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How much power does your amp need for rehearsals and gigs?

Choosing the Right Wattage for Your Guitar Amp

Thanks to "Doc" Emmett Brown, everybody knows that you need 1.21 gigawatts for a DeLorean to go back to the future when its flux capacitor runs out of plutonium.

Unfortunately, his tests show that you can’t rely on that for guitar amps because we are dealing with acoustic power. So, we’ll have to do without him in order to answer the following existential question: How many watts does a guitar player need?

It’s the watt, stupid 

choisir la puissance de son ampli guitare

There are several ways to measure the power of an amp. All of them use the watt as unit of measurement. In other words, the same amp can have different power ratings corresponding to the same acoustic performance. The only one you should trust is the one called RMS, which indicates the mean power of the amp and is comparable from one model to another.

But it gets even more complicated if you consider that an amp equipped with tubes in the power section will produce higher levels than an equivalent solid-state amp. On the other hand, the tubes in the preamp do not affect the overall volume, but rather the perceived loudness.

Finally, you should also know that modeling amps are just like solid-state amps, in terms of power.

In rehearsal

The main concern of a musician during rehearsal is to be heard over the drummer, who won’t be able to play below a certain decibel level, especially if he is just starting out. So, the 5W amp that is perfectly suited for your room will certainly not be enough.

choisir la puissance de son ampli guitare

It is, unfortunately, impossible to give you an exact figure, because there are a lot of factors to be considered: The style of music, the sound of the drummer, the presence of the bass, the number of guitars and other instruments with a lot of mids, the size and materials of the room, the impedance, and the efficiency of the speakers, etc.

If your bassist is properly equipped, you can divide the power of his amp by two to obtain the minimum wattage that yours should have.

But if that’s not the case or you want to be sure that you won’t have power problems, you’ll need an 80W solid-state amp or a 20W tube amp, which ought to be enough in most cases.

In concert

choisir la puissance de son ampli guitare

Logic would say that the size of the amp ought to be proportional to that of the venue, which means you need a truckload of Marshall amps to play outdoors. But that’s not true! You could say that, the larger and better-equipped the venue, the less important is the wattage of your amp. Since your sound will be amplified by the PA system, the volume will depend on it (and the kindness of the sound engineer), even if your amp is loud as hell.

If the PA system is only for the vocals, because it is not powerful enough or the venue is too small, you will need more or less the same wattage as for a rehearsal.

Power is in the air

One last advice that could really make a difference, without affecting your wallet: Place your amp so that you can hear it! Even a small combo can be easily heard if its sound is projected to your ears. So, try to put your amp up high (on a stable surface, preferably) or to tilt it towards you and you will have the impression of having gained a good handful of watts and a pinch of intelligibility.

  • jaysalam 1 post
    New AFfiliate
    Posted on 05/10/2014 at 17:20:19
    I hate to comment on this article, but feel I should. Only in one spot was it mentioned that the efficiency of the speaker was a contributing factor. Wattage is simply the most misunderstood and misleading statistic in the audio world. When a guitarist, bassist, keyboardist or whatever asks, "what is the wattage?" in almost 100 cases out of 100 what they are really asking is "how loud will it go?". It is a fact that you need to multiply your wattage by 10 to sound twice as loud as before. Without going into great db equations etc, that means that to sound twice as loud as your 5 watt effort, you need 50 watts (all other conditions remaining the same). And to sound twice as loud as that you need 500 watts.
    What I refer to here is the ears PERCEIVED loudness. So the rule is, it takes 10 times the power to be perceived as twice as loud.
    Speaker efficiency is critical in this regard. Speakers are measured as xxDB @ one watt @ one meter. Roughly speaking, a speaker with 102 dB efficiency will be perceived as twice as loud as a speaker rated at 92 dB. Again, all else being equal. Therefore the 102 dB speaker at 5 watts will sound about the same as the 92 dB speaker at 50 watts.
    The original Fender Twin (not Twin Reverb) of the '50s had 2 6L6 power tubes. Those tube in that circuit could produce 40 watts of nearly clean power and about 50 watts jammed to the hilt. Those 40/50 watts driving into two Jensen 12" speakers would fill a mid sized coliseum with no PA system help. Changing the speakers to JBL D120s would have made that amp much louder (and too heavy to carry). That is just one example. There are many others.
    Don't forget that tone matters at least as much, if not more than, raw power.
    Thanks for starting this thread.

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