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Hills and Valleys

Discussion in 'Subwoofers' started by user34, Oct 4, 2004.

  1. user34

    user34
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    I just bought a sub to augment my B&W CDM1Ses. During setup, I was astonished to find that the B&Ws excite the lowest room resonance at 31.5 Hz! Equally there's peaks at 63Hz and 126Hz. There are relative low points at c. 45-50Hz and also at 100-110Hz. I've been playing around with speaker and sub positions and I've found that moving the speakers closer to the front wall diminishes the troughs relative to the peeks. I've also been drawing the sub out of the corner, it's actually about 90cm from the left side wall and the front of the sub is about 60cm from the front wall. The sub is positioned just to the left and just behind the left speaker.

    In the beginning I set the crossover at 30Hz, but I think it's now closer to 70Hz, the markings on the frequency adjustement are (30Hz - min, 180Hz max). I set the gain, originally, on the sub by getting the same reading at 80Hz on the SPL meter from the main speakers and then from the sub.

    Can anybody give me an idea of what I should move and how I should move it to get the troughs to come up in level ? Short of the Behringer Feedback destroyer, that is.

    What about the gain setting, less or more ? I know I can fiddle that as much as like and at the end of the day it's a question of taste. For the moment I'm trying to minimise the nulls rather than fight the resonant nodes.
     
  2. Nimby

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    You seem to be suffering from even harmonics of the room's length mode. :rolleyes:

    Can you remind us of your room dimensions?

    Any chance you can do a graph on squared paper of your response? Marked with frequency against level in dBs. You can then scan it and upload it. Even a rough hand drawn graph make much more sense than quoting figures. A picture being worth a thousand words. (or numbers in this case) :)

    Have you tried the sub just inside one of your main speakers?

    It works for me. Though I don't have quite the speaker bass extension that you do.

    You must balance the output of the sub against the output of your speakers at a point where both responses are fairly flat. Otherwise you may be trying to balance a trough in the sub's response with a peak in the speakers' response. "And never the twain shall meet". :blush:

    Regards
    Nimby
     
  3. user34

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    Nimby,

    When I get a moment I'll work out how to upload the graph that many people show when BFDing their subs. The room dimensions are 5.23m * 4.75m * 2.42m. The sub between the speakers is not an option, there's a humungous bookcase between them.

    What's so astonishing for me about CDM1Se's response unsubbed is the 31.5Hz bass peak, because the official specs put the 3dB and 6dB points at 58Hz and 46Hz respectively.

    The system doesn't sound bad in it's current state, the sub is unobtrusive but I know if it's turned off. I'm getting useable response at 25Hz, because while the B&Ws excite the primary resonance it's quite a lot peakier than with the sub added, which fattens the response to either side of the peak.
     
  4. Nimby

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    Hi

    If you roll down below the "Reply to thread" new message box to "Additional Options" you'll see a "Manage Attachments" button. Click on that and then "Browse" and you'll have access to your pictures folder on your own computer. "Select" your chosen image and then click on "Upload" and wait. You won't see much before you read your message on the forum's website. I don't think the thumbnails show up on "Preview Message". There is a limit on image size. I usually just re-size to small in XP before posting images.

    Regards
    Nimby
     
  5. Kazman

    Kazman
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    I have a nasty trough at 56Hz which I can't iron out, I've gone up to +10db on the BFD, and it is still there, although not as much, I'm going to give up on that one segment and live with it I guess, I'll say it adds character :D Apart from that, the curve I have is acceptable, and fairly flat.

    The PC Ultra is wuvly, :D
     
  6. user34

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    Kazman,

    when I look at the graph, I say Oh that looks dreadful, But when we're listening to music it sounds brilliant. the 31.5, 63 & 126Hz peaks and the trough at c. 50Hz where there without the sub, and the sub hasn't made them worse... au contraire. At the end of the day, I'll settle for the 'best' result. I thought the BFD might be a useful option, but I don't want to put one in the main system path, where it would have to be, to do anything about the 63Hz and the 126Hz bumps.
     
