I suspect you have a bad cable, a poor ground or a bad
power supply inside the speaker amplifier. The amplifier
(inside the sub-woofer) could also be defective.
1) Bad cable or connector:
If the (braided shield/outer tube) of the coaxial input cable is
not grounded, the cable will pickup line frequency "hum"
from surrounding power lines, house wires, lights and
This hum is then amplified by the speaker's amplifier
causing the constant bass sound you speak of.
Because the hum frequency fundamental is 60 Hertz in
North America, 50 Hertz in Europe, you hear it coming
mostly out of the sub-woofer, because the midrange and
high speaker circuits filter it out.
Check the input connectors, cable at both ends, wiggle
the jacks at a low volume setting to see if it changes.
Make sure that you are indeed using a properly shielded
A coaxial cable consists of a thin inner conductor, surrounded
by a flexible tube made up of a braided metal shield, which
must be grounded. This prevents hum from being picked up
by the sensitive amplifier inputs.
2) If the power supply within the sub-woofer's internal amplifier
is defective, the the power supply hum will also get coupled
into the amplifier and speaker with same results as above.
Power supply hum is typically twice the line frequency,
i.e. 120 Hertz, but not always, depending on what
component failed: Rectifier diode, filter capacitor, or
the voltage regulator.
3) Ground loops:
When you run very long cables between the source and
destination of an audio signal, multiple ground paths (must)
exist between the two points in space, creating complete
Power line hum from the environment can (will) induce
heavy AC currents around these loops, creating a voltage
gradient across these cables, and in-between the end
Once again, this AC hum is coupled into the amplifier inputs.
Ground loops become a problem with cables over 10
feet long, and an astronomical problem for stage audio
engineers. To avoid ground loops, they must break
the circuit's continuity by using isolation transformers,
optical isolators, and/or differential input amplifiers.
So how long are your cables?
Most house stereo components are only designed to
handle 6 to 10 feet of cabling max.
30 feet is already asking for major trouble.
4) Feed back oscillation: This occurs when the output of
an amplifier is fed back to the inputs with a round trip
gain greater or equal to unity. The tiniest little electrical
disturbance is then amplified and re-amplified, over and
over again, usually at one preferred frequency, causing
the typical (ear-splitting) microphone squeal or howl.
In your situation feedback and/ loss of original signal
could be the result of mis-wiring the input cables.
Note that this is NOT as silly nor as unlikely as it sounds,
because many computer audio cards and even some
home stereo systems have re-configurable inputs and
SOFTWARE configuration decides which jack at the
back does what !!!!
On my computer, for example, the Realtek audio driver
tries to automatically figure out what cable is connected
to each jack (usually it gets it wrong)
Using the Realtek control panel applet, I can then
manually re-configure the gray jack as input,
the green jack as bass, pink jack as center.... etc.
If this situation also applies to your system, please check
the software configuration. Connecting an output cable to
an input jack will certainly cause a lot of HUM and not
5) Finally, don't rule out internal sub-woofer failure. Unlike
the passive stereo/hi-fi speakers of days gone by, modern
multi-channel theater systems with front, center, rear and
sub-woofer speakers are internally amplified, with active
frequency cross-over filters and special effect/ surround
Usually, the large sub-woofer contains most of the
electronics, amplifiers and filters.
It feeds the other speakers, and it is controlled by
an external volume control module which can be separate
or built into one of the tweeters.
These sub-woofer electronics are prone to poor design,
overheating and early failure. (Even fresh out of the box
If you cannot get it working, take it back to the store,
and make the NICE salesmen **** with it.
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