselves and setup and use their own micsor use The ForceSumming/mixing together the 7 microphones above makes for a sharks teeth comb filter akin to 'a day at the races in the bush' sound qualityGood luck trying to set up gating or delay parameters for a 7 mic setupespecially dealing with a quiet or non consistent speaker

author: Messtechniker
author_rank: Frequent Contributor
timestamp: January 03, 2018, 11:31:05 am
content: Quote from: ciccio on January 02, 2018, 01:23:52 pmDetails here:http://digitalaudioservice.de/microtech-gefell-kem-975.html

author: b_force
author_rank: Super Contributor
timestamp: January 03, 2018, 11:35:07 am
content: An array of microphones definitely works, is often being used, as well as the opposite (array of loudspeaker).It's just a matter of delaying each mic so the distance to the source will be exactly the same.This works great, since it gives the speaker much more space to move, as long as they stay the same in the vertical plane (but mostly they sit anyway)Nowadays you can do even more corrections with a DSP (gain, frequency response and all).Another way f doing this, is to build a mic rig that's like a circle around the speaker.The biggest problem is that it will just look very odd.Second is of course reliability.They also used to use multiple mics for a better overall polar/off axis response.Or in other words, canceling out environmental noise etc to prevent feedback loops, which was pretty bad in times like the 2nd world war.Nowadays they can do that already in one single mic.But to summarize, basically you want to get a few things.1 - give the speaker most freedom and most natural experience2 - get rid of feedback and noise.3 - need to be reliable at all times.Feedback is the main issue here, keep in mind that most of these speeches are in big halls with an huge PA speaker system.A lot of times you WILL get feedback at some point.

author: Bassman59
author_rank: Super Contributor
timestamp: January 04, 2018, 05:31:40 am
content: Quote from: Brumby on January 02, 2018, 11:10:00 pmDan Dugan's automixer(scroll down) is a successful implementation of what you describe. My friends who mix audio at corporate talking-head gigs swear by it. It really works. But it is designed to be used in situations where you have, say, a table full of people talking, with one microphone per person.The Kim Jong-Un thing is completely ridiculous. It's just for show. Having never heard the results, I can't say whether all of those microphones are on, or just one. If they're all on, it's a phase nightmare. Intelligibility goes to hell.

author: Brumby
author_rank: Unknown
timestamp: January 04, 2018, 02:53:33 pm
content: Quote from: Electro Detective on January 03, 2018, 10:20:34 amI'll just jump in here ...This particular system needed to be set up so that it could run by a single person - the minister out front. Yep - no-one running the desk, just everything on presets. The only time there was an operator at the desk, was for recording - and they were running a separate mix for that. Occasionally, there might be a special event where the desk was manned for a custom mix - but not that often.This system had to allow one person to plug in the mics required, turn the system on and after a 3 second delay, the system was live and ready.QuoteCompressor/limiter and 31 band EQ ... Check!Quote from: b_force on January 03, 2018, 11:35:07 amAn array of loudspeakers is somewhat different to an array of mics. Delaying each mic is an answer - but what about the small fact that the delay will need to be continually adjusted as the speaker moves around? Keeping the speaker in the same vertical plane is the most impractical constraint I could imagine.QuoteThat would be some DSP solution.QuoteOdd - yes. I still can't see it working.Quote from: Bassman59 on January 04, 2018, 05:31:40 amI've heard of something similar at a larger scale - but both your example and mine had one microphone as the principle source for a given speaker ... which is a bit different.