What's in a watt?!

Author: Six   Date Posted:13 May 2023 

When shopping for an amp, one thing often comes up in the decision making process that pains many a musician; how many watts do I need? The answer is; well that depends. I know, sounds like a cop out but stick with me here. Firstly, we need to discuss something many don't know and that's how watts are actually measured and what they mean. We all know bigger number means more, but it's a little more complicated than that.

When we talk about watts, we're talking power as a measurement of voltage and current through a load which in our case is a speaker. We all know about the classic 100W Marshall heads that doiminated backlines in the old days, the AC30 which had 30 watts of power available, or the baby Champ with a measly 3 watts coming through a tiny 6 inch speaker. Maybe you know about bass heads that pump out 1000W or a PA speaker that churns a massive 3000 watts. These numbers seem hugely distant from each other, so you'd think there's a massive difference in volume between the 3W amp and the 30W amp, not to mention the behemoth 100W one. They're actually closer than you may realise. 

Power for amps is measured logarithmically, which means that big numbers may not be that much different to small numbers. Huh? Let me break it down. We perceive volume in this logarithmic way so doubling something doesn't just mean going from 1 to 2. 

Let's take the 100W head as an example. Lots of people say they want a 50W amp because they can crank it harder and not have it so loud. This is true, to a degree. Whilst a 50W amp is quieter by half, we can only just perceive it. But half is half, how can it not be a huge difference? Because of that word from before, logarithmic. A 50W amp head is half the power of the 100W head but in a logarithmic measurement it's 3dB less which is near the threshold for us as humans to detect there being a difference in volume.

To truly reduce the power of a 100W amp by half and have us perceive it as half the volume, we need to reduce the power by 90%! That's right, half the power of a 100W amp isn't a 50W amp, it's actuallly a 10W amp. Reduce that by 90% again, and you end up with a 1W amp which is a quarter the output of a 100W amp. 

Power is only one factor in the total volume of an amp and it can be greatly affected by the number and type of speakers you use and the cabinet they're in. You can easily drown out a drummer with a 5W head plugged into a 412 cab with high efficiency speakers, and vice versa you can jam out a 100W amp at home with a small cab and inefficient speaker (however I wouldn't trust your neighbour to be too happy).

Keep this in mind when you're shopping for a new amp and don't get too caught up in the numbers if you're looking for something for home use. Not sure what amp is right for you? We'd be more than happy to help you find the right amp from our range of new and used gear. 

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