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Thread ID: 32335	2003-04-15 22:43:00	whats PMPO wattage in PC speakers...?	forrest44 (754)	Press F1

Post ID	Timestamp	Content	User
136086	2003-04-17 06:58:00	Quote: "Peak Music Power Output (P . M . P . O . ) is the combined output power of all channels of an amplifier measured by the highest decibel level an amplified signal reaches at any point of time . In short it is the total music power output an amplifier is rated to produce . " So to get a more realistic idea of what these power outputs mean for a two speaker system, the first thing you do is divide by two to get a rating for one speaker . Now 650 watts becomes 325 watts PMPO per speaker . Next we have to consider that this is (supposedly) a measurement of sound output level which we don't actually measure in watts at all, we measure this as sound pressure level or SPL and it is measured as an instantaneous db peak . This is not actual music, this is one transient splot in time, and unfortunately this takes no account of distortion effects . Trying to get a grasp on this to make sense of it all, we can reduce that 325 watt peak to RMS by multiplying by . 707, which gives us 230 watts . Now, cheap audio these days is a modular design sort of thing and the integrated circuits that power these speakers are often used in battery powered portable equipment as well, so most small amplifiers run a power rail of around 12 volts . To get 230 watts RMS of audio output from a 12 volt supply you need about 25+ amps of input current . (If you don't believe this, take a look at the connectors and cable sizes for a serious car audio system, and while you are about it, ask yourself why it is that car audio systems are never given PMPO ratings . ) This level of current is simply not available from the tiny power supply supplied with the speakers, not even as an instantaneous peak, so at this point we must divide that 230 watts by the designer's hat size (say 6) multiplied by his shoe size (8) and we get just a little over 5 watts . Back the volume down to a level where distortion is bearable and now we are running about 3 . 5 watts rms . This final figure is pretty much for real folks, except that I had to guess the hat and shoe sizes . However, if the designers are halfway honest :8} RMS output can be as high as 10% of PMPO but there is no mathematical correlation because once again, hat and shoe sizes are unknown . Using this formula, 650W PMPO is about 65W RMS . Divide this by two for the per channel rating and we have around 30 watts per channel . Bring the distortion down to acceptable levels and you can expect about 15-20 watts RMS into a quality set of speakers . This can be achievable in mains powered equipment, but is way beyond the capacity of portable battery powered gear unless you own a farm of battery hens that lay sealed lead-acid eggs . The answer to all of this is quite simple really: Favourite music + typical listening environment + listening test + satisfaction with volume levels and sound quality = Purchase decision . No other formula can guarantee satisfaction . Cheers Billy 8-{) Oh yes, I nearly forgot: Speaker power ratings (real ratings for real Hi Fi audio) tell nothing more than the maximum power that the voice coil can handle without melting down . This is usually expressed as "continuous RMS power input" . Peak (or transient instantaneous maximum) power input is the most the speaker can handle as a one-shot pulse without derailing the voice coil and turning the cone inside out . Audio power output in terms of sound pressure level is another matter altogether and is a function of the efficiency of the speaker . For a given power input an efficient speaker will generate high SPLs and sound a lot louder than an inefficient speaker . The following is abridged from an earlier posting: The subjective loudness of an amplifier, valve or otherwise is a function of: (a) the instantaneous (undistorted) peak power output, (b) the efficiency of the speakers, (c) the characteristics of the signal input, (d) the listening environment, and (e) the preconceived expectations of the listener . Measured power output is quite another matter . Take away (d) & (e), use a professional-grade sound pressure meter, and compare watts with watts from different amps on the same signal source and speakers, and you will find that there is no difference in sound pressure levels . Substitute inefficient speakers on the solid state amp, put high efficiency speakers on the valve amp, and the sound pressure figures will be quite different . Speakers designed for valve amplifier use are commonly of much higher efficiency because the available input power is strictly limited . Solid state amps have an abundance of raw power, consequently speaker systems have been designed to handle that power and they are often significantly less sensitive . Note that I do not hold these propositions up to be absolutes . There are efficient speakers designed for solid state amps and inefficient speakers designed for valve amps . Neither do I comment on the subjective quality of the sound from the two different amplifier types, that is for audiophiles to debate, ad nauseum . Billy 8-{)	Billy T (70)
136087	2003-04-17 08:12:00	Holy Crap . That is the biggest post I have ever seen . You must have lots of time on your hands dude .	promethius (1998)
136088	2003-04-17 08:21:00	Nah I cut and paste from previously written documentation, find my old posts and edit the lot together. Actually took no time at all. Cheers Billy 8-{)	Billy T (70)
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