Answer
2—Hoth
noise is used to model indoor ambient noise when evaluating
communications systems such as telephones. The first study
of this was done by D.F. Hoth, and published in “Room
noise spectra at subscriber’s telephone location” (Journal
of Acoustical Society of America, 1941). The official
definition of Hoth noise is IEEE Standard 269-2001 (revision
of IEEE Standard 269-1992), “Draft Standard Methods for
Measuring Transmission Performance of Analog and Digital
Telephone Sets, Handsets and Headsets.”
The
table below gives the spectrum density adjusted in level
to produce a reading of 50 dBA.
|
Frequency (Hz) |
Spectrum Density (dB SPL/Hz) |
Bandwidth 10 log_f (dB) |
Total Power in each 1/3 octave band (dBSPL) |
Tolerance (dB) |
|
100 |
32.4 |
13.5 |
45.9 |
±3 |
|
125 |
30.9 |
14.7 |
45.5 |
±3 |
|
160 |
29.1 |
15.7 |
44.9 |
±3 |
|
200 |
27.6 |
16.5 |
44.1 |
±3 |
|
250 |
26.0 |
17.6 |
43.6 |
±3 |
|
315 |
24.4 |
18.7 |
43.1 |
±3 |
|
400 |
22.7 |
19.7 |
42.3 |
±3 |
|
500 |
21.1 |
20.6 |
41.7 |
±3 |
|
630 |
19.5 |
21.7 |
41.2 |
±3 |
|
800 |
17.8 |
22.7 |
40.4 |
±3 |
|
1000 |
16.2 |
23.5 |
39.7 |
±3 |
|
1250 |
14.6 |
24.7 |
39.3 |
±3 |
|
1600 |
12.9 |
25.7 |
38.7 |
±3 |
|
2000 |
11.3 |
26.5 |
37.8 |
±3 |
|
2500 |
9.6 |
27.6 |
37.2 |
±3 |
|
3150 |
7.8 |
28.7 |
36.5 |
±3 |
|
4000 |
5.4 |
29.7 |
34.8 |
±3 |
|
5000 |
2.6 |
30.6 |
33.2 |
±3 |
|
6300 |
–1.3 |
31.7 |
30.4 |
±3 |
|
8000 |
–6.6 |
32.7 |
26.0 |
±3 |
Contributor: David Tweed
Published
September 2003
