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Hardware

Reducing Intereference in Your Speakers? 59

Posted by Cliff from the ditching-that-annoying-hum dept.
PolicyWonk asks: "I just bought a new stereo, a Sony CMT-EP707, into which I intend to plug my laptop when watching DVDs, and my iPod when listening to music. When I first turned the stereo on I was horrified to hear interference from a local radio station, as well as a general hum emanating from the speakers. The hum and the radio emissions are audible even when the stereo's volume is set to 'min' and irrespective of what setting the stereo is on (i.e. Tuner, CD, or MD), or what input is (or isn't) plugged into the stereo. (I have tried my laptop, iPod, and no input). That means that during a quiet pause in a movie, or the intro to a song, this background noise is clearly audible. No amount of moving the speakers around the room, or plugging the stereo into different grounded outlets seems to fix the problem. I've checked my outlets, and they appear to have a ground connection, but I live on the fifth story of a circa 1900 apartment building in Manhattan, so it's anyone's guess what happens to the wires once they are in the walls. Anyone have any good solutions for reducing or eliminating interference from nearby radio sources?"
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Reducing Intereference in Your Speakers? More

Reducing Intereference in Your Speakers?

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  • RFI chokes (Score:5, Insightful)

    by Kizzle ( 555439 ) on Thursday November 28, 2002 @08:07PM (#4777454)
    A fairly cheap method of reducing radio/TV signal interference involves just the opposite of "grounding". Go to your local Radio Shack store and get a bag full of "RFI chokes". They have several different shapes and sizes. They snap together and are supposed to be placed over wires and interconnect cables in order to prevent RF currents from flowing along the outside of the wires. You don't have to disconnect anything to install them. Just place them over the cables and snap them closed.

    • Re:RFI chokes (Score:3, Informative)

      by waytoomuchcoffee ( 263275 )
      Actually, RFI chokes are just magnets that clamp over a wire. A better solution (one I have done successfully) is to buy that magnet tape stuff [tuffware.com] -- it has sticky stuff on one side, and is made to fasten things to metal. The stuff is much cheaper, and you just wind it around the wire you want to protect. Put some duct tape over it so it won't come loose and you are good to go.

      • Re:RFI chokes (Score:5, Funny)

        by Wakko Warner ( 324 ) on Friday November 29, 2002 @03:17AM (#4778774) Homepage Journal
        Yeah, duct tape will look great wrapped all over the wires on my new G4.

        Not all of us build our computer desks out of sawhorses and discarded dining-room doors.

        - A.P.
        • Yeah, duct tape will look great wrapped all over the wires on my new G4.

          What matters more, that it does the job or looks pretty? If you are going to prioritize style over substance, you've little grounds for complaint when performance is poor.

      • Re:RFI chokes (Score:3, Informative)

        by Liquor ( 189040 )
        RFI chokes are NOT simple magnets (nor are they permanently magnetized like a magnet).

        What they are is a ferrite core that makes a complete closed loop around the cable. Radio frequencies currents can't go through the middle - it blocks high frequencies. (If you want to get technical, the radio frequency current induces a magnetic field in the choke, and the change in magnetic field induces a voltage that exactly opposes the current.)

        While strip magnets are made from a similar material, you simply cannot make it as effective as a proper choke.

        On the other hand, the original question mentions hum - presumably AC 60Hz - and a choke will have negligible effect on a frequency that low.
        • On the other hand, the original question mentions hum - presumably AC 60Hz - and a choke will have negligible effect on a frequency that low.

          I would hope not! Otherwise that choke would get real hot, real fast. The AC on that line is at 60Hz, and if the choke was actively "damping" that much current at that high of a voltage, it might be a Very Bad Thing.
      • No, RFI chokes are -not- magnets.

        Go ahead- try and stick a ferrite suppressor to metal. Try even to stick a real magnet to a ferrite suppressor. Try looking it up on the web or even (gasp!) in the library.

        But that might violate the precepts of the know-it-all. Actual research and testing.

  • How-To (Score:5, Informative)

    by the eric conspiracy ( 20178 ) on Thursday November 28, 2002 @08:08PM (#4777460)
    http://www.aca.gov.au/publications/info/cbradio.ht m

    Done. Now we can close this topic.

  • To quote google (Score:4, Funny)

    by anthony_dipierro ( 543308 ) on Thursday November 28, 2002 @08:09PM (#4777462) Journal
    "Did you mean: Interference"

  • Urg! (Score:3, Informative)

    by McCarrum ( 446375 ) <mark,limburg&gmail,com> on Thursday November 28, 2002 @08:09PM (#4777463)
    There are quite a few issues to look into. The top two would be to:

    a) get someone in (professionally) to test the grounding .. and for much more reasons than just the interferance, and ..

    b) try turning off hotspot applicances, like microwaves, the fridge, air conditioners -- and then try it. More sensative equipment may pick up what less sensative equipment will not.

