Polk LSi-15s with SVS 20-39 PC-Plus... good combo?

Discussion in 'Speakers & Subwoofers' started by KyleT, Sep 16, 2004.

  1. KyleT

    KyleT Stunt Coordinator

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    Do you think the two of these will mix well for music and movies? (I only have a 2-channel setup right now).

    For most music I am unfortunately going to have to use the high-level inputs, and from what the guy at SVS told me, 80Hz and below automatically be filtered out by the sub. This is not adjustable or defeatable at all using the high-level inputs.

    So my questions are:

    -Will the LSi15s (8" built-in woofer) still do justice to the music, or might I have just as well have gone with some smaller LSi9s (6.5" driver for bass) and been just as well off?[​IMG]

    -Will the SVS 20-39 PC-Plus extend strongly and cleanly all the way up to 80Hz? Or am I going to have somewhat of a gap in my sound between 60 and 80Hz or so because of that high pass filter?

    -Will the power that was being sent to my LSi15s for bass just be absorbed and grounded out, or will it be somehow redirected and used as extra energy to power the frequencies above 80Hz?

    Maybe a bit too late to be asking these questions though since I just ordered a couple days ago. I'm just getting nervous.

    I thought the 25-31 would have been a better match for my speakers, especially since I do quite a bit more music listening, but the guy at SVS told me he still strongly recommended the 20-39 even for music, especially since the sub will be in a very large open area... which he said the "plus" model would also help with as well.

    Thoughts?
     
  2. Eric Hargrove

    Eric Hargrove Stunt Coordinator

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    I am using Lsi15's a two CS Ultras. The Ultras handle the bass chores below 100Hz as crossed over from my Marantz receiver. No problems whatsoever with phase issues. You should be very happy with this combination.[​IMG]
     
  3. JohnSmith

    JohnSmith Supporting Actor

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    1) Figure out where the LSi15s's start to trail off in your room, the spec says 32hz but it could be much lower or higher than that. IMO for music you really don't need a sub with those speakers, as they go pretty low already.

    2) In a music system, 80hz L/R and 80hz subwoofer crossover is a bit too high, really want a lower setting (if you mains can handle it, which they can) so I wouldn't go through the SVS if it has a fixed crossover on the speaker outputs. What about the line-level outputs? Is that fixed at 80hz too? I would have thought the crossover filter + outputs could be used to divert bass from one other, depending on the setting (and not be fixed)

    3) Depends how you connect it. Since it's via speaker cable it's after the poweramp section. So it'll make no difference. You'll need to have line-level high pass filter between pre and power stages to remove low frequencies before the amp stages.

    I would leave your speakers direct connected, subwoofer directly connected to amp (high or low level). Then enable subwoofer crossover, dial in subwoofer to 30-40hz (as a starter point) and then adjust gain.

    You didn't make a wrong decision buying the floorstanders. n a music system quality towers are a better choice, as long as amp/room suits it.

    What amp are you using to power the speakers? You could try bi-amping them (if the 8" subs are passive) that should help a bit.
     
  4. KyleT

    KyleT Stunt Coordinator

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    So then might it be better to "split" my speaker cable and have a cable leading to the high pass input on the sub, except nothing coming out of the high pass output on the sub, and then the other part of the split cable leading to the LSi15s?

    This is in a large room, by the way. I had the LSi15s in a small carpeted room before and they did pretty well with bass (still not outstanding), but in this large tiled open area they are really falling flat in terms of bass.
     
  5. JohnSmith

    JohnSmith Supporting Actor

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    Connect your Polks to your stereo amp as you've probably got already.

    If your amp has two sets of speaker outputs, either A/B or bi-wire then use the other pair of terminals. Rel recommend high level (speaker cable)

    You could use line level, if you've already got a long enough pair of RCA'a.

    Then connect either high or low level from the amp to the subwoofer. Dial in crossover on the sub 30-40hz to get a seamless blend.

    If your amp has no problems driving the Polks then it's probably better this way, as the internals of a subwoofer could introduce sound degradation. You'll need to insert a good quality high pass filter between pre/power to gain the advantage of routing 40hz to the poweramps.

