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8ohm vs 4ohm single speaker cabinet

Discussion in 'Amps and Cabs [BG]' started by nil, Sep 10, 2003.

  1. I had been recently using a 4ohm 12" Eminence car audio sub in a ported box with my Eden WT800. After a good 3 hours of solid thrashing I managed to blow the voice coil (found out later the speaker was rated at 200w).

    As the Eden puts out somewhere around 250w @ 8ohms (400w @ 4ohms), I can probably souce a cheaper 8ohm speaker than a 4ohm'er that can handle the amp.

    What's the main difference between using a 4 and an 8ohm speaker - volume or clarity?

    I'm a little surprised the Eminence died so easily - would I be pushing things with a replacement rated @ 300w (pushing 400w into it)?

  2. Petebass


    Dec 22, 2002
    QLD Australia
    the main difference is that an 8 ohm speaker won't draw as many watts out of the amp, so you're down a few dB initially. However you'll more than get that back by switching from a car audio speaker to a pro Audio speaker. Car subs are very innefficient. Check out the Sensitivity rating of the speaker and it's probably in the low 90's or high 80's. Most pro audio drivers have a sensitivity upwards of 96Db. I other words, efficient drivers need less watts to produce the same volume as the innefficient drivers.

    You'll also get a shift upwards in frequency response. The car sub is probably good for, I dunno, 35Hz to 1000Hz. A pro audio driver of the same size is more likely to produce 45Hz to 5,000Hz. I just made those figures up but you get the drift........
  3. Cool...is the db difference really noticable?

    The speaker I blew up was nicely spec'ed though - 33Hz - 3KHz, 96dB sensitivity. My goodness, it was almost as loud as my 8x10! (seriously, it totally surprised us) and sounded fantastic.

    Main problems I find with pro audio speakers is that they're a)expensive and b)few run @ 4ohms.
  4. Petebass


    Dec 22, 2002
    QLD Australia
    96dB for a car sub? Are you sure it's a car sub? Or did you assume it was a car speaker because it is 4 ohms?

    What exactly is thes make and model of this speaker?
  5. Definitely a car sub. It's an Eminence Corvette 383...4ohms, 200w RMS, 2" voice coil, 96db. Not much info on the web, I gleaned these figures from a russian site (google will find it).

    I managed to pickup a cheap HiFonics sub yesterday that worked a treat @ practise...held together brilliantly, and hit a little harder low down. 300w, ~91db, 4ohm, 2.5" coil, huge magnet. Did the job nicely!
    I used to use a HiFonics 15" driver in my old SWR WM15 that hit way harder than the POS PAS speaker that came with it originally!

    It's funny talking to "pro audio" people regarding using car subs for applications like this...always negative comments, but nearly always from people that obviously don't play. And then argue 'til they're blue that you don't need an 8x10 for backline in a large venue. :rolleyes:
  6. Well, my feeling is that any woofer will work, providing it can handle the power and that you have an amp capable of driving it. There's lots of amps out there now that can put out over 1000 watts, and there not even that expensive any more.

    But the the biggest difference ot me in a "pro-audio" driver is that they are made to play and continuous power, hifi subs are not. As far as efficiency, a 3dB change is "just noticable". And it takes twice the power to give you that. So you can go from a 200W amp to a 400w amp and get "barely noticable" difference in loudness, or get a speaker that's 3 d more efficient and have the same thing. So you decide where you want to spend your money.
  7. True, although you have to watch the frequency specs of the driver (many subs these days only run up to 500 or 800Hz). The drivers i've had good success with usually run around 35-3500Hz, which allows them mids to come through nicely.

    You are totally correct about constant driving though - hifi/car subs aren't meant to take it. So far so good though, and the single 12" box is a darn site easier to load and move for practise than the 8x10 behemoth! :p

    The silly thing is that the 12" can stay in the car between practises and double as a sub! :D
  8. ESP-LTD


    Sep 9, 2001
    I don't know, I like my JBL GT-120 's just fine. I agree they will suck some power though, and they drop off pretty badly above 200hz.
  9. Munjibunga

    Munjibunga Total Hyper-Elite Member Gold Supporting Member

    May 6, 2000
    San Diego (when not at Groom Lake)
    Independent Contractor to Bass San Diego
    ... until it blew up.

    Reminds me of an old drag racing adage, before the "no substitute for cubic inches" trend took hold. A lot of guys were running the little De Soto 361-inch hemis, and the path to more power was increasing the amount of nitromethanol in the fuel mixture. This gave birth to the "100 percent, at least once" motto. Sounds like you ran your speaker at 100+ percent once too often.
  10. I beg to differ.

    Perhaps cheap drivers aren't designed for a vigorous duty cycle, but the good ones certainly are. I have my pair of Rockford RFR-2215 on the receiving end of 900 watts for hours on end, and they take it just fine.

    I have yet to see a 96 SPL subwoofer, which explains why yours blew up. Most likely from over excursion of the cone, which is a typical problem when over driving non-subwoofer drivers. True subs have very long Xmax (linear excursion), which brings the inherent trade-off of lower efficiency.
  11. Damn exchange rate means cheap is often the only way I can go (well, especially for a practise setup)! Nah, actually, come to think of it, i'm always looking on the cheap side of everything! Spend more money and get it right the first time? Nah, where's the fun in that? ;)

    I particularly liked the shower of sparks you could see thru the spider after it blew. :D
  12. I dig your style, man... :)