Audio power

The music performance is a non-standard and commonly used in advertising for audio devices such as audio amplifier and speaker power rating in watts. The electric power with which a loudspeaker is energized determined by the speaker, the sound output efficiency.

The music performance and in particular the related specification of the PMPO, also PMPO English for Peak Music Power Output, be little reliable measurement methods or even any calculation methods determined in order to specify in data sheets or customer documentation as possible high apparent power values.

Basics

Respectable performance information for speakers and amplifiers were not based on the musical performance, but on the power rating as early as the 1970s. It refers to the maximum continuous recording or power output at a power supply with a pink noise, the standard is the (now withdrawn ) DIN 45324th

Until about the year 2000, more common in Anglo-Saxon indication of RMS power or RMS power ( Watts RMS english ) was used in place of the nominal power, which are determined with an electrically well-defined method. Because of the higher by the measuring method of RMS power values ​​had become the indication Watts RMS soon enforced for reasons of competition as the sole indication. One reason is that the sole indication of the RMS power of an amplifier or speaker characterizes not make sense. The sine wave power has the lowest value, but for music playback is not particularly relevant ( they correspond to a continuous tone); Music, however, usually contains a ( rhythmically related ) high dynamic range that spans multiple orders of magnitude. Therefore, often the sine and the music performance is specified.

When specifying the music power a short time achievable power peak per channel is specified, which is a measure of the maximum headroom at volume peaks of a music signal in which the signal is just processed without clipping. The distortion factor is to not usually specified, the time period is also not fixed.

Structurally, the music power of an amplifier generally by the design of the power supply, in particular the power supply capacitors, determines which need to provide the energy for short duration current peaks ( bass rhythms ) are available. Values ​​up to 50,000 uF are used and useful. A small difference between the rated output ( continuous) and music performance represents a figure of merit for the design of the power supply, as the power supply turns designed it to be better for it to provide current and voltage required, even with repeated peak load available.

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

In a purely ohmic resistors R the effective values ​​of voltage U and current I can be equivalently used:

Example

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

Assumed, as a sinusoidal voltage waveform in this case is the effective value of the voltage U:

Which in this case, an average electric power of:

Corresponds to the speaker.

Term PMPO

Around since 2000, is to application of devices often not clearly defined additional PMPO be used. This enables secure competition law the disclosure of performance values ​​that can exceed the power rating of a device by several orders of magnitude. When specifying the PMPO is not measured, and there are no accepted definitions and methods of measurement. Times that of rated electric power is given, which could be discharged as the sum of all channels even without destruction of the components measured during a fraction of an acoustic vibration. To assess the quality of performance and signal processing devices in this specification is inappropriate.

For amplifiers, the quotient of the square of the idle supply voltage and the minimum permissible load impedance is expressed as PMPO of times. This value already amounts to more than twice that of music performance, since it is the peak value of a sinusoidal oscillation, and also does not include the voltage drop across the output stage. Often, however, the PMPO specified exceeds this value significantly.

Motivation for specifying PMPO values ​​is a marketing point " clever accounting " of values ​​under optimal assumptions, such as short-time pulse, estimate the theoretical maximum value, Distortion 5 % or more, in multichannel systems adding up all the channels, etc. They will for the output power of an amplifier and inputs to the input power of loudspeakers used.

Term RMS power

The effective value, a form of the quadratic mean value, and abbreviated as English RMS root mean square. The RMS power is the average power over a predetermined frequency band, wherein the signal from the RMS power is calculated, a pink noise is within the frequency band. The root mean square is the essential factor for the thermal measurement of a performance variable.

Recognized characteristics

Internationally standardized definitions and methods of measurement of performance characteristics of electro-acoustic devices such as microphones, speakers, amplifiers are laid down in the standards of the DIN EN 60268 or DIN IEC 60268. For the characterization of high-quality speakers for home use only part of the 60268-5 specified in DIN EN characteristics is needed.

For a description of the electrical power following values ​​are common:

• In amplifiers, the maximum deliverable when connecting the nominal impedance of power at supply with a pink noise according to DIN 45324 and the RMS power ( sine tone) into the nominal impedance.
• With loudspeakers, the maximum long-term input power and the maximum short-term input power Tweeter: the rated power specification often names the entire frequency spectrum of pink noise, but they are only fed with that frequency band for which they are specified. They can thus be compared for use in a multiple driver.
• Woofer also be specified, but here 's the difference by the limited frequency band is not as great as with tweeters. However woofer can be destroyed due to high frequencies since it will then be cooled, for example, poor due to a lack of movement of the voice coil.

Speakers can not even approximately reproduce their power ratings than pure tone, without being destroyed, especially at high frequencies. This is not a quality defect, but is based on the lower power content high tones at the same volume. Also speakers are therefore appropriately supplied with a pink noise to determine the power rating in accordance with DIN 45324, which has its greatest power content at low frequencies.

These values ​​characterize only the electric power capacity of a speaker and not yet contain any statement about its sound power, linked by the efficiency, and expressed the distortions of the loudspeaker as harmonic distortion. The efficiency of speakers is given as the mean sound pressure or sound pressure level ( sound pressure level, eg, 1 kHz at 1 watt power supply, measured at 1 m distance ).