Having your hearing tested - observations
I've mentioned before that I have my hearing tested every two or three years. It's painless and surprisingly, here in the UK a hearing test is free. It takes about ten minutes to perform. As the local health center was offering a walk-in hearing test last Saturday I popped in and took my turn.
The first point to make is that equipment is not standardised across the profession. This time, using a very new fancy test set, the highest test frequency was 8kHz - just an octave or so above tweeter roll-up in a typical hi-fi speaker and far below the '20kHz' quoted as the highest audio frequency. It seems that the hearing aid manufacturers (Philips etc.) consider that improving hearing acuity up to 8kHz or so dramatically improves intelligibility, with little benefit beyond that frequency. It was said that the very latest, state-of-the-art hearing aids pushed that upper cut-off to 12kHz or so at very considerable expense - perhaps GBP 7000 for a pair of aids. The acoustic benefits of the 8-12kHz band were said to be marginal.
My test was in a normal doctor's consulting room. There was no soundproofing, and the noise from passing cars/planes made it very difficult to hear quiet tones, especially in the lower frequencies due to acoustic masking. However, all was well and my next appointment is booked for twenty years hence. However, the previous test using different equipment in a rather quieter environment showed (as I recall) that my two ears were (very typically) not exactly matched around 8-12kHz. This test didn't expose any such issue due to the lower upper frequency bandwidth.
In discussion with the acoustician several points are noteworthy -
1. Don't hesitate to check the qualifications of the test technician. No qualifications are required to give a hearing test. This may introduce a degree of variability and uncertainty into the process
2. If you are really serious about accuracy, you have to test in an extremely quiet room or better still in a soundproofed box - this is available in the better clinics. If you don't the masking effect can introduce errors of 10db or more in your reported acuity in what we'd call the midrange and bass
3. Enquire how recently the equipment was calibrated and against what standard
4. Look for big deviations in the sensitivity/frequency graphical results. The test is not designed to tease out fractions of a dB of hearing performance. In my test the levels were dropped in steps of 6dB (half sound pressure) at the test frequencies and that's a very detectable level change
5. The frequencies are widely spaced and it may not be safe to interpolate hearing performance between these spot frequencies e.g. 1khz, 2kHz, 4kHz, 8kHz
6. Age inevitably reduces high frequency acuity but in normal, health (but old) ears that diminution in sensitivity is gradual and progressive with increasing frequency. Everyone above 50 or so - even living in the most remote jungle - will be many dBs down in sensitivity at the very highest frequencies and probably no 50 years old can hear above 15kHz at best
7. Extended high frequency performance beyond, say, 15kHz adds nothing to the enjoyment of music because the amount of energy above 15kHz in classical music is utterly insignificant. Admittedly with pop music (esp. featuring electronic instruments) there could be significant energy above 15kHz but is it musical energy or just noise?
8. Our ears are quite unique and no two individuals will have the same hearing. Even between twins, where one has been exposed to loud noise there will be a measured impact on acuity
9. IF YOUR EARS RING WHEN EXPOSED TO LOUD NOISE YOU ARE MOST LIKELY DAMAGING THEM
10. It is your duty and responsibility to look after your ears. Surgery is not possible on the ear to restore hearing acuity. If in doubt protect your ears
Here's a question: In the countryside here middle aged farmers seek a hearing test complaining that others are mumbling - a sure sign of hearing damage. The acoustician can tell from the hearing test whether the farmer is left or right handed. How?
Alan A. Shaw
Harbeth Audio UK