Dear all

I want to know the relationship between the PMPO value in Watts and the
speaker resistance value

ex. 8 ohm speaker 2No's but the system spefication is 300WPMPO.

Actually how this two has been related.

Anyone can help me to understand this?

pandi

 

PMPO stands for Peak Momentary Performance Output (sometimes Peak Music Power Output) and is a "marketing" specification. Typically, the PMPO is around 10 times the RMS wattage of the loudspeaker, but this is not always true. This is a dubious specification, and isn't mathematically exacting. It actually is impossible to achieve PMPO in the real world. See the Wikipedia Free Encyclopedia for more information: http://www.wikipedia.org/wiki/PMPO

Walt Boyes

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Regrettably, the relation between PMPO and any reality is none. What's more, is that you can be assured that you are dealing with charlatans when thay use dubious rating systems like this. Having properly disclaimed any validation of deceptive advertising, I will give the short course on the rather dubious basis for these ratings.

AC power, and audio is ac power, is rated in watts RMS, which is equivalent in heating value to DC watts. This is the honest method. A given direct coupled ampifier, (transformers are rare in non-distribution equipment) can obviously only swing it's output from ground to VCC at best. This limits a simple car amplifier to something like a 12 volt swing peak to peak. I use car audio because this is where these BS ratings are most often seen.

12V p-p = 6V pk = 6 x .707 = 4.242 V(rms)

Across 8 Ohms this gives: by Ohm's law. (E*E)/R

144/8 = 18 watts p-p 36/8 = 4.5 watts pk 17.99/8 = 2.25 watts(rms)

With a 4 Ohm speaker these double. You can see which the marketing person wants to use. You can also see why some car audio uses 2 ohm speaker loads.

With a differential, (push pull) output the swing is doubled so these increase by a factor of four.

So with the best possible 14.4 V situation, 36 watts _RMS_ is about what is possible.

"Music Power" is a somewhat arbitrary multiplier used to cover the fact that these things can't provide full power for long, but audio has a high peak to average ratio.

So to get more power high end equipment uses a DC to DC convertor to get more swing.

The easiest way to debunk this is to look at the DC in. Linear amplifiers tend to be about 60% efficient at best. A _500_ WATT PMPO amplifier with a 5 amp fuse is obviously so advanced it creates power in defiance of the law of conservation of energy. They must have a slow fusion reactor inside.

Learn Ohm's law and do the math. It's simple and very enlightening.

This has always been one of my more popular electronics lectures. Those of you who teach would do well to use it on a slow day, it saved a few for me.

Regards

cww

 

There is no relation between the resistance an the power of a speaker. Most speakers have a resistance of 8ohm and a few 4ohm. Never look at the PMPO power. Is only a gimick for selling speakers. The real power that You have to look for is the RMS, which is aprox. 100 times lower than PMPO.

 

PMPO is a bs figure developed by some manufacturers to promote their musical systems and is always associated with cheap quality systems. Selling audio systems with PMPO value is prohibited in some countries. The true power is the RMS power into a speaker is calculated as W = E x R. where R is the actual DC resistance of the speaker coil and E is the rms voltage. You multiply this number with any imaginary number from 10 to 100 and you get a PMPO (peak musical power output) value.

Average house may need a maximum of RMS 25 watts amplifier (blast). Also for double the volume of say 100w amp you will need a 400w amp or a speaker system which is 3db more efficient than the other.

To check the maximum RMS output of an amplifier you measure the supply voltage +/- DC less voltage drop of 4 volts for the output transistors and divide this value by 2 to get max rms voltage. Use the W = ExR and you can find the max RMS output power of an amp. Also note the speakers are to have higher power handling capacity than the max RMS power of the amp.

hope this helps

regards,
Sekar,
Singapore

 

Wow,

When you get in to this area, you have moved right out of serious practical engineering and in to the mystical realm of sales and marketing.

