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servo 15 question

Discussion in 'Home Cinema Speakers' started by morg, Apr 28, 2003.

  1. morg

    morg
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    How audible is the hum on this subwoofer meant to be. Just got
    one on sat. When plugged in I can hear the speaker cone humming from the other side of my room which is about 12ft
    long. The humming gets worse when I atatch the phono lead.
    (its only a cheap phono which I am going to replace)

    Also when using the 100-20hz tone on Avia disc with the volume
    control at halfway the sound output stops from 30hz downwards
    Would the cheap phono cause this or is it just that the volume
    needs to be higher to hear it down to 20Hz.

    Thanks in anticipation

    Morg
     
  2. NicolasB

    NicolasB
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    You probably can't hear sound at 20Hz. If it's loud, you can probably feel it. Cable is very unlikely to be cutting out stuff below 30Hz.

    If your phono cables are cheap enough that they don't have adequate shielding then you may be picking up 50Hz mains interference, which would cause humming. Might also be a ground loop (er... maybe? - knowledge running a little thin at that point :) ).
     
  3. Steve.EX

    Steve.EX
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    Morg.
    By your own definition it would appear that the hum that you are getting is earth related, although the Servo itself does not require an earth are other items you are using within your set-up grounded, most people (sometimes unwittingly) myself included suffer to a greater or lesser degree in such instances, mine is an acceptable trade-off against grounding my poweramp (as 1 of 4 of my Rotels wants earthing???), if i ground this particular Rotel the (very minor) sub hum is removed but i get tremendous buzz across the front soundstage - no thanks.
    Just how bad is this hum? I have to put my ear to the driver to hear the difference, in fact the transformer noise is louder!
    Of the Servo's that i use to a unit they start to roll off at around 17-18hz and are about -3d at 15hz.
    I would not exactly be able to tell you why but it may have something to do with your room, are you getting a large peak around 40hz? which makes you "tihnk" the sub has rolled off past this peak.
    In smaller rooms it is sometimes difficult to get these frequencies to propagate and you may well find that you are getting tremendous 20hz response upstairs in the back bedroom or something/somewhere other than the room the sub is in.


    Regards

    Steve.
     
  4. Zig

    Zig
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    First job would be to replace the lead, preferably with a decent shielded cable maybe try one from the IXOS range. My Servo 15 hums with the lead unplugged but goes quiet once it has the lead is plugged in.
     
  5. morg

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    Thanks for the replies. Have purchased monster sub cable today
    will try that and see if it cures hum as in Zigs case. I notice that
    the power cable supplied with subwoofer is a three pin kettle
    type plug which I presume is earthed rather than the two pin
    type on back of subwoofer does that really matter.
    Will also get some test tones and use sound meter to get proper
    frequency readings

    Thanks

    Morg
     

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