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Wattage and volume

Discussion in 'Amps and Cabs [BG]' started by Hepworthbass, Mar 23, 2014.

  1. Hepworthbass


    Mar 11, 2014
    I have a fender rumble, with a 15 inch speaker and 150 watts.
    I've recently bought an ashdown abm head 900w, and for now It's going through an ashdown mag 410, 450 watts.
    Even with 300 more watts, the ashdown isn't as loud as the fender, and I'm confuses to why this is, can anybody give me an insight?
  2. Mystic Michael

    Mystic Michael Hip No Ties

    Apr 1, 2004
    New York, NY
    "300 more watts?" You're suggesting that the 4x10 should be louder - simply because its rated power handling capacity is three times that of the 1x15? It doesn't work like that. :rollno:

    Volume (i.s. SPL) is a function of multiple factors, i.e. power available from the amp, sensitivity of the speakers, efficiency of the cabinet, voicing of the amp and the cabinet, cabinet impedance, etc. For example, without knowing the impedance of your 4x10 cab, it's not clear whether it's drawing the full 900 watts from your amp (presumably @ 4 oms), or considerably less (presumably @ 8 ohms).

    These are just a few of the factors to bear in mind... :meh:

  3. RickenBoogie


    Jul 22, 2007
    Dallas, TX
    +1 wattage, or wattage ratings, are not a good indicator of volume. Speaker sensitivity is much more important in the big picture, which includes many other factors. The amps faq's are a good read, and may help shed some light.
  4. -Asdfgh-


    Apr 13, 2010
    The rough relationship is doubling power (with all else equal) will increase sound pressure level by 3dB. Without doing an A/B test in quick succession 3dB is perceived as 'a bit louder' (You can subconsciously detect smaller differences though).

    So 450W, if you are running the 4x10 at maximum thermal load, is not much more than 'a bit louder' assuming that the efficiency of the speakers are equal at all frequencies. The range of efficiencies of speakers, even at mid frequencies, can span 6dB and exceed the difference due to power levels, and the range from speaker cabinets as a whole is much, much greater. If you know you are putting an amplifier in a speaker that will have relatively little power output below 80Hz then you might prefer to tune the low control on the EQ to operate in the area which for some amps might be considered to be more the low mids. It's not uncommon for some old vintage amps, for example, to have bumps in response around 100Hz to make up for the fact that the bottom octave fundamentals are not being strongly reproduced, relying on the brain to fill in the missing octave. It then means power can be concentrated more above 80Hz where the power can go further in terms of perceived volume, which was a reasonable workaround when power amplification was heavy and expensive but less of an issue with class-D amps that can just throw an extra 500W at the issue and go down more towards 30Hz if needs be and still allow you to lift the thing without a crane.

    You might find that the Fender is biased in its EQ towards low mids rather than lows and it makes best use of the watts it has in terms of what you can hear, but at the expense of being a less true representation of the input. You might also be pushing the Fender into the area of overdrive, which can lead to a sense of things being louder.

    You can test this by dialing back the low EQ on the Ashdown and turning up the volume (carefully - don't blow the speakers). It might be useful to grab a VST host/DAW for a laptop and use that to send a signal from your laptop to each of the amplifiers in turn, and using a microphone with as flat a frequency response you can muster (something fairly flat down to 40Hz) and then use a frequency response graphic to see what the frequency response from the amplifier is and then match them somewhat and see if that equalises the perceived differences in loudness. Start at low volumes, perhaps, where any distortion on the Fender is not an issue, then match the Ashdown to the frequency spectrum, and see if you are actually running the Ashdown with relatively lower power output to match as that will reveal too if part of the issue is that you are trying to match the Fender running into overdrive against the Ashdown totally clean.