What to look for in microphone to capture sound in larger area?

Question

I have a couple classroom-like spaces, where as many as 30 people will meet together. These rooms have a computer and a projector installed. Recently, users in these rooms have wanted to add the ability for one or two members to Skype in to the meetings. This itself is simple enough.

The problem I am running into is selecting a microphone. Most anything I search for has a pick up range of 2 or at most 3 meters, and that's not going to cut it. The microphone will be at the front of the room, and I need it to pick up speech from the back of the room... up to 10 meters away.

What/where should I look for to find candidates?

Everything I'm seeing says that to avoid the problem of the mic picking up any output from the computers speakers (ie: also hearing the person on the other end of the call) I will need several mics spread through the room, each with lower pick-up settings, and that just won't work here.

Is there any way to get around this?

Update:

I've also been looking at cameras, and I'm thinking of this item:

http://www.logitech.com/en-us/webcam-communications/webcams/devices/tvcam-skype?WT.ac=ps%7C8278

I had been assuming there is no way the microphone built into a web cam would be adequate, but reading reviews on this model it might be able to do the job. Since I have to get a camera anyway, I may try it with the built-in mic first and see what happens.

Also, for my own records, I'm looking at this mic:

http://www.amazon.com/MXL-AC404-USB-Conference-Microphone/dp/B001TGTDFM/ref=pd_sim_e_5

Though using a usb mic might mean manually selecting the correct audio source... an additional step for users that I'd like to avoid if possible.

Answer 1

Unfortunately you can't fight the basic laws of physics. You will get a drop of around 6dB (the level will half) for each doubling of the distance from your audio source, ie whoever is speaking. This is known as the Inverse Square Law.

As you have read, if everyone needs to simultaneously be capable of taking part in the conference the most common method to counteract this is to place a number of microphones within the space. This however will provide a whole new suite of issues to do with phase difference etc which must then be counteracted with digital signal processing equipment designed for this purpose.

However, in your case as these are learning environments, rather than everyone having equal participation there is usually one (or a small number of) primary participants - generally the teacher - which will be interacting with the far end. A far simpler (and much, much more economical) approach in this scenario is to provide these people with lavalier microphones. This will also greatly assist with combatting echo cancellation issues that you will face in any amplified conferencing environment.

As far as cameras go that's a whole other problem that I'd recommend splitting out into a new question.