1. Please take 30 seconds to register your free account to remove most ads, post topics, make friends, earn reward points at our store, and more!  

B-12XTC replacement speaker options (four 12's with two different size chambers!)

Discussion in 'Amps and Cabs [BG]' started by christw, Jul 5, 2012.


  1. christw

    christw Get low!

    May 11, 2008
    Dayton OH
    I want to be Tesla (tinkerer at Dayton Amp Co)
    After opening up the newest Portaflex to grace my playing, I realized that it has two separate speaker chambers of unequal volume. I want to replace the speakers with some actual bass guitar drivers, preferably neo. (This thing weighs a ton!) Here's my disclaimer: I know it's going to be a bit of a crapshoot. I just don't want to destroy the beautifully chimey and easily farted speakers that came in this amp. I'd really like to use it with upright bass as a sort of uber Portaflex behind my folk band.

    The top chamber measures 10.5" deep, 20.5" high, and 27" wide. That's about 3.36 square feet when unloaded. The bottom chamber measures 10.5" deep, 16" high, and 27" wide. It's around 2.63 square feet unloaded. The cutout ports on the baffle are is equivalent to a 5" x 5" square/diamond for each chamber.

    Could anyone recommend me a speaker that would play nice in both chambers? Thanks y'all! :D

    IMG320.
     
  2. will33

    will33

    May 22, 2006
    austin,tx
    ???......haven't seen that one. One possibility would be to highpass a pair of the nice chimy ones to keep them from farting out and replacing the other 2 with bass speakers. Could just use a big capacitor to shave the lows off the old pair around say 200hz.
     
  3. will33

    will33

    May 22, 2006
    austin,tx
    The tube amps output taps/impedance have to be taken into account in that scenario.
     
  4. christw

    christw Get low!

    May 11, 2008
    Dayton OH
    I want to be Tesla (tinkerer at Dayton Amp Co)
    It's 8 ohms total impedance with 8 ohm speakers in parallel/series. I know Jess Oliver used to advocate 4 ohm loads on the 8 ohm tap of a B15 but I'm not sure about this one. ;)

    I hadn't considered the high pass idea at all. I'd still like to use a full set of replacement drivers so I don't have to worry about matching sensitivity of the stock speakers.
     
  5. will33

    will33

    May 22, 2006
    austin,tx
    Are the triangle/diamond ports just holes in the baffle or is there some depth to them and is there a shelf running through the middle of those ports to split the cab into 2 chambers or how is it divided?

    Cool if you don't want to do the highpassing thing, but, whatever replacements you get, especially if they can handle more bass won't have the same sort of "chime" in the top. Only way to keep that would be to keep at least some of these drivers, or use a chimey guitar driver, then we're back to the highpassing/need more bass thing again.
     
  6. christw

    christw Get low!

    May 11, 2008
    Dayton OH
    I want to be Tesla (tinkerer at Dayton Amp Co)
    They are just holes in the baffle. Yep, there is a shelf that splits the top/bottom chamber that's centered in the middle of the ports.

    I'm not looking to preserve their chimey quality. That's a sacrifice I already know I'm making. I'm looking to find the best compromise of sensitivity and speakers that work within this particular set of chambers.
     
  7. will33

    will33

    May 22, 2006
    austin,tx
    One of the better, and coincidentally more affordable neo's for this would be basslites. Full bottom, smooth mids and friendly towards different enclosure sizes, including small ones. But yes, you will lose that topend chime. 4 of them wouldn't even break a sweat with that amp and could handle a much more powerful amp if you were so inclined to do so for bigger gigs. Wiring options there would be 8ohms and 2 ohms for tube amps. Some of the farting from the current ones will be due to the high cab tuning/no depth to the ports. Could try adding some port length temporarily and see if it brings these current drivers under control. Really, a portaflex's power divided between 4 speakers shouldn't be able to fart out anything.

    Have you checked these drivers for rips/tears/coil rub/ all that stuff. Certain the amp is in good shape. Couple other things there that could be causing/adding to the distortion.
     
  8. christw

    christw Get low!

    May 11, 2008
    Dayton OH
    I want to be Tesla (tinkerer at Dayton Amp Co)
    Well, I was thinking it was farting them but it could well be the power tubes running out of steam if the speakers aren't super efficient, especially temporarily using 6L6 instead of 7027. I turned down when I ran it ran out of low end with both the Rickenbacker and the Bronco for fear of hurting the speakers.

