Subwoofer 101- I have some questions..

Discussion in 'Subwoofers' started by baldyman, Jan 4, 2007.

  1. baldyman

    baldyman
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    Hi,
    I'm totally new to subs.. I'll be using the KEF PSw2500 that came bundled with my satellites.

    The KEF sub I have has:

    High Pass Output L
    High Pass Output R

    What do the High pass outputs do?

    There are also these:
    Ground In/Out switch
    SLOPE 12db/24db switch

    Can someone please explain what the GROUND and SLOPE functions are for and how best to set them? :confused:
    Thanks!
     
  2. Member 96948

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    Basically, I think you can ignore all of these functions. They're all related to using the sub in a two channel setup.

    The idea is that your speaker cables go to the sub first and then onto the stereo speakers. The 'High Pass Output' is so called because it only passes the high frequencies to the speakers. The 'Slope' function controls the rate at which the signal crosses over between the sub and speakers. 12dB would provide a 12dB/octave slope for instance. I can't remember how the 'Ground' function works.

    Basically none of them effect the inputs you're going to use, so set them to off where possible and other wise ignore.

    All you need to do is connect one of the 'Low Level' left or right stereo RCA phono sockets to the Subwoofer (it might be called LFE) output on your AV receiver, turn the 'Crossover' to maximum and then turn up the Low Level Gain until it's loud enough for your taste. Set the crossover frequency in your receivers menus to 120Hz for starters. That should get you up and running. I am assuming you've got Kef KHT-2005 by the way.

    Russell
     
  3. Steve.EX

    Steve.EX
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    The ground lift switch will, i believe, isolate the ground path of the signal input (screen of the phono if you like) from the common earth-path (chassis of amp-plate)
    This can on occasion help with loop hums.
     
  4. baldyman

    baldyman
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    Thanks for the info guys! :smashin:

    Russ: Its the 5005 bought from Hutters on here.
     
  5. Member 96948

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    As Kef Quote 95Hz (-3dB or -6dB, they don't say) as the LF roll off for the satellites, I'll stick by my suggestion of 120Hz for starters. Live with it for a few days and then try a higher crossover, say 150Hz. Live with it for a few more days.

    What you're trying to achieve is as much bass as you can through the sub, without actually being able to hear where it is. To a large degree, where you position the sub will limit your success. Low bass is omni directional, but as frequency increases your ears become more sensitive to directional information. Below 80Hz it just sounds like there's bass in the room. By 120Hz you may start to be able to locate where the bass is comming from.

    If the sub is positioned in between the front three speakers, this will help as that's where all the sound is comming from anyway. If it's over to one side of the room, it may sound a increasingly disjointed with increasing crossover frequency.

    It's about trying to achieve a satisfactory balance to basically make the sub invisible, but take as much strain off the fronts as possible.

    There's no hard and fast, just what YOUR ears like and don't be scared to ask more questions.

    Russell
     
  6. baldyman

    baldyman
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    Ah right..
    It will be placed to one side (nessesity) in the room, so I will watch out for the problems you have mentioned.
    The sub does have a 30hz-150hz range on the frequency response (according to the KEF brochure), so I will have to experiment.

    I have to finish redecorating the lounge first though! :D
     
  7. chyaweth

    chyaweth
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    Russ,

    I was initially searching this forum to check if I needed a sub woofer in my audio system.

    I'm interested/concerned that you say low bass is omni-directional and suggesting below 120hz its difficult to detect direction.

    120hz is only roughly C3, (C below middle C), and easy to pinpoint audibly. As a bass singer I regularly sing music requiring the E below that, which is roughly 80hz, and again has "direction".

    Actually your post has answered two questions in my mind,

    1 - the reason for my vocal part disappearing below the computer desk when I play back recordings of my quartet. (I have a sound system with a sub woofer attached)

    2 - I don't want a sub woofer in my "real" audio system because the main speakers have a proven response down to 20hz, (TDL Studio 3).

    cheers :thumbsup:
     
  8. welshtommo

    welshtommo
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    Baldyman,

    I have the 5005s and can confirm everything in the first reply regarding ignoring all the other sockets other than left/righ line in. I have my receiver (a Denon AVR 2805) connected from its sub output, via a coax/rca lead into the left line in on the sub. Crossover on the sub up to max as this allows your receiver to override and control the crossover level. Crossover frequency on the receiver set to 100 hz. Input level turned up about a third - you can alter this depending on how loud you want it. Don't know if any of this helps, but after lots of fiddling and testing, I find these settings are the best for my system.
    Incidentally, I've got the slope to 24db, ground switch to out, phase adjust to 0.
     
  9. baldyman

    baldyman
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    Thanks Tommo.
    I shall use your post as a reference.
    I'll post back with feedback as to how I get on..
     
  10. Member 96948

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    Unless your voice is a pure sinewave generator, I'd suggest that it produces all manner of other noises and harmonics, most of which will be higher in frequency. These will certainly be locatable. Harmonic distortion produced by poor subs renders them locatable also, even if the fundamental isn't.

    This is why I refer to the potential pitfalls of poor sub positioning and crossover points. Your sub IS PRODUCING NOTES FAR ABOVE THE CROSSOVER FREQUENCY. Sitting with a sub beneath the desk, I'm not in the least surprised you can locate it beneath you.

    A man happy in his ignorance, is at least happy.;) Speaking as a fellow TL speaker owner with speakers that measure happily, in room, down into the mid 20s, I can catagorically state, they sound a damn sight better when they're not being asked to. A sub with a well matched driver and amp, dedicated to clean, low distortion of the bottom two to three octaves, will make a better job of it than the main speakers. Further more, the main speakers AND amps, shorn of the responsibilty of producing the high cone excursion, power sapping, distortion inducing, deep frequencies, will reward you with cleaner and more open mids and highs and vastly increased headroom. Nice for those big choral cresendos.

    I'm not being cheeky (well, ok, just a bit) but it's well worth looking into. Bear in mind, 'real' audio systems are lacking real bass management, which is what makes the difference. There are a number of serious guys on here running bass managed 'real' audio systems with some serious floorstanding speakers. Not one of them would agree with your last statement.

    In the mean time, I'll continue with my fake audio system enjoying tight, deep low distortion bass, that extends flat in room to 18Hz, starts and stops clearly defined, individually distinguishable notes in a manner that you've yet to enjoy.:thumbsup:

    Cheers,

    Russell
     

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