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Twin Subs - Feedback Destroyer connection question

Discussion in 'Subwoofers' started by Smurfin, Oct 3, 2003.

  1. Smurfin

    Smurfin
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    Just got my BFD, all I need to confirm is how to connect my subs/BFD/processor together.

    As I'm running twin subs, am I right in thinking the following? :

    Both subwoofer RCA cables plug into a Y-splitter.

    Y-Splitter connected to a jack adapter.

    Adapter plugged into one of the BFD output jacks.

    Then on the BFD input side, I'm connected using another adapter, plugged into a single phono cable, which then plugs into my processor's via the subwoofer line level connection?

    Does that sound right?

    This would effectively mean that any equalisation I apply will apply equally to both subwoofers? Is this the right way to do it, or do I need to connect both subwoofers separately?

    As always, any advice for this noob is appreciated:)

    Cheers
    Matt
     
  2. Apocalypse

    Apocalypse
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    As the subs will behave differently due to their respective positions I'd use the 2 seperate engines for each sub and tame them both, after taming them set the level on both subs knowing that neither is booming. A few days from now you'll wonder how you ever survived without one................or your money back

    Victor Kiam
     
  3. Smurfin

    Smurfin
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    Damn, I need another adapter:(
     
  4. Apocalypse

    Apocalypse
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    At £2.99 I'm struggling to find any sympathy for you :devil: j/k
     
  5. Smurfin

    Smurfin
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  6. Smurfin

    Smurfin
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    This is the frequency response of my dual servos.

    I was right about that damn trough:eek: :eek:

    Any suggestions for filters? If you ignore the dip am I right in thinking the rest of it looks good? No wonder the deep deep bass has been superb, shame about the rest of it.....

    :lesson:
     

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  7. nathan_silly

    nathan_silly
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    You do know that sine waves can fry your subwoofer's voice coils?

    Why are you setting the output so high?- 98dB is pretty high! I would set much lower, say 75dB.
     
  8. Smurfin

    Smurfin
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    yeah maybe that was a bit loud...:eek:
     
  9. avanzato

    avanzato
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    Matt you've lost all the 'impact' bass :(

    From your pics in the DIY area you have both the subs at the front of the room. I know it's a big job, but you should be buff now with all the recent exercise, have you tried moving one of the Servo's to the side or back of the room. It's a classic way of evening out bass response and might work. Front centre and back centre are where Harman recommend putting them and then equalising flat.

    If it does work you'd have one awesome system. Though not with music of course for that you'd need a REL :devil: :rolleyes:
     
  10. Smurfin

    Smurfin
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    I tried that. I've tried the following:

    1 sub only in both positions.
    1 sub in each corner
    Both subs in the corners
    1 sub at the front, 1 at the back of the room


    I've tried every mix possible....the dip is still there whatever I do. When one sub was at the back of the room the dip wasn't quite as bad as it is on the spreadsheet, but then I lost some of the sub 20hz impact:(

    But you're right...all of the impact bass has gone.

    Just starting to try and work out how to set the filters now, today is BFD day:D
     
  11. Apocalypse

    Apocalypse
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    Matt - Try and raise the trough with the BFD, it may only need 2 filters using a +5db rise, with 2 huge subs you shouldn't notice any drop in overall output. I had a 10db trough from 65Hz to 78Hz, 2 filters with a max rise of +3db evened it out. My sub is +1/-1 from 10Hz to 75Hz now :eek:

    However there is a substantial trough from 80Hz to 110Hz that I can do nothing about, I'm hoping placement and Auralex can cure this.
     
  12. lmccauley

    lmccauley
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    Yes, even with my relatively piddly SVS ;) I could flatten out my troughs pretty well without any noticeable effect. A powerful, accurate sub and a BFD can certainly help overcome some room problems. When someone can combine these elements into one sub (like the velo DD), and make them work automatically (like the Pioneer amps MACC), then I think that will make the biggest real-world difference for most people (discounting enthusiasts like us that are prepared to put the time into researching, adjusting and measuring).

    Cheers,
    Liam

    Cheers,
    Liam
     
  13. Apocalypse

    Apocalypse
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    I always thought you were a schizo Liam and now I have proof :laugh:
     
  14. Smurfin

    Smurfin
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    Ok, this thing is really easy to get the hang of. I've re-measured the response @ -35db, and replotted that onto the spreadsheet.

    After applying 2 filters:

    45hz Bandwidth 10 Gain +6
    55hz Bandwidth 10 Gain +6

    I now have the following:
     

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  15. Smurfin

    Smurfin
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    There's still a 5db gap between 71hz and 40hz, should I just whack the gain up on my 2 filters? I'm just a bit wary about increasing the gain too much, views?
     
  16. lmccauley

    lmccauley
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    Looking good, Matt :cool:

    Are you going to stick it up a couple more db & remeasure?

    lol - er, :blush:

    Cheers,
    Liam

    ...

    no, that's all ...
     
  17. Smurfin

    Smurfin
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    I'm about to bump the gain up another 2 db, but that will take both filters to +8db :)eek:). I really don't know if thats a good thing or not....

    The only other thing I can think of is to reduce everything else in line with the 2 filters. But it would mean adding a load more filters to the existing 2.

    Apocalypse where are you!:)
     
  18. lmccauley

    lmccauley
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    There is no difference between lowering everything else down to the level of the troughs, or increasing the troughs up to everything else, because once you're finished with the BFD you will re-calibrate your sub level to that of your mains...

