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Output power and cab impedance question.

Discussion in 'Amps and Cabs [BG]' started by Whitey1980, Apr 12, 2009.

  1. Whitey1980


    Feb 27, 2009
    I have some questions regarding output powers and cab impedances as I'm a little baffled! :confused:

    I tried a Warwick Profet 3.3 through a WCA411 pro at 4 ohms and it sounded great! I need a little more power but not a great deal more so I'm probably gonna get a Profet 5.1 whilest there still some new ones left and £85 cheaper than a 5.2.

    In terms of cabs though I'm not sure whether to get a 411 or a 410. I know the 411 has a total of 600 Watts power whereas the 410 has 300 so my 1st question is..

    Does it actually make the amp sound louder?

    Personally I thought the only reason for getting a 600 Watt cab is to match the output of a say 1 KW head running at 8 Ohms. Is this theory correct though cos there seem to be a bunch of people using 411 cabs into 500 Watt heads at 8 Ohms so they're only using 50% of the cabs power handling. Supposing there is a difference in sound between a 410 and a 411 cab hooked up to a Profet 5.1 at 8 Ohms..

    What would that difference be?

    Last one..

    If a Profet 5.1 puts out 500 Watts at 4 Ohms then does anyone know what it uses at 8 Ohms?

  2. Rick Auricchio

    Rick Auricchio Registered Bass Offender

    1. Doubling power typically gives you about 3dB increase in volume, which is often negligible. That assumes the cabinet(s) can handle the additional power.

    If you hold that extra power in reserve (i.e. don't actually use it), then the amp has more headroom. Headroom allows the amp to work less hard. That headroom is never used full-time (it's a power reserve).

    2. Most cabs begin to fart out---hitting mechanical limits of the speakers---long before you reach the max power. Once a cab reaches that point, more power would only damage speakers.

    3. Many cabs reach a point of power compression, where more power just heats the speakers and doesn't get louder. Here again, more power just damages speakers.

    4. Most solid-state amps put out half the power at 8 ohms as they do at 4.
  3. VisualShock


    Feb 19, 2008
    North Wales
    Firstly, head over to the amps FAQ.

    However, since you're here, what i understand of amps is this:

    What your head amp says it outputs will be in reference to impedance, measured in ohms.

    If your amp says 1kw (or 1000 watts) at 4ohms, this means if it is hooked up to a 4 ohm load (being the cabs) then it will be able to unleash it's full power. However, if it is hooked up to an 8 ohm load, it halves the power (typically, double impedance=half the power)

    For example, My head is 150 watts at 8 ohms, or 300 watts at 4ohms.
    This means i'd best be looking for a 4 ohm load, to reach it's full 300 watt potential.

    4 ohms is achievable by a few methods.
    Firstly you could just get 1x 4 ohm cab
    You can get 2x 8ohm cabs.

    To work out impedance of cabs on the amp, use this rul

    1/((1/first cab ohm)+(1/second cab ohm)+(and so on))

    in the simplest terms, 2x8ohms=4 ohms...

    If you're still unsure, or would like to double check my information (i'd recomend you do, it's mainly guess work and what i've heard/seen elsewhere) then head over to the amps FAQ, or do a search of the amps board.
  4. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    No. Speaker output is limited by the displacement of the drivers, not the power rating. Unfortunately no cab manufacturer reveals the displacement limited power handling of their cabs. They would like you to believe that higher power ratings result in higher output, but truth be known the opposite can be the result.
  5. Implosion


    Oct 19, 2007
    The 410 and 411 are differen't form each other. Different speakers and the 411 has got a tweeter.


    Power rating: 300W (max. 400W)
    4 ohms
    4 x 10" speakers (power rating 75W, max. 100W, 16 ohms, 95dB, resonant frequency: 60Hz, frequency range: 40Hz-7000Hz)
    Bass reflex housing
    Weight: 31 kg
    Dimensions (W/H/D): 0,62 x 0,67 x 0,49 m


    Power rating: 600W (max. 800W)
    4 ohms
    4 x 10" speakers (power rating 150W, max. 200W, 16 ohms, 94dB, resonant frequency: 50Hz, frequency range: 35Hz-3500Hz)
    HF horn with attenuator (power rating 30W, max. 40W, 8 ohms, 95dB, resonant frequency: 2,5kHz, frequency range: 1,2kHz-20kHz)
    Bass reflex housing
    Weight: 39 kg
    Dimensions (W/H/D): 0,62 x 0,67 x 0,49 m
  6. Whitey1980


    Feb 27, 2009
    Thanks all for the replies! :)

    I'm still in debate as to what I actually need so maybe you can help. I'll be playing clubs and medium sized halls. The plan is to get the 500 Watt head and go 8 Ohms which I'm hoping will be enough but not too much power for the smaller venues. Then maybe add another 8 Ohm 115 cab if the venue sizes increase.

    How much at risk would the 300 Watt 410 be of farting out if I played a hall and needed the extra volume?

    If I did end up getting another cab and running the full 500 Watts at 4 Ohms then how is the power distributed between the cabs? 500 Watts each or 500 between them?
  7. Implosion


    Oct 19, 2007
    Well if you are considering the Warwick cabs you should take note that besides the power handling, they sound different. To my ears the 411 is better than the 410.
  8. Rick Auricchio

    Rick Auricchio Registered Bass Offender

    There's no way of telling without trying it. It depends on volume and how you EQ your amp. Lots of bottom end will cause it to fart sooner.

    If the cabs are the same impedance, they will split the power equally.
  9. Just remember the amp head puts out the power, the cabs can only try to accept the power sent to them by the amp and how loud the user turns the amp up. :bassist:

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