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SBLs

Discussion in 'd.i.y.' started by robbyd, Sep 7, 2021.

  1. fraser.

    fraser. pfm Member

    Yeah - double checked and they're both stamped 1010
     
  2. peterm

    peterm pfm Member

    Good luck!

    Did the large stickers say P.W.B Electronics as alluded to in post #12?
     
  3. peterm

    peterm pfm Member

    A twinkle in Roy George's eye then.
    SBLs were introduced in 1986!
     
    Bob McC likes this.
  4. Bob McC

    Bob McC Living the life of Riley

    That’s what I thought
     
  5. colasblue

    colasblue pfm Member

    it's clearly a non standard serial number so either a staff build or built for a special purpose.
     
  6. peterm

    peterm pfm Member

    Testing the efficacy of "balancing stickers" perhaps:D
     
  7. colasblue

    colasblue pfm Member

    I think Nero could well have got it a few posts back. Some sort of development units.
     
    peterm likes this.
  8. fraser.

    fraser. pfm Member

    Thanks! Still trying to work out how to imbed pictures but hopefully this helps... https://ibb.co/wz3bnRP
    [​IMG]
     
    peterm likes this.
  9. fraser.

    fraser. pfm Member

    Upon further reading of some of the stuff on that PWB electronics website this is starting to make sense... there were some stuff written on bits of foil stuck onto the speakers which I assumed were for decoration / satanic communication but it sounds like they were actually intended to improve the sound!

    [​IMG]
     
    paulfromcamden likes this.
  10. Alex N

    Alex N pfm Member

    stephen bennett and fraser. like this.
  11. Bob McC

    Bob McC Living the life of Riley

    I was right!
     
  12. fraser.

    fraser. pfm Member

    The seller has confirmed he has some kind of box from naim which may or not be the crossovers, so fingers crossed there's something useable there as i'd like to see what the original passive set-up is like before doing anything else. Do these units look original unmolested?

    [​IMG]

    The foam in the mid-bass cabinet has rotten away so i'll replace with something i have lying around. The wool in the lower cabinet looks good so no issues there. There's magnets affixed to each wall of the cabinet, presumably for deadening / stiffening. Is this factory fitted as well? They are dead sounding cabinets when given a knock so doesn't sound like there's any mileage in playing with them.

    [​IMG]

    You're right about the blue stuff being sticky!
     
  13. peterm

    peterm pfm Member

    Those aren't magnets, they're lumps of aluminium attached to the cabinet walls by pieces of (double sticky sided) neoprene foam* - all part of the cabinet damping Naim used to "deaden" the cabinets.
    Apparently Roy George found that some contemporary speakers radiated more sound from the cabinet walls than from their drive units, and in an uncontrolled and time-delayed fashion, so he set out to design a speaker where the cabinet and drive unit chassis were isolated from the driver cones and well damped.
    Similar ally/neoprene damping can be seen on the back of the bass driver's magnet along with small pieces of neoprene foam on the back of the bass unit's cone ( the Mark 1 SBL used a lot more of this sort of damping on the Mordaunt Short drive unit's pressed steel chassis which was less well intrinsically damped than their own designed bass unit (I don't think they "built" the Mark 2 bass driver - I never saw a pressure die casting plant at Southampton Road!)

    *the sticky backed neoprene foam looks just like the bits cut out of the middle of the infamously expensive (these days) "gaskets". Waste not, want not!
     
    Ben&Ted likes this.
  14. fraser.

    fraser. pfm Member

    Thanks for that Peter, interesting. If the aim was to produce a dead cabinet they've done a good job of it anyway. Certainly more than most modern speakers I've come across.
     
  15. fraser.

    fraser. pfm Member

    A huge thanks to Brian for supplying some crossovers for these - that's been a huge help and incredibly generous!

    I've tested out the removal of the black finish on one tweeter section. It went reasonably well, with the only major concern being how to deal with some rounded / damaged corner. The veneer itself seems to be pleasantly thick and good quality. Seems strange to me that coating the whole thing black was considered the best way of presenting this material!

    [​IMG]
    image uploader


    Could this thread be moved to the DIY section? It's primarily now a rebuild thread.
     
  16. fraser.

    fraser. pfm Member

    Current progress... roughly sanded the two units below and will attempt to tidy up the front baffle of the main driver later. I'm going to re-spray the baffles black anyway so not too fussed about making a mess of them at the moment. Still no progress on tweeter removal though which is a concern!

    Excuse the carpet... it's days are numbered

    [​IMG]

    [​IMG]
     
    linnfomaniac83, Brian and Rug Doc like this.
  17. fraser.

    fraser. pfm Member

    This is the metalwork from one cabinet, which has seen better days. I'm soaking these parts in a chemical bath using a product by bilt Bamber which I've used before on brake calipers. It's an amazing product and very easy to use.

    [​IMG]
    [​IMG]
     
    stephen bennett likes this.
  18. fraser.

    fraser. pfm Member

    Few hours later...
    [​IMG]

    [​IMG]
     
  19. fraser.

    fraser. pfm Member

    I'm unsure if the small round magnets pictured here were part of the original design or one of the black magic 'improvements'... I can't remember where I found them on the speaker as they aren't on the other!

    [​IMG]
     
    Ben&Ted likes this.
  20. garyi

    garyi leave blank

    I replaced some tweeters in sbls once, in short I think you will be very lucky to get them out without knackering them.
     

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