Knowledge

How do we understand and judge whether a set of audio meets the sound quality requirements, it becomes necessary before tuning. The so-called sound quality includes these four aspects: loudness, tone frequency, tone color, and sound field. Let’s briefly analyze below ↓

1) Loudness: it can be understood as the volume, which is related to the amplitude of the sound vibration and the propagation distance.

2) Tone frequency: the frequency can be understood as the number of vibrations per second of a single tone. The frequency range of human ear hearing is 20 ~ 20,000Hz (K = 1000 often seen), which is what we often say treble, midrange and bass. ,very low voice.

3) Tone color: Through the waveform representation, the waveform contains basic and overtones in a frequency band, enabling us to distinguish different people and instruments.

3) Tone color: Through the waveform representation, the waveform contains basic and overtones in a frequency band, enabling us to distinguish different people and instruments.

How do we understand and judge whether a set of audio meets the sound quality requirements, it becomes necessary before tuning. The so-called sound quality includes these four aspects: loudness, tone frequency, tone color, and sound field. Let’s briefly analyze below ↓

1) Loudness: it can be understood as the volume, which is related to the amplitude of the sound vibration and the propagation distance.

2) Tone frequency: the frequency can be understood as the number of vibrations per second of a single tone. The frequency range of human ear hearing is 20 ~ 20,000Hz (K = 1000 often seen), which is what we often say treble, midrange and bass. ,very low voice.

3) Tone color: Through the waveform representation, the waveform contains basic and overtones in a frequency band, enabling us to distinguish different people and instruments.

3) Tone color: Through the waveform representation, the waveform contains basic and overtones in a frequency band, enabling us to distinguish different people and instruments.

When designing and installing a sound system, it is unavoidable to encounter the problem of matching the amplifier and the speaker. From an artistic point of view, the matching of power amplifiers and speakers should be warm and cold, soft and hard in terms of tone, and finally the whole set of equipment will return to neutral tone. From a technical point of view, the following points should be noted when the amplifier is connected to the speaker: power matching; impedance matching; damping coefficient matching. If we realize the above three points when mating, we can make full use of the performance of the equipment used.

A power match

In order to meet the requirements of high-fidelity listening, the rated power should be determined based on the optimal listening sound pressure. We all have this feeling: when the volume is small, the sound is weak, thin, and dynamic, and there is no gloss, and the low frequency is significantly lacking. The fullness is poor, and the sound seems to be confined in it. When the volume is appropriate, the sound is natural, clear, round, soft and plump, powerful and dynamic. But when the volume is too high, the sound is stiff and not soft, rough, and feels ear-piercing. Therefore, the playback sound pressure level has a greater relationship with the sound quality. The sound pressure level in the listening area is preferably 80-85dB (A weighted). We can calculate from the distance from the listening area to the speaker and the characteristic sensitivity of the speaker Speaker’s rated power and power amplifier’s rated power.

Speaker: In order to make it able to withstand the impact of burst strong pulses in the program signal without damage or distortion. Here is an empirical value for reference: The nominal rated power of the selected speaker should be more than twice the theoretically calculated power.

Power amplifier: Compared with the transistor power amplifier, the required regular reserve is different. This is because the overload curve of the tube amplifier is relatively flat. For peaks of overloaded music signals, tube amplifiers do not obviously produce clipping, but only round the tip of the peaks. This is what we often call flexible clipping. After the transistor power amplifier overload point, the non-linear distortion increases rapidly, which severely clips the signal. It does not round the peak but neatly flattens it. Some people use resistors, inductors, and capacitors to compound speakers to simulate the actual output capability of several high-quality transistor amplifiers. The results show that in the case of load phase shift, there is a nominal 100W power amplifier, the actual output power is only 5W at 1% distortion! Therefore, the reserve of the transistor power amplifier is selected: high-fidelity power amplifier: 10 Times, civilian high-end power amplifiers: 6 to 7 times, civilian mid-range power amplifiers: 3 to 4 times. The tube power amplifier can be much smaller than the above ratio. How much margin should be left for the average sound pressure level and the maximum sound pressure level of the system depends on the content of the program and the working environment. The minimum amount of redundancy is 10dB. For modern pop music, bundi and other music, 20 ~ 25dB redundancy is required, so that the sound system can work safely and stably.

Two impedance matching

The output of the amplifier and the input impedance of the speaker should also be the same. Although there are some slight deviations between the two, it will not have a significant impact on the sound quality, but will only have an effect on the output power of the amplifier, but it must be reminded that if the speaker input impedance is much lower than the amplifier output impedance, it will cause a significant increase in distortion. In severe cases, the amplifier will be damaged. Therefore, it is better to choose the same as much as possible.

Matching of three damping coefficients

The damping coefficient KD is defined as: KD = rated output impedance of the amplifier (equal to the rated impedance of the speaker) / internal resistance of the output of the amplifier. Because the internal resistance of the power amplifier output has actually become the resistance of the speaker, the KD value determines the resistance of the speaker. The larger the KD value, the heavier the resistance is. Of course, the KD value of the power amplifier is not as large as possible. If the KD value is too large, the speaker resistance will be too heavy, so that the pulse leading time will increase and reduce the transient response index. Therefore, when selecting the power amplifier, one should not pursue a large KD value. As a household high-fidelity power amplifier damping coefficient, there is an empirical value for reference. The minimum requirements are: the KD value of the transistor power amplifier is greater than or equal to 40, and the KD value of the tube power amplifier is greater than or equal to 6.

What you need to know is that if the damping coefficient is too high, the sound from the speaker will be dry and not round; if it is low, the sound will tend to stick together. Therefore, when you configure the power amplifier, you must pay attention to the damping coefficient of the stone machine is controlled between 30 and 40, because the internal resistance of the amplifier is high, it must not exceed 10.