Speakers themselves have no power generation capacity - all they do is convert energy from electrical to sound. The power generation is done by an amplifier. Nonetheless most reputable speaker manufacturers used to quote an approximate value indicating the power that their speaker could handle from an amp. This was commonly expressed as an RMS value relevant to a particular impedance value. For historical reasons, 8 Ohms has been an accepted interface value between amps and speakers for many years. Of course, the physics of loudspeakers means that the actual (as opposed to 'nominal') impedance varies with the frequency of the sound. In some speakers it can dip as low as a couple of Ohms at places in the response curve. This can give some cheap amps a problem - they can't maintain enough current delivery at these low impedances and so either the speaker sounds dreadful with the amp clipping at its peak current output all the time, or the amp blows up, or the speakers get damaged, etc. etc.

Anyway, where Watts are concerned it some became obvious to some companies that consumers thought "more = better". So the marketing departments started playing tricks to make people believe they were getting more for their money.

First thing, it's easy and cheap to build an amp to deliver power to a speaker at high impedances. It's tricky and expensive to build a speaker which is impedance-stable across the entire frequency range. SO, let's quote our amps and speakers at one nominal impedance, usually high, say 8 Ohms. Whether they actually get there or not is irrelevant - it's only nominal.

Second, what gives with this RMS thing? That makes it look too low. Why can't we take the highest peak value? That'll gives us another 40% on the spec sheet which the consumer buys from.

Third, hey, why not count the difference between the highest peak and the lowest trough? That's really what we hear isn't it? And that doubles the power value again, right? And we'll give it a snazzy new name like 'Peak Music Power Output'. Yeah - way to go!

So, let's look at this power inflation again. Let's say we started with a speaker quoted at 100W RMS. Now multiply by Root 2 to get the peak power - 141W. Now double it to get the PMPO - 282W. Wow, nearly three times the power, all from the same speaker! It's magic! The customers will love this!

Of course, let's say our 8 Ohms speaker is a real speaker whose impedance dips across the frequency range. But let's say it's a well-controlled (i.e. expensive) speaker that stays above 5 Ohm the whole time. So, to get 100W in to our 8 Ohm spec we need to deliver a current of root(100/8) = 3.5A As I said, let's assume the amplifier is also spec'd a 100W in to 8 Ohms, but in practice can only support about 5% more than that should the need arise. In other words we're current limited at about 3.6A - 3.7A When the impedance goes down to 5 Ohms, we need nearly 4.5A to maintain our power output. But where's that current going to come from? Our amplifier can't supply it. So either we end up driving the output devices way beyond their limits (with likely damage to speaker and amp) or else it all goes very quiet.

PMPO is an abomination - it tells you nothing about how a real speaker operates. And yet, so many manufacturers, especially of car audio, use it these days. I've never yet come across a serious manufacturer of true hi-fi who uses this term.

There we are. Time to climb down off the soapbox now.

Ken

 

They are not related - each represents a different speaker feature: Impedance (Ohm) - most speakers are in the 4 or 8 ohm range (for household purposes) Max Power (W DIN or W PMPO) - maximum power beyond which speaker severely distorts sound, burns out, or disintegrates.

For best performance (efficiency) impedance must match that of source (e.g., amplifier, receiver, etc.) For safety, source max power should not exceed speaker max power. DIN and PMPO are different power measuring standards.

Meir

 

Dear Pandi,

There is a relation between Peek Music Power Output(PMPO) and the impedance of the speakers, but other factors are also applied to this relation. For example, the output voltage limit of the amplifier, and the maximum otput current that can be delivered to the load from the output stage. Actually, the RMS output power is:

Pomax=Vomax * Iomax = V^2/R = I^2 * R
hence, as PMPO is related to Po(RMS) so that:
PMPO = Peek-To-Peek Po * 2 (stereo);
PMPO = Po * 2 * 1.41 *2 = 5.64 * Po

In case you have 300W PMPO, you'll actually get:

300/5.64 = 53.191 Watts (RMS) per channel output!

As you can see, manufacturers tend to express the output power of their audio amplifiers in PMPO instead of RMS power, which looks a high power.

You may choose to parallel speakers (8 ohms) to get more power out of your amplifier beacause of higher output current delivered to the total speakers, ofcourse if the specifications allow you to do so!(use 4 ohms speakers).

need more info, contact [email protected]
A.M.Bagheri

 

The power output of a speaker is only related to its resistance in that P = V^2 / R

For example, if you have an amplifier that can output 70 Volts Peak to Peak and connect it to a speaker with a resistance of 4 ohms, then the power output of the amp (assuming the speaker can handle it) will be 70 ^2 / 4 = 1225 Watts Peak to Peak.

