Problems

1. Prepare a paper on the methods of measuring the sound-absorption coefficients of the various materials, furnishings, and objects used in radio studios.

2. Calculate the reverberation time for the auditorium considered on page 24 if plain plywood chairs are used, and with the auditorium empty, with 250 people, and with 500 people present. Would the auditorium be satisfactory for speech and music? If not, what would you recommend?

3. An auditorium is 125 feet long, 40 feet high, and 75 feet wide. The walls, ceiling, and floor are of glass, plaster, and painted wood. Assume that the average sound-absorption coefficient of these surfaces is 0.05 at 512 cycles. There are 1800 plain chairs in the room. Calculate the reverberation time when the room is empty, and with 500, 1000, 1500, and 2000 people present. Plot a curve showing these relations. How many square feet of sound-absorbing material having a coefficient of 0.47 should be used to reduce the reverberation time to an acceptable value when 900 people are present? Where should this material be placed?

4. One motor is mounted in each wing of an airplane. Analyze the means by which sound can be transmitted into the cabin, and explain the steps that should be taken to ensure that the cabin is reasonably quiet.

5. A room is 25 feet long, 15 feet wide, and 12 feet high. The walls and ceiling are plastered, and the floor is covered with linoleum. There are 10 desks, 10 chairs, and 10 persons in the room. Two of the persons are supervisors, and the remainder are typists and clerks. The noise level is 78 db. What should be done to reduce the level 5 db? To reduce it 10 db? What effect will this have on private conversations between the two supervisors, whose desks are adjacent?