Renovated cable cars hum a sour note for many San Franciscans

When the cable cars rattled back on track here in June after a two-year $60 million renovation, the look and the feel were authentic - but not the sound. The hum and the buzz of the constantly moving cable is as familiar as fog horns here. But natives, an exacting lot when it comes to pride in their cable cars or a good night's sleep, have measured the cable noise at 20 decibels louder than city standards permit.

These antiques on tracks are the object of such affection that genuine hostility is unlikely to surface, although residents along the tracks are eager to tone the noise down.

Meanwhile, city officials and the system designers are gingerly probing the cloud around the silver lining.

What do you do when you find that your multimillion-dollar cable car system cemented into 10 miles of streets and built to last 100 years is too loud?

Whatever you do, it's likely to cost more money.

The San Francisco Public Utilities Commission has authorized $80,000 for an acoustical and engineering study of the problem. The firm that designed the system is also launching its own study of the situation.

The problem, explains Lynn Pio, project manager for cable car construction, lies in the channel that houses the constantly moving cable.

The speculation is that the normal sound of the cable moving at a constant nine miles per hour may be amplified by the new concrete-and-steel cable housing that replaced the old, crumbling brick and mortar channel.

Mr. Pio says he noticed the sound himself ''not because it was loud, but because it was different'' from the old system. ''The tension on the cable is like a guitar string, you loosen it and it gets lower, tighten it and it gets a higher pitch.''

The noise occurs mainly at two points along the tracks where the cable wraps around corners through sets of pullies. Hatch covers where the cable conduit can be reached for maintenance also were not fitted properly in place. They now provide a clanking percussion for the humming cable when cars roll over them.

The hatch covers are likely to be easily refitted, but the solution to the cable noise depends on the cause of the problem, says Jamie Levin, a spokesman for the Municipal Railway - San Francisco's transit system.

It could be an echo problem in the conduit, a cable tension problem, a lubricant problem, or a combination of all three, he says.