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Old 15th September 2012, 09:06 AM   #21
AndrewT is offline AndrewT  Scotland
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Most of us monitor voltage.
That is NOT the same as monitoring power!

To monitor power one must instananeously read both current and voltage at the load and then multiply the two readings/measurements, the result is instantaneous power delivered to the load.

There are IC chips that do that. But, in general they do not have a big range, unless they are very complicated and thus expensive.

Even our household electricity meters only monitor current and make an assumption on the supply voltage, to allow a read out in Power units.

As far as I have read in the above replies all have fallen into the trap that an assumption on resistance has been made without realising it. They all take the drive voltage and convert that to power using the standard formula: Power = Volts squared divided by load resistance. This ignores the variation in load resistance. That inadvertent assumption leads to gross errors in power readings.
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Last edited by AndrewT; 15th September 2012 at 09:12 AM.
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Old 15th September 2012, 11:15 AM   #22
forr is offline forr  France
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Hi,

Quote:
Most of us monitor voltage.
That is NOT the same as monitoring power!

To monitor power one must instananeously read both current and voltage at the load and then multiply the two readings/measurements, the result is instantaneous power delivered to the load.
Mutliply current and voltage and cosine of phase between both.
This is why, at low frequencies, there is not much power dissipated in the voice coils.

Quote:
There are IC chips that do that. But, in general they do not have a big range, unless they are very complicated and thus expensive.
I am interested. Can you give some references ?
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Old 15th September 2012, 02:57 PM   #23
DUG is offline DUG  Canada
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AD633JRZ

In Digi-Key search for multiplier ic

Linear - Analog Multipliers, Dividers

then select 4-quadrant

learn well
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Old 15th September 2012, 03:19 PM   #24
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Default The way is to plug a scope, to read the peak to peak

and calculate.

Carlos
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Old 15th September 2012, 03:29 PM   #25
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by forr View Post
Mutliply current and voltage and cosine of phase between both.
you don't need cosine.
The instantaneous power is simply the current times the voltage at that instant.
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Old 15th September 2012, 03:40 PM   #26
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by destroyer X View Post
The way is to plug a scope, to read the peak to peak
and calculate.
No, that does not tell you or any one else the current.
P=IV

You need both to calculate power.
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Old 15th September 2012, 03:45 PM   #27
Pano is offline Pano  United States
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Yeah, with a digital source, it isn't that hard. Actually measuring the current and voltage, or finding a fast watt-meter is best, but you can get a very good idea just from measuring a test tone.

As for dynamics, most CDs don't have as much as you might think.* A typical ratio of average to peak is 18dB. Some better CDs will have 22dB or more range . If the recorded passage is lower than that, it probably is not meant to be loud. Think about it. Quiet passages are mot meant to be at 80dB SPL.

*I've analyzed about 16000 tracks. 16dB from average to peak is typical of good pop, jazz, rock. Classical and well mastered stuff can be at about 22dB peak/average. Recent "squashed" mastering is about 10dB below peak with a good bit of clipping.
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Old 15th September 2012, 06:42 PM   #28
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Default All you need is a scope, the music playing and a scope

of course the knowledge how to measure is needed too.... you need speaker too

It is simple and there's no tips and tricks for that.

regards,

Carlos
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Old 15th September 2012, 07:42 PM   #29
forr is offline forr  France
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Quote:
Originally Posted by AndrewT View Post
you don't need cosine.
The instantaneous power is simply the current times the voltage at that instant.
Instantaneous voltages and instantaneous currents are significant values.
Instantaneous powers are not. Electrical power needs some amount of time to show its effets.
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Old 15th September 2012, 07:47 PM   #30
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Quote:
Originally Posted by Pano View Post
As for dynamics, most CDs don't have as much as you might think.* A typical ratio of average to peak is 18dB. Some better CDs will have 22dB or more range . If the recorded passage is lower than that, it probably is not meant to be loud. Think about it. Quiet passages are mot meant to be at 80dB SPL.

*I've analyzed about 16000 tracks. 16dB from average to peak is typical of good pop, jazz, rock. Classical and well mastered stuff can be at about 22dB peak/average. Recent "squashed" mastering is about 10dB below peak with a good bit of clipping.
I collect this kind of data. Yours agree with others I already have.
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