    I guess if the room is large with bass suck-out then you could need a sub. It's just that in the UK large floorstanders ~35hz FR point is more than good enough.

    See my post on avsforum, with another method routing bass in a similar setup -stereo system, slightly different in principle, as high pass is done at line level before any amp stages.

    here
     
  6. KyleT

    KyleT Stunt Coordinator

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    There is no way for me to get a second set of speaker cables ran from the amp, and no way for me to get an rca cable to the sub either.

    The amp (Rotel 1090) and source (music server) are way upstairs in a wiring closet. One pair of 14 guage speaker cable from the distribution block in my wiring closet to this location downstairs in the 'social area' of the house, about 60 feet away.

    The cable lead to an impedance matching volume control in the wall and from there to two seperate wall plates.

    So I'm thinking maybe just keep my speaker cable going from the wall to my speakers, but then also run a second pair of speaker cable from the wall plates to the sub, and then just play around with the high frequency cut-off point on the sub until it sounds good with the speakers. True, my speakers will still be playing the entire frequency range which will be wasted since the lower frequencies will be dominated by the subs. But to me it still sounds like the best idea given my limitations... at least in my uneducated opinion it does.

    Do you agree?

    Will doing this create any weird anomolies with the resistance that my amplifier sees or the amount of power my speakers see?

    In other words, would running a second pair of speaker cables from the wall plates effectively cut the power my speakers end up seeing in half?

    Help! The should be on my front porch when I get home this afternoon and I don't want to screw anything up![​IMG]
     
  7. JohnSmith

    JohnSmith Supporting Actor

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    hmm can't help with the distribution area or if wiring speakers terminals to sub input is ok, but the high level speaker inputs are basically attenuated line-level, the amount of power taken from the amp is neglibable (if connected to amp)

    Since you've already got the cable wired in, you could try both..

    amp---->speakers--->sub
    and
    amp---->sub----->speakers

    and see which you prefer. The first might sound better due to lower crossover for mains + subs, but could also sound worse if the speakers/amp stuggle.
    The second might sound more cleaner, but L/R a bit "thin" due to much higher crossover.

    Suck it and see :)
     
  8. KyleT

    KyleT Stunt Coordinator

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    OK well I got the sub in a few days ago. I have not yet had a chance to try it out with movies or with localised music, but I did get it connected to my 'whole house' audio system and have played quite a variety of MP3s through it.

    I basically just have my speaker cable leading to both the speaker and the sub's highpass input.

    In other words, it splits off at the wall and goes to both devices, thus, at least as far as I can tell, not dropping the power going to the speakers at all, and keeping them playing full range (so that the SVS doesn't cut them off at 80Hz). I've actually got the SVS cutoff at 60Hz... I've found this is the highest frequency at which the SVS will currently play and still sound mostly transparent alongside my LSi15s... any higher than 60Hz and the music starts to sound unnatural and inaccurate. Below 60Hz with proper adjustment of the gain, it sounds flat-out amazing even for music.

    So far the volume of the sub is anything I could have asked for and more. It's not quite the sheer 'blow your shirt off' sheer impact I was expecting... but it's more than suffiecient for any sane level of listening. And considering the very large and very open area its in... I don't really fault it on this point. My LSi15s sounded very good in terms of bass in my old room. Onec at this new location they sounded pathetic in terms of bass. So I imagine if I moved this SVS to a smaller more closed in location, it would make any sane man cry for mercy.[​IMG]

    My one question is how do I know what to set the phase to?
     
  9. JohnSmith

    JohnSmith Supporting Actor

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    Don't set the SVS crossover too high, otherwise you'll get too much overlapping bass; a boomy effect- even with volume quite low.

    It'll take time and experimentation by ear to estimate where the ideal xover position is. At first you'll probably have subwoofer too loud and/or crossover too high. Once you have the sub for a while you'll probably realize because of this the subwoofer sticks out a bit. A quick readjustment on both crossover/gain should integrated the two better.

    You shouldn't have to adjust phase unless the sub is placed other than near the main speakers; ie side walls etc, or have 2 subs in different positions. However try 90' and 180' and see what you think.
     

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