Watts; the worst measurement unit ever for amp output?

[Wesley R]

I believe a Watt is a Watt, until marketing gets a hold of it.

 

[beans-on-toast]

When Ampeg was building their amps in New Jersey, they had a nice brown sound. Maybe it had something to do with the water. There's a long tradition of bagel making in Brooklyn. Everyone knows that when it comes to tradition, they're full of it.

 

[megafiddle]

Hm, yes and no, I agree and I disagree.

If you are really sure you have exactly 8 Ohm all along the line than you are fine.
But if you don't know the Ohm exactly you will have got a problem.

That's always true though. You'd have the same problem "measuring" wattage.
The way amps are typically measured, the voltage used would suffice as well
as the wattage. That was my only point.

Also was answering this statement which I thought was misleading:

"Originally Posted by agedhorse
1. A power amp is indeed measured in watts, since watts is a unit of power. For those of you who say that it's all about voltage, if the amp can not deliver the current required by the load at the particular voltage, it will not deliver power in proportion to (the square) of the voltage. Current is as essential as voltage..."

It implies that you could have a voltage that was sufficient to give you a calculated
value for power, but not the current required for that amount of power, simultaneously.
In other words, a voltage present on the load might not indicate power accurately, due
to insufficient current. And that's simply not true. If the voltage is there, so is the current.

.

 

[agedhorse]

Amplifiers may fail to deliver the current which will cause the voltage to fall, but this failure to deliver current may occur due to a variety of mechansms including highly non-linear ones. It's not a straight line relationship as one might casually assume.

As well, with reactive loads, voltage and current are not in phase. An amplifier can source/sink current at zero voltage due to reactive V-I components, so for non-resistive measurements the straight line resistive assumption is not correct. This is especially important where sensing current but acting on voltage, such as in protective limiting circuits.

 

[agedhorse]

Thanks for the elaboration. I have read about the situation you are describing. It's strange that they expect 2Ω amps to handle 1.25Ω without an issue. Is reaching an impedance of 2.5Ω from a nominally 4Ω speaker a misrating of the speaker or a result of the cabinet loading or both ?

I think it's a combination of misunderstanding the specs., ignorance about what the specs mean, and how the specs change in a cabinet. It's also possible that some just don't care.

 

[agedhorse]

Is there a way that you could post some oscillograms of sine wave, pure & clipped and the wave forms for notes that were plucked, slapped and picked with measured output for each? If this could be done at low output, medium and high output, it would show the changes to the waveforms and it might make the concept easier to comprehend. To remove variation in the signal, it could be recorded and sent to the amp's input.

You might search on videos of this subject on the web. The stuff I have is from very old books that are filed away somewhere that I probably can't find in a reasonable amount of time. Videos (high speed shutter) would be a better representation of what's happening anyway.

 

[nukes_da_bass]

When Ampeg was building their amps in New Jersey, they had a nice brown sound. Maybe it had something to do with the water. There's a long tradition of bagel making in Brooklyn. Everyone knows that when it comes to tradition, they're full of it.

Ya- Jersey Ampegs sounded "brown". SLM ampegs sounded "blue" (WC Handy reference...)
And of course LOUD Ampegs sound RED.

Its the watta!

 

[P Town]

Since volts, amps, (and especially reactive) ohms are difficult for some people to visualize, I propose, (jokingly) that we convert these units into equivalent physical phenomena that people can more easily conceptualize.

Since power is work divided by time, and work is force times distance, (roughly), I propose we rate the output power of an amplifier in the equivalent of moving a mass, measured in stones, (6.35029 kilograms), a distance measured in furlongs, (291.168 meters) in a period of time measured in nanofortnights, (1.2096 milliseconds).

I hope this makes it easier for the average consumer to understand amplifier output power ratings.

 

[nukes_da_bass]

Since volts, amps, (and especially reactive) ohms are difficult for some people to visualize, I propose, (jokingly) that we convert these units into equivalent physical phenomena that people can more easily conceptualize.

Since power is work divided by time, and work is force times distance, (roughly), I propose we rate the output power of an amplifier in the equivalent of moving a mass, measured in stones, (6.35029 kilograms), a distance measured in furlongs, (291.168 meters) in a period of time measured in nanofortnights, (1.2096 milliseconds).

I hope this makes it easier for the average consumer to understand amplifier output power ratings.

That was easy to visualize!
I imagined a catapult or more likely a cannon of immense power to hurl a 12 kilo ball that far in just over a second.

 

[megafiddle]

Amplifiers may fail to deliver the current which will cause the voltage to fall, but this failure to deliver current may occur due to a variety of mechansms including highly non-linear ones. It's not a straight line relationship as one might casually assume.

