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2 X CS Ultra's and 1 K1 amp - looking for a little more thump - advice appreciated

Discussion in 'Subwoofers' started by Infinity, Apr 23, 2005.

  1. Infinity

    Infinity
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    I have had the pleasure of two CS ultras running from a Crown K1 amp and I think that I am getting used to them :(

    I was scared when they first arrived, but, I had my sister round to listen to some music and found myself hitting a red light on the amp.
    It was a great track, and I wanted to go a 'little' louder but I ran out of headroom.

    This got me to thinking. With one PC ultra running of each channel of the sub, would I gain a little more oomph running them in parallel to lower the impedance. Which then raises the following question, what impedance is a PC ultra driver.

    Other options to get a bit more welly would appear to be:
    One more K1 amp,
    or, try and sell the K1 and grab hold of a K2

    at least the above two options would still enable me to run the subs out of phase as necessary.

    All input greatly appreciated.

    Thankyou in advance. :thumbsup:

    ( edited: PC changed to CS - sorry for the confusion )
     
  2. alexs2

    alexs2
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    Hi and welcome....I assume you mean 2 CS-Ultra's,as you describe using a Crown power amp to run them.

    If you run them in parallel,you will obviously halve the impedance,which will in turn run the amp somewhat harder,but still within Crown's operating specs(see the link below).
    You will also halve the damping factor,for what it's worth,which may result in a loss of overall bass control to a degree.

    http://www.crownaudio.com/amp_htm/kspecs.htm

    Ideally,for two passive subs,having 2 mono power amps would be ideal,but do bear in mind that doubling the power will only result in a 3dB increase in SPL.

    For the specs of your sub's drive units,you could give SVS an email,and I'm sure they'll advise not only on that,but also solutions to your problem,as most of us here who use them have found them very helpful and fast.
     
  3. Infinity

    Infinity
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    thanks for the fastest reply ever.

    i think i am either seeing "clip" or "IOC"
    would have to move the sofa to get to floor level to check which one.

    would distortion be caused by subs being driven too hard, or not not enough power on tap at the amp running 2 x seperate channels.

    looking forward to the little bit of extra juice :D
     
  4. alexs2

    alexs2
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    Ok...I understand what you're saying....you DO have CS-Ultra's and not the powered PC-Ultra's.

    Whilst it's not easy to see,you need to find out if it's the clip or IOC led that's coming on....clip is obvious in terms of what's happening,but IOC indicates the onset of distortion above 0.05% and is well before the onset of clipping.

    In either case,distortion will eventually be caused by running the amp too hard into any given load,either into one or two channels.

    If your amp is clippingor approaching that point as indicated by the IOC led lighting,then one solution is another amp,for the other channel,with the amps run in bridged mode,one for each sub.

    That should give you approaching 5dB more headroom assuming the same amp is used for the other channel.

    Do also give SVS an email....they really can be very helpful.
     
  5. Infinity

    Infinity
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    Yes, they are CS, not PC ultras.
    Amazing what happens when typing without brain turned on.

    Gonna check clip / IOC this weekend and drop SVS a line next monday:)
     
  6. alexs2

    alexs2
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    No worries....we all do the same.

    Also very difficult to see what one green/orange LED on an amp front is doing when there are 2 others beside it,probably all doing the same thing!

    Good luck with that,and I'm sure SVS will have some useful advice also.
     
  7. Ian J

    Ian J
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    I have amended the thread title to reflect the correct SVS model.
     
  8. Nimby

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    Are you running your CSUs co-located?
    (Techno-posh for "close together")

    Nimby
     
  9. Infinity

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    Thanks for the interest Nimby.
    They currently sit at each end of the settee. But this is pushing the seat a little too far into the room.
    The solution for both seating, and making them a little less eye catching, would be for them to both lay down, bottom to bottom. and sit within a custom made long, low bunch at the front of the room. I will leave a circle open at each end for the grills and find a way of porting the centre of the box. I assume this might represent corner loading ?

