The purpose of this lab is to find out what the reverberation time (RT60; Rossing ch. 23) is in the lecture hall. This was measured under four different conditions:

1. at 300 Hz. with the mic in the middle of the room (the normal mic placement);

2. same as above, but with the mic about 2 feet from the speaker (!)

3. same as (1), but with the frequency raised to 3000 Hz.

4. same as (3) (i.e., frequency still 3000), but this time with the curtains drawn in front and back of the room.

Your assignment, due Thursday Nov. 20, is to measure the reverberation time ("RT60") of the room in each of these cases. Which of the three modifications had the biggest effect on the measured reverb time?

Here are the four runs:

Run 1 (above), is the original setting. The horizontal axis is tenths of a second and the vertical one is decibels.

Here some lines have been addded to demonstrate how to find reverb time. (Note: I moved them since class to fit the data better, I think.) The question is: over how much time does the decaying portion of the sound level drop by 60 dB? The answer is the difference between the points of interstection of the vertical and slanted lines with the time axis.

Here (above) is the second one, with the mic closer to the speaker. Note the higher initial level of sound. The reverb time is the final slope of the decaying level.

Here (above) is the result at 3000 kHz.

... and here it is when the curtains were drawn.

The data collection in this lab was done in class, Nov. 18.