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Twin Peaks

Discussion in 'Subwoofers' started by AngelEyes, Sep 5, 2005.

  1. AngelEyes

    AngelEyes
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    Bugga... :(

    PB12 Ultra

    Blue is raw spl data
    Pink is raw spl with sub tuned to 16hz (1 bung in port).

    Not really sure what any of this means but it doesn't look very flat to me. I did try some tuning with the peq (not shown but it didn't improve things much). Phase seems to have no effect at the frequencies I have problems with.

    From these results does anyone see an advantage of running at 16hz tuning?

    Please no :rotfl: replies :mad:

    PS for those not familiar with my sub placement may be able to see the problem here :rolleyes:
     

    Attached Files:

  2. eviljohn2

    eviljohn2
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    The 16Hz tuning drops your low-level output significantly so you're best off leaving that and trying to reduce the peaks. Bass traps or EQ should do the job. :)
     
  3. AngelEyes

    AngelEyes
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    Ok, will do.

    mmmm ...yes *nods*

    If only I knew what they were :confused:
     
  4. eviljohn2

    eviljohn2
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    Hehe, you could use a BFD to equalise out the humps (there's loads of information on it - check out the SPL meter sticky at the top of this forum). That could be done for about £60.

    A better way would be using bass traps, have a word with mattym in the Room Acoustics power buy section and see what he would suggest. :)
     
  5. bob1

    bob1
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    A bfd will definitely bring the peaks down,have you got the room to fit another shelf. :)
     
  6. AngelEyes

    AngelEyes
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    I am sure I have few old bits of oak knocking about... I guess I'll have to dust down my tools :)

    I had hoped I wouldn't have to spend any more... another £100 or so for the BFD and some cables. However spending a grand on a sub and then not getting the most about it seems rather stupid too. :)
     
  7. bob1

    bob1
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    You could try a different location, what about my house. :D
     
  8. AngelEyes

    AngelEyes
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    I am not quite that desperate yet! :)
     
  9. Gary_W

    Gary_W
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    You can get them for <£70 if you shop around. And I'm sure you'll have a half-decent Phono lead knocking about.

    When I first put my BFD in circuit, I had salvaged an old stereo phono interconnect bought years ago from Tandy to connect amp to BFD. My main sub cable was the Silver Serpent job from SVS at point of sale.

    I dialled in a 50Hz cut and played the test disk. I was overjoyed that the peak had vanished. I was somewhat perplexed that the next test tone down was also very quiet and started wondering what I'd done to the Q factor.

    It took me another few minutes to realise that interconnect quality does make a difference. Absolutely diddly squat <50Hz was going along this cable. I replaced it with a short length of something rather better and the problem vanished. I was actually glad to see my room spike back again :)

    I can't really praise the BFD highly enough.

    Gary
     
  10. eviljohn2

    eviljohn2
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    The best place to get a BFD at the moment is www.bluearan.co.uk
    http://www.bluearan.co.uk/shop/item.php?search=BEHDSP1124

    I got mine from there at Christmas (for quite a bit more moolah I might add) and it was a first class service. If you're after one then snap one up soon as the DSP1124 Pro that is of use to us is being phased out in favour of a more expensive model that provides us with no extra features as a parametric equaliser. :)
     
  11. AngelEyes

    AngelEyes
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    Thanks for the info guys, much appreciated.

    Is the BFD similiar to the PEQ controls on the back of the sub (just with control over the whole spectrum)?

    Is it difficult to use?

    I will probably speak to Mr Grant about some new interconnects anyway.
     
  12. eviljohn2

    eviljohn2
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    The BFD is just like that. You can put in 12 different filters varying the gain, bandwidth and central frequency of all of them. You can even overlap them to flatten out almost anything. It's not difficult to use once you get used to the controls although it's not immediately obvious how to go about it. You can only use it to treat peaks though - there's very little that can be done about any troughs you might have now or in the future.

    There's a very comprehensive guide here:
    http://www.snapbug.ws/bfd :)
     
  13. Gary_W

    Gary_W
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    John - Why do you say this? Each filter can give 24dB or thereabouts of cut or gain. The PEQ on the back of the SVS is purely cut, however.

    I had troughs as well as peaks and treated them with the BFD.

    Gary
     
  14. bob1

    bob1
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    You can boost the bfd but its a bad idea, a 3db boost will cut the effective power of the sub in half, something you don't want to do.
     
  15. eviljohn2

    eviljohn2
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    As above, it is possible but the reason you have troughs in the room is because the room modes are "sucking out" those frequencies. No matter how much you boost those frequencies you still need to fight that which requires outputting a much higher signal from the sub. Don't forget also that the BFD's primary purpose is to cut frequencies rather than boost them, it provides up to 24dB of signal reduction but only 12dB of additional headroom because any more would require a much more powerful supply.

    Subs don't mind giving less output but making it do more work will suck up it's power reserves like nobodies business - it's worth remembering that any boosts you apply to even a small range will effect the power output across the whole range.

    The only sensible way of improving any room troughs is by changing placement to move them or by using a supplementary subwoofer to cancel them out which can add a number of different problems to the mix. Some things just have to be left alone I'm afraid and I'd recommend removing any boosts from your BFD program. :)
     
  16. Gary_W

    Gary_W
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    Well there you go. You learn something new every day. Many thanks to you both for pointing this out.

    Your statement 'it's worth remembering that even boosts applied to a small amount of the range will affect the power output across the entire range' was something totally unknown to me.

    I'll go and look through the BFD settings; I should actually get an hour or so playtime tonight so I guess the SPL meter will be in for some abuse :)

    Gary
     
  17. eviljohn2

    eviljohn2
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    Glad to be of help, I doubt you'll notice getting rid of those boosts anyway and you'll be putting your amp and driver of the sub under much less stress. :)
     
  18. AngelEyes

    AngelEyes
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    Wow, I am glad you guys bought this up, I just ordered my BFD and was going to try and create a 'perfect' flat curve.

