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audio watts vs. electrical watts

Discussions of conventional and alternative energy production technologies.

Re: OK

Unread postby Kingcoal » Thu 30 Dec 2004, 21:01:01

[quote="MissingLink"]The formulas were not what I was questioning. I failed to notice your link to the meter you were referring to. Sorry for that. Talk about over kill! God!

I generally use my companies RMS amp probe on everything because my old analogue doesn’t always give an accurate reading on every piece of equipment such as an AC drive. Our Fluke RMS amp probe “basicallyâ€
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Audio Power

Unread postby ThreeOfFive » Thu 13 Jan 2005, 08:22:31

Hi guys.

I've read several comments here, and I can say that they are generally true.

1 - Power consumption:

All sound systems have a stamp telling the rated power required to work. This value is only a maximum consumption value. This means that the equipment is not always spending all that energy.

2 - Speakers power

This is the most tricky aspect of all sound systems. Great numbers sell a lot , and that's why manufacturers are displaying PMPO values in their systems. Due to the special behavior of sound reproduction, and if we don't want to make a detailed analysis of peak power, PMPO power, etc, we can stick to the RMS power, wich is the average mean power delivered to the speakers. This power is the same power you drain from your power supply plus circuit losses.

So remember, RMS power is the most important. But this is the power delivered to the speaker, only 5% of this power is converted into sond power ( sound pressure ), The remaining is converted into heat, and that's why high power speakers get warm.

Anyway, dont' forget that power isn't the only thing that matters.

Don't forget bandwith, THD - Total Harmonic Distortion and Dynamic Range. Very few brands give this figures, but when they do, is a sign to recognise a good product.
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Ya`

Unread postby Cool Hand Linc » Fri 14 Jan 2005, 01:34:19

Ya, This is why we actually want to look at the power into a stereo rather than looking at speaker power.

If a person has a cheaper system that has a cassette, cd player, turn table, 8 track tape :-D combo. It will consume more power than a unit of similiar rated power output that is just a stereo running fm. Each component consuming its own little bit of juice.

Is anybody hear an expert in the field of electronic sound reproduction? I remember learning some about THD when I was a kid. I always looked at it on every system I have ever seen sense. Its kind of interesting to look at the brands and noise level ratings. I remember going into Ultimate Electronics one time and Harman Kardons were the highest level of distorsion I could find at 1%. (This was several years ago)

So if we have an expert or just others who like quality sound. I have a question about THD.

total HARMONIC distortion, what about the distortion that isn't harmonic.
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Re: OK

Unread postby small_steps » Tue 18 Jan 2005, 16:32:17

[quote="MissingLink"]I generally use my companies RMS amp probe on everything because my old analogue doesn’t always give an accurate reading on every piece of equipment such as an AC drive. Our Fluke RMS amp probe “basicallyâ€
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Unread postby Guest » Tue 18 Jan 2005, 18:12:52

I understand it as follows:

If an amplifier distorts a waveform in a consistent fashion - then each similar part of the waveform will be distorted in the same way.

A distortion which occurs synchronously with a signal will always generate harmonics of that signal. (The distortion will contain frequencies that are integer multiples of the frequency of the main signal - the fundamental). So any systematic distortion will always be 'harmonic' distortion.

If the distortion is not consistent, then it is unpredictable and non-repetitive and therefore 'noise'.

Some amplifiers therefore list a THD+N specifiation which includes noise.
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Unread postby ThreeOfFive » Wed 19 Jan 2005, 13:54:16

You're right. Harmonic distortion comes whenever the amplifier response becames non linear. All audio amplifiers became non-linear in the vicinity of their maximum output power and that's why the maximum THD value is achieved with maximum power. The transfer function of the amplifier originates several sine waves with frequency multiple and submultiple of the fundamentals signals, ( this can be calculated with fourier transforms ).

Another kind of distortion that can happen with max power, it's called "clipping", and it's just the final stage output amplifier saturation. Sine waves are cutted in the upper edges and this gives rise to a very strong and unpleasant distortion.

As someone said already, signals not related with the input signal are just rated as noise.

Now that we have clarified the electrical aspect of a sound system, we deliver an undistorted, noiseless,a powerfull electrical signal to a loudspeaker, and now what ?

The loudspeaker convert this signal in a sound pressure variation with a certain efficiency, typically 2 to 5 %!
The box where the speaker is installed is as much important as the speaker istself. A bass reflex system is only a closed box with an open hole connected to an internal short tube, and is very efficient. This box has a self ressonant frequency and this gives rise to a bass peak response related to the box phisical dimensions. This peak can be smoothed with some sound absorption material inside the box.

Hi Fi systems, on the other hand, use closed boxes with internal absorption material, to prevent interference between the speaker front and back wave. The sound reproduction in this case is better but the efficiency is smaller.
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