On Wed, 26 May 2010 14:25:51 +1000, Franc Zabkar wrote:

On Sun, 23 May 2010 23:03:29 -0500, "William R. Walsh"
m put finger to
keyboard and composed:

I have a Technics SA-929 stereo receiver that is in good working order.
However, when I was inside it replacing a burnt out light bulb and
repairing the protection relay, I noticed that there is a wire coming
from the printboard that holds both the AC power input and accessory
outlet connections going to the "speaker -" connector for the "B"
speaker terminals.

There is a resistor inline with the wire coming from the AC wiring
board.

That gives me an idea for testing subwoofers ...

Connect each speaker terminal to the active and neutral of a mains
supply. The frequency is not critical -- either 50Hz or 60Hz is fine. A
sinusoidal 240VAC source would be preferred, but 120VAC will do, too.

If you damage your speaker, don't be discouraged. In fact you may need
to test quite a few units before you have weeded out all the inferior
ones, especially those used in car audio.

- Franc Zabkar

Cerwin Vega used to demonstrate one of their professional low frequency
audio drivers by plugging it into 120VAC line.