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Wattage and Dbs

Discussion in 'Amp Central Station' started by Count, Mar 6, 2017.

  1. Count

    Count Friend of Leo's

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    I just carried out a simple experiment. Using a Db meter app on my iPhone set three metres away from the amps. I did a Decibel comparison. The guitar used was a Strat with the volume knob set at three, the selector set to neck and middle pickups combined. A C scale was played and one C chord.The guitar setting and what was played was repeated for each amp.
    On each amp the volume control was set at 5 (halfway) and the three tone knobs also all set at 5.
    The first amp, a Frontman 212R, solid state 100watt RMS, two 12" speakers gave a peak Db reading of 105.
    The second amp a Frontman 25R, solid state 25 watt RMS, one 12" speaker gave a peak pf 96Db.
    The third amp a proprietary Chinese made valve amp (2 EL84 power tubes, 3 12AX7 preamp) rated at 20 watts RMS with one 12" speaker gave a peak reading of 106Db. (Both the channel and master volumes were set at 5)
    When the valve amp volumes were turned down to 3 the Db peak was 100 Db.
    Those readings were all at the indicated halfway volume capacity of the amp. In all probablity the max volume readings would be somewhat different. However, i gig with the Frontman 2121R set at 5 and it is well audible over a heavy handed drummer. The experiment would seem to indicate that a 20 watt RMS valve would be pretty close to a 100 watt RMS Solid State in volume/loudness capacity. The 25R struggles to be heard over a drummer but is quite capable when no drummer is present. The diference between 96Db and 105Db does not look like much on paper but in practical reality there is quite a difference. I'm curious as to what results others would get if they carried out a similar test.
     
  2. Sandhill69

    Sandhill69 Tele-Holic

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    I don't think that you can relate the position of a volume knob to anything except that for a given amp with a given input you could expect the same dB...it should be repeatable. I think that on paper, increasing power from 25W to 100W should increase volume by 6dB using the same amp and speaker.
     
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  3. Wally

    Wally Telefied Ad Free Member

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    +1 with Sandhill69 on different pots. There is really no way to know what those various pots were sending on through the circuit by simply setting them all to halfway on the dial. One would need to do an actual power measurement at the output of the amps to know how much power one was applying to the speakers.
    And....speakers are the other variable. If you really wanted to compare the amps, run them all through the same speaker. This would eliminate the variable of the speakers' different efficiencies.
     
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  4. philosofriend

    philosofriend Tele-Holic

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    The volume knob on a guitar amp is not in any way a calibrated output power control. In most cases what it does with a normal guitar plugged into it is that for the first part of its travel the guitar gets louder and louder. After that turning it up makes the tone more rich and raunchy and compressed without getting one bit louder.
    Theoretically, doubling the power causes a 3 Db gain. In reality speakers also compress the dynamic range, after a certain point more power in gives more speaker distortion with less gain in output than theory predicts.
     
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  5. Count

    Count Friend of Leo's

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    Daren't do the same test with volumes at full- neighbours. [emoji37] I was just interested in measuring the actual loudness instead of relying on wattage as an indicator of volume in amps of different types and configurations. We hear a lot of discussion about wattage and perceived volume but rarely get actual decibel readings.
     
  6. horseman308

    horseman308 Tele-Holic

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    I think probably the most useful result here is the reminder that a 10 Db difference is huge difference. While there are too many confounding variables in the OP's test to generalize beyond his own equipment, it's still a good way to learn some of the basic elements of choosing a well-thought-out rig for a given purpose (e.g., gigs with a band vs home practice).
     
  7. Count

    Count Friend of Leo's

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    Thanks horseman, I was interested in knowing the actual sound level of my amps at their usual settings as opposed to what I thought was the sound level. I would be intrigued to find out what others get if they measure the Dbs of their amps at their normal playing settings. Just for info I tested the app against an industrial meter and it was spot on.
     
  8. jorbjorb

    jorbjorb Tele-Meister

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    I think it's 5db increase per 10 watts of power.

     
  9. Wally

    Wally Telefied Ad Free Member

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    It takes an increase of 10db in speaker efficiency to double the perceived volume. It also takes an increase of 10x watts(power output) to double the perceived volume through the same speaker system.
     
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