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Gear / Technical Help => Microphones & Setup => Topic started by: RemotelyLocated on November 15, 2013, 08:41:34 PM
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In a few days I'll record a brass ensemble at a local college. The director prefers no regular mic stands be seen in front of the group but will permit something short, very low on the stage. Not allowed to put a stand on the audience floor in front of the stage. (It's an auditorium, so the stage is raised.)
So I picked up one ProLine MS112 stand and will put my small condenser cardioids on it, likely ORTF. I've heard another ORTF recording done at that location on that stage with the same ensemble with good results.
My concern is with footfalls, feet shuffling, and yes, any possible proximity effect that might muddy the sound from being so close to the floor. And I'm wondering if there's anything I could place under the stand, like a big piece of foam or whatever that might be a good idea.
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neoprene sheet. mouse pad works well.
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Proximity effect isn't caused by sound reflections from nearby surfaces; it's caused by a sound source being close (or close-ish) to a pressure gradient microphone.
The thing to be concerned about when a microphone is near but not directly on a large, rigid reflecting surface is called "comb filtering"--the alternating cancellation and reinforcement of different frequencies as a function of their wavelength and the distance between the microphone and the surface.
If on the other hand your microphones are mounted flush with (or within) the surface, you have a boundary layer microphone, with interesting and useful properties. I have sometimes gotten surprisingly good stereo recordings by mounting a pair of directional microphones just a few mm above the floor of a stage, placed centrally and angled apart (see http://www.schoeps.de/en/products/blc). However, you're right to be concerned about solid-borne noise in that situation, and also about people kicking or stepping on your microphones.
--best regards
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Thank you DSatz, I had a feeling my terminology was wrong. Yes, comb filtering. I guess it'll be what it'll be.
Lord Best Tools for the Job --- am I wanting the largest sheet I can accommodate, to catch broad reflections, or in the case of something like a mouse pad, something small just to reduce vibration under the stand's base?
The stage floor is what I'd describe as a typical black, "semi-rubbery," matt surface you see on school and community stages.
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footprint sized. more about isolating stage vibrations. shock mounts for the mics will help even more.
I record onstage with 18 inch stands with my omnis. rubber feat on the stands, and shockmounts, haven't had any issues.
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I do a decent amount of on-stage recording with the mics a few inches to a foot or so above a wooden stage without any additional surface absorbtion and haven't had comb filtering problems. When using directional mics I often angle them upwards to point more directly toward the source, which probably helps to a limited degree in reducing the pickup of reflections off of the floor. I was initially concerned about combfiltering effedcts but that hasn't been a detectible issue for me on any of these recordings, so I never bothered with using sound absorbing surfaces around the mics. Like the othes mention, I'm more concerned about picking up solid-born vibration and noise through the floor and stands.
I've grown to really like the down close to the stage-surface technique for more than just it's low-profile visual impact. Even at what would be very large 'boundary layer' distances of several inches or several feet I find there is boundary-layer effect at the lower frequencies that seems to nicely offset the bottom end roll-off response the directional mics I'm using exibit. But that could be good or bad depending on the quantity of low bass, with big heavy pumping subs it could be unwanted. Also, sounds from distant amps and instruments located near stage level, traveling longer distances across the stage surface seem to have a 'boundary layer-like' clarity to them that could simply be due to a reduced floor reflection (or just the shifting of the arrival time of that reflection) more than actual boundary effect. It seems like the spound 'flows' more cleanly and easily just over the floor than through the open air above it. That's all speculation, yet the good results are ear-confirmed.
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I have [2] Calumet MF6045 stands, and they BOTH have cane bottoms on them to help out from vibrations on the floor, and I must say, they work GREAT!!!!! I superglued the cane bottoms[rubber feet] to my stand legs so that theyre always helping floor vibrations wherever the venue may be. I probably shouldnt have superglued them on, but I did and it is what it is ;)