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Contents Copyright 2006 Final Sound Solutions.
11. SUBWOOFER FAQ
How can I connect my subwoofer and avoid hum and noise?
Hum and noise in audio systems is caused by many interference sources. Most likely is the existence of a so-called
ground loop. If there is more than one ground connection path between two pieces of equipment, a ground loop
occurs. You can identify ground loop problems because they mostly produce a 50Hz or 60Hz hum into the system. If
the hum is 100Hz or 120Hz, without the 50/60Hz part, there are probably other sources of interference. Think about
light dimmers, heavy equipment on the same power group or strong incoming rfi/emc pollution. If hum and noise
problems are persistent, the best advice is to consult your dealer. These problems can be pretty complex in daily life.
In this FAQ, we cannot describe all the existing knowledge about ground loops in depth. We can provide you with
some basic solutions to prevent hum and noise problems.
• 100/120Hz hum can be avoided by feeding the equipment using a ‘clean’ AC line. So, don’t connect light dimmers,
refrigerators, vacuum cleaners, fluorescent lightning and other current hungry and interference inducing
equipment to the same AC-group or wall-outlet.
• Don’t put all kinds of wireless equipment, including cordless cell phones and remote controlled children’s toys in
the neighborhood of audio and video gear.
• Use shielded AC power cables to avoid incoming rfi/emc interference. Sources can be radar equipment,
transmitters for broadcast or cellular communications or your neighbor’s wireless LAN.
• Mains transformers cause an AC magnetic field around them. If you stack equipment, or if you position gear close
together, the magnetic fields can be coupled and hum may result.
• Magnetic fields can also be coupled to cables. So isolate signal cables, AC cables and cables transporting control
signals from each other. If there is a need to cross signal cables and power cables, cross with a 90-degree angle.
• Be sure that all the cables and connectors are in good shape, and that you made the connections according to
the dealer’s instructions.
• Mains voltage quality problems can cause hum and noise. Sometimes, the sine wave is distorted and the line will
contain harmonics. Please consult your dealer about using isolation transformers, mains filters and AC power
stabilizers and conditioners.
• A typical ground loop problem can occur when two interconnected pieces of equipment (FI. cd player and
amplifier) are plugged into grounded AC wall outlets at separate locations. The signal ground is connected to
earth in each of them. Try to use ‘single-point grounding’. Connect your equipment to the same wall outlet.
• Using the subwoofer’s high-level input, can present a new league of potential hum problems. It’s known that
some amplifiers in the market come with reversed loudspeaker connections. So, red is actually ground and the
black terminal contains the ‘hot signal’. When connecting to a subwoofer, hum may result. Try to reverse the
connections (subwoofer ‘off’ and volume to minimum). Power the sub again and gently raise the volume. If hum
still occurs, it’s probably caused by some other phenomenon.
• Amplifiers with ‘balanced’ outputs can also be incompatible with the sub’s high-level inputs. Transformer isolation
at the amplifier’s input side may be the right solution. Please consult your dealer.
• Problems may also occur when you connect the subwoofer, using its high-level inputs, in set-ups consisting of
bi-amplified loudspeakers. Please consult your dealer.
Is it possible to use multiple subs in my stereo or home theatre set-up?
Most professionals agree that using two subwoofers in a stereo set-up will provide you with better and more
dimensional low frequency reproduction. Using more subwoofers will also be a remedy against acoustic problems
and a way to accomplish a more even bass distribution in the listening room. In a stereo-system, you can connect
each of the two subwoofers ‘high level’ to the left and right loudspeaker. Depending on your electronics, in case of
a separate pre amplifier, it’s sometimes possible to connect the subwoofer direct to the pre amplifier’s rca low level
output connectors. Use the corresponding subwoofer’s low level rca input terminals.
Using multiple subwoofers in a home theatre set-up can be a little more challenging. From the single processor’s
LFE-output, it’s simply possible to daisy chain subwoofers. It’s also possible to connect one sub to the left and one to
the right front loudspeaker, using the high level connection. Using this set up, it’s most likely to adjust your
processor’s bass management features. In case of doubt, please ask your dealer’s advice.
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