The basic composition of the listening system and the selection of amplifiers and speakers

The basic composition of the listening system and the selection of amplifiers and speakers

Basic components of a listening system

First, let’s talk about the composition of a complete system. Simply put, it can basically consist of the following three parts:

Audio source, amplifier, speakers.

Sound source:

Regardless of digital or analog signal sources, they include common mobile phones, CD players, DVD players, computers, various digital players, MIDI, vinyl record players, even tape players, etc.

It can be roughly divided into two types: digital and analog. Tapes and vinyl records are carriers for recording analog signals, while the 120mm CD records that we commonly use and are common in the market are typical digital signal carriers.

Cambridge CD player purchased more than ten years ago (Part 1)

If it is a digital sound source, because our speakers receive and play back analog signals, there is a DAC (digital-to-analog conversion) process to convert the digital signals into analog signals. And the conversion quality of this DAC varies widely. Because we usually use computers a lot, and many people want to build their own Hi-Fi systems, so take computers as an example. Nowadays, the motherboard usually has an integrated sound card, and the sound card has a built-in DAC chip, so there will be a 3.5mm chip on the back of the motherboard. Analog plug (green is the plug we use when using a stereo system). Of course, many people think that the digital-to-analog conversion quality of the motherboard's integrated sound card is relatively low (this is generally true), so many computers are equipped with optical fiber outputs (picture below) (at the rim), through this port, the computer's audio digital signal is output to the next part for digital-to-analog conversion, that is, it is handed over to the power amplifier for processing. At this time, the analog output port of the motherboard becomes a decoration and begins to collect dust.

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In short, we think that the quality of the integrated sound card is indeed average, and the manufacturer knows this, and in order to cater to the widest possible range of users, it gives us a variety of choices.

The red circle in the picture above is the "Magic USB" interface on the Gigabyte motherboard. This port is specially used to connect us to the USB port of the external DAC. Of course, the DAC with the USB interface can work when connected to any USB port, but this The circuit of the gold-plated "Magic Sound USB" port has been specially optimized and is more suitable for working with an external DAC connected to the USB interface than other USB ports.

You see, DACs also come in the form of external USB interfaces. At this time, the USB-DAC will perform high-quality digital-to-analog conversion and output the analog signal to the power amplifier.

2. Power amplifier:

Power amplifier is what we often call power amplifier. It generally refers to the amplification of weak electrical signals from the signal source (from the mixer in professional audio systems) in the audio system to drive the speakers (commonly known as speakers and speakers) for sound playback. .

The power amplifier can receive analog signals and digital signals from the signal source, and there may be an independent DAC device between the power amplifier and the signal source, such as the USB-DAC we mentioned earlier.

For the transmission of analog signals, the most common one is the RCA (commonly known as the lotus head) signal line, and the better one is the balanced line.

As shown in the picture below, a USB-DAC is connected to the RCA port (but this is the interface output to the speaker, just for illustration. We can see that there is an optical fiber port on the lower right, which can receive computers, PS4 game consoles, digital players and other devices digital signal).

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A USB-DAC rear interface

For digital signal transmission, common audio interfaces include coaxial audio interfaces (Coaxial), optical fiber interfaces (optical), etc.

Common power amplifiers also integrate digital-to-analog conversion modules and are equipped with coaxial and optical fiber input ports. At this time, we can choose to use an external DAC or directly use the DAC of the power amplifier.

There are many ways to classify power amplifiers. According to the type of power amplifier tubes, they can be divided into tube amplifiers (tube amplifiers) and stone amplifiers (transistor amplifiers). Transistor amplifiers are the product of modern technology, but due to the characteristics of electron tubes, even very old technology , but it is also relatively common in today’s Hi-Fi systems.

In a two-channel Hi-Fi system, the main power amplifier parameters we need to consider are:

Output power: The unit of output power is watt (W) or kilowatt (kW). Due to different measurement methods, there are some names with different names, such as rated output power, maximum output power (dynamic power), etc., and informal products from some unscrupulous manufacturers often use this to deceive users. We mainly look at the rated power.

Frequency response range: The working frequency band that the power amplifier can amplify, usually 20-20kHz. There is usually a suffix after this data, such as -1/+1dB, which represents the error range of this frequency range. This value is approximately Small, indicating that the frequency response curve in the frequency range is flatter. Today's products generally have a frequency response range greater than what the human ear can perceive. For example, the Japanese Marantz PM8006 has a parameter of 5-100kHz (±3dB). It is unknown whether someone can perceive ultrasonic waves and infrasound waves.

