Why my subwoofer hums

Induced noise, if entering through cabling, is usually fairly simple to solve. The key to understanding how to fix it is the square-of-the-distance rule: the intensity of an electrical or magnetic field diminishes by the square of the distance from its source. So if a power line one inch away from your subwoofer interconnect is inducing a signal in it, that induced signal will be a quarter as strong at two inches, a ninth as strong at three inches, a sixteenth as strong at four inches, and so on -- the farther you can keep the two separated, the weaker the effect will be, so it's time to move some cables and see what happens.

If you've got power cabling lying directly on or under a sub cable, just a couple of inches of separation can make a profound difference. Shielding, too, plays a role in dealing with induced noise. The most effective shielding for low-frequency signals is braid, not foil, and a highly-conductive, high-mass shield will shunt more noise to ground than something more lightweight -- see our article on hum rejection in analog audio cable, which inspired our design of the Blue Jeans Cable LC-1 audio cable with its double-braid high coverage shield.

It's important to recognize, however, that the kind of low-frequency, high-energy field set up by a power cord is the hardest thing there is to shield against -- all shields are somewhat ineffective against it, and so while a heavy shield such as that on the LC-1 can help, minimizing close contact between power and audio circuits will almost always be the most important thing you can do to solve an induced noise problem.

Now, induced noise can be trickier than that, not least because the problem can be occurring inside of equipment -- bad isolation of power circuits from line-level audio inside a powered sub is something which no amount of work with cable placement or shielding will affect -- but with any luck, the problem isn't internal and these solutions will address it.

The other common cause of subwoofer hum is completely different -- ground loop current flows -- and attempts to fix the hum problem that work well for induced noise will be quite ineffective against ground loops noise, and vice versa.

A ground loop problem occurs where there are differences in ground potential between pieces of equipment, which causes a small amount of power current to flow along lines which connect the two. This flow, in an unbalanced circuit that is, where the signal is carried on a single conductor using a ground return path, e.

Ground loops can often be resolved without spending any money on the problem. The trick is that one needs all of the grounds on all of the gear to have the same potential. Sometimes this is as simple as getting them all plugged in to the same power circuit; sometimes it's a matter of making sure that you're only using modern, three-wire, earth-grounded circuits at all points in your system rather than using old two-prong ungrounded circuits.

Changing where things are plugged in, making sure your home power circuits are all properly grounded an outlet-checker from the hardware store can be handy! Beyond that, if your home wiring has serious grounding issues, you may need the aid of an electrician. There can be ground loop issues that even an electrician can't solve, though -- many home theater devices are not earth-grounded these will usually have a two-prong, rather than three-prong, power plug , and instead use a kind of pseudo-ground which is tied through resistance to the neutral side of the power circuit.

These sorts of pseudo-grounded arrangements can cause ground loop problems that can't be resolved through ordinary grounding techniques. If trying to resolve grounding issues isn't getting the job done, though, there's a simple device that can solve the problem for you by breaking the ground loop: an audio isolation transformer. The principle that current in a wire induces current in nearby wires -- which we've just talked about in connection with induced noise -- is put to its fullest effect in a transformer.

If you didn't know anything about how induction works, the inside of a simple transformer would be very puzzling indeed -- it consists of two wires that aren't connected to one another, but which are wound tightly together over a core. If you have a ground loop locate the source by disconnecting equipment with grounds connected to your receiver with either a video or audio cable until the hum goes away.

This excludes optical audio connections. Common causes are cable TV or satellite TV connections to the cable box or TV, different ground potentials caused by equipment plugged into different outlets, different electrical phase on devices and poor equipment design. If that does not locate the source try replacing the cable running to the subwoofer. Sometimes a defective cable can cause this.

If the source is the cable TV either correct the grounding error or use a Jenson isolator. You can also consider using an optical audio connection from the cable box to stop this, but if you are switching video through the receiver this is not likely to work. If the source is the satellite TV you must fix the grounding problem on your satellite system or use an optical audio connection and remove video switching from the receiver.

If the source is differences in electrical grounds you must either have an electrician fix the electrical ground problem in your home or use products like these.

If the source is the receiver or subwoofer itself it may be necessary to send it back for repair or replace it. Only resort to this after exhausting all other options. Cheap Electronics December 16th, Super-Duper blog! Cheap Electronics June 5th, very nice posting… i have a set home theater at home and i use subwoofer however.

Allan McQueen February 9th, Awsome site! Vaibhav Desai September 1st, I started getting the hum issue when connecting a second sub to the AV receiver. Br ve January 3rd, pick up powered subwoofer lately velodyne impact mini. If nothing helps, disconnect all the audio cables from the subwoofer. Leave the subwoofer plugged in and switched on. If the subwoofer hums, it points to a defective unit. Contact the company's customer service to technical support [source: PartsExpress].

Subwoofer FAQ How do subwoofers work? Subwoofers act as loudspeakers that are responsible for amplifying the bass.

Low-frequency sounds are enjoyed best on sound systems that have subwoofers as they cause the "boom" of the bass to reverberate.

What is the difference between a subwoofer and a speaker? Subwoofers and speakers have the same purpose. However, their frequency range differs. Subwoofers are responsible for the bass while speakers are basically electro-acoustic transducers responsible for the amplification of sound. Is a subwoofer in a car worth it? What is the best size for a subwoofer? Why does my subwoofer make a humming noise?