Using two cabs: one 8 ohms, the other 4 with a Carvin B1500

Discussion in 'Amps and Cabs [BG]' started by 11Rob, Dec 9, 2012.

  1. 11Rob


    May 6, 2012
    Can you wise folks here on talkbass enlighten me!

    I have a Carvin B1500 head which is a "mono block" head (one power supply). I also have a 4 ohm 4x10 and an 8ohm 1x18.

    Can I use both cabs with this head?

    If so, should I run each off the head or should I chain them together?

  2. It's not good to mix ohms like this, because you get an uneven rating.

    2 8ohms cabs make a 4 ohm load.

    2 4 ohm cabs make a 2 ohm load.

    A 4 and an 8 would get you about a 3 ohm load. Not good on the amp.

    depending on the speakers in the 4x10 you may be able to rewire it for 8 ohms.
  3. basscooker

    basscooker Commercial User

    Apr 11, 2010
    cincy ky

    do tell....
  4. smogg


    Mar 27, 2007
    NPR, Florida
    I'm not crazy, I'm just a little unwell
    Q: Can I use both cabs with this head?
    A: Yes, your amp is 2 ohm stable.
    8ohm + 4ohm = 2.6ohm which is less than the 2ohm minimum.
    Rough guesstiment power output about 75% of the 2ohm output rating with twice the power going to the 4ohm cab vs the 8. (do the battery test to make sure the two cabs are IN phase)

    Q: If so, should I run each off the head or should I chain them together?
    A: No difference.
  5. LowEZ


    Mar 29, 2011
    Central NJ
    Wrong. It would be fine 'on the amp'.

    Wrong. Impossible.
  6. gearhead1972


    Feb 21, 2012
    Kent NY
  7. Does amp handle sub 4ohm loading? If not it's a good time to trade up to a nice matching pair of 2x12 if you must have stupid loud.

    At least the impedances are compatible with the probable power handling capacities of the two cabs. It could easily sound muddy as hell though.
  8. Suggest familiarising yourself with the amps forum sticky contents before dishing out any more advice this year.
  9. smogg


    Mar 27, 2007
    NPR, Florida
    I'm not crazy, I'm just a little unwell
    AFAIK/and to the best of my limited knowledge, that concept only applies to all tube amps and maybe real old school SS amps that were passively cooled. That Carvin is a modern fan cooled SS amp that can handle a 2.6 load no problem.
  10. Jaco who?

    Jaco who?

    May 20, 2008
    Yes, you can. You will have a 2.667 Ω load. Your amp is rated @ 2 Ωs minimum load.

    You can run each off the head or chain them together, the result will be the same, a parallel 2.667 Ω load with either method.
  11. jumblemind

    jumblemind I also answer to Bryan Supporting Member

    Aug 27, 2011
    Would the 4ohm cab overpower/overshadow the 8ohm in the mix?
  12. Yes, and that would likely save the 18 from being blown out.

    Multiple 10's handle more power and move more air as a collective than a similar sized cab with 15". Afaik 18's are in a similar boat to 15's.

    Without full disclosure of what drivers are in the cabs we can't say if the 18 might still be struggling to keep up with the 4x10, even with the impedance handicap but it's certainly possible.

    Assuming the 18 adds something rather than handicapping the 4x10, some amount louder is usually "better" unless nasty phasing happens.

    We don't know the sensitivities but it's a pretty good bet the single 18 lags behind, making less use of its 1/3 share of power. Probably not going to add nearly as much "louder" as hoped.

    Personally I can't imagine this experiment sounding very good but it doesn't automatically fail on account of the impedances making it dangerous for the amp or the speakers.

    Beware of farting. Highly distorted tones make it hard to hear the farts when you're in the middle of business.
  13. gumtown


    May 7, 2007
    New Zealand
    good to see bad advise is being corrected,
    seeing too much of this lately.
  14. bertbass666


    Mar 6, 2009
    I used a B1500 for a few years and always ran it at 2 ohms, no problem at all. Using both cabs, the 4x10 will be louder than the 1x18.
  15. 11Rob


    May 6, 2012
    Thanks for the advise everyone! I appreciate everyone's feedback.

    The 18 is a Carvin BRX18 (8) rated at 800W. I also have an Ampeg PR410HLF (4) which is rated at 600W (1200 peak).

    I used them together last night. It sounds like they are probably in phase because combined they are much louder and there is no loss of bass.

    In fact, from the basement, I knocked some dishes off the shelf upstairs at my drummers house.

    Yes, I do want my bass rig to be "stupid loud". My drummer is very aggressive and the guitar player insists on practicing at face melting levels. We are a rock band. Our practice level are around 85 dB. I wear ear protection.

    I play a 5 string dropped 1/2 step. The 18 does a nice job with the sub bass freqs.

    Oh, and with the B1500 in a heavy tour case my bass rig is outrageously heavy!
  16. 11Rob


    May 6, 2012
    Here's the stats on the two enclosures:


    - Power handling: 800 Watts
    - Reproduces Frequencies from low B (26 Hz to 2 kHz)
    - Freq. Resp: 30 to 2K Hz ± 5 dB
    - Sensitivity: 98dB @ 1w and 127 dB @ 800W


    RMS Power Handling: 600-Watts
    Frequency Response (-3dB): 33Hz - 18kHz
    Usable Low Frequency (-10dB): 29Hz
    Crossover Frequency: 4kHz
    Nominal Impedance: 4-Ohms
    Sensitivity: 96dB
    Maximum SPL: 124dB
  17. bertbass666


    Mar 6, 2009
    85db isn't loud.
  18. smogg


    Mar 27, 2007
    NPR, Florida
    I'm not crazy, I'm just a little unwell
    It is in a 10x20 concrete basement. :eek:
  19. 11Rob


    May 6, 2012
    I used a phone app to measure the SPL. Maybe its not the most accurate. I have ran it side by side with a real meter at a venue and they appeared to agree.
  20. 85dB is the same wherever. It's not loud on the rock band scale. Shaking stuff off shelves your practice room is probably more like 120dB most of the time and peaking higher.

    If the 18 was all its specs say I'd be very surprised.