    Oh, and a final though, do a google search on your sterio equipment in case there are others who have found this problem .. it may be a (semi)common problem.
    • Get your house electrics checked over by a qualified electrician.
    • Cover everything with tinfoil! ITS TEh GOVARMENT & ALIONS!!!!!!!
    • Shorten any low-signal wires as much as possible. Replace them with shielded ones if possible.
    • Thread ferrite beads onto said wires.
    • Get some kind of power filter on your mains connection.
    • Double up on your tinfoil.

  • Change the length of cable (Score:3, Informative)

    by isorox ( 205688 ) on Thursday November 28, 2002 @08:10PM (#4777469) Homepage Journal
    We sometimes pick up Radio 5 [bbc.co.uk] on the external mike of one of our cameras - We plug a different lead in of a different length, and it just works

    Interestingly it only seems to happen in theatres

  • My Sony player does this too (Score:4, Interesting)

    by Cyclone66 ( 217347 ) on Thursday November 28, 2002 @08:17PM (#4777496) Homepage Journal
    My mini sound system does this too. You're going to need to buy a better system.. The mini's just aren't built for enthusiasts. They aren't built to last either. My system is 3 years old and the volume control randomly increases or decreases the volume when I turn the knob...
    • I gave up on the knob and now only use the remote... well, before I installed a better system.
    • Another thing, I just tried to play cds.. It doesn't even play cds any more. Meanwhile my dads 25 year old 8-track player still chugs away playing those awesome old tunes! :)
      • I have a thirty year old Marantz tuner/amplifier combo that I bought from a stereo repair shop (http://www.thesoundwell.com/) six years ago for about $150. It continues to sound excellent after a few moves and with no maintenance whatsoever. In the same time I've gone through probably ten computers at $1000 a piece, but that's another matter. The hilarious thing is that I looked up my stereo on a antique audiophile site the other day, and it's looked down upon as being one of the inferior post-sellout Marantz models. If this is the cheap knock-off, the good ones must be able to break crystal wineglasses when playing Maria Callas :-)

        Meanwhile, my friends have all gone through at least one modern stereo component.
        • I'm really not impressed with this thing. I don't think I'll ever buy a mini sound system again. Is it too much to expect at least 5 years of service (not used too much either)?
          The CD player may just be dust, but the volume control is just low durability..
  • You might wish to ask some of the other tenants whether they've experienced the problem recently. Also, did you have a stereo before this? If this is a new problem that is specific to this particular system, I'd be inclined to return it for repair under warranty. The Sony should not only not emit significant RFI, but should reject it, too. It's not just a good idea, it's the law.

  • Grounded Outlets (Score:3, Insightful)

    by Anonymous Coward on Thursday November 28, 2002 @09:53PM (#4777765)
    You know you can buy a ground tester at a hardware store, right?

    I don't know but your landlord might be legally required to supply you with grouned electrical outlets.
  • The bigger the better. Place nearby. Portable! If block becomes warm, or starts to smoke, run away and find cover. Do not taunt copper block.
  • At night, from around 11pm to 6am, I hear the radio station Voice of America over my speakers. At first, I thought I was going insane, hearing quiet voices in different languages when nothing was playing over the speakers. Over headphones I don't get any interference at all, just on the speakers. It's a low end 4-speaker Koss surround set, btw, with a subwoofer. (Complaint to Koss: Don't market a surround system as 4.1 when the bass is just pulled from the front and rear channels. It's misleading and makes me wonder if the rest of your products are accurately labeled.)
  • I have speakers for my computer that sometimes (only for a second or two) pick up radio signals of passing aircraft and other radio transmitting devices (although I haven't actually picked up a radio station yet). This could be happening to yours and if it is - replace the speakers with different ones.

  • Ground Loop Isolator (Score:3, Insightful)

    by Gormless ( 30031 ) on Thursday November 28, 2002 @11:31PM (#4778092)
    I had the same problem while trying to play DVD audio from my PC to my home stereo.

    I bought an "Audio System Ground Loop Isolator" (# 270-054A) from Radio Shack for $20CDN... problem solved.

    Here [epanorama.net] is a link to some info on the problem and possible solutions.

  • Powerlines (Score:3, Informative)

    by droyad ( 412569 ) on Friday November 29, 2002 @12:27AM (#4778323)
    Could try filtering the power outlet. I've heard of the powerlines picking up a signal and transfering to the speakers via the AC electricity stream
  • If your power cables and your speaker cables are running parallel some times it turns your speaker cables into radio antennas. You can solve this either by
    a) Moving your power and speaker cables further apart.
    b) If they have to cross put them at a 90 degree angle to each other. This minimizes the effect.