Damping factor: Damping factor is an important technical parameter that directly affects bass quality. The larger the diameter of the unit, the better the bass, but the larger the speaker basin, the greater the mass, and the inertia of its movement also increases. This inertia makes it difficult to move in synchronization with the audio signal, often showing the sound Turbidity, especially at low frequencies of 100-400Hz, can easily cause sound coloration, making it sound fuzzy and unnatural. When designing the power amplifier, engineers take some technical measures to increase the damping coefficient so that it can produce an electrical damping effect in response to the inertial movement of the speaker, so that the movement of the speaker cone moves synchronously with the audio signal, so that the speaker cone can be driven by the driving signal as much as possible. After the end, it quickly returns to the zero position (i.e., the center position). This blocking effect is the damping coefficient (Damp Factor), D=Rs/Ri, Rs=speaker impedance, Ri=power amplifier output internal resistance, the larger D, the smaller the sound cone. The better the synchronization effect with the signal, the purer and cleaner the bass, and the better the reproduction effect. Still taking Marantz PM8006 as an example, its nominal damping coefficient is 100 (8Ω/ohm load, 40Hz~20kHz).

Signal-to-noise ratio: Signal-to-noise ratio (S/N or SNR or Hum and Noise): refers to the ratio of the power amplifier signal voltage and the background noise voltage. The larger the value, the lower the noise of the power amplifier.

Output impedance: refers to the ratio of the voltage and current of the speaker input signal, the unit is Ω (ohm). Some power amplifiers are compatible with speakers with a certain impedance range. For example, the Marantz PM8006 supports speakers with 4~16Ω/ohm. There are also some power amplifiers that only Mark a specific impedance, for example the most common impedance is 8Ω.

Among the above parameters, with the advancement of technology, the signal-to-noise ratio, frequency response range and other parameters can be better, and what we need to focus on is the rated output power and output impedance.

Speaker

The picture below is the KEF IQ30 bookshelf box that the editor purchased more than ten years ago. It uses KEF's Uni-Q coaxial unit. Some of its main parameters are as follows:

Frequency response range: 45Hz-40KHz; Impedance: 8Ω; Sensitivity: 89dB; Crossover point: 2500Hz Unit diameter: 165 mm (6.5 inches) mid-bass unit, 19 mm tweeter.

Generally speaking, if you want to get good bass, the diameter of the unit should be larger, so that it can push the air to produce a sufficient sense of low frequency. It is recommended to start with 6.5 inches.

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KEF IQ30 coaxial bookshelf box

When we buy speakers, we mainly need to pay attention to two points:

Rated power: Generally speaking, the rated power of the power amplifier should be greater than the rated power of the speaker so that the device can work normally, preferably 1.5 times. In the field of professional high-fidelity Hi-Fi, the power of the amplifier is required to be twice the power of the speaker. Only when the power reserve is sufficient can we have better control.

Impedance matching: When matching a power amplifier with a speaker, the output impedance of the power amplifier should be consistent with the input impedance of the speaker; otherwise, phenomena such as reduced output power and increased distortion will occur. Nowadays, many power amplifiers are compatible with speakers with common impedances, and some are only limited to a certain impedance value. For example, the common impedance is 8 ohms. At this time, you'd better buy 8 ohm speakers.

Generally, 4Ω, 6Ω, and 8Ω boxes are more common. Many of the fever boxes of Dynaudio, a famous fever brand from Denmark, are 4Ω.

Active speakers and passive speakers

In desktop systems, there is a typical combination of power amplifier + speaker split. The speaker here refers to a passive speaker. It does not have a power amplifier itself, and you need to purchase an additional power amplifier to promote its sound.

There are also speakers with built-in amplifiers, called active speakers, also known as "active speakers." Common monitor speakers and multimedia speakers all fall into this category.

When we plan to buy active speakers, we don’t need to consider the matching of power amplifiers and speakers. They are all in the box anyway. Active speakers are divided into symmetrical designs and asymmetrical designs. In symmetrically designed active speakers, the left and right channel speakers have built-in power amplifiers, with the same structure and weight. In asymmetrical designs, only one side of the speaker has a built-in power amplifier, and the other side has a built-in power amplifier. The speaker does not have a built-in amplifier, but is driven via a cable connection from one side of the built-in amplifier.

Usually, active speakers with higher prices and better quality are generally symmetrical in design.

Today's active speakers integrate some new technologies, and some have built-in DACs (yes, if your power amplifier does not have a DAC, and the DAC quality of the sound source is too poor and you don't want to use it, then you can consider speakers with integrated high-quality DAC modules) , there are added wireless functions such as Apple's airplay, Bluetooth, etc., which greatly facilitate our use. However, if you care about sound quality, just connect those messy cables honestly.