Page 707 - Automotive Engineering Powertrain Chassis System and Vehicle Body

CHAP TER 2 1. 1 Interior noise: Assessment and control

(a) 100 (b) 10
NR
SRI
90 9
80 8
Reverberation time (s)
70 7
60 6

dB 50 5
40 4
30 3

20 2
10 1
0 0
0 2 4 6 8 10 0 2 4 6 8 10
Frequency (kHz) Frequency (kHz)
Fig. 21.1-16 Measured NR and SRI (TL) curves along with reverberation times.

contiguous 1/3 octave bands between 125 Hz and 4000 21.1.10.4 The significance of acoustic
Hz inclusive. These measured values are then compared seals and controlling flanking
to a family of reference curves as shown in Fig. 21.1-17. transmission
To determine the STC of a panel, the reference con-
tour is chosen so that the maximum deficiency (deviation The need for tight acoustic seals between adjoining
of the data below the contour) at any one frequency does panels cannot be overstated. Even the smallest air gap
not exceed 8 dB and the total deficiency at all frequencies will limit the maximum TL that can be achieved, par-
does not exceed 32 dB. The STC of the panel is then the ticularly at higher frequencies. A simple yet effective
value of TL corresponding to the value of the chosen way of detecting sound leaking around a seal between
reference curve in the 500 Hz band. STC values are panels is to use a length of narrow bore (5 mm) plastic
published widely in the literature, for example in Kinsler tube, place one end in one ear and pass the other end
et al. (1982).

50

45

Transmission loss (dB) 40 Measured TL

35
STC = 42

30

25

20
10 2 10 3 10 4
Frequency (Hz)
Fig. 21.1-17 STC curves: data after Kinsler et al. (1982).

718