Expert: Cleggsan - 1/20/2012

Question
QUESTION: I recently inherited a pair of AR-3as. I replaced the foam surround and Im getting a distorted echo from one woofer on low volume. How can I test-tell if the coil is bad or did I miss align the cone when I replaced the foam? My amp is a Pioneer A-70 and I've swithed wires and speakers from the other unit so it's coming from one woofer. Thanks  Paul

ANSWER: I cannot conceive of a woofer producing an echo.  If the cone is not aligned properly you would hear the voice coil rubbing against the pole piece or basket rim.  You can test the woofer easily by just carefully with uniform force all around the outer edge of the cone depress it inward whilst listening for any rubbing or scraping sounds.  Such sounds are very audible.  Another test is to pull the cone out into free air and drive it with your amp and a low frequency sine wave to test the excursion limits of the cone. Usually a sine wave of 1 or 2 hertz is a good test. You can get these test signals on some CD test recordings if you don't have a signal generator.  You can also download tones from the Internet for testing purposes.

For a quick check, just revers the speaker wires on the back of the amp and see if the sound you mentions switches to the other side.

Good Luck.'



---------- FOLLOW-UP ----------

QUESTION: Yes I do hear the rubbing sound when I push on the cone. Does this mean I need to realigne the cone?-surround foam? TX  Paul

ANSWER: Yes,  there should be no rubbing or sounds of any kind when the cone is depressed uniformly.  If you push on one side only it will distort the cone assembly so you must push with both hands evenly from three points around the cone in order to keep it moving straight.

Rubbing voice coils will not only sound noisy but will wear out and eventually destroy the coil form which will require rebuild or replacement of the woofer.



---------- FOLLOW-UP ----------

QUESTION: Thank you I loosened one side of the surround and repositioned it and the noise stopped. Nice pair of speakers for almost free-$30. I forgot what speakers like this sound like, you would need a pretty big set of book shelves to hold these, These are old school floor standing, crank up the volume kind of speakers. Thanks  Paul

Answer
Thanks.  They were nice speakers; better than many on the market today.  I met Edgar Villcher (http://en.wikipedia.org/wiki/Edgar_Villchur} in person on several occasions.  As you know he is sort of the father of acoustic suspension loudspeaker theory.  

Happy listening.