TABLE 2. Overall estimate of the mean spectrum of conversational speech with an overall level of 65 dB SPL.

Frequency, Hz	Mean N0	1/3-Oct level, dB SPL	Diffuse field to eardrum, dB	1/3-Oct level at eardrum, dB SPL	MAP
100	26.2	39.8	0.0	39.8	27.5
125	29.3	43.9	0.1	44.0	23.2
160	33.6	49.3	0.3	48.8	19.2
200	36.9	53.5	0.4	53.9	15.9
250	37.0	54.6	0.5	55.1	13.3
315	36.9	55.5	1.0	56.5	11.0
400	36.5	56.2	1.6	57.8	8.8
500	36.4	57.0	1.7	58.7	7.0
630	34.5	56.1	2.2	58.3	6.4
800	29.9	52.5	2.9	55.4	5.7
1000	25.2	48.8	3.8	52.6	5.7
1250	24.0	48.6	5.3	53.9	7.6
1600	23.2	48.9	7.2	56.1	9.2
2000	20.6	47.2	10.2	57.4	11.6
2500	18.7	46.3	14.9	61.2	13.5
3150	16.5	45.1	14.4	59.5	10.1
4000	12.3	41.9	12.7	54.6	9.7
5000	10.9	41.5	10.8	52.3	10.1
6300	9.1	40.8	8.7	49.5	13.3
8000	7.3	40.0	8.5	48.5	15.3
10000	3.8	37.4	5.0	42.4	13.2
12500	−1.7	33.0	4.0	37.0	18.1
16000	−6.4	29.2	2.0	31.2	44.1

The first column shows the center frequency. The second column shows the spectrum level (N0) at that frequency (re 20 μPa). The third column shows the level per 1/3-octave band. The fourth column shows the diffuse-field to eardrum transfer function. The fifth column shows the estimated level per 1/3-octave band at the eardrum, obtained by adding the numbers in columns three and four. The sixth column shows the estimated normal minimum audible pressure (MAP) for monaural listening.