Port calculations

Discussion in 'Amps and Cabs' started by merkaba22, Mar 20, 2008.

  1. merkaba22

    merkaba22 Member

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    I want to build a 2 x 12 cab within certain size constraints -- does anyone know of or can provide either worked out calculations given various speaker resonant frequencies or "port calculator" that will provide these dimensions that will work on a Mac?
     
  2. Matt Gordon

    Matt Gordon Senior Member

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    Radiotron Designers Handbook has some data worthy of looking. I don't see a real need in a lot of technical math though. Aren't you overthinking it a lottle? From all I can gather, the porting needs to add up to half the total speaker size, in your case, 4X 3" ports. Two 3" ports per 12" speaker. Any smaller and you get a wooshing sound from the ports. Any larger and it starts to sound too flat. The cabinet size can be a bass issue IMHO. Too big and too much woof. Too small and it makes the midrange sit funny against the bass. I'm no expert tho! :eek:
     
  3. merkaba22

    merkaba22 Member

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    That's pretty cool info and a great perspective -- thanks.

    I see that a couple of cab manufacturers are also using a narrow slot across (somewhere around) the mid-section of the back of a closed back 2 x 12 and some on the front, usually in the lowest portion of the cab.

    Do you know if the area of the four 3" dia ports is meant to be equal to the area of these slots -- do I presume correctly this creates a similar response? Or is there something else to consider?

    Further, do you have any insight on how this might be managed with a vertical 2 x 12?
     
  4. Matt Gordon

    Matt Gordon Senior Member

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    Yeah, I've always just considered those as bass reflex cabinets, not really ports but again, I'm no expert. I'll read through my Radiotron handbook to see if I can sus something but I've not seen those types cabinets refered to as being ported in my book. Unfortunately a lot of that info is trying to capture a flat(er) freq response and a more hi-fi sound, kinda anti guitar slamin jamin stuff you and I love! :MMM
     
  5. Tone_Terrific

    Tone_Terrific Member

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    You can buy pre-sized port tubes (plastic) that are inserted through the front of the cab. They are chosen by both area and length and must be calculated with respect to cab volume and speaker resonance.

    Basically, it is to extend the speaker's bass response and shift the dynamic impedance curve to smooth the output. My building attempt showed me that porting, stuffing and cab size all have an effect, but even if the spec's are good you still may prefer a 'wrong' combination for your preferred tone. Mucho time consumption.

    Sometimes it is better to just buy someone else's work that you know you like.

    Open, or semi-open back, big as possible :cool: is the least hassle, best tone combo IMO, YMMV.
     
  6. merkaba22

    merkaba22 Member

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    I agree, you can get too into this stuff and personally I think there is very little really known about acoustics compared to other sciences and as guitarists in this world we like what we like.

    Its just that no one has cracked how to make a 2 x 12 sound like a 4 x 12 ... and many of us want a smaller cab for a variety of reasons.

    When I see ports and these slots I wonder about how close they get but it seems that there is no substitute for the size of the cabs, since detuned ones (4 x 2's w/o 2 of the speakers, for example) are lighter and sound great too.

    I like making my own out of hardwoods (not so much because of the beauty but) because the do seem to come alive more. I have made two 1 x 12's and they are notable enough to consider a 2 x 12 design. Right now I am considering making a hardwood clone of a MB 2x12 Rectifier Vertical Slant that could take either two Celestions or be detuned with one Altec 417 H in the top -- could be like the older vertical 2 x12's MB used to make with one portion closed and other open -- dunno:)
     
  7. devilrob1979

    devilrob1979 Member

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    Tim at Earcandy cabs has come close with the Buzzbomb.
     
  8. Tone_Terrific

    Tone_Terrific Member

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    So what can you do?
    How about a deep (14"?) 4/10, but still about 30x22 (offset the speakers), pine boards, semi-open, Neo speakers?

    Pine would get beat up so cover with that goopy liner material for durability.

    Anyone try this sort of size and speaker configuration?
     

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