The basic elements of car audio

Audio Source

Generally speaking, anything that can produce sound is called a sound source, but in terms of audio, any device that can produce sound and convert it into electrical signals can be called a sound source, such as CDs, LPs, tapes, FM/AM radio, microphones, etc., but sound sources alone cannot produce the sounds we hear. Signals must be transmitted through related media and amplified into sounds that our ears can hear.

What is a preamplifier

? The preamplifier is the device after the sound source and before the power amplifier. In simple terms, the preamplifier is a "signal control" device, such as EQ, DSP, Line Driver, electronic crossover, etc. Do all these things have to be installed one by one? In fact, it is not necessary, because in fact, many preamplifier functions are now included in the host or the power amplifier. Just like some functions on the host, you don’t know it is a preamplifier if I don’t tell you! For example, the control interface for selecting CD and TAPE signals. If the car audio host does not have a control interface, then you have to move one machine after another like a home audio machine to the car, and you must connect an amplifier to each sound source. In this way, you will go crazy before you even want to listen to the audio. Let’s first introduce several preamplifier functions included in the general car audio host:

Volume control or signal control (Volume Select, signal), generally speaking, uses a variable resistor with a variable resistance value to change the voltage value of the output signal to control the volume (signal). If there is no such control interface, the sound you hear will be amplified at the maximum, then either your device is broken or your ears are broken.

The front and rear, left and right balance control (Fader, Balance) works similarly to the volume control, but is designed to accommodate differences in speakers or amplifiers, or because of asymmetrical speaker installation locations in cars. The tone control is designed to allow the sound quality to be adjusted to one's own preference, but this function has been replaced by other additional functions of current consoles.

Loudness (loudness gain) When we listen to music, sometimes we cannot hear the lower low frequency like 100Hz or the higher high frequency at a low volume. Loudness gain is when we turn on Loudness, a gain action is made in the lower frequency band and the higher frequency band, making you feel that the sound effect seems to be better, but it becomes less flat compared to the complete frequency response, and you will feel that the high pitch is harsh and the bass is fuzzy at a high volume. The above are the pre-amplifier functions that are generally available on the general affordable host. The next is to introduce the pre-amplifier that is currently sold independently.

Line Driver (also known as Pully, signal amplifier)

The function of the Line Driver signal amplifier is to amplify the signal before it is sent to other pre-stage or post-stage signals. At present, the general post-stage (power amplifier, under standard conditions, a 1V signal input can achieve a full-open output, so basically the Line Driver must at least achieve a 1V low-distortion output), but when considering the large dynamic range, a Line Driver is added to amplify the signal.

EQ (Equalizer)

The main function of EQ is to compensate for the poor listening environment and prevent the influence of sound absorption or reflected sound, which makes the treble too sharp and the bass too fuzzy. Generally speaking, the frequency that people can hear is 20Hz~20KHz, and EQ divides this range into many frequency bands, and then gains or attenuates some of the affected frequency bands to achieve better sound effects.

In fact, some mid-priced host machines now have the above-mentioned pre-amplifiers added into them, but these functions are separated out due to the inherent deficiencies of the host machines. However, some higher-priced host groups on the market have almost included all the functions. Perhaps we should think about whether these pre-amplifiers are still necessary.

DSP

Digital sound processor is a machine that uses program control to process digital signals, and creates so-called sound field effects by enhancing or reducing frequencies in spaces like an opera house, or by turning a song into a Jazz, Pop, or other musical experience. These are all masterpieces of DSP.

Electronic crossover

The function of an electronic crossover is to cut and divide the full-frequency signal. Due to the certain physical characteristics of the speakers, small speakers can only produce higher frequency bands, and large speakers can only produce lower frequency bands. Therefore, a crossover is required to cut and distribute the signal to the amplifier, and then transmit it to the amplifier and speaker to produce appropriate sounds.

Post-stage (Power Amplifier, Power Amplifier)

The function of the preamplifier is to amplify the voltage of different signal strengths into a voltage of sufficient strength to drive the power amplifier (hereinafter referred to as the amplifier). The function of the amplifier is to amplify the signal amplified by the preamplifier by voltage and current, so that the amplifier has enough power to drive the speaker. Generally, when we choose an amplifier, it must at least meet the following conditions: 1. High signal-to-noise ratio (S/N ratio), 2. Not easy to distort, 3. Can drive the speaker (this is the most important), 4. High stability, 5. Reasonable price and meet your requirements.

The amplifiers are classified into A, B, C, D, G, etc. They are classified according to their working characteristics, not just because I say it is A. In car audio, we can see these categories A, B, AB, D. I will briefly describe their advantages and disadvantages. A: low distortion, but the efficiency is too low about 20%~30%, easy to overheat, generally low-power amplifiers. B: easy to distort, high efficiency about 60%. AB: working characteristics and efficiency are between A and B. D: using modem (this is not a modem, what is said here is a modulation and demodulation circuit technology) to amplify the signal, and then use the computing chip to restore the signal waveform, its efficiency can reach more than 90%, and it is less likely to heat up.

Speaker

is an important device in audio equipment. Without it, you can't reproduce the sound you want to hear. It is also the last and final device in audio. You must understand that the function of the speaker is to convert electrical signals into sounds that can be heard by human ears. The general frequency is about 20Hz-20KHz. However, among the current speaker brands, it can be said that there is almost no speaker that can have a complete, flat and full-range sound. Due to physical characteristics, the low-frequency response of speakers with good high-frequency response will naturally become worse. Special speaker designs are not limited to this, such as electrostatic speakers, flat speakers, and ribbon speakers. Therefore, a combination of more than one speaker is produced in the market, such as a treble and a bass is called a two-way sound, and a high, a medium, and a low sound is called a three-way sound.

It is really more difficult for speakers in the car to perform in terms of sound quality, timbre and volume than those in home audio systems, because the installation location inside is not good, the listening position is even more asymmetrical, and there are many decorations that cause sound absorption and reflection effects, and the resulting resonance, standing waves, time difference, phase shift, phase difference and other unfavorable factors. Therefore, the installation of car audio is a science.