The Performance Index of A Speaker

- Aug 21, 2018-

The speaker is a key part of the speaker system. The sound quality of the speaker is mainly determined by the performance indicator of the speaker, which determines the whole set of playback indicators. The performance indicators of the speaker mainly include rated power, rated impedance, frequency characteristics, harmonic distortion, sensitivity, directivity and so on.

1. Rated power (W)

The rated power of the speaker refers to the output power that the speaker can work for a long time. It is also called undistorted power. It is usually marked on the nameplate on the back of the speaker. When the speaker works below the rated power, the coil will not be overheated or mechanically overloaded, and the emitted sound will not show distortion. The rated power is an average power. In fact, the power state of the speaker is changed according to the strength of the input audio signal. In the dynamic range of music and audio signals, the sudden peak pulse signal will exceed the rated power. Times, because the duration is short, the speaker will not be damaged, but distortion may occur. Therefore, in order to ensure good sound quality even when the peak pulse occurs, the speaker needs to leave enough power margins. The maximum power of a typical speaker is 2-4 times the rated power.

 2. Frequency characteristics (Hz)

The frequency characteristic is a pointer that measures the width of the speaker's operating frequency. The high-fidelity playback system requires the speaker system to be able to play back the 20Hz-2000Hz human ear audible range. Since it is not easy to realize a full-range audible range with a single speaker, the current high-fidelity speaker system generally uses high, medium and low frequency divisions to drive three corresponding speakers to achieve full-band coverage. In addition, the frequency response characteristics of high-fidelity speakers should be as flat as possible; otherwise the frequency of playback will be introduced. The high-fidelity playback system requires the speaker to be within the frequency range of the playback, and the frequency response unevenness should be less than 10 dB.

3. Rated impedance (Ω)

 The rated impedance of a loudspeaker is the ratio of the voltage applied to the input of the loudspeaker to the current flowing through the voice coil of the loudspeaker under rated conditions. Now, the rated impedance of the speakers is generally 4, 8, 16, 32 ohms and so on.

 4. Harmonic distortion (TMD%)

There are many kinds of distortions in the speakers. Common distortions are caused by the distortion of the magnetic field of the speaker and the distortion of the linear piston movement of the air that pushes the air, often at low frequencies. Intermodulation distortion (because two different frequency signals are added to the speaker at the same time, the sound quality caused by mutual modulation is degraded) and transient distortion (the inertia of the cone vibration cannot be changed closely with the change of the audio signal, causing the sound to be distorted). Harmonic distortion refers to the addition of harmonic components that are not in the original signal during playback. The harmonic distortion of the loudspeaker is derived from nonlinear distortion of the magnetic field, the characteristics of the diaphragm, and the displacement of the coil. At present, better speakers have a harmonic distortion index of no more than 5%.

 5. Sensitivity (dB / W)

The sensitivity of the speaker is usually the sound pressure measured at a distance of 1 meter from the front side of the speaker when the input power is 1W. Sensitivity is a measure of whether the details of the speaker's music signal can be reduced. The higher the sensitivity, the more the speaker can respond to all the details in the music signal. The sensitivity as a Hi-Fi speaker should be greater than 86dB/W.

 6. Directionality

 The sound pressure frequency characteristics of the loudspeakers in different directions are different. This characteristic is called the directivity of the loudspeaker. It is related to the caliber of the speaker. When the caliber is large, the directionality is pointed, and the aperture is small and the directivity is small. Directivity is also related to frequency. Generally speaking, for low frequency signals below 250 Hz, there is no obvious directivity, and high frequency signals above 1.5 kHz have obvious directivity.

 

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