The Most Comprehensive Audio Parameter Explanation

- Jun 05, 2020-

Output power (output power):

It indicates the output power of the power amplifier under a certain load. Generally, the output of the power amplifier is marked in the state of 8 ohm load, 4 ohm load or 2 ohm load, and it also indicates that the power amplifier is in the bridge state, 8 ohm load Output power at 4 hours or 4 ohm load. This output power represents the rated output power of the power amplifier, not the maximum or peak output power.



Load impedance (load impedance):

It indicates the load capacity of the power amplifier. The smaller the impedance of the load, the stronger the current capacity that the power amplifier can pass. Generally, the minimum load impedance of most power amplifiers is 4 ohms, and the minimum load of good quality power amplifiers is generally 2 ohms. It can load a 4 ohm power amplifier in dual channels, and can load a minimum of 8 ohms in the bridge state, and can load a 2 ohm power amplifier in dual channels, and 4 ohms in the bridge state. In the bridged state, only 8 ohm power amplifier can be loaded, and lower impedance cannot be loaded, otherwise it will cause the amplifier to burn due to excessive current.



Stereo (two channel) mode (stereo mode or dual mode):

The general power amplifier has two independent amplifier circuits inside, which can respectively receive two different signals for amplification and output. This working state is called stereo (two-channel) mode.




Bridge mode:

The bridge mode is a method of using the two amplifier circuits inside the power amplifier to push and pull each other to generate a larger output voltage. After the power amplifier is set to the bridge mode, it becomes a mono amplifier, which can only accept one input signal for amplification and output. The terminal is between the positive terminals of the two power amplifier outputs.



Parallel input mode (parallel mode):

In this way, the two input signal channels of the power amplifier are connected in parallel, and only one signal is input to drive the two amplifier circuits at the same time, and the output signals of the two output terminals are the same.



Frequency range:

Indicates that the working frequency band of the amplifier can be amplified, generally 20-20000 Hz, generally there is a suffix behind this data, such as -1/+1dB, which represents the error or floating range of this frequency range, this value is about small, indicating the frequency The frequency response curve within the range is flatter. If the frequency response range of the power amplifier is -3 dB as the test condition, the sound from this power amplifier may not be so straight.



Total harmonic distortion (THD):

It shows that when the power amplifier is working, due to the inevitable oscillation or other resonance generated by the circuit, the third and third harmonics are superimposed on the actual input signal. The signal output at the output is not simply the same component as the input signal, but includes The harmonic components of the signal, these excess harmonic components compared with the actual input signal, expressed as a percentage is called total harmonic distortion.

Generally speaking, the total harmonic distortion is the smallest around 1000 Hz, so most power amplifiers indicate that the total harmonic distortion is tested with a 1000 Hz signal, but some stricter manufacturers also provide total harmonic distortion in the range of 20-20000 Hz data. The total harmonic distortion is less than 1%, and generally the ear cannot distinguish it. If it exceeds 10%, the distortion component can be clearly heard. The smaller the value of this total harmonic distortion, the purer the sound. The total harmonic distortion of general products is less than 1%@1kHz, but the smaller the value, the higher the quality of the product.




Intermodulation distortion (IMD):

Intermodulation distortion is caused by the operating characteristics of the transistor inside the power amplifier, which causes distortion of the sine wave waveform. The existence of intermodulation distortion directly affects the sound quality of the sound. The tube amplifier does not have intermodulation distortion, so in general the transistor amplifier sounds less soft and comfortable than the tube amplifier. Generally, if the value of intermodulation distortion is greater than 0.1%, the sound of this amplifier feels blunt, astringent, and not expressive.



Common Mode Rejection Ratio (CMRR):

Common mode rejection is a comprehensive indicator used to measure the degree of common mode signal being suppressed by the amplifier. This parameter is generally expressed with a negative value, such as -60dB. This indicator is also an indicator that seriously affects the sound quality of the amplifier. The lower the number of this indicator, the better the sound quality of the power amplifier.