Using an 8 ohm speaker with the same amp will result in half the power output, or 612.5W.

(I have sort used Amp power output and speaker power output interchangeably, but I think you get the idea.)

 

Also known as WLS. i.e. When Lightning Strikes. If lightning were to hit the antenna, there would be one glorious moment of 300W output before the whole thing was reduced to ash.

WLS is more commonly used when referring to amplifiers, actually....

--Joe Jansen
ICQ# 39 182 450

 

I have to say I enjoyed this last post, very well expressed Ken, you had me laughing (becuase I worked in car audio for a while and heard these very discussions on how to sell systems to young, unknowing, young men who wanted the MOST POWER for their car system, they bought junk with lots of fluffly sounding terms to make them believe they were getting this massive 400 watt system for their car. Usually they wre back and I was tasked with making it work after it had be shoved into the car by a bunch of knuckle draggers who went after speed vs a quality install.) Anyways...

I think you have all prety much made the same point here - PMPO is a bunch of BS and means nothing in the real world of audio or electronics, can we now stop beating this dead horse. Oh, to the original poster, did your question get answered?

Matt

 

Except that the formula is actually W = I x E.

or, to extract I,

W = E^2 / R

Then you can take PMPO = W * 10^Q

where Q is a random number.......

--Joe Jansen
ICQ# 39 182 450

 

On July 17, 2003 12:34, Ken Muir wrote: <clip>
> PMPO is an abomination - it tells you nothing about how a real speaker
> operates. And yet, so many manufacturers, especially of car audio, use it
> these days. I've never yet come across a serious manufacturer of true hi-fi
> who uses this term.
<clip>

I bought a fairly nice stereo a couple of years ago, and quite frankly I've never heard of this term until now. Generally, the better the stereo, the less inclined they are to quote detailed specifications. It's easy to have good specs and still sound bad. Stereo specs are like the multiple knobs and dials on cheap amps - they're only present to look impressive in the show room.

The point to this reply is that this principle applies to a lot of other things besides stereos. Its more of a general problem of trying to distill a complex problem down into a simple set of numbers which can be sold to someone who either doesn't understand the subject, or who doesn't have the time (or can't be bothered) to look into the details.

This is why "profitable" companies go bankrupt (Enron) and why virtually every large computer manufacturer or software vendor can use benchmarks to "prove" that they are better than any of their competitors. Generally the more money that is at stake, the less trustworthy the benchmark numbers are.

So, when someone writes and asked "who makes the best widget (Scada, PLC, drive, etc.)", its not really possible to give a proper answer. Any rating or ranking will be subjective, and most people can come up with enough numbers to support whatever it is they decided they wanted to prove in the first place.

This doesn't mean we shouldn't compare products or ask opinions. It does mean though that simple answers to complex questions are often misleading, whether intentionally or otherwise.

--

************************
Michael Griffin
London, Ont. Canada
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( Complete thread: http://www.control.com/1026177121/index_html )

 

Hi All,

Just to set the record straight:

1. Power = E x E / R = I x I x R = E x I

2. RMS power is a bs term also but not as bad as PMPO. Volts and amps are
measured RMS, power is average not RMS.

When you square the RMS voltage the root part goes away and you're left with average power. If you're really serious you also need to say continuous average power and specify the load resistance and distortion level.

Regards

Peter Whalley

 

I agree with you Peter, but RMS is what the FTC settled on to debunk this whole mess once. I'm not sure why these deceptive terms are creeping back again, but all home stereo gear is rated under standard conditions. Perhaps car audio and musical instrument amplifiers are exempted. Or perhaps, audio ratings have been deregulated so the marketing people can lie again.

Regards

cww

 

now I have an other topic for you!!!

bits v/s bytes!!!!!!!!!!!
jejejejejejje

 

RMS is an acronym for root mean square. Its VAC RMS value is the VDC’s equivalent to do the same work. That’s why when dealing with VAC (analog) we use RMS. Hope this helps.

Mike