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The following is a laboratory report from Acoustical Physics Laboratories:
Acoustical Physics Laboratories has conducted
tests to compare the acoustical performance of the CARDIOCARE
stethoscope with the 3M Litmann stethoscope.
To compare the two stethoscopes, the acoustical output from each
stethoscope's earpiece was analyzed as each stethoscope was
excited by a reference sound source.
The reference sound source consisted of a 3" loudspeaker in a sealed enclosure. A perforated grill witha felt cover was positioned over the front of the loudspeaker to provide a surface upon which to place the stethoscope. The loudspeaker was driven with random noise from 30 Hz to 20 kHz to a reference level of 3.5 pascals (the pascal is an absolute linear measurement of sound pressure level and is expressed as force per area (newtons/square meter).
The stethoscopes were individually placed in contact with the reference loudspeaker's felt cover. The acoustical output from each stethoscope's ear piece was analyzed by coupling a Bruel & Kjaer 4133 microphone to the ear piece and utilizing a Bruel & Kjaer 2123 frequency analyzer. A chart type record was plotted to compare the acoustical output of the CARDIOCARE stethoscope with the 3M Litmann stethoscope.
Chart #1 shows the comparison in acoustical performance between the two stethoscopes. The horizontal axis of the chart represents the frequency or spectral content of the sound in 1/3 octave frequency bands from 31.5 Hz to 16 kHz with A-weighted and unweighted levels shown on the right hand side. The vertical axis of chart #1 represents the linear sound pressure level in pascals. The red line represents the acoustical output from the CARDIOCARE stethoscope in response to the reference sound source. The blue line represents the acoustical output of the 3M Litmann stethoscope in response to the same reference sound source.
The chart shows the the CARDIOCARE stethoscope has a higher level of acoustical output, especially in the high frequency region (1 kHz - 4 kHz) range than the 3M product.