November 2002 Meeting
Date: Sunday, Nov. 24
Time: 6:00 PM
Place: Room 120
National Transportation Systems Center
55 Broadway, Cambridge, MA
Sub: The Results of the BAS Headphone Test Clinic
Featured Guests: Dave Hadaway, Alvin Foster, & Jim Doucas
There are numerous measuring standards in the headphone industry and wide disagreement on how and what to measure. On Saturday,
March 23, 2002, three testing gurus undertook the substantial job of testing thirty-four headphones at the BAS clinic. Jim, Alvin, and Dave developed
a system utilizing the B&K Telephone Test Head, a pressure microphone, and a spectral analyzer. Our BAS findings from the 34 headphones indicate
good reliability and results that correlate well with members' subjective evaluations.
At the clinic the testers examined and measured the following items: (1) impedance, (2) frequency response, (3) sensitivity, (4)
IMD at 100 dB SPL and at the 10% distortion level, (5) THD at 100 dB SPL, (6) a scope trace of a 400 Hz square wave, and (7) subjective audio quality.
We could not persuade any BAS member to sit through the insertion of a prob into his/her ear to obtain our required flat diffuse-field
function; we, therefore, substituted the human ear canal with the B&K Test Head. It uses a tiny horn like structure to couple the distance between
the microphone and the ear. The cup is about ¼ inch deep and one inch wide, small enough to prevent colorations caused by reflections while providing
a near anechoic environment required for a representative frequency response.
Our meeting Sunday will provide each attending member a printout of our summary findings. The complete report will appear in an
upcoming journal. An overhead projector will be used to illustrate some of the distortion examples, and some parts of the clinic will be set up to
explain in detail how the tests were done.