So far, so good; but what happens as the music gets louder, or if you turn up the volume? Well, quite a lot - but regrettably none of it good. Firstly, moving though the broad realm of mezzo-piano, the sound starts to fray around the edges, what my wife was later to describe as “a bit fizzy”. Thereafter, distortion increases rapidly, the sound quickly degenerating into ever-more indistinct mush, and the more complex the texture, the more mushily indistinct it is. By the time the level has gone up to anything even approaching a robust double-forte, the noise is almost unbearably harsh and confused, and the less said about Shostakovich firing on all cylinders, the better.
Matters are made worse by transient break-up, which in particular affects tympani or bass drum beats. This effect was very well illustrated on Mercury’s original monaural LP of Tchaikovsky’s 1812 Overture. In the sound sample of the cannon firing directly towards the microphone, you hear, not a mighty “boom”, but an emaciated, splintered “crack”, the result of severe sound-pressure overload.
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Bone Conducting Headphones Paul Serotsky- November 2009 MusicWeb-International