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Crash course in multi heads/amps? Ohm calculations, slaving? Wha?

Discussion in 'Amps and Cabs [BG]' started by Zuhzuhzombie!!, Sep 12, 2008.


  1. Zuhzuhzombie!!

    Zuhzuhzombie!!

    Jun 4, 2008
    Howdy.

    I'm currently using a 350 watt Hartke 3500 Transient Attack, running through an Ampeg 410. Sounds great. Love the amp. I just want more volume. On initial inquiries I was told that I could run the Hartke through to two cabs, but I would simply be "pushing more air" and wouldn't affect my volume too much and it was suggested that I either play through two heads/cabs, or slave. I have never gotten much information on either of these techniques.

    Just for the sake of it, here's a shot of the back of my Hartke.

    2lcsaog.

    What really scared me was a short post about matching ohms, not watts, with a link to this website:

    http://ampservice.de/impcalc.php?lang=e

    So, I turn to the venerable TalkBass community to learn me a thing or two, and hopefully alleviate my fears.

    As stated, I was suggested to either play through two heads/cabs, or slave, which would give me the ability to finer tune things.
     
  2. Rick Auricchio

    Rick Auricchio Registered Bass Offender

    1. Adding a cabinet will increase your volume by 3dB, which is the same as doubling the amplifier power (assuming the original cab could handle it). Adding a cab is by far the best way to boost volume. That said, 3dB isn't a lot. (Twice the volume would be 10dB, and that requires ten times the power!) Your tone, however, will be much fuller with a pair of cabinets.

    2. Your amp can drive 350 watts into a 4-ohm load. Your cabinet options are:

    - one 8-ohm cab; the amp puts out 240w
    - one 4-ohm cab; the amp puts out 350w
    - two 8-ohm cabs; the amp puts out 350w and you get an additional 3dB [edited to fix]

    It doesn't make much difference how many speakers are in the cab, as long as the impedance (ohms) are marked.

    There are no other (reasonable) connection options. (Forget about a series cabinet connection; they're extremely rare and prone to errors if you don't use a special cable.)
     
  3. Kitsapbass

    Kitsapbass What key is this?

    May 26, 2005
    Bremerton, WA
    Don't you mean two 8 ohm cabs???
     
  4. scottbass

    scottbass Bass lines like a big, funky giant

    Jul 13, 2004
    Southern MN
    Yeah, two 8-ohm cabinets in parallel equals a 4-ohm impedance. That would be 175 watts to each cabinet. Two 4-ohm cabinets won't work unless you connect them in series, in which case the total impedance would be 8 ohms and you would be driving each one with 120 watts.

    IME the 3dB plus the increased volume of air being moved makes a significant PERCEIVED difference - more than you would expect - when used with amps of 150 watts or more. YMMV.
     
  5. Zuhzuhzombie!!

    Zuhzuhzombie!!

    Jun 4, 2008
    Thanks for the replies.

    What would I need if I simply wanted to play through two heads and two cabs?
     
  6. Rick Auricchio

    Rick Auricchio Registered Bass Offender

    Yikes, I did indeed mean two 8-ohm cabs for the third option!

    Edited to correct that.
     
  7. RickenBoogie

    RickenBoogie

    Jul 22, 2007
    Dallas, TX
    2 full rigs (?) The above answer is your key to increased volume. If you're talking about running 2 rigs together, you'd need another head and appropriate cabs for each, and a splitter for your signal.
     
  8. And then you get to worry about phasing problems.
     
  9. Zuhzuhzombie!!

    Zuhzuhzombie!!

    Jun 4, 2008

    Could you elaborate please?
     
  10. It's only happened to me once. If any of the speakers are out of phase (i.e., one is moving out when the other is moving in), it sounds bad.

    Less likely is a phase difference in the amps - I have never seen that. This would be when one amp inverts the signal from the bass and the other doesn't. You would have a signal that is going positive coming out of one amp and going negative out of the other.
     
  11. Zuhzuhzombie!!

    Zuhzuhzombie!!

    Jun 4, 2008

    Ah. I've encountered this once when a friend took a combo amp, gutted the amp out of it, and wired the speaker incorrectly.
     

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