Old cabs - new drivers

Discussion in 'Amps and Cabs [BG]' started by SubMonkey, Apr 6, 2005.

  1. SubMonkey


    May 3, 2004
    Denver, CO
    I have acquired an old Fender BXR Spectrum cabinet (1x18 and 2x10, no tweeter) that I'd like to resurrect (maybe even bring it up to something approacing modern standards)

    1 of the 10" speakers is just plain fried and the 18" farts badly at any sort of volume. I'm kind of like the old thing as the tolex and grille cloth is in good shape and it looks to be constructed of good quality plywood etc.. etc...

    I'm wondering if any of the resident speaker scientists could offer any info or help regarding this unit... for example;

    1. Any idea what the cossover frequency was in these, and how to test the crossover? (could a crossover failure have caused the demise of the 10 and 18 inch drivers?)

    2. Given the following internal dimensions of the 2x10 chamber(H-10.75" W-25.5" D-17.25") and the port size (two triangular ports in this chamber totalling 16-ish square inches with no depth) can you recommend a pair of drivers?

    3. Given the following internal dimensions of the 1x18 chamber(H-21" W-25.5" D-17.25") and the port size (1 rectangular port in this chamber H-1.25" W-25.5" D-11") can you recommend a driver?

    Thanks for reading all that....

  2. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    In all likelyhood there was no crossover. Even today very few manufacturers use crossovers between woofers and midbasses. If you do decide to use one (and you should) I'd put it at 200 Hz.

    Download WinISD (it's free) and you can figure out what works in the cab, although the better way would be to choose drivers and alter the cabinet tuning to suit them. It will also calculate crossover component values for you. I'd seal the tens chamber tight, they don't need ports with an eighteen handling the low end.

    I'd also be inclined to bag the second ten. If you use a crossover then one ten will be adequate power wise, and not having two side by side will give much better HF response.
  3. Petebass


    Dec 22, 2002
    QLD Australia
    The possibilities are endless.

    Bills idea of using a crossover and sealed 10's is a good one. It makes the cab size of the 10's less important, and by removing the bottom end from them, the 10" speakers don't even have to be as good in quality. It of course means the 18 has to be a beauty. It will provide a bulk of the bass sound.

    You could also ditch the crossover and make the 10's and the 18 overlap from say 80Hz upwards until the 18 starts to roll of in the high frequencies. This is a more typically commercial design but means the 10's have to be pretty good. They'll likely be ported and will be fed a full range signal, so they have to be better all round for it.

    Then there's the in-between approach where some low freq. filtration is given to lighten the load on the 10's.

    Assuming you want to keep the original 2x10 + 1x18 , all-ported configuration, lets have a look........

    The chamber holding the 2x10's is about 77 litres (38.5 litres for each driver). I'd consider a couple of Eminence Deltalite 10's. Gamma 10's will also work.

    The 18" chamber is 151 Litres. There's quite a few 18's that will work in that size cab:-

    Beyma 18P1000, Selenium 18SW2P, Eminence Magnum 18HO, Eminence Sigma Pro 18, B&C 18PS46, RCF L18P200-8, Eminence Omega Pro 18c are all contenders.

    But before we start doing the math in detail, working out nominal impedance issues etc, we need to have a better idea of what cab you want to have at the end of the whole process.
  4. SubMonkey


    May 3, 2004
    Denver, CO
    Bill, there is something in there masquerading as a crossover at least (a few thumb sized capacitors and a couple of toroidal devices mounted on a circuit board) I'm not terribly familiar with these devices though.... is there a way a fellow with a multimeter and a few other electronic tools might test this unit for function and configuration (x-over freq) ? If it is blown, and I go with a crossover arrangement, I'll definitely aim at 200Hz per your suggestion.

    This is great stuff... I gotta say I like the idea of sealing the 2x10 chamber... it ties in very nicely with your last question... If I had to describe the end result I'm looking for, think SVT-ish but with the ability to reach (at least closely) to a low "B" fundemental (oh say 30-ish hz), not so concerned with crystal clear high-freq.

    After reading a bit of this I'm on the fence about the use of a crossover... seems like it might not be necessary by using a sealed chamber and the inability of the 18" driver to reach very high... this leaves me with one less part to fail, on the other hand, wouldn't I be wasting a lot of energy sending full range signals to speaker arrangements that can't actually reproduce that range (and is that necessarily a bad thing)???

    FWIW I'll be running a Peavey Classic 400 on top of this (400 watts of steaming tubes, awww yeaaahhhh) so I'm limited to either 4 or 8 ohms.

