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Figure 1. Frequency spectrum of the wide band noise (WBN) used for the exposure. The curve drawn with a thick line displays the frequency distribution of the WBN at level of 90 dBlin SPLrms measured with free field condenser microphone (B&K 4133). The curve drawn with a fine line display the frequency distribution of the WBN measured at the ear drum with an ER-7C tube microphone of an anaesthetised rat, laying in the bottom of the cage. The overall noise level was 9 dB higher when measured in the ear canal, and in the 6-12 kHz range even up to 15 dB higher than the measurements made with the free field microphone.

Figure 1. Frequency spectrum of the wide band noise (WBN) used for the exposure. The curve drawn with a thick line displays the frequency distribution of the WBN at level of 90 dBlin SPLrms measured with free field condenser microphone (B&K 4133). The curve drawn with a fine line display the frequency distribution of the WBN measured at the ear drum with an ER-7C tube microphone of an anaesthetised rat, laying in the bottom of the cage. The overall noise level was 9 dB higher when measured in the ear canal, and in the 6-12 kHz range even up to 15 dB higher than the measurements made with the free field microphone.