    I haven't checked the speakers except for fixing a loose wire. The amp is dead silent and I just rolled almost all of the tubes in it. I did run the amp to where it was loud enough that I feared for the speakers a couple of times and that's what led me to believe they were farting. :smug:

    Anyways, I was hoping the S2012 would be a good candidate. I know four of them would be right up my alley. Anyone know where to find four for $400 or less though? :help:
     
  9. will33

    will33

    May 22, 2006
    austin,tx
    Get the amp checked out first. And have a closer look at the current speakers. Certainly don't need much lowend capability to handle a portaflex. Beautiful tone, but not enough power there do be dropping hundreds on drivers that it'll barely tickle.
     
  10. christw

    christw Get low!

    May 11, 2008
    Dayton OH
    I want to be Tesla (tinkerer at Dayton Amp Co)
    I'll probably wait it out until I get to run the 7027's I've got in the mail. I'm thinking a three prong power cable and check-up might be in order. The amp is happily putting out some serious power with just the 6L6. Everything I've read about the 412 XTC cab notes that it's not particularly good for bass. I'd guess the speakers roll off a bit around 100 hz. The head is the same as in a B18X so I know it'll work well for bass. With four basslites I'd have ~103 dB 1w/1m sensitivity and that's not bad. I'm sure they'd let my 50 watts go far enough. I'll always be able to run a slightly more powerful head into the cab if I need to too. ;)
     
  11. will33

    will33

    May 22, 2006
    austin,tx
    Those are all plus marks, but for now, the amp bias is probably off at least from just subbing in a power tube. I'd get that sorted first. Yeah, the basslites would be a good improvement as far as turning it into a bass cab. May still want to do some hidden improvements on the inside like lining, port tuning adjustment and possibly tossing a chunk of styrofoam in the big section to take up some space, make it the same size as the small one. Can do a little modeling with it when I can figure out how to make my PC un-crash itself......too bad it's not a speaker too.;)
     
  12. will33

    will33

    May 22, 2006
    austin,tx
    Those are kind of odd box sizes. 3.4 cu.ft. on the top and 2.6 on the bottom. Pretty big difference. Means they'll be tuned quite different as well. Should figure out somwthing there to get the 2 sizes and tunings closer to even, but, making them both the size of the small one would choke off a good bit of lows and make dumping money in new drivers make even less sense. Have to do some 'cipherin' here.;)
     
  13. will33

    will33

    May 22, 2006
    austin,tx
    You opposed to swiss-cheesing the divider inside and just turning it into one big 412? Would look the same from the outside.
     
  14. christw

    christw Get low!

    May 11, 2008
    Dayton OH
    I want to be Tesla (tinkerer at Dayton Amp Co)
    I like the styrofoam idea. I knew it was going to need a bias check when the guy broke the 7027 the morning I was headed out. Subbed a pair of 6L6 he had on hand to test it and threw my new Winged C's in there as a temporary solution until the new pair he's sending me for it arrives.

    I wanted to model it but I didn't have a document for it on WinISD. I think I couldn't find one particular number I needed to model it. (I've had a little to drink! :D)

    If I can unbolt it and bring it out, I'd consider that if there was a benefit in performance. I'm not doing anything irreversible though!
     
  15. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    I'd go for the 2012's if light weight is a must, but Beta 12's if cash is more important.
     
  16. christw

    christw Get low!

    May 11, 2008
    Dayton OH
    I want to be Tesla (tinkerer at Dayton Amp Co)
    Beta 12's wouldn't probably wouldn't weigh much more than the stock speakers in this thing and may have a small gain in sensitivity if they play nice in this cab. Off to WinISD! :meh:
     
  17. will33

    will33

    May 22, 2006
    austin,tx
    Model four 12" basslites in say, 5.6 cu.ft., guesstimating allowing for some internals there. Call it 2 square ports 5" x 5" each. Port depth would be the baffle thickness, probably 3/4". Then see how long you have to build the ports to get the tuning below 55hz at a bare minimum. 45-50hz prolly be better.

    That would be for drilling some holes in the divider so it's one airspace inside instead of 2 separate boxes each sized and tuned differently.

    Hurry up before JimmyM comes along and puts a hex on you for cutting up an old Ampeg.:D
     
  18. will33

    will33

    May 22, 2006
    austin,tx
    Damn....too late.
     
  19. will33

    will33

    May 22, 2006
    austin,tx
    Try modeling both the basslites and betas sealed too at the smaller 2.5ish cu.ft. size. Fashioning some port plugs would be reversible, non-chopping stuff up.
     
  20. christw

    christw Get low!

    May 11, 2008
    Dayton OH
    I want to be Tesla (tinkerer at Dayton Amp Co)
    Modeling the Beta 12A sealed versus ported (3.5" length) didn't really make much difference. Either way, it's -6 dB point was just under 70 hz. The ported model had a slight hump over 100 hz that's not as present in a sealed cab.

    I need the datas for the basslites and I'm about to go to bed but I'll be sure to come back to this thread. Thanks for the input so far and anything I might not see until sometime tomorrow. ;)
     

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.