    Thanks again Bill and Pete, this is exactly the kind of info I'm looking for...
  5. Ben Clarke

    Ben Clarke Liquidating to fund a new business. Buy My Gear!

    Jan 6, 2005
    Western NY
    I'd do a crossover. They very rarely fail if you use reasonably good components.

    Think hard about Bill's advice on the single ten vs. using both. You will get more even dispersion with one, and you can use the money saved towards better drivers.

    How about leaving the fried ten in there as a passive radiator?
  6. Petebass


    Dec 22, 2002
    QLD Australia
    The possibilities are still endless :)

    OK the crossover first. Does the existing crossover have any numbers printed on the components? The caps will have a value that looks like "number" uF, and the inductors will have a value measured in mH. If you can give us those values, we can work out the crossover frequency.

    But it might be easier to make your own crossover. Capacitors and Inductors aren't expensive. We can help you determine the values of the components to whatever frequency you want.

    That said, coming back to the SVT sound you're chasing, the SVT sealed cabs accepted a full range signal and to me, that's a big part of their sound. Plus, buy adding the 18, there a certain amount of natural frequency filtration happening at the 10" because you're less likely to need to boost any of the low frequencies.

    When you said SVT I imediately thought of the Eminence BP102. Trouble is, it's has a very low sensitivity rating. All of the 18's I suggested would bury them when fed equal power. You'd need 4 of them to compete.

    As for the 30Hz problem. None of these 18 are flat to 30Hz. However many of them will do a good job of reproducing the low B. I've printed the list again and included in brackets the -3dB points (using only the SBB4 alignment for now).

    Beyma 18P1000 (42Hz), Selenium 18SW2P(38Hz), Eminence Magnum 18HO (54Hz), Eminence Sigma Pro 18 (53Hz), B&C 18PS46 (47Hz), RCF L18P200-8 (45Hz), Eminence Omega Pro 18c (55Hz). Based on this the Beyma and Selenium go lowest, and I'll think you'll find the price tags will reflect this.

    We have to also consider the possibility of making the 18 sealed as well. I'm just playing along with the SVT philosophy here. The -3dB points will be higher, but the low end roll-off is shallower. So you may very well end up with more happening at 30Hz than you would with a vented enclosure.

    So many possibilities :)
  7. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    If there are coils and caps in there they are undoubtably crosover components, but measuring their values without sophisticated testing gear is next to impossible. What's odd is that if it was crossed over at 100 Hz or higher there should have been no need for venting of the tens. In any event I'd still start from scratch, with a Delta 10 for the top in a .35 cu ft (net) subenclosure, which will leave about 7 cu ft left over, perfect for a Sigma Pro 18 and a very respectable 45 Hz f3. You don't have to remove the existing tens compartment, just put in partitions to get the subenclosure volume right and cut some 3" or so diameter holes in the remaining panels to open up the rest of the old tens compartment to the main box.

    As for the crossover, without it not only will half your power be wasted going to drivers that can't use it but also you'll end up with a 4 ohm box, and your amp will be operating with twice the amperage draw for no good reason. Even a 1st order crossover would be worthwhile for both power allocation and impedance purposes. Just be sure to use a high quality high power inductor for the LP filter.
  8. alexclaber

    alexclaber Commercial User

    Jun 19, 2001
    Brighton, UK
    Director - Barefaced Ltd
    I've noticed the various Accugroove cabs (which are apparently 4-way with subwoofer, midwoofer, mid and tweeters) not only have the subwoofer and midwoofer in ported enclosures but also the little 6" midrange has a small port in its own enclosure. Any idea what advantage this has?

  9. If you decide to go the crossover route, a low pass filter might be a better choice, something like the Eminence px:250.
  10. Whappo Grande

    Whappo Grande

    Feb 9, 2002
    Santa Clara, CA.
    Manager: AccuGroove Speakers
    Drivers are usually designed to favor either sealed or ported enclosures. Some drivers have a wider range of flexibility where you could go with either a ported or sealed box.

    The drivers we’ve designed to incorporate into our multi-way systems have a better tonal response & volume for "our needs" when correctly ported.

    Part of the equation is that the cabinet is built around the driver, not visa versa. Therefore a ported cabinet is not better or worse than a seal cab, unless the drivers strongly favor a ported box, etc.

    AccuGroove Music Systems
  11. SubMonkey


    May 3, 2004
    Denver, CO
    Right, So I've committed a Crossoverectomy ; what we have here are three of those prevoiusly mentioned thumb sized caps

    1. 63 uF
    2. 189 uF
    3. 126 uF

    all are rated at 100v

    and two coils;

    1. renco 8747 stamped 954 uH (not mH)
    2. renco 8750 (part # rls1256-3-2000) as luck would have it, this does not have a rating printed on it however rencousa.com has datasheet listings for this series of parts, in in all cases the last four digits are the rating in uH (so 2000uH , again not mH)...whew...

