navigation bar

Using AUDIO-CD with Speakers

Use of the AUDIO-CD is not limited to the investigation of hearing thresholds with just headphones and earphones. Headphones are useful in noisy situations, since they can reduce the background noise by about 10-30 dB (depending on the frequency and the headphones type). The testing of hearing thresholds with speakers allows for so-called "free field testing". This type of testing should be performed in a quiet room, such as an audio booth, anechoic chamber or a sound studio. This kind of measurement technique can also be used for testing of hearing thresholds in animals (from small to big), since there are no headphones readily available for them ... :-).

If the speakers' response is flat (say better than +/-3 dB in the range 20 Hz - 20,000 Hz) then the calibration only needs to be performed at 1000 Hz (the STS signal on track No.10). In this case the sound level meter should be used for calibration. Play track No.10 from time 1:10 to time 1:20. The maximum sound level measured around the ear/head position should be 80 dB SPL (on a flat scale, fast response setting), which is reached at time 1:20.

If the speakers' response is not flat (say it varies more than +/-6 dB in the range 20 Hz - 20,000 Hz) then the calibration should be performed at 1000 Hz (the STS signal on track No.10) and a correction factor for every STS frequency above and below the 1000 Hz STS signal should be measured with a sound level meter. These correction factors can be in turn used to correct measurements of thresholds using the AUDIO-CD.

If only one STS frequency is used (for a single-frequency threshold value) then the calibration should only be performed at this particular STS frequency.

Note 1: Room acoustics plays an important role in the evenly distributed sound field.

Note 2: The frequency response can be considerably affected by reflections and room resonances.

Note 3: To obtain a more even distribution of sound in a room, The STS should be fed to more than one speaker. The best results can be obtained with 4 - 8 speakers.

Note 4: In this test both ears are exposed simultaneously to the sound field. To test only one ear an ear plug or masking noise should be used in the ear not being tested.

Note 5: Be careful while adjusting the volume on the amplifier. Start from low levels and gradually increase it to get 80 dB at time 1:20 on track No.10. You can also use ear plugs as an extra safety precaution during this calibration. Never leave the AUDIO-CD in your CD player. Store it in a safe place, away from the reach of children.

Symbols / Terms Used:
  • Hz - unit of frequency
  • dB - unit of SPL
  • SPL - Sound Pressure Level
  • STS - Special Test Signal (described as part of AUDIO-CD)
  • Sound Level Meter - instrument to measure SPL
Test your
WWW Hearing Test
the first comprehensive and entirely web-based hearing test

Test your hearing with AUDIO-CD

Use Digital Recording's inexpensive semi-professional coupler DR1-R with a Radio Shack Sound Level Meter to calibrate headphones, earphones, microphones or other SLM's.

Terms of Use | Return Policy | Privacy Policy

Copyright (©) 1996-2014 by Digital Recordings. All Rights Reserved.
No part of the information provided on this www page may be reproduced for any purpose, in any form, without prior written approval.
This site uses frames. To enjoy them your screen's resolution should be at least 800 x 600, preferably 1024 x 768. To invoke frames click here.