Peak Momentary Power Output PMPO
Printed From: Graham Slee Hifi System Components
Category: And the rest
Forum Name: Amplification
Forum Description: Share your interests or views on amplifiers, preamps, etc
URL: https://www.hifisystemcomponents.com/forum/forum_posts.asp?TID=2991
Printed Date: 16 Apr 2024 at 2:58pm
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Topic: Peak Momentary Power Output PMPO
Posted By: Graham Slee
Subject: Peak Momentary Power Output PMPO
Date Posted: 31 Jul 2016 at 1:57am
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Seen all those amps and systems that supposedly do thousands of watts? And some are from previously reputable brands. Some may think they're still reputable but how can they be when they start misleading people? OK, most of these misled people are the youth generation right now, and I guess the reputable brands have to compete but in doing so they are being very economical with the truth. PMPO stands for peak momentary power output, and at one time the brands would qualify their power output claims by saying PMPO - but now it seems they've stopped qualifying it at all! My attention was recently drawn to a couple of amped plastic desktop speakers claiming 3000 watts with no qualification and an asking price of over £2000. This being sold on Amazon so it must be OK? How loud is 3000 watts going to be? Very loud! A band with a 300 watt PA can sound very loud in a concert room (around 3000 sq ft) so 3000 watts is going to sound twice as loud and probably be just sufficient for an arena? And all that power is coming from a couple of desktop plastic bluetooth speakers? I don't think so! It would have been more honest to claim 3000 watts PMPO. At least that would say what its peak momentary power output is. But what is peak momentary power output? It is the absolute maximum of power output that can be produced in a very short interval of time - possibly a microsecond - nobody ever says. So let's see how much PMPO my Proprius amps can do... If I short out the speaker terminals whilst running the amp flat out into an 8 Ohm load at full output swing - a continuous sine wave - the power supply shuts down, but it cannot do that instantly - it is probably a microsecond or so. But into a short circuit there cannot be any sound output. We will have to make it less than a short circuit. Let's call it 0.1 ohms. You see, PMPO is never quoted into any particular load. OK, if it does 25 watts into 8 ohms, the square of the voltage swing is 200 (14.14V rms), so let's now divide that by 0.1. I get 2000 watts PMPO. But I could make the load 0.05 ohms which gives me 4000 watts PMPO, so if I was up against a brand advertising a 25 rms watt amp at 2000 watts PMPO, I could get away with saying 4000 watts PMPO, so the youths would buy mine instead! However, because I would never dream of advertising a 25 rms watt amp as being anything other than that, I will never sell one to a typical youth. ------------- That none should be able to buy or sell without a smartphone and the knowledge in how to use apps |
Replies:
Posted By: BAK
Date Posted: 31 Jul 2016 at 4:04am
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Graham, Very well stated. PMPO is for the uneducated. RMS power (root-mean-square) is real power and is qualified by giving a tested load impedance... ie, 25 watts RMS into 8 ohm load. ------------- Bruce AT-14SA, Pickering XV-15, Hana EL, Technics SL-1600MK2, Lautus, Majestic DAC, Technics SH-8055 spectrum analyzer, Eminence Beta8A custom cabs; Proprius & Reflex M or C, Enjoy Life your way! |
Posted By: BackinBlack
Date Posted: 31 Jul 2016 at 8:25am
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IIRC, in the 60s and early70s PMPO was a commonly quoted spec in budget "HiFi" and Music centres, predominantly those coming from Japan along with all the meaningless acronyms describing their supposed features. Some things don't change. ------------- Just listen, if it sounds good to you, enjoy it. |
Posted By: JamesD
Date Posted: 31 Jul 2016 at 1:07pm
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From college many years ago I thought maximum power transfer was when the load resistance equaled the source resistance so maybe there's room to push the PMPO figure even higher... ------------- Aren't ears brilliant |
Posted By: BAK
Date Posted: 31 Jul 2016 at 1:13pm
Yes, Ian, that is the prevailing advertising method. The manufacturer will state the PMPO as Peak Music Power Output to make the uneducated think their amplifier produces more power than it actually can. In 1973 I worked in a C***H***T stereo factory. I was testing & repairing complete stereo chassis sent from Japan and China that were put into cabinets here. Their stereo amplifiers were advertised with a rating of 80 watts per channel Peak Music Power Output... the power amplifier ICs they used actually put out: 2.5 watts RMS into 8 ohms with 1% THD, 5 watts RMS with 10% THD. People were buying this stuff under 5 different brand names! ------------- Bruce AT-14SA, Pickering XV-15, Hana EL, Technics SL-1600MK2, Lautus, Majestic DAC, Technics SH-8055 spectrum analyzer, Eminence Beta8A custom cabs; Proprius & Reflex M or C, Enjoy Life your way! |
BackinBlack wrote: