How are Watts for bass combo amps calculated?

[iiipopes]

Watt were we talking about?

Improving Thomas Newcomen's engine for pumping water out of a mine.

 

[HMZ]

Shenron,

There is a hoary old urban legend that somehow British amps are louder watt for watt than American ones. This goes along with the urban legend that tube amps will be louder watt for watt than solid state amps.

British tube amps are therefore the loudest

If a spec sheet simply says “watts” without specifying RMS, speaker impedance load and frequency range then take it with a pinch of salt. My first bass amp was sold as a “60 watt” amp when the actual RMS rating was only 20 watts. Another great example is those off-brand powered speakers you can find at Amazon and eBay that sell for about $100 and claim to be 1000 watts or more while running off batteries...

British amps go to 11 I think that’s why they’re louder.

 

[groovepump]

Watt were we talking about?

Exactly

 

[brianrost]

British amps go to 11 I think that’s why they’re louder.

Tweed Fenders went to 12, take that you Limeys!

 

[trevcda]

I think people put way too much stock into the number of watts and the diameter of a speaker, without give any consideration to the other variable of the equation and the resultant outcome. You can pretty much discount any post on here that tells you that you have to have XXX watts and XX" speakers and that all XX" speakers sound the same and will deliver the same sound. You can get a lot more out of XXX watts by running it through more speakers than you will by adding 100 watts to that number. And you will get three different sounds using the same exact amplifier through a ten inch version of an Ampeg, a Bag End and a Fender cabinet. Watts do not matter. The whole equation matters. Use your ears.

 

[YourGuitarist]

Generally, the input power is based on 1/8 rated audio output power into the lowest rated load. There are exceptions and additional values that can be used though.

Where does the 1/8 come from? Is this a crest factor thing and they're just quoting the average power spec, neglecting peaks?

 

[JeezyMcNuggles]

I am confused by multiple values mentioned...

For example, I am looking at a Gallien-Krueger MB110, reviews and product pages say 100W, but pictures of its back side show "full power 140W, average power 28.6W"?

Then, I also see a Peavey TNT with "150 RMS American Watts". I know RMS means root-mean-square average, but to which values of the GK above should I compare it with? And as far as I know Watts aren't different between the metric and imperial systems so why "American" Watts, do you calculate them differently than in Europe?

That's current draw, not output power. Input power.

The peavey's rating is output

 

[agedhorse]

Where does the 1/8 come from? Is this a crest factor thing and they're just quoting the average power spec, neglecting peaks?

It comes from the regulatory agencies and their testing protocols, because 1/8-rated audio power generally equates pretty accurately to the average power demanded of of an amplifier when driving unclipped, uncompressed program material. It does relate to the crest factor.

That's current draw, not output power. Input power.

The peavey's rating is output

Current draw is "amps", power draw is "watts".

 

[Hoochie Coochie Man]

According to the specifications published by Mesa Boogie my Mesa D800 is capable of supplying approximately One Horse Power.

Makes sense to me considering the fact that the designer is known around here as agedhorse.