    This happened to me while I was doing sound back in High school and wireded me out until the band instructor told me about this. Same thing happened first night in the dorms in college, I thought it was my neighbors radio for the first two nights. (:
    • Riff's solution is the only thing that has ever worked for me to combat severe speaker hum. Simply moving cables around until it goes away is the only way I've gotten around it. My current setup has all the power cables twist-tied together and segregated from the speaker wire. I also notice that if the speaker wire touches something metal -- like the wheels casings on the TV stand, etc., the effect is just as bad. Experiment with the wires before you shell out a lot of money and break your equipment open.
      • All low voltage wire that must cross paths with 120V should cross at a 90 degree angle, this goes for speaker wire, cat5, everything. You don't want the 120V getting inducted into the low power wire. Strange things can happen when the 120V bleeds a bit into low power stuff.

        The speakers I have take shielded XLR mic cable for input. I had to assrig a connection one day and couldn't understand why the speakers were humming until I realized that the connection I made was unshielded. Tinfoil didn't work for me, so I just moved it away from the AC it was near and the hum went away.

        Remember that power lines can carry signals, and with the old wiring in the building, I'm sure the problem could be 10 times worse than I'm used to dealing with.

  • RFI (Score:4, Informative)

    by Detritus ( 11846 ) on Friday November 29, 2002 @12:59AM (#4778427) Homepage
    It is common for the unshielded speaker wires on audio systems to behave as antennas. The received signals are coupled into the final amplifier stage of the device that is driving the speakers, where they are detected and converted into audio frequency signals that you can hear, sort of like an old crystal radio.

    The ARRL [arrl.org] has a web [arrl.org] page with some information on the subject.

    You might ask the engineer at the local radio station for suggestions. Even though it is not the radio station's fault, he may be willing to offer some assistance. Local amateur radio clubs can also be sources of people who are willing to help.

    Ask the support department of the manufacturer of your audio device for assistance. They may have technical bulletins on how to solve the problem.

    If you are asking people for help, be nice, not confrontational. Remember that it is your audio equipment, not the radio station, that is at fault. Consumer electronic equipment manufacturers could avoid most of these problems by adding less than a dollars worth of parts to their equipment. Most do not, reasoning that it is cheaper to deal with some complaints of susceptibility to RF interference than to prevent the problem.

  • You have to face the facts; that system is not exactly top-of-the-line audio equipment. But still, it seems that a $200 item shouldn't have a flaw like that right out of the box. Kind of reminds me of the new Compaq Evo computers they gave us at work. The sound hardware is horrible, and there is no isolation from the rest of the computer. So there's a continous humming, hissing, clicking and popping.

    Anyway, many of the previous posters mentioned a few ideas that might help. One more thing to try though: it looks like the speakers are removable. Try disconnecting the speakers, then listening through the headphone jack. If the hum isn't there, attach the speakers and see if it returns. If the hum goes away with the speakers, then ferrite beads on the speaker wires MAY help. There is no guarantee though. The amps are probably not very carefully designed, and remember that a speaker coil has a lot of wire wound in it. That's not really a problem in FM, but remember that AM receivers use a lot of thin wire wound around a magnetic core...like a speaker. If this is the case, the speakers sound pretty cheaply made as well.

    If the interfering station is AM, then you have an idea of where to try to fix this. Personally, the best solution seems to be returning the stereo. Find another model/brand, and if it doesn't have the annoying noise, the problem is solved. You can waste a lot of money on voodoo powerstrips and filters, and waste a lot of time fretting about the noise, wiggling different metal objects in the room, and twisting cables around just so. Just pack it up, take it back to the store, explain your problem, and say you'd like to try a different model.

    On a side note, good quality speaker+subwoofer-only systems can be had for much less than $200. That would be my first approach to amplifying laptop and iPod audio. Check your store's computer section. I've never even paid for a set of computer speakers; one set came from a technical college that didn't want their bundled Labtec speakers; another set was free from a friend. Actually, on that last set I kept the subwoofer/amp section and threw away the cheap satellites...and used the speakers from a dead Sony bookshelf system. The sound is clean, and a bit more powerful than 15 watts per channel.
  • ... it was two different grounds. One from the computer (and thus from the power outlet), and the other from a common antenna outlet that carries radio and TV for the whole house. Although the grounds are connected at the roof, with me living on the first floor they're not acting like connected for high frequencies anymore.
    I solved the problem by disconnecting the stereo from the common antenna and using my own antenna to receive radio.
    Conclusion: Always use one ground only. Star/tree topology is a must for grounding. Never create loops.
  • If it's at all connected to your TV, VCR, or anything that connects to a cable TV system, the system may be the culprit. I had to take one of these [allelectronics.com] and one of these [allelectronics.com], connected them back-to-back, and ran them inline with every cable line in my house. Evidently the cable system was wired by an idiot, and the distribution amps on the pole (or something like that) aren't very good quality.

