GENOCIDE BY SILENT SOUND

Ultrasound can also be produced inadvertently in a number of cases. One of them is a magnetic field that causes metallic com-ponents to vibrate mechanically as before, except that the frequen-cy is higher. And where would that be?

In a VDT, for example. In the picture tubes of both TV sets and VDTs, an electron beam scans the screen line by line. There are 525 lines per screen in many, but not all, VDTs. The circuits that control the line scan run at a frequency which is always a multiple of 60 Hz (that ties it in with the power net frequency). For VDTs, that frequency is most often 15.75 kHz (for the others it is higher). This would, at first sight, still be audible, but an alternating field attracts a magnetic material twice per cycle, so that the resulting frequency of a vibrating part is 31.5 kHz, far beyond the audible limit.

[So why do headphones and loudspeakers not reproduce every-thing at double the frequency, i.e., an octave higher than the original? If that question does not worry you, skip this paragraph. If it does: their coils are wound on permanent magnets, so that the field is the sum of a constant plus alternating (signal) field. It never goes through zero and does not change direction as the current does, but attracts the membrane or speaker cone more so or less so according to the current, but always in the same direction.

A field that does not alternate, but pulsates in one direction. will ause only one vibration per cycle.]

Moreover, the waveform (time chart) of the current producing the line scan is not a nice, round wave (sinusoid) such as your utility delivers at 60 Hz. To produce an undistorted image, the beam has to go across the screen at constant speed, which requires a deflection current that rises linearly. Then the beam must return very rapidly to the beginning of the next line in the "fly-back," which means a fast drop in current. The result is a jagged curve known as a "sawtooth," and the only thing important about it here s that it will produce higher harmonics at integral multiples of the basic frequency. So the components would vibrate and produce ultrasound at 31.5 kHz, 63 kHz, 945 kHz, 126 kHz, . . . or at fre-quencies at least 300 times higher than where charlatan Paul Brodeur (who started the whole hysteria as one of his meal tickets) is looking.

Does ultrasound do things to people?

Yes, to some. A good friend of mine cannot visit certain art ex-hibitions for long because the ultrasound alarm gives him a bad headache. Some physics professors also complain of headaches after they demonstrate ultrasound to their classes. What else prolonged exposure to it does to the body I do not know, and I am not Paul Brodeur to frighten you with things that are far removed from my field of expertise.

What I do know is that the New York Times is not beating the alarm about this possibility, which is surely more plausible than an electromagnetic field to which people are exposed regularly and more intensely in their homes. True, TV receivers do not bear it out, but people do not sit as long and as close as with VDTs, and many VDTs have higher synchronization frequencies (up to double). Nor do I claim that ultrasound is the only cause (see below); I do not even claim that ultrasound must be a cause at all. Quite possibly the ultrasound from VDTs is too weak to have any effect (which would be no reason for the NYT to ignore it); but surely it is worth investigating, and if justified, refuting.

But when have you last seen Walter Reilly, so fond of media-coveted theatrics, running round a VDT in white gown and cap, with a grim, yet knowing expression on his face and an ultrasonic probe in his hand?

And why is Brodeur not serializing a new book called Genocide by Silent Sound?

Because ultrasound is easy to understand; and you can scare people only with the mysterious.