Watts, RMS, PMPO etc.

|tera|

|tera|

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Concerning speakers. Can anyone explain a few of these terminologies to me in easy to understand terms?

What should I be looking out for? Eg. a higher value RMS and lower Watt?

Thanks a lot ;)

tera
 
Theres a way of working it out, I cant remember it though.
PMPO mean Peak Music Power Output.
RMS is similar, I think 200W RMS is around 3400W PMPO (could be wrong).

I think they mean the same thing, depending what you looking for, HiFi, Home Theatres, car sound.
 
First, what the abbreviations mean:
PMPO: Peak Music Power Output (Or similar abbreviations). This is basically a useless measure for reasons that will be clear soon.
RMS: Root Mean Square. The root of the mean of the square. Taking some sinusoidal signal, you take the square root of the integral over one period of the signal SQUARED divided by one period. It refers to the measurement method used for determining voltage or current. This is NOT to be used for power.
Power = P = iv = i^2R = (V^2)/R

When you encounter products that quote power specifications, you will generally (in this country) see them quote both Watts PMPO and Watts RMS. PMPO is meaningless, as detailed HERE. What matters is the AVERAGE POWER rating, as determined by measuring RMS VOLTAGE, which is often (mistakenly) abbreviated "RMS POWER". The mistaken term doesn't mean that the term is meaningless. On the contrary, it says how much power the speakers (or amplifier or ANY equipment) will be able to sustain, whereas PMPO usually refers to what the equipment will be able to produce over a differential time.

There is NO correlation between PMPO (as used today) and RMS. This is because
1) PMPO measures a power (albeit a fictional rating) while RMS does NOT refer to power
2) PMPO today is not as it once was (a valid but still not meaningful quantity)

Concerning speakers, another important quantity to note is the impedance, which is where this discussion really comes into its own.

Some background:
Ohm's Law is usually quoted as V = iR meaning Voltage through some component is equal to the resistance it offers multiplied with the current through it. This can be adapted to other passive components that offer impedance. Resistors offer a means to impede the REAL part of the signal whereas capacitors and inductors offer a means to impede the IMAGINARY part of the signal. This involves complex numbers (not complex as in the adjective, but complex as in http://en.wikipedia.org/wiki/Complex_number ). Impedance takes all of this into account (both real and imaginary parts).

When deciding what impedance is best, one has to observe that the most efficient way to deliver power to some system is to impedance-match the source (amplifier) to the load (speaker): http://en.wikipedia.org/wiki/Impedance_mismatch

Another parameter of interest is Sensitivity: http://en.wikipedia.org/wiki/Sensitivity_(electronics)
This should be clear from the (short) article.

Perhaps one of the most important things to remember about the power ratings: I can easily pump 5kW Average power into a set of R50-00 speakers. They'll probably blow. Or if I'm lucky, they'll stay intact and simply distort the sound so badly that you won't be able to distinguish it from what it SHOULD sound like. For this reason, the measurement of the power involves driving the speaker at a specified power level and noting the level of distortion: http://en.wikipedia.org/wiki/Distortion#Audio_distortion
Most ratings will be quoted @ percentages of distortion. Less distortion is obviously better. So at the same levels of distortion (should realistically be measured at less than 1% distortion. Any more than this sound KARK), look at power ratings.

For loudness, you have to remember that it varies logarithmically. So 200W will not sound twice as loud as 100W.
According to http://en.wikipedia.org/wiki/Audio_power 1dB (a logarithmic measure) which corresponds to a 25.9% increase in audio power is the smallest perceivable increase in loudness by the average human ear.

Sorry for the patchy nature of this article. Should have written all at once instead of in pieces ;)

If there's anything else, just ask
 
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Im also not 100% sure. But in general terms Ive learned to trust RMS or nominal power.
"max watt" is a load of BS as a speaker can peak at xxxxxW for a split second, not even long enough for you to hear it. On the other hand If A speaker deliveres 200W RMS/nominal power you know that this power is constant.

You will also notice that alot of low budget speakers/amps tend to rather focus on "max power" ect. Some dont even mention RMS.

My Logitech Z5500 only has 500W RMS. That doesnt sound like much if you think that is includes 5 speakers, AND a sub. Trust me, 500W RMS is alot.
 
Plasticmonkey said:
Im also not 100% sure. But in general terms Ive learned to trust RMS or nominal power.
"max watt" is a load of BS as a speaker can peak at xxxxxW for a split second, not even long enough for you to hear it. On the other hand If A speaker deliveres 200W RMS/nominal power you know that this power is constant.

You will also notice that alot of low budget speakers/amps tend to rather focus on "max power" ect. Some dont even mention RMS.

My Logitech Z5500 only has 500W RMS. That doesnt sound like much if you think that is includes 5 speakers, AND a sub. Trust me, 500W RMS is alot.
Click to expand...

My hifi says 3400W PMPO, 200W RMS x 2. So ya 500w RMS is loud!
 
sn3rd said:
First, what the abbreviations mean:
PMPO: Peak Music Power Output (Or similar abbreviations). This is basically a useless measure for reasons that will be clear soon.
RMS: Root Mean Square. The root of the mean of the square. Taking some sinusoidal signal, you take the square root of the integral over one period of the signal SQUARED divided by one period. It refers to the measurement method used for determining voltage or current. This is NOT to be used for power.
Power = P = iv = i^2R = (V^2)/R

When you encounter products that quote power specifications, you will generally (in this country) see them quote both Watts PMPO and Watts RMS. PMPO is meaningless, as detailed HERE. What matters is the AVERAGE POWER rating, as determined by measuring RMS VOLTAGE, which is often (mistakenly) abbreviated "RMS POWER". The mistaken term doesn't mean that the term is meaningless. On the contrary, it says how much power the speakers (or amplifier or ANY equipment) will be able to sustain, whereas PMPO usually refers to what the equipment will be able to produce over a differential time.

