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Opinions on Cabs, Impedance, Volume

Discussion in 'Amps and Cabs [BG]' started by pbasswil, Jun 6, 2011.

  1. pbasswil


    Feb 17, 2008
    I'm having to "up my ante" in the volume department.
    I'm used to polite society gigs and jazz gigs, but now I'm playing for someone who keeps asking for more volume and punch from my bass.

    Small and medium sized cabs used to always do the trick for me, but now I'm about to buy a loud 4 x 10. (I won't get into brand names right now.)

    I'll be driving it with a GB Shuttle 9.0 -- 500W/8ohms; 900W/4ohms.
    The 4 x 10 is rated for 800 watts, in 4 or 8 ohm versions.

    I'm aware that it requires 10 times the power to double the perceived loudness. So yes, the difference between feeding the 2 versions of the cab -- 500watts at 8ohms or 800-to-900 at 4ohms -- is not very significant.

    But my instinct is still to order the 4 ohm, and have more than enough power to extract the maximum SPL out of it, if/when necessary. (E.g., huge room or outdoors with limited/no PA subs -- hey, it could come up.)

    Btw, I'm not worried about overpowering the cab; I use my ears before I turn up the Master.

    However, the store has the 8ohm in stock; getting the 4ohm would take a while.

    Aside from the instant availability, the other argument for going for the 8ohm is that in the future I could add a second cab, if I needed another 3db of volume.

    Frankly though, for my modest level of career, at the moment it's hard for me to imagine ever needing the second cab.

    Anyway: Any opinions? 8 ohm version now, limiting me to 500watts, or wait for the 4 ohm -- limiting me to the one cab in the future?

    Thanks in advance.
  2. That "800 watt rating" is the thermal rating for the voice coil only.

    Most commercially available cabs can only handle about half the "rated power" before hitting it's mechanical limits and farting out.

    I would go for the 8 ohm version, as the difference in output between that and the 4 ohm version are not even audible.
  3. RickenBoogie


    Jul 22, 2007
    Dallas, TX
    +1 it's always the best option if the only difference is the impedance. The 8 ohm cab allows for expansion, AND gives you all the booty you need. A 4 ohm cab in this case is more of a liability.
  4. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    It would be 6dB, actually. But IMO you're better off with a pair of vertically stacked 2x10s anyway. That gives all the stage volume anyone needs, and as for the room, that's the PA's job.
  5. pbasswil


    Feb 17, 2008
    So you're suggesting that with the 8ohm version of this "800watt" cab, hitting it with the full 500 available watts is likely to be already challenging the limits of the drivers?

    Do others agree with that?
  6. FWIW, in 25 years of gigging experience, everywhere from small lounges to arenas, I've never found it necessary to have more than one cabinet.
  7. pbasswil


    Feb 17, 2008
    Ah, thanks for that.

    Say, by way of comparison: About what would the volume difference be between hitting the cab with 500 and 900 watts, in db?? Less than 1db?

    When I suggested the option of two 2x10s, the salesman (who's a decent guy, not an unscrupulous sales opportunist -- but neither is he a sound expert) suggested that I wouldn't get as much bottom end out of the two smaller cabs stacked, compared to one 4x10.

    Is that true?? I was under the impression that if you stack them, the lows of two cabs would sort of reinforce, and be more than the sum of the parts, so to speak.

    Another thing he said: When choosing his own main cab, he tried the 8 and the 4 ohm versions, and he found that the 8 ohm version sounded better to him: "more immediate -- as if it reacted more easily."
    I've never heard of that before -- re. tonal differences in otherwise identical cabs of different impedance. Comments??

    As it happens, lately I keep coming across gigs where the venue only has tops -- no subs. :-/ Twice in the last two weeks, yet! My current modest cabs really struggled to dish out the lows.

    Thanks for the great responses, everyone!
  8. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    No. In all likelihood 400 watts will exceed the driver excursion limits.
    And that's why he's a salesman, not an acoustical engineer. :D
    It's possible. When you alter one driver spec, such as impedance, you alter all of them.
    That's the venues problem, if they don't care enough about how the PA sounds to have a good system why should you? In any event the solution isn't for you to blow the rest of the band off the stage to fill the room, it's a good PA. Want to supply it?
  9. pbasswil


    Feb 17, 2008
    Just to be 100% clear: If I take two of the 2x10 versions of the same model family (assuming exactly half the cab internal volume), stack them vertically as you suggest, I will get the same lows as from the 4x10??

    One thing that was starkly apparent at the music store: the same cab delivered completely different amounts of lows when it was directly on the floor, compared to when it was sitting on another unused cabinet.
    So that made me wonder about the advisability of vertically stacking cabs.
    But so long as the bottom one of a pair of stacked cabs is directly on the floor, I should be good to go, for lows?

    Thanks again.
  10. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    True. By not having a full line of active drivers extending to the floor some floor coupling was lost. Plus by having the cab over an unused cab the drivers in said unused cab literally sucked away some low frequency output of the top cab like a sponge. And lastly there would be a perceived loss of bass with the cab higher, the result of hearing the mids and highs better. An acoustical engineer is well aware of these concerns, and would never place the cab that way. A salesman, not so much.
  11. pbasswil


    Feb 17, 2008
    Bill, thanks so much for patiently answering my questions.

    You've cleared up some of my misconceptions and made me conscious of some fresh variables. Now I'm better armed to make smart cabs choices. Much appreciated, buddy!

    Peter Wilson (Montréal)
  12. pbasswil


    Feb 17, 2008
    Oh and thanks to the other responders as well -- what a helpful community.


    - Peter

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