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How does porting influence bass extension?

Discussion in 'Home Cinema Speakers' started by giantteabag, Nov 29, 2004.

  1. giantteabag

    giantteabag
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    Sorry to be dim, but I was wondering about speakers with porting.
    My KEF Q55.2s are ported & go down to 45Hz, my Q15.2s also ported go down to 50Hz.
    My new 200c drop off is 55Hz unported.
    But without ports would the bass drop off be higher & by how much?
    Thanks.
     
  2. eviljohn2

    eviljohn2
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    Tricky one this, it depends on a number of factors such as port length, number of ports, cabinet design etc.

    In general, a sealed unit will have a fairly smooth frequency drop-off with a comparatively high frequency -3dB point. A ported unit, however, will generally go "deeper" (ie. with a lower frequency -3dB point) but will have a much sharper drop-off below this. Both designs are comprises in one way or another, I always liked the idea of transmission lines though :)
     
  3. Jules Tohpipi

    Jules Tohpipi
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    Excellent answer :clap:

    (Apart from the transmission line bit) :p
     
  4. giantteabag

    giantteabag
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    Thanks Eviljohn,
    Given my speaker set, what sub cutoff freq do you suggest?
    I currently have it at 60Hz.
    Cheers.
     
  5. danny daniell

    danny daniell
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    Dad has his sub (Velo 200w) set at 80hz alongside his Model 4`s/200c. Yesterday evening he forced me to listen to his new "Shadows" Dvd :zonked: but i have to admit that the bass integration was first rate,literally as tight as a ducks ar*se. Oh,& he has his speakers set to "large" on his processor.Adjustment wise,i dont think he could get it any better than he has it.

    Regards Dan
     
  6. eviljohn2

    eviljohn2
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    Can't really comment on that, it depends entirely on how your amplifier implements bass management and how that integrates with the speakers. What this unfortunately means is that you'll have to experiment and try and work things out for yourself. ;)

    I'd suggest starting with your speakers set to large with 80Hz crossover on the amp and the sub crossover bypassed. Then you'll have to adjust things until you're happy, remember that these crossover frequencies aren't "brick walls" so there will be discernable output above/below as applicable. :)
     
  7. giantteabag

    giantteabag
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    Thanks Guys,
    One final question, how long will it take for my new 200c to run in & is it more the point that an improvement in sound will mainly be due to sensory adaptation?
    Cheers.
     
  8. eviljohn2

    eviljohn2
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    A bit of both I expect, again there's no easy answer. I gather that the 200C is a very capable centre speaker so will be made of high quality materials that will take longer to "warm up". That's pure guesswork but maybe a few weeks or so, I don't really think it's worth worrying about it too much and just enjoy it for what it is. If it gets better in the future then it's a bonus :smashin:
     
  9. danny daniell

    danny daniell
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    I know it is stating the obvious,but it`s crucial to warm your amp for half hour or so before a listen.My system sounds terribly brittle if the amps are cold.With regards to running in times,i understand that the new ref series can take up to 100hrs before the drivers/components fully loosen up,so i guess you can expect subtle improvements over the course of a month or so of normal listening.

    Regards Dan :)
     
  10. giantteabag

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    Thanks guys, superb advice as usuall.
    Incidentally, had a go to sort out my REL Strata 3 integration into the set up last night & have found that it sounds best with an amp crossover of 40Hz!
    Tried at 80 & 60 & even the latter gave a slightly muddy bass on non DD sources & dreadful when playing a DD 5.1 movie.

    So I have kept it at 40Hz, set amp sub level at +5db (fronts are 8.5 db) & the amp LFE level at -2db.
    This seems to give subtle bass extension to music whilst retaining a good thump for 5.1.

    Reading that so many on these forums have higher sub cross overs made me question my settings but I guess you must go with the sound rather than the logic...perhaps its due to my room/furniture/wife cosmetic control over speakers being out of view as much as poss thats the cause. The REL is tight in one corner & the front pair are close (1') from the wall.

    Why do folks with mega floorstanders eg KEF Ref 2, 3 & 4 have sub crossovers of 80Hz when the pair can go down to 35Hz?

    Sorry about all the questions, but it seems answering one, raises a whole lot more!
     
  11. danny daniell

    danny daniell
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    I agree with you on the point of gross crossover settings,on paper it looks like the bass is going to be way too thick,over bearing & stodgy,but in dads case it just works.And yes,room acoustics/sub placement play such a huge part in the final performance.Dads room is very acoustically dead,with quite low ceilings (also heavy carpet/curtains etc) & i think this is why he gets such a tight/rich damped sound.It is good for both bass & dynamics as the room is almost non reflective.There doesent seem to be any "rule of thunb" with this stuff,so if 40hz works for you then thats it. :smashin:

    Dan
     
  12. eviljohn2

    eviljohn2
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    40Hz doesn't seem too bad to me, I used to have my sub set to ~50Hz. In my experience it depends a lot on how the amp implements the bass management. You might do well to try and set the amps output back to 0dB and adjust the subs gain to compensate for it rather than overloading the line output at high levels.

    The 80Hz figure is thrown around quite a lot but I've never found it gives good results myself. I suppose that's THX for you :rolleyes:
     
  13. recruit

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    That 80hz Xover does apply when you're sats are restricted to 80hz and the THX Xover on my sub blends in perfectly with the Sats... :)

    John
     
  14. Londondecca

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    Agreed :thumbsup:

    You can also experiment with the port, stuffing something like a sock in the port will decrease bass but can improve the sound elsewhere. If you have lots of time to play, bundled straws can also improve matters.
     
  15. NaimBoy

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    Me too...... 22Hz isn't too shabby for floorstanders :D
     

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