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Thread ID: 58038 2005-05-19 12:30:00 Passive Crossover george12 (7) PC World Chat
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356718 2005-05-21 03:35:00 The "best" sub-woofer I have seen used, according to the "specifications" on the box, nuclear fission technology. Unfortunately it had a power plug, not a socket. ;) Graham L (2)
356719 2005-05-21 09:38:00 Actually George, the performance difference between your 1 watt mini-amp and your larger stereo system is not simply sound pressure level, dynamic range comes into the equation as well . By that I mean the ability of your amplifier to deliver an instantaneous peak without clipping, so in reality you might find it inadequate for orchestral music or anything else that has very soft movements followed by huge dynamic crescendos, but quite adequate for popular music that has a compressed dynamic range .

As regards PMPO, I wrote the following explanation just on two years ago, and rather than repeat the whole thread I have just copied out that post .


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, the quoted value is for one transient 'splot' in time, and unfortunately 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, 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)
356720 2005-05-22 00:50:00 Your house is fitted out with electrical supply outlets . These are used to carry power at the audable frequency of 50Hz . I'd like to rate them audio terms (RMS), and then rerate them in marketing terms (PMPO) .

From each socket you can pull 10amps . The suply is 230volts (or thereabouts), so for the purpose of this exersize, lets rate the outlet at 2,300watts . AC mains would survive being rated as RMS, and remain pretty close to the 2,300watt figure . Correct me if i am wrong .


PMPO is largely fictitious .

It is the instantaneous current available (even if it is destructive) x the supply voltage .

Mains is of course a AC sinewave, not DC, so 230volts varies between 0 and nearly 400volts depending what exact moment you measure it . Now lets say i short it out at a point where its 300volts, and we get a shortciruit current of say 6000amps, which is not an unreasonable figure, 300 x 6000 = 1,800,000watts . One could argue that it wont be full voltage at the time of the shorting out, but PMPO difines "rail voltage" not voltage at speakers, so here lets use the voltage at the hugest street transformers output not voltage at socket, thus ignoring losses such as cable resistance etc .

Isn't PMPO great?
There we have it . . using excepted logic i have just rerated our cute wee domestic power socket from 2 . 5KwRMS to 2MwPMPO . No improvment of quality was needed, just a little totally bent numbercrunching that people actually except in the consumer audio world! Righto, now that i've tripped your circuit breakers, blown your supply fuse, vapourised your wall socket or burnt your house down, i now wish to prove black is white so we can all get killed on the next zebra crossing . :illogical :help:

PMPO is never used in the audio markets that are aimed at those who know what they are doing . Funny that . :thumbs: 		personthingy (1670)
356721 2005-05-22 04:48:00 Your house is fitted out with electrical supply outlets . These are used to carry power at the audable frequency of 50Hz . I'd like to rate them audio terms (RMS), and then rerate them in marketing terms (PMPO) .

Mains is of course a AC sinewave, not DC, so 230volts varies between 0 and nearly 400volts depending what exact moment you measure it .

Not so PT, 230 volts rms rarely exceeds 230 volts rms . If you take the peak voltage (1 . 414 x rms) you still only get 325 volts peak .


but PMPO difines "rail voltage" not voltage at speakers, so here lets use the voltage at the hugest street transformers output not voltage at socket, thus ignoring losses such as cable resistance etc .

Your analogy falls down even further at this point, because peak music power output is effectively a measurement of sound output levels in db, and is unrelated to the electrical input to the speakers or the rail voltage to the amplifiers (hence my hat size & shoe size multiplication factor) .



PMPO is never used in the audio markets that are aimed at those who know what they are doing . Funny that . :thumbs:

That's why I made reference to car audio, always a good reality check for portable audio equipment . Personally speaking, I have never seen PMPO used in relation to a mains only audio item other than computer speakers . Make of that what you will, but it says something about the marketing industry's view of computer users .

I don't mean to pick PT, but if you want to draw a credible analogy, first you have to have an adequate understanding of the technology on both sides of that analogy, otherwise your efforts become nonsensical .

Cheers

Billy 8-{) 		Billy T (70)
356722 2005-05-22 05:24:00 It's OK, I get PMPO now.

