Design of Multimedia Classrooms and Laboratories

Suggestions for Layout and Design

Audio Design

Audio Sources:

Using Mackie 1202 mixer: Mix wireless microphone and PC/workstation line outputs to Alt 3/4; assign remote audio to main mix. Connect Alt 3/4 output to workstation input for distribution to remote sites. Assign Alt 3/4 to main mix [or patch it back to another stereo input], with remote audio added; connect main mix to house audio (amplifier).

Alternative: Tap remote send from AUX1 or AUX2, and set remote source (from network) to AUX zero, all other sources mixed onto AUX. Main mix goes to amplifier and recording.

Instead of or in addition to having per-student microphones, it may be possible to use a parabolic or shotgun mike on the audience camera. However, voice quality (frequency response) may be degraded.
Student, instructor and remote microphone treated as independent multicast participants; speaker only plays remote participants Remote audio may leak back through student microphones, although this can be made less likely if gating is used and speaker is at front of class. (Should not be a problem any more than acoustic feedback?) Cannot use single echo canceller since its microphone input would have to connect to the local mix only and feed the echo-cancelled (minus delayed version of remote) to remote. Problem: delay. Recording needs all network sources.

Audio tool maps local network participants to left channel, remote participants to right channel. Recording mixes both channels plus local wireless microphones, amplifier for house audio only plays right channel. If amplifier has input selector, define two channels: one that copies right channel onto both, one regular.

Students, instructor and remote microphone treated as independent multicast participants; per-workstation echo cancellation (such as CallPort) Expensive; may not work as room is larger than assumption of cubicle. Sound may leak from neighboring speaker.
Local microphones are mixed by the network and fed to microphone input of echo canceller; remote audio is connected to phone input
Need to modify network audio tools to indicate current talkers or make it appear like a mixer.
Fully integrated solution, with echo cancellation in each workstation workstation
Nice research project. Delayed version of remote sound is subtracted from microphone inputs. Note that delay between the remote sound seen locally and the loudspeaker may change as student and master workstation adapt to delays independently.
Gated mixer (Shure, Biamp, Audio-Technica, IRP) mixes all local microphones into single workstation
Automatic mixers may not work well with students rustling papers or tapping desk. Need to switch microphone to be connected to workstation for use in for multimedia applications and collaboration.
Students wear headphones
May not be practical (loss, not natural), but may be acceptable if one-eared and lightweight.

Instead of single speaker, have two speakers sets (middle, front, and monitor for instructor)


CVN uses fluorescent lights with a light temperature of 3500 K. Daylight is 5500 K and incandescent light produces 2700 K. Video can white balance to any temperature.


Video sources (instructor monitor (see nv!) or selected windows, camera image of student, audience camera, document camera, camera image of instructor) must be combined into single NTSC output for recording onto tape.

One approach would display these sources on a second (640x480) monitor in the control room, manipulated by controls on the first monitor. The second monitor output is then scan-converted as usual. Windows on the second monitor would be tiled and not have decorations. This assumes that local video cameras can produce smooth 30 fps video.

In a more traditional approach, all non-student cameras and a copy of the projection monitor output are mixed by a digital video mixer.



Bose 102F72 with 102G speaker grill
Amplifiers, surround sound:
Digital mixer:
Automatic mixers:
Listing; note: may require special microphones
Feedback prevention:
Shure DFR-11
Video mixer:
Videonics MX-1 ($887.99).
Mix minus subtracts "caller" from program:
Henry Engineering; works only if no delays
VCR controller for Sony (RS-422
RS-422 controller
Acoustic treatment: AlphaTec (Don +1 800 782 5742)
Echo cancellation:
Coherent, Gentner

Room Sizing

Tablet-arm chairs: room size minus 50 sq. ft. for teaching area and divide by 15 sq. ft. per student. Classrooms with only one entrance/exit door are limited to a maximum of 49 occupants. When seats are fixed as little as 12 square feet per student may be required by code.
depth depth to rear corner seat sq. ft. students screen size screen width screen height screen mounting height overhead projector distance
< 30 35 900 20-50 6' 72" 72" 8.2' 8.6'
30-35 35-42 900-1200 50-100 7' 84" 72" 9.25' 10.3'
35-40 40-46 1200-1600 100-150 8' 96" 72" 10' 11.8'
40-46 46-52 1600-2100 150-210 9' 108" 78" 10.75' 13.3'
46-52 52-58 2100-2700 210-300 10' 120" 90" 11.5' 14.8'
52-58 58-64 2700-3300 300-400 12' 144" 108" 13' 17.7'
58-64 64-70 3300-4100 400-500 14' 168" 126" 14.5' 20.6
depth students front space
< 27' < 30 9'
27'-32' 30-50 10'
32'-37' 50-100 11'
37'-42' 100-150 13'
42'-48' 150-210 15'
48'-54' 210-300 16'
54'-60' 300-400 18'

Last modified: 1997-08-24 by Henning Schulzrinne