Post by Dori-Kin on Oct 1, 2006 13:04:49 GMT 7
There are different methods for measuring the power ratings for amplifiers and speakers. And different measuring methods give different values so it is vital to understand the difference between those different power ratings to be able to make at least some comparison between different power ratings.
[glow=red,2,300]RMS power[/glow]
To make it short, an RMS power value is directly related to perceivable energy (acoustical, heat, light - or what else applies).
"RMS" is really a rather meaningless figure, when measuring power. R.M.S. is useful for measuring the "power-producing equivalent" voltage. Thus 10 Volts RMS will produce the same power into given impedance that 10 Volts DC would produce (onto a resistance) any waveform of 10 V R.M.S. will produce the same power into that impedance. This is because it's the root of the mean of all the average squared voltages to which Norbert Hahn referred in the prior post. It is if little meaning to compute the mean of squares of all the power values in a wave.
RMS, when applied to power measurements, has come to mean "sine-wave power." A 100 Watt "RMS" amplifier can produce a 100 Watt sine wave into its load. With music, the total actual power would be less. With a square-wave, it would be more.
[glow=red,2,300]DIN power[/glow]
The DIN 45000 defines different methods to measure power, depending on the device under test. Well, this is what I remember from reading the DIN some 25 years ago.
For home appliances there are three different numbers for power: Continuous power, Peak power and power bandwidth; the latter does not apply for speakers.
Power measurement of an amp requires that Ohmic resistances of nominal value both at input and output properly terminate the amp. The continuous power is measured when the amp is supplied by its normal power supply. It must then be able to deliver the rated power at 1 kHz for at least 10 minutes while the maximum THD does not exceed 1 %. To measure the peak power the normal power supply is replaced by a regulated power supply and the time for delivering the power is reduced. Thus, higher values for peak power are obtained. You may skip measuring the peak power by simply multiplying the continuous power by 1.1.
The power bandwidth is defined as the bw for which 1/2 of the rated continuous power can be obtained.
Actually, DIN 45 500, CNF 97-330, EIA RS-426 and the encompassing IEC 268-5 specify not pink noise, but pink noise filtered by a filter that provides significant attenuation in the low and high frequency region of the spectrum to more closely model the long-term spectral distribution of music. Pink noise itself does not accomplish this
[glow=red,2,300]PMPO (Peak Music Power)[/glow]So called "music power". This power figure tells the power which the amplifier can maximally supply in some conditions. PMPO rating gives the highest measuring value, but this info is quite USELESS, because there is no exact standard how PMPO power should be measured.
The reason for this power rating was to show the max capability of equipment for recreating strong musical transients like kettledrums and the like. Similar thing (music power rating) was used in the sixties, and I think it assumed a square wave that swung the whole supply range of the output stage. This alone gives them a factor of two over a clean sine wave note. But the ugliest thing they did was to assume that the high power lasted such a short period of time that the power supply caps would hold the voltages steady without any drooping. In the real world, an underpowered PS could be hidden by this ruse and the PMPO might be a factor of 10 or higher than what could be sustained on a nice instrumental performance.
Forget what adverts say about peak power or other "power terms" because they are not standardized and anyway comparable between equipments. Just look for "RMS continuous Power" or other reliable power rating (like DIN power).
[glow=red,2,300]RMS power[/glow]
To make it short, an RMS power value is directly related to perceivable energy (acoustical, heat, light - or what else applies).
"RMS" is really a rather meaningless figure, when measuring power. R.M.S. is useful for measuring the "power-producing equivalent" voltage. Thus 10 Volts RMS will produce the same power into given impedance that 10 Volts DC would produce (onto a resistance) any waveform of 10 V R.M.S. will produce the same power into that impedance. This is because it's the root of the mean of all the average squared voltages to which Norbert Hahn referred in the prior post. It is if little meaning to compute the mean of squares of all the power values in a wave.
RMS, when applied to power measurements, has come to mean "sine-wave power." A 100 Watt "RMS" amplifier can produce a 100 Watt sine wave into its load. With music, the total actual power would be less. With a square-wave, it would be more.
[glow=red,2,300]DIN power[/glow]
The DIN 45000 defines different methods to measure power, depending on the device under test. Well, this is what I remember from reading the DIN some 25 years ago.
For home appliances there are three different numbers for power: Continuous power, Peak power and power bandwidth; the latter does not apply for speakers.
Power measurement of an amp requires that Ohmic resistances of nominal value both at input and output properly terminate the amp. The continuous power is measured when the amp is supplied by its normal power supply. It must then be able to deliver the rated power at 1 kHz for at least 10 minutes while the maximum THD does not exceed 1 %. To measure the peak power the normal power supply is replaced by a regulated power supply and the time for delivering the power is reduced. Thus, higher values for peak power are obtained. You may skip measuring the peak power by simply multiplying the continuous power by 1.1.
The power bandwidth is defined as the bw for which 1/2 of the rated continuous power can be obtained.
Actually, DIN 45 500, CNF 97-330, EIA RS-426 and the encompassing IEC 268-5 specify not pink noise, but pink noise filtered by a filter that provides significant attenuation in the low and high frequency region of the spectrum to more closely model the long-term spectral distribution of music. Pink noise itself does not accomplish this
[glow=red,2,300]PMPO (Peak Music Power)[/glow]So called "music power". This power figure tells the power which the amplifier can maximally supply in some conditions. PMPO rating gives the highest measuring value, but this info is quite USELESS, because there is no exact standard how PMPO power should be measured.
The reason for this power rating was to show the max capability of equipment for recreating strong musical transients like kettledrums and the like. Similar thing (music power rating) was used in the sixties, and I think it assumed a square wave that swung the whole supply range of the output stage. This alone gives them a factor of two over a clean sine wave note. But the ugliest thing they did was to assume that the high power lasted such a short period of time that the power supply caps would hold the voltages steady without any drooping. In the real world, an underpowered PS could be hidden by this ruse and the PMPO might be a factor of 10 or higher than what could be sustained on a nice instrumental performance.
Forget what adverts say about peak power or other "power terms" because they are not standardized and anyway comparable between equipments. Just look for "RMS continuous Power" or other reliable power rating (like DIN power).