natus Madsen A450, Руководство пользователя

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White noise for Pure Tone masking
Conversion between displayed “effective masking level” and sound pressure level
The level of white noise used for masking of pure tones is indicated in dB of “effective masking level” in Otosuite. This
means that the sound pressure level of the power contained in a third-octave band around the presented pure tone fre-
quency will equal the attenuator setting, plus the RETSPL at the pure tone frequency, plus the noise correction factor
from ISO 389-4:1994, Table 1.
The following tables can be used to calculate the actual sound pressure level of the white noise signal for a given atten-
uator setting (Table 1), or to select the attenuator setting required to obtain a specific level in dB SPL (Table 2).
Note: As the sound pressure level of the white noise signal will be quite high even for moderate attenuator settings, a
warning sign will be displayed in Otosuite for levels above 100 dB HL.
Table 1 - Offset from Effective Masking Level to Sound Pressure Level
Frequency (Hz) 125 250 500 750 1000 1500 2000 3000 4000 6000 8000 9000 10000 11200 12500
Offset (dB) N/A* 53 37 32 31 29 30 29 27 31 27 26 26 25 25
This table indicates the number (“Offset”) to be added to the displayed masking level in order to calculate the sound pres-
sure level in dB SPL.
* White masking noise is not available at 125 Hz
Table 2 - Attenuator settings required to obtain a white noise level of 80 dB SPL
Frequency (Hz) 125 250 500 750 1000 1500 2000 3000 4000 6000 8000 9000 10000 11200 12500
Attenuator setting to
obtain 80 dB SPL
N/A* 27 43 48 49 51 50 51 53 49 53 54 54 55 55
This table indicates the attenuator settings required to obtain a sound pressure level of 80 dB SPL at indicated frequencies.
Stimulus modulation
FM (Warble): Adjustable modulation rate and depth
• Modulation rate: 1-20 Hz (default: 5 Hz).
• Modulation depth: 1-25% of center frequency (default: 5%).
SISI: 5, 2, 1 dB increments
Accuracy of sound level
Entire level range (AC): 125 to 5000 Hz: ±3 dB, 5000 to 8000 Hz: ±5 dB
Entire level range (BC): 250 to 4000 Hz: ±4 dB
The reference conditions for the specification of frequency response and sound pressure level depend on the type of audi-
ometer. Madsen A450 can be calibrated as either a “corrected” (Type AE) or “uncorrected” (Type A) speech audiometer:
24 Madsen A450
16 Technical specifications