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Using up some old speakers in a DIY cab design?

Discussion in 'Amps and Cabs [BG]' started by alexclaber, Feb 16, 2006.


  1. alexclaber

    alexclaber Commercial User

    Jun 19, 2001
    Brighton, UK
    Director - Barefaced Ltd
    I have just acquired a selection of speakers from an elderly Yamaha electronic organ, which due to their age and OEM status it seems to be impossible to find any specs other than those printed on them (i.e. power handling and impedance). They are respectively 12", 8", 5", 3" and 2" paper cone drivers, 8 ohm impedance and 40W down to 5W power handling.

    Compared to my hi-fi they appear to be of ~90db@1W1m sensitivity, (though it's hard to tell without the larger drivers in a cabinet) so nowhere near loud enough for any sort of gig, but they could be quite handy in solving the iPod in the kitchen to practice singing whilst cooking/washing-up to, or as a way of getting my bass up to acoustic guitar volume for laidback practising/writing sessions.

    My inclination is to build a small sealed box with the 12" woofer downloaded, and the 5" and 3"/2" drivers on the front to cover the mids and highs. Then build a little preamp and power amp to make sound come out. Obviously without any specs it's down to my ears to work out what to do.

    So does anyone have any hints, tips or bright ideas on how best to approach this, including suggestions on how to derive the specs so I can 'engineer' this more accurately?

    At some point I may get into building serious speakers and do things properly, but as a novice with a fair amount of theoretical knowledge and a background in engineering, when I came across these speakers I thought I might as well get my hands dirty and see what I can create!

    Alex
     
  2. greenboy

    greenboy

    Dec 18, 2000
    remote mountain cabin Montana
    greenboy designs: fEARful, bassic, dually, crazy88 etc
    No Thiele-Small/mechanical specs? Sounds like repeated experimentation is the only solution. Or using one of those Acme B2 cabs ; }
     
  3. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    The beauty of sealed cabs is they are far more forgiving if you get the cab volume wrong. So I'm glad you're considering going sealed. It's probably the best option.

    Without T\S specs it's certainly more hit-and-miss. There are ways to measure T/s specs, and there are products out there that can do it for you, but in this case I wouldn't bother spending the money. It defeats the "new speakers for virtually nothing" purpose of the cab.

    Seeing the speakers cost nothing, I would worry about that too much. I'd treat this project as a bit of fun and a cool chance to get cab building experience.

    Have you still got access to tht old organ? If so, try to make the new cabs so the speakers have got roughly the same amount of cab volume as they had when they were in the organ. You didn't happen to keep the crossovers from the organ did you?
     
  4. greenboy

    greenboy

    Dec 18, 2000
    remote mountain cabin Montana
    greenboy designs: fEARful, bassic, dually, crazy88 etc
    Hard to find drivers that deal out much low end in a sealed cab... Just an observation. Myself, if I owned an Acme, I wouldn't even bother with the leftovers.
     
  5. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    That's a bit of a myth based on -3dB points. However of you look at -10dB points of a sealed cab compared to a vented one, that's where the sealed cabs win.

    A Typical vented cab rolls off at 24dB per octave. Sealed cabs roll off at only 12dB per octave. So you could have a vented cab which is -3dB at say 60Hz and a sealed cab that's -3dB at 80Hz. The vented cab is -24dB at 30Hz, but the sealed cab is -12dB at 40Hz and -24dB at 20Hz. Plot both graphs and the sealed cab has more area under the curve than it's sealed counterpart.

    Vented cabs go louder, but in cases like this where ear-bleeding SPL isn't required, you shouldn't imediately rule out sealed cabs. And that's without even considering the comparitive speaker excursion characteristics which again favour the sealed cab.

    I'm not sure about your Acme reference. Acme's are ported.
     
  6. greenboy

    greenboy

    Dec 18, 2000
    remote mountain cabin Montana
    greenboy designs: fEARful, bassic, dually, crazy88 etc
    I know about the sealed vs ported rolloff stuff, thank you. And comparing a well-chosen driver f3 and cab tuning I find far preferable to a sealed -10 dB down figure which I myself consider a near-useless figure since it takes HOW MUCH power to make up for even 6 dB (four times) let alone 10 dB.

    Sealed cabs have their uses and their admirable lack of group delay but it's STILL tough to find drivers for sealed use that go very low. As I originally said.