  7. Kazman

    Kazman
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    The BFD has helped to iron out some boomy peaks which did spoil the sound somewhat, but I'm happy with the 'character' of what I have now, I didn't iron out the peak I have at 22hz completely, as a little kick down that low is always nice :)
     
  8. user34

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    here's the response curve that I curently have. Blue is mains alone.
     

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  9. recruit

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    Hi User34,
    Is that the response of your sub?
    John :)
     
  10. user34

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    John,

    yes, That's the response of my sub ... so I need an SVS ?
     
  11. recruit

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    Hi,
    I don't think it means you need a new sub but just a bit of work to get the optimal performance from you existing setup.
    Here is link to the snapbug site and gives you a good basis if useing a BFD

    www.snapbug.ws/bfd.htm

    If you don't have a BFD then placement is the key, but i do think it is a worthy investment as your respone does not look that good :(

    John :)
     
  12. user34

    user34
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    I'm frustrated with the Sub for the moment, although it's not doing anything horrible. I want to avoid the BFD if I can. More setup tonight.
     
  13. recruit

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    Stick with it and you will get there in the end ;) i have just bought a new sub and it took me quite a while to get it tamed to my room but the results are truly superb :smashin:

    Good luck User34

    John :)
     
  14. user34

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    This is what I have now, with the sub out of phase with the mains, I have to run the sub level higher, but the resonance at 31.5Hz is somewhat controlled. I think I may be running the sub level too high. Crossover is about 55-60hz I think.

    Peter.
     

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  15. recruit

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    Hi User34,
    Have you tried different placements of the sub or are u limited, it must not sound right if the sub is out of phase
    John :)
     
  16. user34

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    John,

    I have limited options for the sub. I felt yesterday's results were the best I'd had. You may be right about sounding 'right', I spent about 1h30 fiddling the set up and then listened to music after. Kept thinking the sub was too hot. I have one other placement option for the sub. That's to the side wall, instead of the front wall. The out of phase suggestion came from Merlin & Michealab on Zerogain, basically the idea being that the resonance peak of the speaker is controlled by the same resonance out of phase with the sub. Gain on sub is roughly 10h30/11h on the dial. In phase I was running more like 9h.

    I may have to invest in a Paradigm X-30, or similiar, if I can find one! I could use the crossover facility of the sub, it has stereo in put and output, but I have to run 5m interconnect as it is and don't fancy having twice that plus the crossover in the main signal path.

    Peter
     
  17. recruit

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    Going for the sidewall maybe the answer as alot of people have expirmented with this location and found it works best because of the wall boundaries and corner locations increasing the boundary gains,also you don't want the sub to really be noticed but underpinning your other speakers so you may well be running it too hot hopefully by changeing location this works but the other alternative is say a BFD :eek: I know you dont want one but surely if it is going to help and then you would not have to change location why not try ;)
    Also why don't you try setting your Xover higher and see if that alter's the response.

    John :)
     
  18. user34

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    John,

    I'm going to tweak some more tonight, cut the gain a couple of dB and maybe also adjust the crossover some more. The sub is an Audience Absolute A10, maybe not available in the UK, and it's barely two weeks old. I'm dealing with my learning curve and the sub changing, most probably, on a daily basis. The dealer suggested that it need a very long break 'in period. The B&Ws have much more low output than I imagined, but I'm not convinced it's clean.

    Here's a link:

    http://www.mosquito-groupe.com/englishversion/base.html

    you'll have to look for Audience, Absolute and then A10.

    Peter
     
  19. recruit

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    Hi Peter,

    They look like a very interesting range of speakers and subs, i must say i have not heard of them before but the A10 sub looks quite potent from the specs you certainly have enough power for such a small unit.
    Let us know how you get on.

