Trace Wattage, I Know, Old Topic, But...

[prowla]

3 hours ago, Stub Mandrel said:

Why RMS?

 

As most AC signals are symmetrical around zero, their mean value is zero.

 

As 'a minus times a minus is a plus' the process of squaring a negative value then finding its root makes it positive.

 

So RMS effectively means 'flipping' the part of a waveform below the zero live and then averaging all the values.

 

If this is reminiscent of calculus, that is because it is. Theoretical RMS values are easily calculated. 

 

True RMS values are more tricky to measure. Most meters assume a sine wave. True rms meters are more complex and costly, although for audio signals a good moving iron meter will do the job.

 

 

Aye - it's a means of saying there is push energy and pull energy going to a speaker; whilst it naturally goes back to its zero position, we want to measure the energy expended on its travels.

[Count Bassie]

4 hours ago, Sparky Mark said:

That I get! 😂

I'll give that info a little time tonight, thanks you guys, I appreciate the interest and help! 

[agedhorse]

On 15/06/2025 at 21:06, Count Bassie said:

The guy who's been repairing my amps the last 6 or so years there me that measuring at 1KHz takes less power than lower frequencies, so the rated power brings a higher number. This is incorrect? 

 

Yes, for the most part that is incorrect. There may be a trivial difference at very low frequencies due to filter cap time recharge constants, but it will be less than 1/2dB at 30Hz on a properly designed amp and often much better.

 

Note that meters can be inaccurate at very low frequencies, which why special meters are used for broad band audio measurements.

[agedhorse]

17 hours ago, Downunderwonder said:

If you search for a picture of RMS of a sine wave it will show the RMS point at .707 of the clean peak.

 

The RMS of a pure square wave is the full peak value.

 

Power is Current x Voltage.

Current is Voltage ÷ Resistance.

 

Substituting for Current we see Power is Voltage squared ÷ Resistance.

 

Noting that 0.707 is 1÷ square root of 2,

The power of the square wave is double the RMS power of the clean sine.

 

Trace rating an amp as 250W/500W Peak, maybe a little off the wall as nobody would pay to listen to one putting out the full 500W for more than a few microseconds, could handle mighty transient peaks.

Almost. The power of a square wave is equal to the RMS power of a sine wave and 1/2 the power (.707 x the voltage) of the peak power of a sine wave.  

 

Peak power is defined for a sine wave at 2x the RMS power, and when Trace advertised 500 watts peak power, that's exactly the same as 250 watts RMS. It has nothing to do with burst power (which has an entirely different definition and applied primarily to broad band signals).

 

Power RMS is equivalent to the area under the voltage curve x the current curve, and when integrated over time becomes energy. 

[Downunderwonder]

4 minutes ago, agedhorse said:

The power of a square wave is equal to the RMS power of a sine wave and 1/2 the power (.707 x the voltage) of the peak power of a sine wave.  

Isn't that what I said??

 

Sine peak volts X to -X

Square X/X

 

Power twice as much for the square.

 

Sometimes I feel I am losing my mind.

[agedhorse]

3 hours ago, Downunderwonder said:

Isn't that what I said??

 

Sine peak volts X to -X

Square X/X

 

Power twice as much for the square.

 

Sometimes I feel I am losing my mind.

Not quite, unless I read it wrong...