Yes, but does that occur during normal power output testing, at low distortion?
Wouldn't those conditions be avoided when spec'ing an amp?

As well, with reactive loads, voltage and current are not in phase. An amplifier can source/sink current at zero voltage due to reactive V-I components, so for non-resistive measurements the straight line resistive assumption is not correct. This is especially important where sensing current but acting on voltage, such as in protective limiting circuits.

The output would no longer be rated in watts, in that case, it would be VoltAmps
(apparent power). But the current ( E / Z ) would still be related to the voltage.
If actual measurements were made with a reactive load, wouldn't they likely
be made within the amp's linear region?

.

 

[B-string]

Well it wasn't set to x1000 or anything it was set to the 200 ohms max setting and measured down to a hundredth of a decimal. I also tested it with a 4 ohm resistor my uncle gave me before testing my cabs and it read 4 ohms (yes i'm sure it was a 4 ohm resistor, it was a large gray resistor with 4 ohms printed on the side of it).

I think it is time for you to invest in a better DVOM. Meters have a +/- accuracy reading (with a FRESH battery) as do resistors. Your 4 ohm "reference" resistor is most likely NOT 4 ohms exactly even if it is a 1% tolerance precision resistor. The fact your lowest scale is 200 ohms suggests very poor accuracy under 10 ohms.

 

[P Town]

That was easy to visualize!
I imagined a catapult or more likely a cannon of immense power to hurl a 12 kilo ball that far in just over a second.

Yeah, I like "Cannon Power" as a unit of amp power.

We would have to agree to abbreviate it with: "CP" so it would not be confused with candle power, abbr:"cp".

Can anyone suggest some other units we could all agree on?

How about "elephant power" for very high powered amps, and "gopher power" for low powered amps. That way manufacturers/marketers would not have extremely large, or small numbers for amps that have a large difference in power rating when they are creating their marketing material.

 

[agedhorse]

I was referring to your comment about voltage and it's implications, showing that it's not as simple as knowing one term and thus knowing the other. This is where real world significantly and meaningfully deviates from a simple number of watts on a piece of paper.

Years ago, a few pro audio amp manufacturers published V-I curves for their amps, essentially the bounds of the safe operating area. Valuable info to hard core engineers but totally useful to the other 99.9% and a turnoff to many. Thus, these specs were discontinued.

 

[B-string]

I suggest a new measurement BM. The ability to produce brown notes (Bowel Movements or bm: booty movements).

 

[P Town]

Vox has announced today that going forward their amps output power will be rated in Btu.

Quote: "The British thermal unit (BTU or Btu) is a traditional unit of energy equal to about 1055 joules. It is the amount of energy needed to cool or heat one pound of water by one degree Fahrenheit. and we here at Vox believe that this best reflects how to measure Vox amplifier output power. God save the Queen."

 

[megafiddle]

I was referring to your comment about voltage and it's implications, showing that it's not as simple as knowing one term and thus knowing the other. This is where real world significantly and meaningfully deviates from a simple number of watts on a piece of paper.

Years ago, a few pro audio amp manufacturers published V-I curves for their amps, essentially the bounds of the safe operating area. Valuable info to hard core engineers but totally useful to the other 99.9% and a turnoff to many. Thus, these specs were discontinued.

For all the examples you gave I agree with you.
Mine were very specific cases.
.

 

[Major Softie]

Since power is work divided by time, and work is force times distance, (roughly), I propose we rate the output power of an amplifier in the equivalent of moving a mass, measured in stones, (6.35029 kilograms), a distance measured in furlongs, (291.168 meters) in a period of time measured in nanofortnights, (1.2096 milliseconds).

This is perfect. Who doesn't want their amp to be the one with the biggest Stones?

 

[agedhorse]

Vox has announced today that going forward their amps output power will be rated in Btu.

Quote: "The British thermal unit (BTU or Btu) is a traditional unit of energy equal to about 1055 joules. It is the amount of energy needed to cool or heat one pound of water by one degree Fahrenheit. and we here at Vox believe that this best reflects how to measure Vox amplifier output power. God save the Queen."

BTU is energy, not power. In order to get power, you need to consider the rate at which energy is converted... such as BTU/hr.

 

[B-string]

BTU would also require listing a reference to temperature. BTU is not an absolute either.

 

[P Town]

Come on guys, I'm just trying to have a little fun with the Btu reference. (just like some amplifier manufacturers do when they publish amp specifications).

Please don't try to cloud the issue with facts.

(Yes I neglected to include time). Please let me say that Vox does take time into account when calculating power ratings.

The formula looks like this: Btu/Jiffy.