    Try it and see. I bought 50 of each of those adapters, spent 20 minutes, and went door-to-door in my apartment complex asking if they had a problem with hum on their stereo system. Sold 'em for $3 apiece. :D
  • You might be picking up interference from some radio station because of unsheilded speaker wires acting as antennas (antennae?), and the radio signal getting de-modulated by some non-linear part of the path, but, if you've got a steady hum, that sounds like a fault in the power supply filtering that's letting some AC or some DC ripple through, or maybe a bad bypass capacitor in the audio section somewhere. Take it back where you bought it and have them plug it in there to see if the problem follows the hardware or stays at your home. If it still has the problem at the store then it was bad out of the box--make them take it back and give you a good one.
    If you bought it mail order then go to a couple of different friends places with it and try it there to see if location makes a difference. Even the specifications link doesn't say if this thing has to plug into the wall or if it can run on battery power, but if it can, see if using batteries instead of wall socket AC makes a difference.

    E-mail me if you need further info or advice.

  • This shouldn't happen.

    As previous posters have said, electronic equipment should not emit radition, nor accept radiation. In most western countries, this is part of law.

    If your speakers are accepting radiation, then chances are they may well be a source of unwanted radiation too.

    I'm suprised that Sony would have such a design flaw, so I think the problem is specific to the actual speakers you have -- i.e. my guess is that they are broken.

    Take them back for either exchange or refund.

    • Re:Take it back (Score:1, Informative)

      by Anonymous Coward
      As previous posters have said, electronic equipment should not emit radition, nor accept radiation. In most western countries, this is part of law.

      You're wrong on with regards to the accept radiation.
      From an FCC Declaration of Conformity:

      Pursuant to Part 15 of the FCC rules. Operation is subject to the following two conditions:
      (1) This device may not cause harmfull interference and
      (2) This device must accept any interference that may cause undesirable operation.
  • I used to randomly hear short interjections of the conversations between CBers on my home stereo. The funny thing is, I'd swear it was the same guy every time, although I only heard a few seconds at a time, so who knows. All I had was an NAD CD player directly feeding into a Parasound amplifier, with nothing but 1/2 meter Audioquest interconnects connecting the two. Nevertheless, once in a while I'd suddenly hear 4 or 5 words come crackling out of the speakers, in and out like a flash. It was quite spooky until I figured out that it must have been truckers going by on the highway, which was about 1 mile away from my apartment.
  • Heh, somewhat similar to this, I was setting up for a Vocal Jazz performance at a golf club, when all of a sudden, We started to hear a radio station. Nice to know it just doesn't happen to you.
  • then try here [pricegrabber.com] for a cheap price. The Griffin Technologies [griffintechnology.com] iMic [griffintechnology.com] has both input and ouput options superior to your laptops built-in soundboard.
  • I have similar experiences with my audio equipment. I live about 500 meters from a light house where there is a 1KW morse code beacon. Unfortunatly just a bit of speaker wire ia all that is needed to recieve the signal. I end up hearing the beacon through my PC speakers and on recorded minidiscs(I don't have spdif).

    During my ham radio training I learned a reason why this could happen. In many speaker systems you will find a crossover unit. This is basicly an inductor(coil) and a capacitor. This forms a tuned circuit that is designed to accept or reject signals of various frequencies. In som e cases the small amount of signal picked up by the speaker leads is enough to turn your speakers alone into radios.

    I have even heard of rusty old fences "tuning in" to radio stations and amazing passers by.

    btw, our local(Durban, South Africa) ham radio group set up a field station at the above mentioned light house a few years back. Forgeting about the beacon, they wondered why there were sparks between the antenna leads and a grounded bus bar on the desk. 1KW at 2m from your antenna can be rather scary.
  • I've worked with sound reinforcement for a while, and a few times we just pick up radio on things. It's usually a grounding problem with a guitar or keyboard. Solution? Defeat the ground. For us, we flip a switch on a little blue box. For you, it'll probably look like a ground cheater (those little thingies that have three holes in but only two prongs out). If you only have a two-pronged cord, then you might consider getting the "inverse" ground cheater (two holes in, three prongs out, and a little tab on the two-hole side) and ground the case of the stereo (or since it's probably a plastic case, run a wire from under a screw on the back to the little tab).

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