    I have done a little research, and discovered the following.
    CS Ultra, from handbook - continuous power = 500W, peak = 1000W
    CS Ultra impedance = 4 ohm

    K1 amp = 550W into each channel of a 4ohm load
    will deliver more into each channel @ 2ohm
    but subs represent a 4 ohm load

    the amp has no rated figures for 2ohm bridged, therefore I dont wanna try it :)

    but if I ran the amp at 4 ohm bridged into one sub I see a power increase from 550W to 1500W, which I think equates to more power = more control = less clipping.

    downside of this is yet more expense, however would see that clipping less often.

    As always advice, thoughts and general ridicule are welcomed.

    Thanks
     
  10. alexs2

    alexs2
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    I can see you've had a good look through the Crown website!....most amps dont cope very well with delivering increasing power into decreasing loads,and in general,only things like some of the bigger Levinsons and Krells will double power with each time the load impedance halves.
    A number of the older Krells rated at 100W into 8 ohms would deliver over 800W into a 1ohm load...
    Very few amps indeed will cope with bridged output into 2 ohm loads,hence i'm not surprised that Crown don't specify anything for that condition(except perhaps smoke!).

    Your solution of running a pair of bridged K1 amps for your CS-Ultras would give you the power output you've mentioned,and thus plenty of headroom without clipping,although the maximum output is beyond the sub's short term load handling,and you would need to be careful of that,by setting the input attenuator on each amp to reflect that.

    More power doesnt always equal more control,but should keep the risk of clipping to a minimum,and the Crown amps whilst a little industrial as far as hifi goes,do make very good amps for subs,and also in studio,and auditorium use,where reliability and high power are useful.
     
  11. Nimby

    Nimby
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    From your response I don't think you grasped the advantage of co-locating your Ultras in LF acoustic gain terms. Each end of the settee is a geographical location and has nothing to do with acoustic gain. You might get more headroom from shoving the things together at no cost than doubling up on your amplifiers. Just as putting both tight into the same corner will increase output. Whether you like what it does to your sound quality is another matter. It might also be benificial to add additional Ultras instead of more amplifiers.

    Nimby
     
  12. Infinity

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    I would have loved to put them together.
    However the WAF had more control than extended performance. She puts up with my hobby but does not like seeing the speakers all over the place.
    If I was living by myself the would be sat together, almost cudding one another, in the front left side of the room, on display and looking proud. :)

    I have no space left for additional ultra's. My only choice now is to try and colocate them at the front of the room and hopefully achieve reinforcement with the subs laying down, bottom to bottom.

    Will probably get a chance to try it this week and see how they react. :)
     
  13. Chris Gilbert

    Chris Gilbert
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    From my experience with the PC-Ultra, the ultra driver needs some time to run in. I was initially disappointed with the PC-Ultra, but this weekend I was watching a few DVDs, and thinking it sounds a lot better than it originally did. :clap: This is after owning the sub for 3-4 Months, it's only now do I think it's run in, or perhaps I've got use to not having distortion :)

    I assume you've calibrated the subs (as you've got a Rane PE17) You've not had to pull any troughs up too far have you? I believe that can use a lot of power.

    If you are going to place the subs bottom to bottom you might want to talk to SVS and see if they think it'll help, or even worse, if you risk damaging the drivers, as they'll be pushing/pulling against each other. You may find placing them top to bottom will work better, someone in the states stacked them:
    http://www.sweetnancy.com/stackingultras.htm

    Chris
     
  14. Infinity

    Infinity
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    I mailed tech support at SVS with suggestions for sub being placed bottom to bottom, with base plates still installed. They reckon its fine, just to leave a bit of a gap between the plates to prevent vibration. Now all ive got to do is design a box with a port in the centre, that looks good at the front of the room and dies not impinge air flow.

    I could leave a stonking great hole in the front of the box, but know that would not meet the WAF.

    Also trying to get head round why corner loading works. I accept that it does, but dont have a physics based answer yet.
    If the wave length of a low freq is so long ( believe I read many feet for a 20Hz wave, but that was late at night ) I dont understand where the contructive interferance is coming from. Good excuse for a little more research.

    Would the more informed amongst us be so kind as to point me in the right direction.

    Thanks for the replies.
     

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