Loudspeakers usually have at least two drive units each – commonly known as the woofer and the tweeter. The reason for this is that a large drive unit is necessary to shift lots of air at low frequencies, but it distorts and overly focusses the sound at high frequencies. Therefore it is necessary to hand over to a small tweeter at HF.
So far so good. But the tweeter is small and does not have the ability to withstand high power levels. In normal operation this is not a problem – normal sound sources including music contain much more energy in low and mid frequencies than high. If a music signal delivers 100 watts to the loudspeaker, then once the frequencies are divided less than 10 watts will go to the tweeter.
But this doesn't allow for non-musical signals, and signals that are not representative of the general sounds of life. What about digital glitches?
It is a fact that digital glitches can contain massive amounts of high frequency energy – immensely more than even the harshest electronic music.
Digital glitches are unpleasant to the ear, and life-threatening to the poor little tweeter. It never was designed to cope with such amounts of energy.
Most digital audio equipment, although it may produce the occasional glitch, is kind to tweeters. An even halfway decent CD player will mute when it encounters a serious error on the disc. Thus the tweeter is protected.
However, such courtesy is commonly absent from digital television sets and set top boxes. Any slight error in the signal and the output goes crazy, delivering enough energy to dispatch a tweeter in one shot. Not to kill it completely, but to ruin the voice coil, causing it to scrape against the sides of the magnet.
For ever after until replacement, the tweeter will produce a dirty edgy sound. This will be found to be particularly noticeable on the classical singing voice of tenor pitch and above.
Oh, by the way – if your speakers are more than seven years old (varying with legislature), the manufacturer is not obliged to supply spares. That's tough if you shelled out a big wad for some great speakers that could otherwise have given excellent service for as long as twenty years.
Technology should have moved on beyond glitches. CD players had such problems sorted out back in the 1980s. If governments want us all to shift to digital television – and they all do – then the manufacturers had better start getting their act together on this point.
By the way, the STB illustrated is a big-time offender!