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#1
Problem with Altec Lansing MX5021 Subwoofer
I have an Altec Lansing 2.1 speaker system. (MX5021 90W RMS
output, 30Hz - 22KHz audio range). It has been fine for more
than 3 years, but presently I am having some problems with it.
After power up, the speaker is almost okay. But very low volume
growling noise (i.e. random sound of low frequency in the range
30-50Hz ) comes out of the subwoofer. But noise is audible only
if someone attaches the ear to it. After some 1 or 2 hours
later the growling noise increases in volume and it becomes
audible even from 6 feets (But still low volume). To make the
things worse : this higher amplitude noise interferes with the
bass portions of the music and creates bits of bass which is
very disturbing. When I am hearing music, it perceives as if
the bass is becoming high and low periodically.
However, if I power off the speaker at that time and keep it
off for next 7-8 minues, it seems to become okay again.
However, the problem repeats again after 2-1 hours. I use
windows 7 with X-Fi XtremeMusic sound card, but when the noise
starts, I have experimented detaching the signal cables from
the subwoofer and the noise still continues. So definitely,
this is not a problem related to OS or soundcard drivers.
I've found one more way to make the speaker output "clear" when
it starts the growling noise. This solution does not work always.
I have some single tone wave files which I use to test the speaker
output. Astonishingly, if I play the 30Hz tone and 50 Hz tone for
8-10 seconds, the speakers seem to become "noise-free" again for
some time.
Btw could it be a power line problem ? I power the speaker from
home AC 230V 50~60Hz power supply. Recently we changed
residence and the noise problem started shortly after that. Is
it due to any power factor problem in AC power supply ? I have
tried changing the AC outlet (but at same residence) with same
results. However, I haven't tried powering it directly from an
UPS, so I am not sure if the problem is still there when the
speaker system is powered by generated supply of UPS battery.
But even if there is problem in the AC supply at my new
residence, should it really have any effect on speaker
performance ? After all they are stepped down inside the
speaker system and also there should be filter capacitors and
regulator IC.
I have also tried moving the satellites and the subwoofer, far
from any magnetic device, keeping the signal and power lines
physically distant. I have also tried keeping those lines as
less inducing as I could, i.e. so that no local magnetic field
grows up along the power line which could create
noisy/extraneous electric signal in the signal lines. In fact,
I have been using the speaker system for more than 3 years, at
that time I didn't have to be careful about these things and
the speaker was fine.
I am not so acquainted with AC power devices and audio
amplifiers. It will be fine if someone could explain me where
the problem actually is, and what should be my measures.