Room mic's for small audience
I'm looking to install some fixed mics for a small room (about 35ft wide, 25ft deep) with theatre seating for an audience. This room will be used for presentations (presenter at podium, powerpoint on projector screen next to him/her) and we need to record audience questions audibly. This is for video recording only, and it is not being amplified in the room -so there is no feedback issue. The presenter will have a lapel mic. What type of mics should I install? Should they hang from the ceiling like is often seen for choirs in churches? Any specific mic recommendations? Ideally, I want it to be less 'roomy' sounding and more present, though I know it can't be perfect. These mics will have to remain open since there will not be any sound operator while the presentation is going. The room is very quiet so ambient sound shouldn't be an issue.
Any tips/advice and links to mics/installation equipment is greatly appreciated.
[Tim Neighbors] "I'm looking to install some fixed mics for a small room (about 35ft wide, 25ft deep) with theatre seating for an audience. This room will be used for presentations (presenter at podium, powerpoint on projector screen next to him/her) and we need to record audience questions audibly."
Fixed "room mics" are not going to work like you seem to want. Microphones aren't like the human auditory system. Mics don't just show you what you want to hear and throw away the rest like the human brain does. What you always get from a mic is everything it hears. Everything. The reason to close-mic dialog is to have a decent signal to noise ratio. Where the signal is the dialog you want to hear, and the noise is everything else. As you increase your distance from the signal source, the level of the signal declines until it becomes equal to the level of the noise. Yuck.
What does this mean to your application? If you install "room mics" you'll have to turn up the gain on your mic preamps to get a decent level on your audience member's question. This will in turn raise the level of every noise the rest of the audience is making (coughs, pages turning, noise like squeaks from the chairs, all the murmured conversations, phones, computers, etc.). Not to mention turning up the level on the building HVAC, light hum, reverb from the speaker in the hall, etc. And it will all be at a level just below the audience member's spoken question. You aren't going to like it.
But there's no reason to take my word for it. You can do the experiment yourself. All it takes is the lavalier you use for the presenters, or even a cheap all-in-one "shaver" like a Tascam DR-05 or a Zoom H1. Place it on the podium (to get closer to mouth level so you don't have to bend down so much), get your mouth 60cm away or so, and ask a typical audience member question. Then repeat, but move 2m away, and then again at 4m away, etc. Listen to the recordings you made. See what you think.
What this little experiment will show you is that if you want the questions from widely scattered audience members to be the match for lavalier wearing presenters you need to get the mic closer to them than a fixed room mic can be. You need to be closer than around 60cm to the person talking if you "want it to be less 'roomy' sounding and more present" as you say.
This implies a boom person with a boom pole that has enough reach to get to the person speaking, or a couple of people with hand held "reporter mics" who can move around the audience and put a mic in front of a speaker, or a "question station" with a mic on a stand that people queue up behind to ask their questions.
That's just exactly what you're trying to avoid, I know. But the laws of physics are not easily bent I'm afraid.
Thanks for the response Bruce. I'm aware of this and I know it won't be pretty. I know that without some sort of close-mic solution as you mentioned, a very clear, present signal is not possible. I'm just looking for the best solution that doesn't involve extra crew. As it is, they can't hear audience questions at all. Perhaps a pair of hyper-cardioids cross-shooting the crowd kept pretty low in the mix with the presenter could at least allow a viewer to be able to make out the question? I kinda suspect that passing around a wireless mic or asking people to walk up to a "question station" mic won't work because they are not being amplified in the room, so people will just think the mic is broken and start using it as a pointing stick. I guess one option is to actually amplify it in the room, but its such a small room, people will probably not feel that the amplification is necessary and will again not use the mic.
How about boundary mics, like they use in live theatre? or hanging mics like they do over a choir? By hanging them, we could potentially get 10-20 feet from people. Or perhaps it's a fools errand, and it will introduce more room noise than it's worth.
This question is asked almost weekly if you subscribe to many audio forums. And nobody has ever devised or discovered the solution that Mr. Neighbors is seeking. As Mr. Watson (and famously Montgomery "Scotty" Scott, engineer of the star-ship Enterprise) says: "You cannot change the laws of [acoustic] physics.
After going through dozens of variations on this theme, the solution that usually works best for me is to have the presenter repeat the question. That typically clarifies the question and gives the presenter time to assemble the response. If necessary, put someone on the front row whose job it is to remind the presenter to repeat the question if they forget.
There was an era where you could find "teleconference rooms" where they had a jungle of hanging microphones to attempt to pick up speech from around the room. But that proved to be more trouble than it was worth. And now teleconference systems typically use table-top "barrier microphones". But, of course, that won't work unless the audience is sitting around a big table.
[Tim Neighbors] " I'm just looking for the best solution that doesn't involve extra crew. As it is, they can't hear audience questions at all."
Since this is video only, the best thing I've found is to post the question in a lower third on the video itself. Let the viewer read it and forget about them being able to hear it (or hear any more of it than the presenter's lav can give them). My experiments lead me to think you need it on the screen for about seven seconds or a little more if you can. And try to edit the question down to where you can put it on a single line on your lower third. You can't put a paragraph up on the screen and expect people to read it. Also, do some legibility testing. It takes a surprisingly big font to be seen on a small screen. But all that said, this is done all the time, and is probably the most used solution to your problem for videos of classes and presentations. It won't work for everything, but it works for a lot of things like this.