    (could you recommend a resource where a fellow could find info and teach himself a bit about how these crossover networks function ?)

    Finding where this thing rolls off might go a ways toward answering Bill's qustion about why the 2x10 chamber was ported in the first place...(might just be a crappy design..) It will probably also be the last piece of the puzzle for (or nearly the last anyway) :smug: to select drivers and perhaps a different crossover unit.

    Again, thanks all for helping me out here..

  12. Petebass


    Dec 22, 2002
    QLD Australia
    Whoa this is harder than I thought. I was kinda hoping it would be 2 caps of the same value and 2 inductors of the same value. Instead we've got 3 caps and 2 coils and none of the values are the same..... hmmm.....let me see.......

    I can make a out a 3rd order Low pass filter from the 189uF and 63uF caps together with the 2mH coil. In English that means the 18 may have been getting the highs cut at a rate of 18dB per octave from 320Hz.

    That leaves me with enough components to make a 2nd order high pass filter for the 10's, but I can't make the values work. Maybe the 10'd had a 1st order High pass filter at 320Hz, this accounts for the 126uF Cap. All we've got left is the .954mH coil and I'll be buggered if I know what that was for. It could have been a 1st order low pass filter for the 10's but the value suggests it would have been mildly cutting everything from 700H and above?

    I'll keep playing an see if I can come up with anything else. Gotta run now - the only thing standing between my girlfriend and shopping is ME and I starting to fear for my life :)
  13. SubMonkey


    May 3, 2004
    Denver, CO
    Hopefully this doesn't confuse the issue any further... attached is my sorry hand drawn attempt at tracing the board and how the circuit runs (I wouldn't rule out the possibility of errors :meh: )

  14. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    That's definetely an interesting circuit. I'd toss it in any event. For what you're doing you can live with a simple 1st order crossover, as a ten midbass doesn't need a lot of protection like a tweeter does, and a fair amount of overlap in the range of the drivers isn't that big a deal either. I'd put the crossover at 200 Hz; to calculate the values and get a schematic go here:

    There are crossover tutorials also at that site.

    When you get the capacitor value, probably 100mfd or so, you want to parallel a high value non-polarized electrolytic with a low value polyfilm cap, perhaps a 90mfd/10mfd for best results at minimal expense.
  15. Petebass


    Dec 22, 2002
    QLD Australia
  16. Hey, I'd just like to say a big THANKS to you guys.
    I have this same BXR Spectrum cabinet and one of the inductors on the circuit board / crossover circuit has fried! I've been trying to find schematic info for so long now and today I got lucky on google with this old thread!


    I'm actually powering the cab from a Fender BXR Dual 400 head, with the crossover and 2 line outs, so I can run the cab ok from this one head (using the low and high jacks on the back of the cab), but if I ever wanted to try another power amp, I would be wasting half the cab each time (running just the 10's or the 18 on their own. :(

    Here's my problem:




    I have no idea if it's for the low or high pass filter. I just needed to know what part to replace, and Submonkey, you little rippa :) You listed the part I'm looking for in your post!

    I'll try and digest all this info you've all posted and maybe think if there's a more appropriate value part to replace to get a better frequency cut off. The circuit board appears to be in still allright shape so I think I can rewire this ok.

    More cab pics, just for anyone else wanting more info on this subject. THANKS EVERYONE!!!


    [​IMG] [​IMG]
  17. hrgiger


    Jan 11, 2009
    That is a nice beastly cab!
  18. yeah, driven by the BXR dual 400, it sends a few tremors through the house :)

    bit of a pain to cart around tho...
  19. Petebass


    Dec 22, 2002
    QLD Australia
    Whoaaa I just threw away the 1x15 version of that cab. It had been collecting dust for years and didn't work any more. All the weight of those cabs is in the wood. It's darn thick particleboard, maybe 30mm, definitely more than an inch. The drivers themselves are pretty light (hence the relatively low wattage rating). But that cab served me well in it's time........

    I used to own the BXR dual 400 head too :)
  20. rpsands


    Jul 6, 2007
    Phoenix, AZ
    I'd suggest the possibility of redoing the baffle for a 115, and using a 3015LF or something like that crossed over low (200-ish hz) to a pair of coaxial or whizzer 10s. Eminence B102s perhaps.

    Just a thought :)