1.  "Full Time iPod Use Causing Hearing Loss." The growing popularity of portable music players may be causing widespread hearing loss. "It's a different level of use than we've seen in the past," says Robert Novak, director of clinical education in audiology at Purdue University. "It's become more of a full-day listening experience, as opposed to just when you're jogging." Increasingly, Novak says he's seeing too many young people with "older ears on younger bodies"--a trend that's been building since the portable Walkman made its debut a few decades back.

Hearing specialists says they're also seeing more people in their 30s and 40s--many of them among the first Walkman users--who suffer from more pronounced tinnitus, an internal ringing or other noise in the ears. Today, doctors say many people also are wearing headphones not just to enjoy music, but also to block out ambient noise on buses, trains or just the street. And all of it can contribute to hearing loss. [I wonder what acoustic levels these things can generate?--DBH] AP 13Oc05

2.  "Oh Please Give Me a Sine" written by Andy Ciddor in TV Technology discusses the various light dimming systems used in theaters, and their deleterious effect on audio systems. Typically they operate by chopping the AC waveform into pieces, generating horrendous amounts of EMI (electromagnetic interference) which can corrupt the audio signals in the same theater. These sudden discontinuities cause mechanical vibrations that result in filaments singing along at 120 Hz. Most of the time this noise is barely noticed above the cacophony of air conditioning, hum from power supply inductors of various kinds, cooling fans, etc.

Originally, theaters used salt water (smelly, toxic) or variable transformers (heavy, expensive) which were free from such problems. Now, in addition, the general adoption of switching power supplies causes large amounts of harmonic distortion in the AC line which can cause EMI in the audio lines. In the European Union, regulators decided during the early '90s it would be a good idea to reduce the conducted harmonics and voltage fluctuations generated by electronic equipment, and so wrote some new standards that were scheduled to come in to force toward the end of the decade. When it turned out that no one could actually build compliant equipment, the electronics industries of the EU quietly went about getting the deadline extended until 2001. That deadline too has passed, with very little activity on the other side of the Atlantic.

However in a recording studio this has to be addressed. While the concept of an electronic sine wave dimmer has been around for many years, it was impractical to build them until recently. Now several companies such as ETC, Trusine, and Strand offer such units. Curiously, most of the marketing emphasis is on their acoustic silence rather than their negligible harmonic supply distortion or their almost total absence of EMI. 3Au05

President, Boston Audio Society

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