Subwoofer test

<<I got a KLH ASW10-120 subwoofer and it may have a problem.  I hear
rattling when the sub is turned very high up.  I'm pretty sure its the
sub...>

It's the sub all right. If you continue to drive this speaker when you hear
the metallic rattling that you noticed, the speaker will be badly damaged.

This low-end KLH subwoofer model featured at Costco ($99) and Best Buy
($149) is not capable of developing any deep bass at higher volume. The
rattling that you hear is the speaker magnet bottoming out as it overextends
its usable range. Another irritating aspect of this KLH model is that if it
is switched on and off with an external power strip, a loud pop will be
created as the speaker initializes.

An exchange won't improve the performance that you are already getting as
this speaker is a very poor performer. It is possible to find an adequate
subwoofer in the $200 range if you shop carefully. Look for half-price sales
and closeouts and always be sure that the unit that you are considering is
able to porduce true sub-sounds down to 20hZ. Yamaha subwoofers are some of
the best performers in the $200 street price range.

The discontinued ($299 list price) Yamaha YST-SW160 is a good value and
should still be available in the $160-180 range.

"DUAL 8-INCH DRIVERS AND 150 WATT AMPLIFIER High amplifier power assures
enough power to deliver movie theater-like bass effects and the dual drivers
translates the power into clear bass sound. The YST-SW160 has a frequency
range of 20 to 160 Hz."

http://www.yamaha.com/cgi-win/ webcgi.exe/DsplyModel/?gSPK000 10YST-SW160