    With 2 X Servo 15 in a room of your size, it's like having a big V8 under your bonnet - go for it :D
     
  19. NicolasB

    NicolasB
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    YES, THERE IS.

    If you use the BFD to boost troughs then you are reducing the overall dynamic range of the output. You should always use a BFD to bring levels down rather than up.
     
  20. Smurfin

    Smurfin
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    Nicholas, so you'd set up several more filters to reduce the other frequencies here?
     
  21. lmccauley

    lmccauley
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    Nicholas, no need to shout.

    OK, 2 examples to illustrate my point, based on Matt's graph.

    1) He boosts 45Hz & 55Hz by another 5db and gets a completely flat response from 20-80Hz. He then calibrates his sub and mains to 75db using Video Essentials.

    2) He creates several filters that lower everything down to the level of the troughs at 35 & 55Hz and gets a completely flat response from 20-80Hz. He then calibrates his sub and mains to 75db using Video Essentials.

    It takes exactly the same power to drive a particular frequency in example 1 as 2.

    Cheers,
    Liam
     
  22. avanzato

    avanzato
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    Liam what you're missing is that the signal to the BFD is flat and the room is altering it. The BFD has a limit to it's maximum output before clipping if you boost the Eq it gets closer to that limit. Boost the input by upping the sub level on the amp and you may drive the input into clipping. Both reduce the dynamic range of the BFD. I think, or I might be wrong. :suicide:

    Edit: Edited to make sense
     
  23. Phil Hinton

    Phil Hinton
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    But when recalibrating the sub volume you can even this out by using the subs internal amp gain as well as the gain on the processor, this way by using the available resourses you wont put the BFD into clipping, certainly not in a room the size of Matts or Liams.
     
  24. Apocalypse

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    Smurfin - Your ears are the best judge in deciding if the BFD is affecting your overall sound, I'd boost the troughs to get a flat response from 20-80 and see what it sounds like. To see if you've lost some power try the subs at reference level with a scene you've recently tried pre-BFD. You decide which is better.

    I wouldn't reduce the other frequencies to match the troughs, don't try and get a line that matches your fronts, get a line that makes your subs flat. Once your subs are flat set the sub's volume to the level you want and forget about the line in the graph. Having the sub's db level higher than the mains is fine as long as it sounds ok to you and isn't overpowering. My sub's db level is 5-10db higher than the mains yet the sub is incredibly subtle when required. I have a whopping 8 filters engaged (2 are used to increase output) and I've found no difference in overall power, if anything the system sounds more dynamic now because the crucial 65-78Hz trough I had is now 10db louder meaning impact bass is improved.

    avazanto - The amp/processor's internal lfe level is used to set the LFE output to just below clipping on the BFD, any ammendments Smurfin makes to his setup can be safely compensated for in regard to clipping..............I think that's what you meant but correct me if I'm on a diff page to you.

    Nic B - I used to say the very same thing myself, just trust me that it's a somewhat exagerated, I'd liken it to using a 10m S-Video lead instead of a 2m cable.
     
  25. Smurfin

    Smurfin
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    Thanks guys, off to play again:smashin:
     
  26. Smurfin

    Smurfin
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    Ok, I'm now running 6 filters :)eek: ):

    40hz | Fine +06 | Bandwidth 10 | Gain +8
    50hz | Fine +06 | Bandwidth 10 | Gain +7
    40hz | Fine +00 | Bandwidth 04 | Gain +8
    63hz | Fine +10 | Bandwidth 04 | Gain -15
    20hz | Fine +00 | Bandwidth 10 | Gain +2
    63hz | Fine -02 | Bandwidth 10 | Gain +6

    Lots of + on the gain side, hopefully this won't affect performance of the servos:(

    Overall I'm really pleased with how it looks, I have a very flat response down to 20hz and below, but I have a bitch of a problem @ 71hz. Whatever filters I apply it barely affects it, which is weird, can anyone explain this one?

    Theres a dip at 63hz and peak at 71hz, which is why the filters might look a bit messy....trust me I've tried loads, unless someone can suggest some better alternatives (one problem is I really don't understand bandwidths etc).
     

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  27. Phil Hinton

    Phil Hinton
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    But how different do the servos sound now? Has the BFD made those vital differences.
     
  28. Smurfin

    Smurfin
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    Just recalibrated all my channel levels.....the subwoofer was at the same level as all other channels and way too loud.

    It's currently sitting @ -5db to the rest of the channels, still a bit too loud, about to take it to -7db.

    Just going to run some discs through:)
     
  29. EvilMudge

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    Matt, is it possible that the peak at 71Hz is being caused by your M&Ks which would still have some output at 70Hz, and are not being filtered? I assume you're using a CD run through your DC-2 and using it's bass management to feed the tones to your subs.
     
  30. Smurfin

    Smurfin
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    Correct. Weird though, I just ran the Avia sweep and it looked like there was a DIP at around 71hz:confused:

    I've turned the subwoofer down -8db on the main channels, and it's sounding schweet:D The sound is altogether more solid, and I'm hearing bass back in the spots where it was missing before:)

    Just been playing Titan AE (yes that sequence) and the level during the heavy bass moments kept flickering into red: on one part it stayed there for a good 2 seconds.

    Is that bad? According to the BFD manual (if I'm reading it right) it should turn red, but yet the subs are handling everything I throw @ them. The icefield and Toy Story 2 intro have both gone through @ -5db reference level, and frankly if subwoofers could laugh then my pair of Servos would be(;)). No hint of struggling at all.
     

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