Musical performance

The music power is a non-standardized power rating in watts that is often used in advertising for audio devices such as audio amplifiers and loudspeakers . The sound power of a loudspeaker results from the electrical energy supplied and from the loudspeaker efficiency.

The music performance and in particular the related specification of the PMPO , also PMPO for English Peak Music Power Output , are determined by unreliable measurement methods or even any calculation methods in order to be able to specify the highest possible apparent power values ​​in data sheets or customer documentation.

Basics

Serious performance data for loudspeakers and amplifiers were not based on the music performance, but on the rated output as early as the 1970s . It states the maximum permissible continuous input or output power when fed with a pink noise , the standard is the (now withdrawn) DIN 45324.

Until about the year 2000 instead of rated power, the more common in Anglo-Saxon was RMS power or RMS power ( english Watts RMS indicated), which are calculated with an electrically well-defined method. Because of the higher values ​​due to the RMS power measurement method, the Watts RMS specification soon became the sole specification for reasons of competition. Another reason is that the mere indication of the sinus power does not meaningfully characterize an amplifier or loudspeaker. The sine output has the lowest value, but is not particularly relevant for music reproduction (it would correspond to a continuous tone); However, music usually contains a (rhythmically conditioned) dynamic range that encompasses several orders of magnitude. This is why the sine and music power was often given.

When specifying the music power, a briefly achievable peak power value per channel is specified, which is a measure of the maximum controllability at volume peaks of a music signal at which the signal is still processed without clipping . However, the distortion factor is usually not specified, and the duration is also not specified.

In terms of design, the musical performance of an amplifier is generally determined by the design of the power supply unit, in particular the power supply unit capacitors , which have to provide the energy for brief current peaks (bass rhythms). Values ​​up to 50,000 µ F are common and useful. A small difference between the nominal output (continuous output) and the music output is a quality feature for the design of the power supply unit, since the power supply unit in it proves to be better designed to provide currents and the required voltage even with repeated peak loads.

The electrical power P is, also for music signals, generally formed by the arithmetic mean of the instantaneous values ​​of electrical voltage u (t) and electrical current i (t) according to the following relationship:

${\displaystyle P={\frac {1}{T}}\int _{0}^{T}u(t)\cdot i(t)\,dt\,}$

With purely ohmic resistances R , the effective values of voltage U and current I can be used equivalently:

${\displaystyle P=U\cdot I={\frac {U^{2}}{R}}\,}$

example

A push-pull output stage can deliver a peak value of 6 V into a loudspeaker with an impedance of 8 Ω. This corresponds to a peak power P _peak of

${\displaystyle P_{\mathrm {peak} }={\frac {(6\,\mathrm {V} )^{2}}{8\,\Omega }}=4{,}5\,\mathrm {W} }$

Assuming a sinusoidal voltage curve, the effective value of the voltage U in this case is :

${\displaystyle U={\frac {6\,\mathrm {V} }{\sqrt {2}}}\approx 4{,}242\,\mathrm {V} }$

which in this case is an average electrical power of:

${\displaystyle P={\frac {(4{,}242\,\mathrm {V} )^{2}}{8\,\Omega }}=2{,}25\,\mathrm {W} }$

on the loudspeaker.

Term PMPO

For devices in the cheaper segment, the not clearly defined addition PMPO (Peak Music Power Output or Pure Mystic Power Output ) is often used to advertise. This enables the specification of performance values, secured by competition law, which can exceed the rated output of a device by several orders of magnitude . If the PMPO is specified, no measurements are taken and there are no recognized definitions and measurement methods. Sometimes the theoretical electrical power given is that which, as the sum of all channels, could be delivered during a fraction of a sound oscillation without destroying the measured components. This information is unsuitable for assessing the quality of performance and signal processing in devices.

In the case of amplifiers, the quotient of the square of the no-load supply voltage and the minimum permissible load impedance is often specified as the PMPO. This value is already more than double the music output, since it is the peak value of a sinusoidal oscillation and, moreover, does not take into account the voltage drop at the output stage. However, the PMPO information often exceeds this value significantly.

The motivation for specifying PMPO values ​​is a marketing-related "skilful calculation" of values ​​under optimal assumptions, such as short-term impulse, estimation of the theoretical maximum value, distortions of 5% and more, in multi-channel systems addition of all channels and so on. It is used for the output power of an amplifier and for inputs to the input power of speakers.

Term RMS performance

The rms value is known as a form of the root mean square and also abbreviated as RMS for English Root Mean Square . The RMS power is the mean power over a given frequency band, with the signal from which the RMS power is calculated being pink noise within the frequency band. The root mean square value is the essential variable for the thermal dimensioning of a performance variable.

Recognized characteristic values

Internationally standardized definitions and measurement methods for performance parameters of electroacoustic devices such as B. microphones, loudspeakers, amplifiers are specified in the standards of the DIN EN 60268 and DIN IEC 60268 series. To characterize high-quality loudspeakers in the home, only some of the parameters specified in DIN EN 60268-5 are required.

The following values ​​are common to describe the electrical power:

• For amplifiers, the maximum continuous power that can be supplied when connecting the nominal impedance when fed with a pink noise according to DIN 45324 and the sine power (continuous sine tone) in the nominal impedance.
• for loudspeakers the maximum long-term input power and the maximum short-term input power
  • Tweeter: the nominal power specification often names the entire frequency spectrum of a pink noise, whereby they are only fed with the frequency band for which they are specified. They can thus be compared for use in a reusable box.
  • Woofer are also specified, but the difference due to the restricted frequency band is not as great as with tweeters. Nevertheless, woofers can also be destroyed by high frequencies, as they are then cooled more poorly, for example due to the voice coil not moving.

Loudspeaker boxes cannot even come close to reproducing their nominal power as a sine tone, especially at high frequencies, without being destroyed. This is not a lack of quality, but is based on the statistical power distribution of conventional music signals on the significantly lower power share of higher versus lower tones. Loudspeaker boxes are therefore also appropriately fed with a pink noise to determine the nominal power according to DIN 45324, which has its highest power components at lower frequencies.

These values ​​only characterize the electrical power consumption of a loudspeaker and do not yet contain any information about its sound power, linked via the efficiency , and the distortion of the loudspeaker, expressed as distortion factor . The efficiency of loudspeakers is given as the mean sound pressure or sound pressure level (characteristic sound pressure level, e.g. 1 kHz at 1 watt power supply, measured at a distance of 1 m).

Individual evidence

1. ↑ DIN EN 61305-5: Hi-Fi devices and systems for home use - Procedure for measuring and specifying performance parameters - Part 5: Loudspeakers
2. ↑ The Audio Encyclopedia: A Reference Book for Sound Engineers