RM6750 Sub hums

seaberry
seaberry Posts: 6
edited March 2014 in Subwoofer Hookup & Bass Management
Just bought - Polk Audio RM6750 Black 5.1 CH Home Theater Speaker System, and registered it today. Am now waiting for support to answer me back...Monday. Anyway, the sub hums when plugged into an electrical outlet, by itself...6 different circuits (3 were GFI), hums even when it is turned off (if hooked to an outlet)...hums when connected to Yamaha amp. Only way I have been able to stop it, is to unplug from electric outlet. I like the other speakers, but didn't buy a surround sound to listen to a humming woofer when movie 'Bass' sounds are slow or idle. My Vizio soundbar had a 6" woofer that works fine. Apparently hookups are not the problem, since it hums by itself the moment its plugged into electricity. New at this (other than the Vizio soundbar) so have no clue why a speaker would hum.
Post edited by seaberry on
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  • [Deleted User]
    [Deleted User] Posts: 7,658
    edited March 2014
    Hello,
    Welcome to Polk's forum, sorry you're having a problem. In all likelihood there's a problem with the amplifier in the sub and you should contact where you purchased it and ask for a replacement. If that isn't possible contact Polk's CS department, on Monday, at 1-800-377-7655 and have the serial number handy when calling.
    Regards, Ken
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  • 20hz
    20hz Posts: 636
    edited March 2014
    seaberry wrote: »
    Just bought - Polk Audio RM6750 Black 5.1 CH Home Theater Speaker System, and registered it today. Am now waiting for support to answer me back...Monday. Anyway, the sub hums when plugged into an electrical outlet, by itself...6 different circuits (3 were GFI), hums even when it is turned off (if hooked to an outlet)...hums when connected to Yamaha amp. Only way I have been able to stop it, is to unplug from electric outlet. I like the other speakers, but didn't buy a surround sound to listen to a humming woofer when movie 'Bass' sounds are slow or idle. My Vizio soundbar had a 6" woofer that works fine. Apparently hookups are not the problem, since it hums by itself the moment its plugged into electricity. New at this (other than the Vizio soundbar) so have no clue why a speaker would hum.

    if its a grounded plug ( 3-wire ) put a ground adapter in thats one of those things so if you have a wire with a ground on it you can plug it into the wall , and dont hook up up that loose ground wire , what that does is open the ground wire from the circuit .
    Pro-sound equipment has a built in "ground lift " because its common .
    mt sub did that the manufacture recommended that it helped a lot
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  • seaberry
    seaberry Posts: 6
    edited March 2014
    Thanks to you both...will wait to see what Polk support suggests (should hear back from them tomorrow) and go from there. The other speakers are fine, but something isn't right with the sub. Thanks!
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  • seaberry
    seaberry Posts: 6
    edited March 2014
    Kenneth Swauger wrote: »
    Hello,
    Welcome to Polk's forum, sorry you're having a problem. In all likelihood there's a problem with the amplifier in the sub and you should contact where you purchased it and ask for a replacement. If that isn't possible contact Polk's CS department, on Monday, at 1-800-377-7655 and have the serial number handy when calling.
    Regards, Ken

    Just an update...BTW, this was all handled thru email. I sent a second email yesterday afternoon adding the serial number of the sub. Got a reply from Polk support about 30 minutes ago - stating they will send a replacement, and asking for my address and phone number. Replacement should arrive in 7-10 days.

    Newegg would've taken the entire system back, but couldn't just swap sub's...so, Polk handled the issue perfectly, IMHO.
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  • [Deleted User]
    [Deleted User] Posts: 7,658
    edited March 2014
    Excellent, I'm glad things were worked out!
    Enjoy your system!
    Ken
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  • thomasfolks
    thomasfolks Posts: 1
    edited March 2014
    Seaberry - just in case this doesn't fix it - I had recent problems with my sub - was related to earthing. The sub would hum even when connected to other equipment to the mains and turned on at the mains switch.

