THE SCIENCE AND APPLICATIONS OF ACOUSTICS - H. H. Arnold ...

Problems for Chapter 12 3173. A 0.75 m 2 sample of building material is placed in a window between areceiving room and a source room. Sound transmission occurs only through thesample. The sound level in the source room is 89 dB and that for the receivingroom, with 3.0 m 2 equivalent absorption, is 69 dB. Find the transmission lossand the transmission coefficient for this material sample.4. A wall consists of the following: a 22-dB (transmission loss at 500 Hz) wooddoor which takes up 25% of the exposed area, 2.2% airspace, and the remainderof the exposed wall area is a solid wall with 52 dB TL. Determine the TL ofthe composite wall at 500 Hz.5. Repeat the above problem but with the airspace reduced to 0.2%.6. Repeat Problem 4, using a 36-dB TL door. Also determine the benefit ofreducing the airspace from 2.2% to 0.2%.7. A room is subdivided in its middle by a concrete wall with a transmissionloss of 62 dB. The room is 4.5 m high, and the division occurs across theentire width of 11.8 m. In the middle of the dividing wall there is a door 2.5 mhigh × 1.0 m wide. The door’s rated transmission loss is 29 dB. There is acrack underneath the door that extends across the door’s width and it is 2.6 cmhigh.(a) Determine the effective transmission loss of this structure.(b) If you could reduce the crack to 0.30 cm (by lengthening the door) whatwillbe the change in the overall transmission loss?8. Develop an equation for transmission loss versus frequency for 4-mm glass inthe mass-controlled region. Glass may be assumed to have a specific gravityof 2.6.9. It is desired to increase the transmission loss of a panel in the mass-controlledregion by 5 dB Find the necessary change in thickness.10. Find the transmission loss and transmission coefficient for 8-mm glass at thecritical frequency. Assume a loss factor of 0.06.11. Redo Problem 9 for 14-mm glass with a loss factor of 0.1.12. Consider a double wall panel with airspace h (given in mm). One panel has70% the surface mass of the other, and the sum of the surface masses is m t (inkg/m 2 ). Plot the resonant frequency versus the product of m t and h.13. Determine the resonant frequency of a double-paneled partition constructedof 4 lb/ft 2 and 6 lb/ft 2 panels with 5.2-in. airspace.14. A wall was measured for its transmission loss in one-third octaves beginningat 125 Hz. The values were: 25, 24, 30, 32, 39, 41, 41, 46. 47, 49, 47, 46, 48,49, 45, and 46. Find the sound transmission class (STC).15. Redo Problem 14 with the TL values in the four highest third-octaves being39, 40, 38, and 39.16. Find the SIR for the wall of Problem 14.17. A 6 m × 2.5 m wall with a transmission loss of 35 dB separates two rooms.A noise source in one room yields a reverberant field with a sound pressurelevel of 120 dB near the wall. The other room has a room constantR = 130 m 2 . Predict the sound level pressure near the wall in the latterroom.