There is NO correlation between PMPO (as used today) and RMS. This is because
1) PMPO measures a power (albeit a fictional rating) while RMS does NOT refer to power
2) PMPO today is not as it once was (a valid but still not meaningful quantity)

Concerning speakers, another important quantity to note is the impedance, which is where this discussion really comes into its own.

Some background:
Ohm's Law is usually quoted as V = iR meaning Voltage through some component is equal to the resistance it offers multiplied with the current through it. This can be adapted to other passive components that offer impedance. Resistors offer a means to impede the REAL part of the signal whereas capacitors and inductors offer a means to impede the IMAGINARY part of the signal. This involves complex numbers (not complex as in the adjective, but complex as in http://en.wikipedia.org/wiki/Complex_number ). Impedance takes all of this into account (both real and imaginary parts).

When deciding what impedance is best, one has to observe that the most efficient way to deliver power to some system is to impedance-match the source (amplifier) to the load (speaker): http://en.wikipedia.org/wiki/Impedance_mismatch
Click to expand...


Thank you for taking the time to post this. I have to be honest though, it's just way over my head.

Is there maybe an easier way to understand it? Like, let's say 10watt and 12 RMS is a good speaker?
 
teraside said:
Thank you for taking the time to post this. I have to be honest though, it's just way over my head.

Is there maybe an easier way to understand it? Like, let's say 10watt and 12 RMS is a good speaker?
Click to expand...

Very easy method:
1) Ignore PMPO completely
2) Have a look at "RMS Power" of various speakers
3) Recognise that these are obviously taken at quite high settings of the volume knob, and at those settings, a certain amount of distortion is likely (unless you're looking at Harmon and Kardon or something)
4) Decide if you will be playing at these high volumes often enough to require higher power output
5) If you will be playing at high power output all the time, recognise that 25.9% increase in power corresponds to only 1dB, which is (according to Wikipedia) the accepted SMALLEST increase in loudness perceivable by the average human ear
6) For sound quality, you need to decide what is important to you (and therefore, what is the application?). If you are looking at home theatre speakers, you probably want surround sound and quite a lot of bass. If you are looking at some desktop PC speakers, what will they be used for? If music, get something that has mids (medium-sized speakers). If games, decide what you like from the game (and what kind of game I guess). If you like explosions, get something with both mids and a sub. Perhaps tweaters (smaller speakers) for voice.
7) After contemplating all this, decide what fits your budget

To put things into perspective:
My Panasonic Hifi on max power is fairly loud. Each speaker unit has one mid (approximately 4") and one tweater (approximately 1.5"). Each speaker unit is rated with an impedance of 6ohms. The hifi's amplifier is rated at 100W ("RMS" power) @ 0% distortion. When I crank up the volume all the way, there is a little distortion. Backing off a bit until I can't notice distortion, the people who live below me complain. I seldom put the volume above half-way, and I'm quite happy with the volume level (no problems hearing it clearly).
 
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Yep, I know what I need the speakers for at the moment. But I'd like to make the right choice.

So I just basically choose a speaker set with good reputation and high RMS value? That's it in a nutshell? ;)

thanks.
 
RMS will always be lower than PMPO on the same speaker.
500W RMS True value
3500W PMPO Marketing talk
 
teraside said:
Yep, I know what I need the speakers for at the moment. But I'd like to make the right choice.

So I just basically choose a speaker set with good reputation and high RMS value? That's it in a nutshell? ;)

thanks.
Click to expand...

Kind of. For most cases that aren't very specialised, you won't go wrong with one set of good speakers or another. That is, if the speakers are to be used for some music, some movies, some games, etc, the average Logitech or Cambridge speakers will be enough.

With regards to high RMS values, remember that the high RMS values can be quoted at a certain level of distortion, so be careful there. But yes, in general, higher RMS = better
 
I think they generally like to show PMPO value as a marketing trick...3000w PMPO sounds a heck load louder than 500w RMS cause most people would see 3000>500... and I think sn3rd explained RMS well,sigh just starting learning it at varsity so I'm over it now :p
 
yeah, PMPO is generally just a marketing gimmick. for a real idea on performance you should look at RMS, which is basically the maximum constant power it can produce.
another thing you can check for is THD (total harmonic distortion)
the lower the THD, the better the quality of sound you'll get... but you'll only really hear the difference on higher end equipment or if you're an audiophile of note
 
S1ght said:
I think they generally like to show PMPO value as a marketing trick...3000w PMPO sounds a heck load louder than 500w RMS cause most people would see 3000>500... and I think sn3rd explained RMS well,sigh just starting learning it at varsity so I'm over it now :p
Click to expand...

Exacly!

I just laught when I see people buying a hi-fi at shoprite that lookis like a las vegas casino.... 10000000PMPO!!!! wow, what a piece of crap!:sick:

Stick with B&W and ull be fine:p
 
Seems this thread could help a few people in future then ;) happy about that.

Speakers are expensive though, I'll have to see when I truly can afford it :p
 
teraside said:
Seems this thread could help a few people in future then ;) happy about that.

Speakers are expensive though, I'll have to see when I truly can afford it :p
Click to expand...

It'd be great if ALL threads could help people in the future :p
 
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