Damping factor:

This is the ratio of the internal resistance of the power amplifier and the load impedance, damping coefficient = impedance of the speaker ÷ (internal resistance of the power amplifier + impedance of the speaker line),

The power amplifier with high damping coefficient can strengthen the control ability of the speaker unit, which can make the response of the unit closer to the requirements of the output signal of the power amplifier. However, an excessively high damping coefficient will cause the low frequency ductility of the speaker to deteriorate and the sound to dry. A relatively low damping coefficient can get a soft bass, but too low a damping coefficient will cause the bass to become lingering and unclean.

The damping coefficient of a general power amplifier is between 200-1000@8 ohms. The quality of the speaker cable is not good, and the large wire resistance will also affect the damping coefficient of the power amplifier. The control force of the speaker caused by the amplifier is weakened and the sound is dispersed.



Input sensitivity:

This is a voltage concept, indicating that when the power amplifier reaches full power output, the size of the signal voltage at the input terminal, the input sensitivity voltage of a general power amplifier is between 0.775v (0dB) and 1.5v (+6dB), the higher the sensitivity voltage, The lower the input sensitivity.

Some high-quality power amplifiers have low input sensitivity because they use deeper negative feedback circuits, so they have lower distortion, wider frequency response, and better sound quality.



S/N or SNR or Hum and Noise:

Refers to the ratio of the power amplifier signal voltage to the noise floor voltage. The larger the value, the lower the power amplifier noise. The signal-to-noise ratio of general professional products is around 100 decibels. The higher the positive value, the better (some power amplifiers use negative values, the smaller the value, the better). Attenuating the input level gain of the amplifier (turning off the small amplifier volume knob) will reduce the signal-to-noise ratio of the amplifier.




Channel crosstalk:

It means that the crosstalk generated by the circuit coupling between the two amplification channels inside the power amplifier is not good. The signal of one channel will be connected to the other channel, resulting in an unclean sound in the other channel. The value of crosstalk is generally around -60 dB.

When this value is marked with a negative value, the lower the value, the higher the separation between the two amplification channels and the cleaner the sound.


Slew Rate:

The response speed of the amplifier is generally measured by the voltage conversion rate, which is defined as the amplitude of the voltage rise in 1 microsecond. If it is measured with a square wave, it is the time required for the voltage to rise from the valley to the peak. The unit is V/us, the value The larger the value, the better the transient responsiveness, the faster the sound, and the concentrated energy.

The conversion rate of professional power amplifiers can generally achieve more than 40V/u s.

The sound of the amplifier with a conversion rate lower than 20V/u s will feel procrastination and divergence.



High pass filter (HPF):

In the sound system, sometimes there are some extremely low-frequency infrasonic (infrasonic) signals mixed with the full audio signal. These infrasonic signals are inaudible to the human ear, but when this signal enters the speaker, it will cause the subwoofer to self-excite and cause the speaker damage,

All, some power amplifiers are equipped with infrasonic wave elimination filters, and some are equipped with switches on the rear panel, which can cut off unnecessary frequencies of 30 Hz or below 40 Hz when needed to protect the safety of the horn.



Limiter (limiter):

This is one of the protection measures of the power amplifier. When the input voltage of the power amplifier exceeds the input sensitivity voltage, the input signal is limited to avoid clipping distortion caused by the excessive input voltage of the power amplifier.

The limiter of some power amplifiers is automatically activated, and some power amplifiers have a limiter start switch installed on the rear panel to control the start state of the limiter.



Ground switch (ground left):

The chassis of the power amplifier is generally connected to the power transformer shield. The power amplifier chassis also has a ground terminal, but this "ground" is different from the "ground" of the signal. When there is interference on the ground terminal of the power supply, turn on the ground switch to connect the ground of the power amplifier chassis to reduce the hum interference. If the power ground wire does not interfere, do not connect it.