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18" 4 ohm

Discussion in 'Amps and Cabs [BG]' started by jondog, Jul 16, 2005.


  1. jondog

    jondog

    Mar 14, 2002
    NYC metro area
  2. oldfclefer

    oldfclefer low ended

    May 5, 2005
    Southern Ohio
    You'll want to watch the impedance. Someone on this forum reminded me that it comes to 2.67 ohms. (8 x 4 / 8 + 4 = 2.67) You don't want to go lower than your amp's ohm rating. So if you're amp is rated at 2 ohms you're ok, if it's rated at 4 or 8 ohms, you could damage it.
    CV speakers are ok, but they're usually for stereo use. There are others that are better.
     
  3. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    Going to a 4 ohm driver doesn't necessarily mean you'll get any more headroom at all, and you may end up worse off as a less sensitive driver will cost you output. The only way you can make an informed choice is to model your current rig in a box program such as WinISD and then do the same with the driver/cabinet combination you're considering, and that's not possible without knowing the TS specs of the driver. All the seller seems sure of in this case is the driver size.
     
  4. jondog

    jondog

    Mar 14, 2002
    NYC metro area
    I'm running my sub off one side of my power amp. 8 ohm load = 230W, which is not a lot for lows. 4 ohm load = 400W, which is almost double so it should be noticable. Yes I have no data on this CV, that's why I'm asking here :) It's within my budget and he used it for the same app. I'm going to . . . I'm wondering if it's worth the $ to take a chance.
     
  5. Eric Moesle

    Eric Moesle Supporting Member

    Sep 21, 2001
    Columbus OH
    Barely noticeable . . . unfortunately . . .
     
  6. WOOFMAN

    WOOFMAN

    Mar 12, 2003
    USA, PNW
    Why do you want to buy a 15 year old paper cone woofer? Why not by new, ie. Peavey 18", Carvin(I use two), Accugroove, Fender, SWR? You, can order 8ohms 18" from just about any of these companies. You can even purchase 21" from Accugroove( I think).
     
  7. jondog

    jondog

    Mar 14, 2002
    NYC metro area
    Good question. Budget mostly, I don't think I can get a new one for under $150.
     
  8. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Jondog, that speaker looks suspiciously like the one inside the Cerwin Vega Jnr Earthquake, which was a folded horn enclosure. Actually those Jrn earthquakes weren't too bad as a PA sub, but to get any real thump from them, we had to use 2 of them on each side.

    Here's the thing. You're thinking that doubling the wattage will give more headroom and SPL. This is true if the "new" speaker is equally efficient as the old one. But a mere 3dB drop in sensitivity between drivers could mean the new speaker is actually quieter then the old one.

    This can be shown mathematically. The formula for SPL is:-

    SPL = (Log "Watts" x 10) + Sensitivity.

    We don't have exact figures to work with but lets pretend the 8 Ohm EV has a sensitivity of 99dB. At 230W this translates to:-

    SPL = (Log230 x 10) +99.
    SPL = 122.62dB

    Now lets replace the EV with a speaker that's 3dB less sensitive, but is 4 ohms. So 96dB sensitivity and 400W:-

    SPL = (Log400 x 10) + 96
    SPL = 122.02dB

    You've gained nothing. You've actually lost 0.6 of a dB.
     
  9. jondog

    jondog

    Mar 14, 2002
    NYC metro area
  10. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    So it's a 50/50 bet. I don't spend my hard-earned on those odds. If we can track down some T/S specs we can get a clearer picture............
     
  11. jondog

    jondog

    Mar 14, 2002
    NYC metro area
    OK, it looks like they used that driver in several different PA cabs. Here's what I found on Pro Sound Web . . .

    "Hi
    its look like the old PD-18C
    specifications are
    useable frequency response 30hz to 16khz
    eia power hanling 300w
    spl 1m 1w 100db
    max spl 125db
    dispersion 100h 70v
    components
    lf 188eb 18"
    mf er124 12"
    hi h-25 (fostex tw?)
    crossover 300hz and 3khz"

    So, if all I have is the 188EB, will I still get 100 db sensitivity? Also, I found that it costs more than $100 to recone one of these.