    Any chance you guys can show me what an ideal or realistic curve should look like. I know flat is ideal but just how close can we expect to get?

    Thanks.
     
  19. eviljohn2

    eviljohn2
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    Naturally the biggest factor will be the room and they're all different so it's hard to be sure what sort of results you will have.

    The last time that I had a go at setting my subs up I finally settled for the result in this post - the green line was before correction with lots of big peaks in the subwoofer region whilst the purple one was after correction and sounded much better. :)
    http://www.avforums.com/forums/showpost.php?p=1523732&postcount=66
     
  20. AngelEyes

    AngelEyes
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    I should have mentioned that so far I have only been measuring the sub on it's own direct from my laptop. I take it my main front satellite speakers will also add to the overal bass in the room. Is there any point trying to correct the sub and then the whole shebang? Or should I just do it once with everything running?
     
  21. eviljohn2

    eviljohn2
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    I've been involved in big arguments about this. Really it's best to do it with just your speakers, just the sub and then them all combined so you can have the overall picture. Otherwise you may spend ages tweaking your sub to sort out speaker problems or vice versa.

    Of course that can take absolutely ages if you're doing it by hand in which case I'd plump for having it all going at the same time. :)
     
  22. Gary_W

    Gary_W
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    John -

    Can you give more details as to why 'boosting is bad'?

    I've just spent a very frustrating evening fiddling with the BFD. Basically, without the boosts to bring up the 25-35Hz region, my sub just doesn't cut the mustard in my room!

    If I use cuts only, I can get the low end down to about 80dB, I can get the 50-70Hz region down to 80 - 85dB. The 25-35Hz warbles between 65 and 70dB. Not good.

    The real world test was putting on 'The Incredibles'. The part where Mr. Incredible throws the cable car. With the peaks of my room tamed but no boost in the 25-35Hz region, you do not feel a thing. With the 25-35Hz region gained so as the SPL meter shows around 80dB, this scene sounds great.

    I have my receiver sub gain at 0dB, the SVS bang on half way up. I listen at master volume between -15 and -5 (when I can get away with it :D ) and across this range, the sub is certainly not complaining.

    In my situation, what am I loosing by boosting these frequencies and getting rid of the trough? To my ears, doing things right sounds worse :eek:

    I suppose I could do a 24dB cut on everything apart from the region in question, but then I'll have to put the sub output on the receiver plus the SVS gain up. Which may give distortion problems??? Anyway, at maximum cut, the 50Hz spike is still 85dB, so cutting everything else in this manner will just bring back the spike.

    Gary
     
  23. kbfern

    kbfern
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    You say you have receiver sub gain at 0db I wonder if its running to hot as SVS recommend no more than -5db initially (at least they do with the 20-39pc+)I don't know for sure if this will make a difference but maybe you should give it a shot.
     
  24. AngelEyes

    AngelEyes
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    Same for PB12 Ultra...
     
  25. Gary_W

    Gary_W
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    Hi folks,

    I realise that the instructions tell you to start at -5dB, and I did so.

    I nudged it up to 0dB in response to all the cuts with no gain. Basically, with the old BFD curve, I had the receiver gain at -3dB and the SVS was at about 10 o'clock. The new curve required the SVS gain to go up to 12 o'clock and an increase in the receiver output.

    There is no distortion going on that I can detect. And it still doesn't change the fact that it sounds better without the valley where lots of film LFE takes place.

    Gary
     
  26. AngelEyes

    AngelEyes
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    This may be a case of do what 'sounds' best for you. obviously exploring as many options as you can but you have to go with what works.

    Just for your info mine is set to -5db on the amp and 9 O'clock on the gain (i.e hardly even 25%) and it is very loud compared to the other speakers ( 0db on the amp).

    It certainly seems you have the Amp and Sub cranked up very high compared to me but I may be getting a lot more 'bang for the buck' because of the location :confused:

    ...of course you may just be a mental basshead! :clap:
     
  27. Gary_W

    Gary_W
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    Hi Angeleyes,

    No, not bass mad at all (despite having an SVS :) )

    I just expect that, with the films that everyone quotes as being room shakers, the room should indeed shake with a sub of this quality.

    Unfortunately, it only seems to shake in the right places with gain added at a couple of points. With my original curve it does indeed sound good, but I'm now concerned that I'm giving my SVS a harder life than expected.

    My receiver is past its best before date, and I'll be looking at models in the £800 - £1000 range that have room acoustic calibration (e.g. the new Pioneers and the new Denon 3806). It will be interesting to see how one of those makes my room react without the BFD in circuit, though the specs so far seem to suggest that neither EQ's anything <63Hz. Which is odd.

    Unfortunately, I don't see this happening this side of 2006 :(
     
  28. AngelEyes

    AngelEyes
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    HAHAAHHAAA not as bad as mine... the display packed in over a year ago so i don't even know what is going on with volume etc. OSD allows me to set things up ok but a lot of my functionality is lost!
     
  29. AngelEyes

    AngelEyes
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    Off-Topic but wow!

    I ordered my BFD from Blueran at about 23:00 last night and it arrived at 11:00 today!!

    That is pretty amazing service in my book!
     
  30. eviljohn2

    eviljohn2
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    Gary, if it's really that much worse without the boosts then go with them in place. At least you tried it the other way. You just need to be aware that you're eating into the headroom although with a sub of that calibre it will probably only become noticeable at high volumes. I'd still recommend trying to minimise any boosts that you add using them only where absolutely necessary and keeping them as small as possible.

    I was similarly impressed with Blue Aran, top service. :)
     

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