Results 1 to 14 of 14

Thread: Subwoofer hum

  1. #1
    Junior Member Stapo's Avatar
    Join Date
    Mar 2016
    Posts
    11
    Thanks
    0
    Thanked 11 Times in 3 Posts
    Rep Power
    0
    Reputation
    230

    Default Subwoofer hum

    My son has just installed a home theatre setup including a Paradigm PDR100.

    The amp (Yamaha RX-V679) and other equipment is in a separate room which shares a wall with the screen/loudspeakers/sub on the other side. The sub signal cable connects to an RCA panel on said shared wall, and another RCA cable runs from the back of the panel and into the amp. All was installed by a professional and all equipment is brand new.

    The sub hums when turned on even when everything else is on standby. To identify why it hums we have run a dozen different tests to finally locate the problem.

    1) take out the signal cable from the sub
    2) take out the signal cable from the wall
    3) take out the signal cable from the amp
    4) move the sub next to the amp and use just one RCA to connect them
    5) removed all input equipment from the amp so it's just sub, speakers and projector (HDMI out)

    At this point I noticed that if I removed the HDMI out, or removed the power from the projector - the hum disappears! Strange right?

    6) use an extension power cable to test different outlets for projector, sub, amp to make sure active/neutral wasn't switched on one of the outlets inverting the phasing. Even got them all running from the same power board to no effect
    7) Googling suggested that sub and amp are "fighting for the ground" and to use a "directional" RCA signal cable with earth, and we found a special RCA left/right + earthing cable that we were using with the turntable and tested that, and the hum disappears.

    Now we assume that this cable has some shielding or insulation that works, so we have borrowed a $70 shielded subwoofer cable from the local hifi specialist shop, and it reduces the volume of the hum but it doesn't do anywhere near as good of a job as this record player cable.

    So we have seemed to find a solution for the symptom, but we are not sure why. Any thoughts?

    Regards,
    Steve


    Sent from my iPhone using Tapatalk



Look Here ->
  • #2
    Administrator
    mtv's Avatar
    Join Date
    Jan 2008
    Posts
    19,893
    Thanks
    7,508
    Thanked 15,066 Times in 6,761 Posts
    Rep Power
    5647
    Reputation
    239305

    Default

    It sounds like an earth loop and/or mains inducted noise via the HDMI cable from the projector.

    How was the turntable separate earth cable connected?

    How long is the HDMI cable to the projector?

    Is a power cable run with, or near the HDMI cable to the projector?

    Have you tried connecting a separate earth cable between the amp and the sub?

    Have you tried a different HDMI cable to the projector?
    .

  • #3
    Junior Member Stapo's Avatar
    Join Date
    Mar 2016
    Posts
    11
    Thanks
    0
    Thanked 11 Times in 3 Posts
    Rep Power
    0
    Reputation
    230

    Default

    It wasn't. It just dangled down.

    In fact, the solution will be (we haven't done it yet) to split the turntable RCA cable into two by peeling the R from the L, and just discard the earth wire.

    We have popped the panel off and removed the RCA panel plug to test, and it seems to be AOK. Now to feed the cable through the walls.

    What is your take on the projector HDMI being the apparent root cause? I forgot to mention that we tried a different HDMI also but no change.


    Sent from my iPhone using Tapatalk

  • #4
    Administrator
    mtv's Avatar
    Join Date
    Jan 2008
    Posts
    19,893
    Thanks
    7,508
    Thanked 15,066 Times in 6,761 Posts
    Rep Power
    5647
    Reputation
    239305

    Default

    I was editing my previous post as you made yours, so some questions/answers overlapped.

    Have you connected RCA cables directly, bypassing the wall plate?

    Are the wallplate terminals a fully shielded bulkhead type, or open solder terminals? (The latter having breaks in shield coverage)

    How good is the shield coverage in the 'through wall' interconnect cabling?

  • #5
    Junior Member Stapo's Avatar
    Join Date
    Mar 2016
    Posts
    11
    Thanks
    0
    Thanked 11 Times in 3 Posts
    Rep Power
    0
    Reputation
    230

    Default

    Quote Originally Posted by mtv View Post
    I was editing my previous post as you made yours, so some questions/answers overlapped.

    Have you connected RCA cables directly, bypassing the wall plate?

    Are the wallplate terminals a fully shielded bulkhead type, or open solder terminals? (The latter having breaks in shield coverage)

    How good is the shield coverage in the 'through wall' interconnect cabling?
    Yes went direct to sub by pass the wall plate. Still had the hum until we went to the special lead as mentioned. Wall plate ok even with the new lead plugged into it.


    Sent from my iPhone using Tapatalk

  • #6
    Administrator
    mtv's Avatar
    Join Date
    Jan 2008
    Posts
    19,893
    Thanks
    7,508
    Thanked 15,066 Times in 6,761 Posts
    Rep Power
    5647
    Reputation
    239305

    Default

    Is the turntable cable significantly shorter than other RCA cables tried?