    The problem I had was that all of my audio equipment (except for the sub) was "double insulated" ie, none of the equipment had a proper earth. This is normal. Unfortunately, such equipment is "floating" at the chassis and the signal earth connection, and so can operate at any voltage you put it. To add to this, most mains equipment has "leakage" from the mains to the chassis, either through the capacitance of the power supply transformer, or capacitive mains filtering. My equipment was floating at 50 volts AC, when compared to a "real" mains earth pin on the power outlet. This can operate correctly if the signal earths are all connected together and there is no hum at the output.

    The problem occurs when one component becomes earthed to a "real" earth (eg as with the sub with a 3 pin connector), and then that mains leakage can appear on the input. A better quality lead can help, but the issue is that leakage current is flowing from your other equipment down the earth lead to the sub, to real earth and contributes to hum.

    The way to fix this, is to make sure there is (preferably ONE) "real" earth that is grounded to mains earth on your source equipment somewhere. I fixed my problem by connecting a dedicated power plug with only earth wired, to a FoxTel box chassis (because it had 10 times the leakage of the rest) and so the leakage was bypassed at the source.

    So - if the problem is still there when you get the replacement - then you may try connecting a "real" grounded earth to the chassis of the amp or other equipment and see if this makes a difference.

    A related problem to this is the earth from a cable tv source may also introduce hum, as it is a different earth to your house. An isolating transformer can fix this, but once again it is best to avoid having the whole system "floating" - it should be earthed at one point.
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  • seaberry
    seaberry Posts: 6
    edited March 2014
    Yeah, I'll do an update when replacement arrives. I'm a retired electrician and know that electricity can be tricky at times. Also, the electrical field is enormous, and some motor electrician may not know how to wire a house...a house electrician probably has no clue how to change the transformer on a pole...it's a huge field!

    I read a lot of horror stories before contacting Polk support, just while searching for a possible simple solution. Most of the advice I was reading seemed confusing (at best) and dangerous (at worse). Still, speakers have been around for a long time and should have most of the kinks worked out by now.

    Grounds/grounding (I assume that this "earth" term that keeps popping up is a ground) can cause all kinds of trouble if done improperly or damaged (e.g. rusted ground connection on cable connection). I tried 6 different circuits (3 were GFI) and the hum was there...subwoofer by itself, and hooked to nothing else. This is basically what I wrote to support, and they immediately said they would replace it. Now, my house panel is actually a "sub-panel" since the main panel is outside at the pole, so my neutral bar and ground bar are separate from each other...a 4-wire house system (note: power is sent on 3-wires by electric company - grin). The subwoofer has a 2-plug chord (grin - again). All my circuits are fine...tested with a good line tester. Polk support seemed to think it was a subwoofer problem, and I agree with them...will update later.
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  • seaberry
    seaberry Posts: 6
    edited March 2014
    Well, they didn't replace the subwoofer...they replaced the "subwoofer amplifier" (which requires installing) and it still hums. Had to remove the speaker to install it, due to the mounting of the speaker...the contacts were behind a partition, and I didn't want to hook it up just by feel. I flipped speaker around when reinstalling, so the contacts could been seen and reached easily...w/o removing the speaker!

    I'll contact Polk support Monday and see if they think it's a speaker problem. I like the other speakers, so will probably just 'Eat' the subwoofer problem until I can resolve it.

    $169.00 5.1 system, and from what I've seen that's cheap for surround sound. Have the VIZIO subwoofer hooked in right now, smaller but doesn't hum. After listening to this surround system, I'm not going back to the soundbar (except in case of emergency).

    Maybe Polk support will send a new speaker next...the VIZIO doesn't hum and neither should the Polk, IMHO.
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  • seaberry
    seaberry Posts: 6
    edited March 2014
    Another UPDATE:

    Well, Polk's support is great, that's for sure! They're going to "replace the subwoofer with an upgraded PSW10" which hopefully resolves the problem.
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