AUDIOCLINIC (Q and A) (Mar. 1975)

Record Changer Muting Problem

Q. When the tonearm on my record changer comes down on a record, I hear a thump in my right speaker only. Otherwise the changer performs well. Could this noise be caused by a bad ground on my cartridge or improperly grounded changer frame?

-William Hernandez; FPO, Spain.

A. I do not believe your thump problem relates to grounding. When grounding problems develop, they usually produce hum and/or lowered signal.

Record changers usually have a muting system designed to prevent any sound produced by the cartridge from being audible during the change cycle. This muting system should come into play just before the tone arm lifts from the surface of the disc and continue until just after the stylus has set down on the next record.

The purpose of the muting is to eliminate the annoying thumps associated with the lifting and landing of the stylus. Besides being annoying, this thump is potentially damaging to some speakers used with high-powered amplifiers. Because you hear a thump on just one channel, at the time of stylus set-down, it's apparent that the muting contacts are not working in this particular channel.

This could result from oxidation of the contacts, or being bent so they just don't make physical contact. You'll need to trace this down visually. Often careful examination underneath the chassis will reveal the trouble and permit its repair. In some cases you'll have to get a service manual from the manufacturer, or take the changer to a repair dealer.

Changes in Auditorium Acoustics

Q. Why does dance music played in an auditorium with few people in it let the vocals over-ride the instruments when similar music played in a crowded auditorium tends to submerge the vocals under the instruments?

-Mel Burgess; Oakville, Ontario, Canada.

A. When an auditorium is empty, sound is reflected from one wall to the other, and from floor to ceiling (and back) unless appropriate acoustic treatment has been applied. The sound produced in such an area is often harsh and unpleasant, with highs which are too strong. Under these conditions, singers' voices may be projected clearly and very up front.

When the auditorium is filled, the people act as sound absorbers. Under these conditions the sound does not reflect as much as it did when the room was empty. Because highs are more readily absorbed than lows, the crispness of the singer's voice tends to get lost, placing the voice further down in the mix.

Repairing Cracked Speaker Cones

Q. I have a 12-in., high-efficiency speaker which has a crack in the cone extending 2 in. from the outer rim toward the center. Can I repair this crack without completely ruining the speaker's performance?

-P.G. Ruuth; North Highland, Calif.

A. If a speaker cone is cracked but not badly torn, repair is relatively simple, and will not degrade the performance of the speaker greatly.

Cut a piece of onion skin paper just a bit wider and longer than the crack in the cone. Place a bit of glue, such as Elmer's, both on the cone and on the patching strip. Accurately align the strip over the crack. Place a finger under the cone to support it gently while you smooth the paper down.

When the glue hardens the repair is complete.

(Source: Audio magazine, Mar. 1975, JOSEPH GIOVANELLI)

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