  • #7
    Premium Member

    Join Date
    Feb 2008
    Posts
    3,688
    Thanks
    1,938
    Thanked 2,104 Times in 1,050 Posts
    Rep Power
    967
    Reputation
    32468

    Default

    My hum was caused by the power outlet to the speaker, i did a little research and i had the power coming out of a board. Removed and placed in a separate wall socket and the hum disappeared
    There is a fine line between "Hobby" and "Madness"

  • #8
    Junior Member Stapo's Avatar
    Join Date
    Mar 2016
    Posts
    11
    Thanks
    0
    Thanked 11 Times in 3 Posts
    Rep Power
    0
    Reputation
    230

    Default

    Quote Originally Posted by mtv View Post
    Is the turntable cable significantly shorter than other RCA cables tried?
    Yes only 1 metre long.


    Sent from my iPhone using Tapatalk

  • #9
    Junior Member Stapo's Avatar
    Join Date
    Mar 2016
    Posts
    11
    Thanks
    0
    Thanked 11 Times in 3 Posts
    Rep Power
    0
    Reputation
    230

    Default

    Quote Originally Posted by allover View Post
    My hum was caused by the power outlet to the speaker, i did a little research and i had the power coming out of a board. Removed and placed in a separate wall socket and the hum disappeared
    Yes thanks for that. Did try that and more. That was our fist thought.


    Sent from my iPhone using Tapatalk

  • #10
    Administrator
    mtv's Avatar
    Join Date
    Jan 2008
    Posts
    19,893
    Thanks
    7,508
    Thanked 15,066 Times in 6,761 Posts
    Rep Power
    5647
    Reputation
    239305

    Default

    Quote Originally Posted by Stapo View Post
    Yes only 1 metre long.
    That may be a clue.

    If you have longer cables, especially running near power cables, they are more prone to pick up hum.

    One trick used in audio engineering is to 'lift' the shield at one end. EG: The earth/shield is only connected to one device, say the amp and open at the sub end.

    Another option would be to try a ground loop isolator like .

  • #11
    Junior Member Stapo's Avatar
    Join Date
    Mar 2016
    Posts
    11
    Thanks
    0
    Thanked 11 Times in 3 Posts
    Rep Power
    0
    Reputation
    230

    Default

    Quote Originally Posted by mtv View Post
    That may be a clue.

    If you have longer cables, especially running near power cables, they are more prone to pick up hum.

    One trick used in audio engineering is to 'lift' the shield at one end. EG: The earth/shield is only connected to one device, say the amp and open at the sub end.

    Another option would be to try a ground loop isolator like .
    Ok very good. Thanks very much.


    Sent from my iPhone using Tapatalk

  • #12
    Senior Member
    Antennaman's Avatar
    Join Date
    Jul 2008
    Location
    Tasmania
    Posts
    528
    Thanks
    19
    Thanked 259 Times in 161 Posts
    Rep Power
    298
    Reputation
    4456

    Default

    Quote Originally Posted by Stapo View Post
    All was installed by a professional and all equipment is brand new.
    Shouldn't they be coming back to sort this out, then, would be my call.

    Quote Originally Posted by Stapo View Post
    At this point I noticed that if I removed the HDMI out, or removed the power from the projector - the hum disappears! Strange right?
    Either the sub has only a 2 wire mains connection (more than likely), & the projector may or may not be a 2 wire mains (ie no mains earth.) So there's no common earth anywhere, & you get quirky little things happening, such as you have experienced.
    Never stand under a shadow that's getting bigger

  • The Following User Says Thank You to Antennaman For This Useful Post:

    Tiny (13-03-16)

  • #13
    Junior Member Stapo's Avatar
    Join Date
    Mar 2016
    Posts
    11
    Thanks
    0
    Thanked 11 Times in 3 Posts
    Rep Power
    0
    Reputation
    230

    Default

    Quote Originally Posted by Antennaman View Post
    Shouldn't they be coming back to sort this out, then, would be my call.



    Either the sub has only a 2 wire mains connection (more than likely), & the projector may or may not be a 2 wire mains (ie no mains earth.) So there's no common earth anywhere, & you get quirky little things happening, such as you have experienced.
    Very good. Yes correct on both counts
    2 wires for both including the amp.



    Sent from my iPhone using Tapatalk

  • #14
    Junior Member Stapo's Avatar
    Join Date
    Mar 2016
    Posts
    11
    Thanks
    0
    Thanked 11 Times in 3 Posts
    Rep Power
    0
    Reputation
    230

    Default




    Sent from my iPhone using Tapatalk

  • Bookmarks

    Posting Permissions

    • You may not post new threads
    • You may not post replies
    • You may not post attachments
    • You may not edit your posts
    •