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Thread: Knowledgable speaker Geeks: Help required for a Twelvebears of very little brain.

  1. #1
    Join Date: Mar 2009

    Location: Hemel Hempstead

    Posts: 1,075
    I'm Steve.

    Default Knowledgable speaker Geeks: Help required for a Twelvebears of very little brain.

    Here's the question:

    How does one replace TWO 6.35cm dia, 13.3cm long bass ports with ONE 7.5cm port?

    Specifically, how long does the said 7.5cm port need to be to produce the same tuning of a 45 litre enclosure.

    I'm sure there's a easy way to work it out, but my head's a bit fried....
    Steve aka 'Twelvebears' (it's a long story)
    System: Technics 1210 Mk5, Jelco 750 arm, AT33EV via MF X-LP2 Phono Stage, Oyaide mat and record clamp. SB Touch via Marantz PM-11S1 amp and Wilson Benesch A.C.T. speakers. Mark Grant cables and PS Audio Power Plant Premier mains regenerator.
    (\__/)
    (='.'=)
    (")_(")

  2. #2
    Join Date: Jan 2009

    Location: Essex

    Posts: 23,552
    I'm openingabottleofwine.

    Default

    Hi Steve,

    You might not thank me for this, but you might try:

    http://www.silcom.com/~aludwig/Sysde...l_analysis.htm .

    If you can let me know the internal dimensions of your speaker, I might be able to wade through the maths and come up with an answer. No promises, but I'll try.

    I have to confess that I am a little puzzled: I thought you had simply replaced a wood enclosure with one made of slate, having identical internal dimensions and using the same drive units and damping material. So why do you want to change the porting?

    Barry

  3. #3
    Join Date: Jan 2009

    Location: Essex

    Posts: 23,552
    I'm openingabottleofwine.

    Default

    Steve,

    Here are some more 'accessible' sites with various 'calculators' that ought to be of help to you:

    http://www.lautsprechershop.de/tools..._vented_en.htm

    http://www.mh-audio.nl/spk_calc.asp

    http://www.ronshaw.citymax.com/f/Des...Enclosures.pdf

    Regards
    Barry
    Last edited by Barry; 24-06-2009 at 21:51.

  4. #4
    Join Date: Apr 2008

    Location: Chester

    Posts: 429

    Default

    Steve.
    I tend to agree with Barry on this.
    Have you considered removing some of the internal damping, before you start playing about with port tubes?
    Sometimes speakers can be over damped.

  5. #5
    Join Date: May 2008

    Location: Lancaster(-ish), UK

    Posts: 16,962
    I'm ChrisB.

    Default

    Quote Originally Posted by alb View Post
    Steve.
    I tend to agree with Barry on this.
    Have you considered removing some of the internal damping, before you start playing about with port tubes?
    Sometimes speakers can be over damped.

    Just what I was thinking.
    I'd be suprised if you need all that egg-box stuff in cabs so dead as those, Steve.

  6. #6
    Join Date: Mar 2009

    Location: Hemel Hempstead

    Posts: 1,075
    I'm Steve.

    Default

    Fear not Guys, all is well.

    I actually came across the mh-audio site via Google and after playing with one of their calculators, I knocked up a sliding tube which allowed me to easily tweak the length of the port.

    It seems it wasn't far out, the port just needed to be about 1.5cm longer than it was and it's transformed the bass.

    Yes the damping panels did cause a slight issue with the volume, but they weren't in there for panel resonances but to kill standing waves without the need for loose wadding, which I prefer to avoid in reflex cabs.

    Anyhoo, a few more days of varied listening to make sure I'm happy and I think I've cracked it. I'll just need to fix a perminant extension to the reflex tube once I'm sure it's just right.

    Let's face it, it would have just been wrong if it had been perfect straight away with no need to tweak. Where's the fun in that?
    Steve aka 'Twelvebears' (it's a long story)
    System: Technics 1210 Mk5, Jelco 750 arm, AT33EV via MF X-LP2 Phono Stage, Oyaide mat and record clamp. SB Touch via Marantz PM-11S1 amp and Wilson Benesch A.C.T. speakers. Mark Grant cables and PS Audio Power Plant Premier mains regenerator.
    (\__/)
    (='.'=)
    (")_(")

  7. #7
    Join Date: May 2008

    Location: Lancaster(-ish), UK

    Posts: 16,962
    I'm ChrisB.

    Default

    ..........and I think I've cracked it
    Don't say things like that, it sounds like you dropped one of 'em! (Not that it sounds like you could lift it high enough to do that)

  8. #8
    Join Date: Mar 2009

    Location: Hemel Hempstead

    Posts: 1,075
    I'm Steve.

    Default

    To be honest Chris, if there was a direct nuclear strike on Hemel Hempstead (and some people say that would be a very good thing) and the whole place were to be reduced to smoking rubble, I honestly believe that the one thing, or rather two things, that would survive would be my bloody speaker cabs.

    When we move, I'm half expecting the moving company to want to charge we extra because of them....
    Steve aka 'Twelvebears' (it's a long story)
    System: Technics 1210 Mk5, Jelco 750 arm, AT33EV via MF X-LP2 Phono Stage, Oyaide mat and record clamp. SB Touch via Marantz PM-11S1 amp and Wilson Benesch A.C.T. speakers. Mark Grant cables and PS Audio Power Plant Premier mains regenerator.
    (\__/)
    (='.'=)
    (")_(")

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