Apart from the obvious response that they both amplify sound, you wouldn't expect there to be much in common between a tiny hearing aid
that finds in your ear and a megaphone designed to make sounds lout enough that they can be heard at a a distance of hundreds of metres from the source.
That answer would have been true for the past 70 years. But things are changing!
In recent blogs rewrite about our belief that the principal function of a megaphone is to transmit intelligible speech rather than just sounds and consequently that the appropriate way to test a megaphone is to measure its Speech Intelligibility Index rather than the dB level of the sound.
Something similar is happening with hearing aids.
The conventional and most common way of testing whether or not you need a hearing aid is pure tone audiometry. Pure tone audiometry was first developed to assess soldiers returning from WW II.
The test is conducted in a soundproof booth using a pair of headphones through which externally generated tones or “beeps” are played. The test measures the threshold of hearing (the lowest intensity of sound you can hear) at each of 8 standard frequencies between 250 Hz and 8000 Hz.
The resulting audiogram is a plot of the person’s hearing sensitivity over the range of frequencies tested. If hearing aids are needed, the audiogram is used to assess the amplification required in each of the frequency channels of the hearing aid.
If you think about it, though, the most important function of a hearing aid is not to listen to single frequency “beeps” but to enable the wearer to hear and understand speech.
Professor Peter Blamey and his colleagues at the University of Melbourne in Australia have developed a “Speech Perception Test” that they think is a much more realistic way of testing a person’s hearing.
The Speech Perception Test uses real, monosyllabic words instead of tones and it is so simple that it can be carried out at home using your own headphones to listen to a set of words transmitted through the internet. You can read about the Speech Perception Test here: http://www.scienceinpublic.com.au/media-releases/hearingtest.
The Melbourne group (which, as well as Professor Blamey, included other people associated with the development of the Cochlear “bionic ear” for the profoundly deaf) also developed a method for setting up hearing aids based on the data from the Speech Perception Test.
The process is so simple and effective that not only can the test be carried out over the internet but hearing aids individually tuned to the needs of the listener can be created and sent out by mail without the person who needs them ever having to leave home. See https://www.blameysaunders.com.au.
The writer can personally attest to the outstanding results achieved in practice.
So what we have here is a quite dramatic convergence of the testing methodologies for megaphones and hearing aids. It’s now all about how clearly one hears speech rather than dB readings of sound intensity levels.
Obvious, really, when you think about it!
But none of this would be possible without the years of research and the clever technologies behind the new testing paradigms.