    John :)
     
  20. Nimby

    Nimby
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    The side wall will probably bring the sub nearer to your listening position.
    Making it potentially more potent. You'll need to recalibrate of course.
    Hopefully it will excite different room modes from this alternative position.
    With a (possible) tweak of the phase control you might be able to flatten those humps and fill those troughs. Provided the roll-off is under 80Hz or lower it shouldn't be easy to locate the bass.

    There's nothing wrong with using reverse phase when it helps.
    Otherwise they wouldn't give you the option on most subs.

    I think you really ought to consider trying to roll off the B&Ws using the sub crossover. The CDM1s seem to be the main culprit in your primary room modes.

    Can't you run short high level cables to the speakers from the sub outputs? If it has stereo out speaker terminals(?) No idea what it will do to your precious music signal though. Suck it and see. No need for fancy speaker cables just to give it a try.

    Final thought: You are using the meter correction figures in your graphs aren't you?

    Regards
    Nimby
     
  21. recruit

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    Nimby can't you nip over to him in france your nearer than us lot in the UK and give him a hand to setup :D

    John :)
     
  22. Nimby

    Nimby
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    Geography not your strong point then? :D

    If you don't have an atlas do an image search for <europe map>.
    France is three countries away from here.
    While UK/France/UK is a day trip on the ferry or train.
    People do the crossing just to buy some fags don't they?
    Besides our friend Peter seems to managing okay. :)

    Nimby
     
  23. recruit

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    Youre right Nimby Grade D in Geography :laugh:

    John :)
     
  24. user34

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    John, Chris,

    This weekend saw more experimenting, plus adding the sub on the the hifi lines, instead of the heating circuit. The B&Ws are the main culprit for exciting the room modes, at lower volumes the sub is sometimes not working. For instance I had Rush's 'A show of Hands' playing, and I was in the kitchen and I thought I better turn the sub down, coz it's really going to bother the neighbouts, there was a fairly nasty resonance. But when I got to the sub, it was still in standby mode! I wasn't playing at high levels. I then tried lowest cutover and in phase with the mains for a while and decided that really did give one note bass.

    For the moment I have the sub running out of phase with the B&Ws and the sub crossed over at about 70-80Hz, The frequency pot doesn't have precise calibration. I have maximum level at 31.5 Hz the same as it would be without the sub, The sub fills in the 31.5hz to 63Hz area, but it's working against room mode nulls at the listening position, so it's not 100% succesful at that, but it's better than no sub. Below 31.5Hz the sub tails off too soon, I really need a down to 22Hz sub to make a huge difference here, and I didn't want to spend the c. €1000 for that, I might be regretting that, but still early days. Moving the listening postion, is not possible without WAF consulation and besides the practical organisation of our lounge does not leave many options, at 24m² it's comfortable, it also has to serve as a dining room.

    The sub is extremely clean in it's operation and I can only tell it's working when I turn it off, because the soundstage collapses and the voices become less real. Shortly, I'll be recabling (mains leads) the whole system. When that's settled down, I'll have a serious go at the side wall positioning which may marginally bring the sub closer to the listening position.

    From a frequency response point of view, I could install an Outlaw ICBM, or Paradigm X-30, crossover the mains at 80Hz and I could sort the 31.5Hz and 63Hz peaks with a BFD. But that's two extra bits of kit, but already I consider my Nait5/HiCap/Stageline as too many boxes for an integrated amp!
     
  25. recruit

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    Hi Peter,

    It sounds like you have had a busy weekend playing.
    I would say that it took me about 2 weeks to get my subs sounding good in my room with loads of tweaking i finally have the sound the way i want it for both Movies and Music, so a little bit of hard work does pay off.
    From what your saying it does sound like you want something that plays deeper and louder which to be honest you are not going to get from a small unit and a bigger sub will probably give you that but as you said getting the WAF approval thing does mean alot unless you are lucky enough to have a dedicated room, which i don't think many of us have :(

    John :)
     

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