So if I combined a 9V battery and a 33mF cap, with a short circuit current of 1000 amps, I could say: PPO of 9kW. Lmao, yeah right. I think calculation comprises very little of what manafactures use to find PMPO.

I decided to stuff the crossover and just put the subwoofer across the left speaker. Ghetto and horrible practise, but it works OK.

I drove the amp a bit hard and (literally) melted the chip (didn't know it was that hot). But I was running it at like 3x needed volume to test it, and about 3.6w rms out of it (rated at 1W). Pity I discovered this AFTER the smoke leaked out.

Thankfully I have hundreds of other amp chips lying around and just stuck another identical one in. 		george12 (7)
356723 2005-05-22 05:33:00 Not so PT, 230 volts rms rarely exceeds 230 volts rms. If you take the peak voltage (1.414 x rms) you still only get 325 volts peak.

I don't mean to pick PT, but if you want to draw a credible analogy, first you have to have an adequate understanding of the technology on both sides of that analogy, otherwise your efforts become nonsensical.
oops 325v.. OK good learnt something.
Nonsensical?? I think that was the point, not credability. My side of the analogy doesn't stand up, but neither does PMPO. Both use similar bent logic to achieve rediculously inacurate power ratings. :D 		personthingy (1670)
356724 2005-05-23 04:45:00 Billy:


Personally speaking, I have never seen PMPO used in relation to a mains only audio item other than computer speakers . Make of that what you will, but it says something about the marketing industry's view of computer users

I mentioned one I saw on Friday . . . a Sony mains powered sound (CD, tape, radio) system with about 4" speakers and big "6600W PMPO" sticker on the front . On the same auction table there was a less optimistic one with only 5KW or so . The 6 . 6KW one had "230V 250W" moulded into the case next to the power cord . Probably marketers have a low opinion of the intelligence of all consumers .

I agree 230V rms is usually 230V rms . Chris was describing instantaneous voltage (and 325 is closer to 400 than 230 . ;) ) (Some of his equipment might have seen voltages around 400V rms because he's often using 3 phase systems . :smoke:)

George12: Why not use an active filter/amplifier? Jaycars are selling off cheap amplifiers for vibrating backpacks and cushions for games . They have a 2kHz or so low pass filter feeding about a 20W amplifier . It is intended to drive a coneless speaker which moves a heavy weight instead . 		Graham L (2)
356725 2005-05-23 05:08:00 It's the "Aura Interactor" amplifier (XC1006). Would you believe $4? Graham L (2)
356726 2005-05-23 05:44:00 Chris was describing instantaneous voltage (and 325 is closer to 400 than 230. ;) ) (Some of his equipment might have seen voltages around 400V rms because he's often using 3 phase systems. :smoke:)
None of my audio gear pulls from 3 phase as such, Its allways single phase to each rack or component, however here's a link to some locally made SERIOUS AUDIO GEAR (www.oceania-audio.co.nz) that does use a 3 phase, 32amp power supply. This isn't a joke, i've seen these in use at stadiums and drooled all over them :p Way to go (I want one!) 		personthingy (1670)
356727 2005-05-23 11:56:00 None of my audio gear pulls from 3 phase as such, Its allways single phase to each rack or component

There is good reason for that PT.

Differential loads on a multiphase source can produce inter-phase voltages on neutrals and earths. I have measured voltage levels up to 20v p-p and these can result in micro-shocks on stage for performers handling metal cased mics if they make contact with any equipment connected to an item earthed via another phase line.

Significant noise can be injected into the system via this mechanism, and if waylines to a rear-of-house control room reference a different earth (yes, I know they shouldn't but I have found some that do) then electrical noise can reach unacceptable levels.

What makes the three-phase system you linked work is its modular design with the three-phase input direct to the amp, not supplying separate modules. The common low-impedance earth would work much better under that configuration.

There might still be problems if a mic audio feed had to head off via a wayline to a control room and back again to a different item of single-phase equipment, but I somehow doubt that this would be a likely configuration for these amps.

Back to the subject of mains voltages, by regulation NZ mains is 230 volts rms ±6% or a peak of 306-345 volts.

Cheers

Billy 8-{) 		Billy T (70)
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