How are Watts for bass combo amps calculated?

[Shenron]

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?

 

[Wasnex]

From the manual

Output Power

This should be 100W RMS

 

[abarson]

The power figures that you see near the AC power input socket relates to how much power the amp consumes from the electrical grid. It is not the same as how much power the amp delivers to a speaker.
See page 9 for specifications for the MB110. Note that there is a section for "Output Power" and one for "Power Requirements". As the MB110 does not support connection of a passive external cabinet, all 100 watts are delivered to the internal speaker.
P1 MB Combo Cover (squarespace.com)

I don't know where you're getting this "American watts" stuff from, as it doesn't appear in their manuals and I can't say I've ever seen it printed on any of their combos. If someone is putting that in their ad, they are jerking you around. There are no "metric" or "Imperial" watts.

Also note that there were a number of generations of TNT combos that have different features and power displacement. You need to know which generation it is to have the right owner's manual.

 

[Killing Floor]

Something about Volts and Amps and bits but I can’t find the exact formula.

 

[agedhorse]

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.

 

[5StringBlues]

I prefer Charlie Watts.

 

[spankdaplank]

For some brands the number of watts will be whatever the marketing department thinks they can get away with and will boost their sales.

 

[_One//Man//Mutiny_]

It’s calculated by having 2 people have a conversation in front of the amp being played at full blast for one minute. Depending on how many times they say “what?” That number is then multiplied by 60!

 

[Shenron]

The power figures that you see near the AC power input socket relates to how much power the amp consumes from the electrical grid. It is not the same as how much power the amp delivers to a speaker.
.

Thank you! I think this was the key concept I was missing: power consumed vs power delivered.

 

[LoTone]

In North America, the electric grid is run at 120 Volts on 60 Hertz cycles. This describes how the electricity flows in the electrical wires. In Europe, it is mostly 230 volts on 50 hertz cycles. These values affect the wattage requirement for the head inside the combo. In the amp head, there is a transformer that adjusts the power output to the speaker in relation to the input power provided by the electric grid. These values are just there to let you know how much power you are drawing from the electrical outlet when you plug the amp and run it.

 

[ardgedee]

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?

"American Watts" is probably the unfortunate interference of a marketer on the technical documentation.

James Watt was Scottish. And the TNT115 was made in China.

 

[flatwound62p]

I prefer Charlie Watts.

I wish I could be like ...

 

[brianrost]

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...

 

[KenSmithFan]

For some brands the number of watts will be whatever the marketing department thinks they can get away with and will boost their sales.

 

[flatwound62p]

British watts and US watts used to be an actual thing on advertised specs for stereos when I was a kid, in Australia in the 70s. The guy who owned our local guitar shop used those terms all the time when describing amps. I assume it was pretty much RMS vs Peak. Some stuff was labelled with UK and US ratings.

 

[MattZilla]

tldr: it’s a measure that is irrelevant nonsense without the context of multiple other measures.


Whichever way it’s calculated by which company for which of their products, it’s related to perceivable loudness at the Stack Height & Reach Length coordinate of the player’s ears from the speaker cone(s) in a particular room size like horsepower or torque is related to how much utility/fun one can expect out of a road-traveling vehicle: a 200hp 150ft/lbs engine is huge fun and bordering on dangerously overpowered on a <300lbs motorcycle with a 120lbs rider on twisty & dusty back roads, but that same 200h/150lb moder would be so weak that it’s a legitimate safety liability in a 5,000lbs truck-wagon regularly carrying 6-8 200-300lbs passengers and 800lbs of cargo on the Penna Turnpike.

Watts aren’t totally irrelevant information, especially if you’re adding extension cabinets or swapping speakers, but outside of choosing between a 20-50w combo, a 100-200w combo, and a 400-600w combo for a particular room-band combination, they’re kinda nonsense without knowing and understanding a few other parameters.

 

[abarson]

British watts and US watts used to be an actual thing on advertised specs for stereos when I was a kid, in Australia in the 70s. The guy who owned our local guitar shop used those terms all the time when describing amps. I assume it was pretty much RMS vs Peak. Some stuff was labelled with UK and US ratings.
View attachment 5397691

That’s wild, and perplexing.
Neither of those numbers are RMS. They must be peak (British) versus peak to peak (American).

 

[Basehead]

I prefer Naomi Watts...

 

[agedhorse]

In North America, the electric grid is run at 120 Volts on 60 Hertz cycles. This describes how the electricity flows in the electrical wires. In Europe, it is mostly 230 volts on 50 hertz cycles. These values affect the wattage requirement for the head inside the combo. In the amp head, there is a transformer that adjusts the power output to the speaker in relation to the input power provided by the electric grid. These values are just there to let you know how much power you are drawing from the electrical outlet when you plug the amp and run it.

The power remains the same no matter what the voltage/frequency is. At 230V, the current is ~1/2 of what it is at 120V.

The transformer in the amp insures that the internal operating voltages are the same when operated at the rated input voltage.

 

[lark_z]

Watt were we talking about?