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Porting my bassman 2x15

Discussion in 'Amps and Cabs [BG]' started by BassGreaser, Nov 19, 2004.

  1. BassGreaser


    Aug 22, 2002
    Austin, TX
    I have an old sealed Fender Bassman 2x15 that I want to put ports in. How do I go about finding how many, and how long to make the port tubes?
  2. If I remember correctly, my old Bassman 2x15 IS ported. Only instead of the round ports seen nowadays, it's shelf-ported, with a thin wide opening at the bottom of the front.

    Of course, I'm no expert on the evolution of their 2x15's, so it's possible you do indeed have a sealed cab.

    Regardless, though, you don't just add ports for the heck of it. The port size and length is calculated to "tune" the cabinet to a specific frequency. If the cab and speakers were correctly matched to start with, arbitrarily adding ports (or changing speakers) will almost certainly have a detrimental effect on your cab's performance. In addition...If the cab is sealed and the speakers were selected for a sealed cab, adding ports (thereby making this a vented cab) will allow the speakers to experience more excursion. This is not a good thing, they may exceed their design parameters (especially if they're old) and could be severely harmed...
  3. BassGreaser


    Aug 22, 2002
    Austin, TX
    mine is the sealed type. I was planning on upgrading to newer speakers as well
  4. Raven


    Nov 14, 2004
    Jacksonville, Fl
    Rather than "upgrading" to newer speakers, why not just get a new cab. Putting different speakers in a cabinet that was specifically designed for a certain type is very hit or miss, unless you have the knowledge and equipment to properly tune the cab to the speakers. There are lots of different specs for different speakers, a good bit of math calculating, as well as test equipment involved. You can't just stuff speakers in a box and expect it to sound right.
  5. If you are going to change speakers, download Win ISP (its free) or get some other software to match the speakers to your cab. The software will also tell you what to tune your cab to, and give you port diameter and length.

    There's several people on this forum who are quite experienced in cabinet design, I think bgavin is one.
  6. The Fender literature says the Bassman used to come with (2) JBL D140f speakers.

    Ask yourself what you are trying to achieve by changing drivers and/or porting. If you are looking for a big bottom, and have the above JBL rig, it ain't gonna happen... no matter how much you hack (read: ruin) the cab.

    The above JBLs are loud and punchy, and very efficient. They will never be a "big bottom" sound. If you don't like this, sell the un-ruined cab on eBay to somebody dying to buy the "JBL sound."

    You are nearly always better off in the long run in purchasing another cab that sounds the way you like. I remember far too many projects attempted in my youth that never completed due to lack of tools, money, ambition, etc.

    Most of us who build our own do so because we cannot find what we want in a commercial cabinet. The Tuba 24 is a prime example of this... it does not exist commercially, but is a viable solution.
  7. Le Basseur

    Le Basseur

    Mar 26, 2002
    I'm entirely subscribing on bgavin's comments.
    DON'T port such a cab :rollno: because you'll never get what you want for reasons concerning the mechanichal/acoustical/electrical behaviour of the drivers'+cab ensemble.If this isn't very convincing for you,please do some googling and read some documentation wich explains the differences between sealed and ported cabs and the behaviour of a given driver in both configurations.
    Also,be aware that a certain driver wich has certain Thiele&Small parametres is more suitable for a vented cab but another driver having different T&S parametres is most suitable for being used in a sealed cab,not to mention the other categories (horns,transmission-lines,etc).
    The Fender cab you own is a story of it's own,it's somehow a vintage piece and for a possible buyer/connoisseur any intervention (ports,different drivers installed,another cosmetic,etc) substantially robs down the value.
    Sell it as-is and buy yourself what's best for your taste from the today's market.
    ...or,make your own cab! :hyper:
  8. BassGreaser


    Aug 22, 2002
    Austin, TX
    thanks guys for talking me out of chopping the crap out of this cab. bgavin it's funny you said the Tuba24..I've had Bill's plans for the DR250a/Tuba24 for about a month now. Now only if I can find someone who cab build them for me :D
  9. r379


    Jul 28, 2004
    Dallas, Texas
    Finding someone to build a cabinet shouldn't be too hard. Anybody who builds kitchen cabinetry or some such could do it. Just make sure you use good void-free plywood. Three-quarter inch plywood with around eleven plies should do nicely.
  10. BassGreaser


    Aug 22, 2002
    Austin, TX
    what is Dr. Bass's website address :D
  11. The Tuba 24 should be built from 1/2" ply, not 3/4".

    The design is completely self-bracing, and this is evident on the set of plans I purchased. 3/4" ply will throw off the measurements and add unnecessary weight to the project.

    Per Bill, the (cheap) Beta 10 is more sensitive up to 100 watts input power, but the HL-10a is preferable for maximum (300 watts) input power, due to its much high BL and Xmax factors.

    3/4" material will make it (probably) impossible to mount the HL-10a, which is already cramped when using 1/2" material.

    Building season is gone this year (I work outside), so I will have to wait until good weather is back, say April or so.
  12. I would like to hear your opinion on the tuba 24 or 30. I know you don't have it put together, but based on your experience, how does it look? Thanks, Bob