servo response graph

Discussion in 'Subwoofers' started by sparkymarky, May 3, 2004.

  1. sparkymarky

    sparkymarky
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  2. sparkymarky

    sparkymarky
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    This was my first attempt so not sure if i did it correctly.

    1. . Made sure bass boost was off and lfe set to 0db.

    1a. I set all speakers to 75db inc sub
    (this left the sub at only 66 on the knob at the back? is this right as it only starts at 70 so 66 isn't turned up very much at all??
    its at about 25 to the hour on a clock. Although the sub is quite close to the listening position.

    2. Then, turned the amp volume down to the normal listening level position.

    3. Turned off all speakers except sub.

    4. Played test tones from 100hz down to 16hz

    5. noted them on graph
     
  3. sparkymarky

    sparkymarky
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    when doing the tests at the lower end i could only just hear some tones and some not at all.

    16hz could not hear nor feel anything
    18 hz same
    20hz hear and feel slightly


    i take it that turning the sub volume up on the back would cure this and i would FEEL it?
     
  4. sparkymarky

    sparkymarky
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    Now obviously i need to sort out the peaks and troughs.

    The volume on the back is puzzlng me though. Do i need to turn it up to quarter to the hour as other people seem to in order to FEEL good lfe???


    Any comments/oservations appreciated and welcomed
     
  5. sparkymarky

    sparkymarky
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    Some pics may be helpful too in diagnosis.

    Main viewing seat is obviously the 2 seater sofa opposite the tv.

    [​IMG]

    [​IMG]

    [​IMG]
     
  6. rob_w

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    You've got the beer next to the settee, so the basics are covered:D

    I think with a peak / trough that big I'd try moving the sub about a bit to even out the response, before even considering eq.


    Have you tried it along the wall with the TV, mains? - Looks quite near to your seating position where it is now.

    Also try it in a corner if you can - my subs lost their 40Hz dip when I pushed them back into the corner. (depends on your room dimensions of course)

    The huge peak at 45 is the reason it's turned down so low - get rid of that and you can up the volume about 10-15dB. That should give you the 'feel' that your missing.


    Cheers,

    Rob
     
  7. CoZMoSiS

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    I'm assuming its a Velodyne HGS-15, if indeed thats correct you didn't mention the subsonic cutoff at the back of it (if its the model i think it is) there is a selectable 15/35Hz cutoff so if its currently on 35Hz that could explain why its not shaking the room apart.

    If that doesnt apply, then run say a 15Hz or 20Hz test signal through it and look at the diaphragm movement, it should be fairly noticable even if its attenuated if it's being fed those frequencies. If its doing basically nothing at 15Hz the i could only guess that there is a cutoff somewhere in the system.

    Dunno if this was helpful, please give more info if not.

    EDIT: One thing to bear in mind, at those subsonic frequencies the wavelengths are several meters long. Your room doesnt seem that large so you wont notice them as much as say for example if you were at the opposite ends of a long room.
     
  8. Ian J

    Ian J
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    It's a Paradigm Servo 15.

    The confusion arises as the Excel spreadsheet that everyone is downloading from the snapbug site has HGS-15 as it's title and whilst everyone is using the spreadsheet, no-one seems to be changing the header.
     
  9. rob_w

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    ""It's a Paradigm Servo 15.""



    I was about to post that Ian:) , will add that the output at 20Hz is higher than at 80Hz - no high pass filter there...

    Cheers

    Rob
     
  10. CoZMoSiS

    CoZMoSiS
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    Ah my bad ! I have heard one of those in action, they certainly have more than enough capability to shake a room about (better hold on to that beer). I'm thinking like Rob says it could well be positioning due the extreme length of wavelengths involved. Authough i still think it would be a good idea to look at diaphragm movement, that will speak 1000 words as to what kind of a signal its getting- i cant help but feel its not receiving much in the way of subsonics.
     
  11. sparkymarky

    sparkymarky
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    Thanks for the replies guys.

    Unfortunately i am limited in sub position due to WAF.
    Could possibly put it where i was standing when i took the pic of the sub (the doorway into the kitchen). May try it here when i'm next allowed (!) and post a new graph.

    Room length is 13m x 13.5 wide so not the biggest but possibly big enough??? The pictures make it look a lot smaller than it actually is.

    If it has to stay there, would a BFD be able to sort out a peak that large???

    Thanks agaain chaps and chapesses
     
  12. Gordon @ Convergent AV

    Gordon @ Convergent AV
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    Where were the measurements taken?

    If you cannot move the sub. Try moving the seat....forward would be an idea. Try 2 or 3 feet.

    Gordon
     
  13. sparkymarky

    sparkymarky
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    The measurements were taken from the main viewing seat, the left hand seat of the 2 seater sofa.

    I can't move this sofa forward but i could move it sideways towards where the pictures were taken from. This may have an effect. Thanks for the idea.
     
  14. Gordon @ Convergent AV

    Gordon @ Convergent AV
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    If your peaks and troughs are caused by room modes then the first point of attack is to move sub. If you can't then the other thing is to move the seating locations out of room mode peaks.

    I don;t know whether these modes are from width, length or height modes. Probably length. Moving forward 3 feet should knock a big junk out of that peak and if the trough is a length mode it will help smooth it out too. Of course it will also probably move you in to problem areas from other modes.....but that's half the fun!

    Put your test tone disc back in and stick on the nutter peak tone and then move your meter forward 3 ft see what happens. Or just turn up the volume and walk around and you'll hear the peaks and troughs of that mode.Try to move your own seating location to where it's neither loud or quiet. Then measure again.

    Have fun

    Gordon
     
  15. rob_w

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    Hi Gordon,

    ""I don;t know whether these modes are from width, length or height modes. Probably length.""


    The room is basically square (13 x 13.5') I'd imagine this is why the peaks/troughs are so big, and so centred around 2 freq's..

    Sparkymarky,

    Looking at the photo's I'd say swap the sub with the cd rack ? / bookcase ? in the corner (where the black triangle thingy is) for a start, then see if SWMBO notices as it creeps rightwards towards the left main speaker..maybe even widen the mains and try and squeeze it in between the mains and the tv....

    WAF doesn't look to be too much of an issue, going by that centre channel placement;)


    Keep on experimenting!

    Cheers

    Rob
     
  16. sparkymarky

    sparkymarky
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    unfortunately the centre channel doesn't live there. Is has to come out every time i put a film on. But i don't mind as a compromise.

    i think i will try it where the dvd rack as you suggest. Thanks guys.
     
  17. rob_w

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    Any progress ?

    Rob:)
     
  18. sparkymarky

    sparkymarky
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    Nah, not had chance yet rob. Will either try Fri or sat and will report back.
     
  19. sparkymarky

    sparkymarky
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  20. sparkymarky

    sparkymarky
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    i will get some pics up this week but basically now the sub is inside the front left speaker firing towards the front of the listener at the front of the soundstage as oppposed to firing inwards from the rear of the left hand side wall onto the left ear of the listener.
     

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