Notes

Outline

Ottorino Respighi (1879 - 1936)

Energy in Waves

Energy in Waves

Power E = Energy t = Time P = Power   P = E/t =Joule/s = Watt = W

Examples Gasoline Solar Energy

Intensity P = Power S = Surface Area I = Intensity I = P/S  (W/m2)

Intensity Example: over a 5 minute period 3 x 105 Joules of energy from the sun hit a surface.  What is the power?

Intensity and Distance I2/I1 = (r1/r2)2 or I ~ 1/r2

Examples Audio demo Track 11 If the Intensity at 25 cm was 8 x 10-6 W/m2, what are the intensities at 50 cm, 1 m, and 2 m?

Sound Intensity Sound Source         Intensity (W/m2) Saturn rocket at 50 m                                     108 Jet engine at 10 m                                            103 Jet engine at 50 m                                            10 SST takeoff at 500 m; Pneumatic drill          100 = 1 Amplified Rock Music                                   10-1 Machine shop                                                  10-2 Jackhammer at 1 m; Subway train                10-3 Factory                                                              10-4

Sound Intensity Sound Source         Intensity (W/m2) City traffic                                                        10-5 Normal conversation at 1 m                          10-6 Office; Classroom; Quiet auto interior        10-7 Library                                                              10-8 Empty auditorium; City street, no traffic    10-9 Whisper at 1 m                                                10-10 Rustle of leaves; Falling pin                          10-11 Limit of audibility                                           10-12

Sound Intensity Level (SIL) If I2/I1 = 10, then, by definition SIL2 - SIL1 = 10 dB

SIL Difference SIL2 - SIL1 = 10 log(I2/I1) thus if SIL2 - SIL1 = 20 then I2/I1=100 SIL2 - SIL1 = 30 then I2/I1=1000 SIL2 - SIL1 = 40 then I2/I1=10,000

Sound Intensity/SIL Sound Source               Intensity/SIL Saturn rocket at 50 m                                   108   = 200 dB Jet engine at 10 m                                         103    = 150 dB Jet engine at 50 m                                         10     = 130 dB SST takeoff at 500 m; Pneumatic drill       100    = 120 dB Amplified Rock Music                                 10-1  = 110 dB Machine shop                                                10-2  = 100 dB Jackhammer at 1 m; Subway train             10-3  =   90 dB Factory                                                            10-4  =    80 dB

Sound Intensity/SIL Sound Source                         Intensity/SIL City traffic                                                       10-5   = 70 dB Normal conversation at 1 m                         10-6   = 60 dB Office; Classroom; Quiet auto interior        10-7   = 50 dB Library                                                             10-8   = 40 dB Empty auditorium; City street, no traffic   10-9   = 30 dB Whisper at 1 m                                                10-10 = 20 dB Rustle of leaves; Falling pin                          10-11 = 10 dB Limit of audibility                                          10-12  =   0 dB

Examples Two sounds have a ratio of intensities of 4,700.  Find the difference in SIL for the two sounds. If the difference in SIL for two sounds is 8 dB, what is the ratio of the intensities?

Examples Audio demo Tracks 8-10

SIL and the Ear SIL (dB)    Occupational                Occasional      80            No limit                         4 hours      85            No limit                         2 hours      90            8 hours                           1 hour      95            4 hours                           30 minutes    100            2 hours                           15 minutes    105            1 hour                               8 minutes    110            30 minutes                       4 minutes    115            15 minutes                       2 minutes

SILs in Music In traditional music, the sound intensity level is usually in the range of 45 to 95 dB. dB meter

Combined Sounds What happens if we add a 60 dB sound to a 70 dB sound? 60 dB + 70 dB \ 120 dB!!! Instead, Intensities Add. Ic = I1 + I2

Combined Sounds What happens if we add a total of n sources of sound having the same SIL?