What are the best hanging microphones to pick up students in classroom?

dlanktree

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I am trying to microphone a classroom with approx. 40 to 50 students. They are sitting on chairs with tables in fron of them. The room size is approx 30 ft wide and 40 ft deep. I was thinking of using nine hanging microphones. I am trying to pickup questions that the teacher will answer. The teacher is wireless miked. The students questions will not be broadcast through the speakers, just for recording purposes. Any thoughts?
 

zuixro

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We have a 444 seat theatre, and a single SM-81 will pick up anyone talking in the house or on stage. Someone was walking on stage, talking on his cell phone, and I was able to hear the other person talking.

That was with the mic sitting on the balcony at the back of the house though. If the classroom is wider than it is long, you may need two.
 

DuckJordan

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We have a 444 seat theatre, and a single SM-81 will pick up anyone talking in the house or on stage. Someone was walking on stage, talking on his cell phone, and I was able to hear the other person talking.

That was with the mic sitting on the balcony at the back of the house though. If the classroom is wider than it is long, you may need two.
Biggest problem theatre's are designed to amplify noise (most of the time), class rooms are generaly square boxes designed to fit as many students as possible (generaly not the best acousticly).

I wouldn't expect you'd need more than 4 mic's as long as you don't have issues with feedback (since they won't be played through the speakers) this would allow you to adjust the gain to whatever extent you needed before you hit the point where it starts picking up cable noise.

What are you planning on using this for, Recording? live? or something of a mix, if its a recording then after you get the tracks you can edit the loudness of specific people (AKA the people closest to the mics, to the farthest).
 

museav

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The goal of getting a recording where you can clearly understand the student questions may be more difficult than simply picking up their voices. There actually is a Standard for classroom acoustics and some schools apply it, but many do not. As a result, the room acoustics and mechanical system noise may have a significant impact on what works best as could factors such as the ceiling height and how high you could mount the mics. I've seen systems that do a great job of picking up all the noise from air conditioning vents or all the reverb in the room and filtering and editing can only do so much in trying to address these.

How do you plan to mix the mics? Multiple mics can work well if you can get each mic to cover a specific area but often the difficulty is in not having sounds picked up by multiple mics with varying levels and delays due to how far the mics are from the sound source. Also, how do you get the mics to not pick up the Instructor's voice? Are you planning on having an operator doing a live mix or some form of automatic mixing? Again, there is only so much you can practically do if such issues are not addressed in the original recording.

Also consider that if you install a sound system in a classroom with that many students then ADA may require that it also be used to support assistive listening.
 

pmolsonmus

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Milwaukee
It sounds like you're creating some sort of broadcast (podcast) recording. The wireless that the teacher uses works for that purpose but the questions that students ask cannot be heard on the recording. Correct???

When you combine signals from any multiple mic set-up you create problems with phase cancellation/comb filtering (one mic's pick up pattern crossing with another mic's pattern) 9 mics for a classroom of 40 sounds like overkill and a cancellation nightmare.

Unless you plan to multitrack and edit out the non-used mics (not a typical scenario for educational videos) you have a challenging recording scenario.

Best would depend on the room and the eventual mic configuration. For that I would recommend bringing in someone to physically scope out the set up and give advice with your needs clearly identified. The layout is critical to the configuration.

Easiest and cheapest fix (and not a bad educational tool either) is to have the instructor repeat the question. Another good trick is to add text to the video for student's questions.

Good Luck
 

DuckJordan

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One thing i didn't think of, would it be too much of a distraction to have someone come over with a wireless hand held, for their questions? like studio broadcaster style.
 

FMEng

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I have done this sort of recording for broadcast. You will have to keep the number of open microphones to a minimum, or all you will record is a cacaphony of room noise, along with comb filtering from multiple mics picking up one voice. One way to do it is by multi-tracking so you can remix after recording. Another way is to use an automatic mixer. The hardest method would be to mix the recording on the fly, but that can be tough if the back and forth is spontaneous.

I would use a PZM on each table, assuming 4 to 5 students per table. They will vastly outperform hanging mics.

Another method would be to use a couple of wireless, roving mics on fish poles. You would need assistants to move the mic to the person speaking. This is low tech, relatively cheap, and the most likely to provide good results.
 

museav

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I have done this sort of recording for broadcast. You will have to keep the number of open microphones to a minimum, or all you will record is a cacaphony of room noise, along with comb filtering from multiple mics picking up one voice. One way to do it is by multi-tracking so you can remix after recording. Another way is to use an automatic mixer. The hardest method would be to mix the recording on the fly, but that can be tough if the back and forth is spontaneous.

I would use a PZM on each table, assuming 4 to 5 students per table. They will vastly outperform hanging mics.
My initial thought was even a mic for every student or two. When you think about it, the application is not that different from audio or video conferencing except with no far end audio unless you consider the instructor's mic as such. So the approach should also perhaps be similar to that commonly used for conferencing applications which is usually to minimize the talker-to-mic distance and the number of open microphones and to maximize the direct-to-reverberant energy ratio at the mics.
 

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