What is a good way to measure peak watts I'm using during music? - diyAudio
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Old 13th September 2012, 06:49 PM   #1
cotdt is offline cotdt  United States
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Default What is a good way to measure peak watts I'm using during music?

My normal listening level is 80 dB at 1 meter, so on average I'm using less than 1W of power, but I want to figure out how much power the speakers are drawing during the fast transients during real music. What is the best way?
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Old 13th September 2012, 07:07 PM   #2
Lavcat is offline Lavcat  United States
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A Test. How much Voltage (power) do your speakers need?
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Old 13th September 2012, 07:26 PM   #3
sreten is offline sreten  United Kingdom
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Hi,

You can measure, but you can't figure it out. Depends on peak to mean
ratio, aka as crest factor, aka the dynamic range of the recordings.

Varies from about 6dB (x4) to 24dB (x256), usually 10dB to 20dB.

rgds, sreten.
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Old 13th September 2012, 07:52 PM   #4
cotdt is offline cotdt  United States
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If I play the 220Hz test tone at 98dB, it is already painfully loud. I sit only 1m away from the speaker. That's about 8W of power. So is that as much as I'll ever need?
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Old 13th September 2012, 07:57 PM   #5
sreten is offline sreten  United Kingdom
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Hi,

No. You have to understand crest factor and dynamic range of recordings.
You also have to understand loudness curves, bass needs more power.

rgds, sreten.
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Old 13th September 2012, 08:21 PM   #6
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some DVM's have a min/max setting such as Fluke 87, I am not sure how fast they are, but I have used them to measure transients when I used to work and customers were always suprised how high line spikes would go or how low the line would drop. If they didn't believe the meter then I would ask for the fancy one with the printout and time display. ie one spike or dropout @ 8:13AM = system crash. A scope is good too.
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Old 13th September 2012, 08:54 PM   #7
cotdt is offline cotdt  United States
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I don't think my multimeter can measure transients fast enough, but I'll look into it.

I've just analyzed the digital waveforms of my MP3's and the peaks seem to be +12dB over the average. I listen at 80dB average so does that mean I only need 92dB?
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Old 13th September 2012, 08:56 PM   #8
cotdt is offline cotdt  United States
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If true I'm surprised by how little power I need. Hehe, even my headphone amp can deliver 60W and weighs 80 pounds.
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Old 13th September 2012, 09:05 PM   #9
sreten is offline sreten  United Kingdom
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Hi,

No. Bass heavy material needs far more power than a string quartet.

rgds, sreten.

If you have a 60W 80 pound headphone amplifier I'm
clearly wasting my time trying to explain anything.
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Last edited by sreten; 13th September 2012 at 09:08 PM.
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Old 13th September 2012, 09:06 PM   #10
Struth is offline Struth  Canada
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Hi Guys

I scoped my amp output the other day while blasting music. I expected to see a 1W average level for the loudest SPL I could stand. It was about as expected. My DVM is not fast enough to capture peaks.

Most modern music is highly compressed to make the most use out of the limited output of the medium. 2V is a big signal but you only get distortion past 16-bits all as ones. The LED meters on the CD players just go solid to the max for many discs. Older discs and other music styles will have bouncing LEDs and a bouncy signal on the scope. With pop the scope just displays a constant amplitude envelope of about 5Vpp. The dynamic music displays a lower average level but has peaks that are mostly twice the average.

For dynamic headroom purposes, you could allow a 4x voltage space for transients. This suggests that if you wanted to build a low-watt amp, with very good performance at 1W and below - since you can't listen to it that loud for very long before you won't be hearing anything! - then 4x V produces 16x P, so 16W for assurance against clipping. You could build this easily with +/- 24V rails and set it up to be class-A to eliminate XO distortion. You could take it a step further and make it class-G with lower rails at +/- 12V. Transition would occur at about 9Wrms, so not very often.

The nice thing about modern class-G amps is that the rail transition does not invoke distortion when the drivers are supported by the high rails all the time and the low-V diodes are shottky. Operating class-A maintains very low THD and the low-V helps keep dissipation in check.

Have fun
Kevin O'Connor
londonpower.com
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