The most important of these three principles is the first point. Here we reiterate once again that the matching of the amplifier and the speaker is better than a small horse, but not a small horse.

The physical + electronic circuit is mainly the mutual conversion of acoustic signals and electrical signals. To put it simply: The sound is generated by vibration and medium. The vibration generated by the sound signal causes the audio equipment to receive vibration. The vibration can generate the corresponding audio current in the current coil. The current is transmitted to the speaker. Amplifying circuits are used, which are generally triodes. Amplifying the current has the effect of sound amplification.) When the audio current passes through the coil of the speaker (also called voice coil), a corresponding magnetic field is generated in the voice coil. The magnetic field generated by the permanent magnets on the speakers generates an interaction force, so this force causes the voice coil to vibrate with the audio current in the magnetic field of the speakers’ permanent magnets. The diaphragm of the speaker and the voice coil are connected together, so the diaphragm also vibrates. The vibration produces the same sound as the original audio signal waveform. The same waveform is the corresponding tone

〈1〉 Magnetic speaker: also known as “reed speaker”, its structure is shown in Figure 4. There is a movable core electromagnet between the two poles of the permanent magnet. When there is no current in the coil of the electromagnet, the movable core Attracted by the attraction of the two magnetic pole phases of the permanent magnet, it remains stationary in the center; when a current flows in the coil, the movable core is magnetized and becomes a strip-shaped magnet. As the direction of the current changes, the polarity of the strip magnet changes accordingly, so that the movable iron core rotates around the fulcrum, and the vibration of the movable iron core is transmitted from the cantilever to the diaphragm (paper cone) to drive the air thermal vibration.

〈2〉 Electrostatic speaker: It is a speaker that works by using the electrostatic force applied to the capacitor plate. In terms of its structure, the positive and negative electrodes face each other into a capacitor, so it is also called a capacitive speaker. As shown in the figure, there are two thick and hard materials as the fixed plates, which can transmit sound, and the middle plate uses a thin and light material as the diaphragm (such as an aluminum film). The diaphragm is fixed and tightened around it to keep a considerable distance from the fixed pole, and even on a large diaphragm, it will not touch the fixed pole.

The original DC voltage between the two electrodes (called the bias voltage). If the audio voltage output by the amplifier is added between the two electrodes and overlaps with the original output voltage, an alternating pulsating voltage is formed. This pulsating voltage is generated by the change in the attractive force of the gap between the two poles, and the diaphragm vibrates and sounds.

The advantage of the electrostatic speaker is that the entire diaphragm vibrates in phase, the diaphragm is light, the distortion is small, and it can reproduce extremely crisp sounds, with good resolution, clear details, and realistic sound. Its disadvantages are low efficiency, high-voltage DC power, easy vacuuming, and increased distortion of the diaphragm, which is not suitable for listening to rock and heavy metal music, and the price is relatively expensive.

(3) Piezoelectric speakers: Speakers that work by using the inverse piezoelectric effect of piezoelectric materials are called piezoelectric speakers. Dielectrics (such as quartz, crystals of potassium sodium tartrate, etc.) undergo polarization under pressure to cause a potential difference between the two ends of the surface, which is called the “piezoelectric effect”. Its inverse effect, that is, the dielectric deformed in an electric field, undergoes elastic deformation, which is called “inverse piezoelectric effect” or “electrostriction”.

Piezo speakers do not require a magnetic circuit compared to electric speakers, and do not require bias voltage compared to electrostatic speakers. They are simple in structure, cheap in price, and disadvantages are large distortion and unstable operation.

(4) Flame speaker: When the flame of air and gas passes through the electrode, the electrode is applied with a DC voltage and a high-frequency signal, and the flame is modulated by the audio signal to make a sound. The flame is almost massless and the sound dynamics are good. But it has fatal drawbacks: insecurity and inconvenience.

(5) airflow modulation speakers: also known as airflow speakers. It is a loudspeaker that uses compressed air as its energy source and uses audio current to modulate the airflow. It consists of air chamber, modulation valve, horn and magnetic circuit. Compressed air flows from the air chamber through the valve and is modulated by the external audio signal, so that the fluctuation of the air flow changes according to the external audio signal, and the modulated air flow is coupled through the horn to improve the efficiency of the system. It is mainly used as a sound source for high-intensity noise environment tests or long-distance broadcasting.

<Seven> Magnetically Distorted Speaker. This is a special strong magnet that can vibrate under the action of a magnetic field.

1. The difference between whole and part.

That is, the sound is a complete system, and the speakers are only part of the system. It belongs to sound generating equipment, and the system also includes other mixing equipment.

2. The difference between professional and amateur.

Both can also make sound. But the sound is a professional-level sound system from the function to the configuration. A loudspeaker is a simple sounding system usually composed of one or two ordinary loudspeakers. Just like home theater can be called audio, and computer speakers are usually only called speakers because of their simple function and low effect.

Speaker Introduction

A speaker is a device that converts audio signals into sound. Generally speaking, it refers to the power amplifier built into the speaker cabinet or subwoofer cabinet. After the audio signal is amplified, the speaker plays back the sound to make it louder.

The speaker is the terminal of the entire sound system, and its role is to convert audio power into corresponding sound energy and radiate it to space. It is an extremely important part of the audio system, and it is responsible for converting electrical signals into acoustic signals for human ears to directly listen to.

The composition of the speaker:

There are a variety of speakers on the market, but no matter which one, they are composed of the two most basic parts: the speaker unit (referred to as the speaker unit) and the cabinet. In addition, most speakers use at least two or more The speaker unit implements so-called multi-way split playback, so the crossover is also an essential component. Of course, there may be other components in the speaker, such as sound-absorbing cotton, inverted tube, folded “maze pipe”, ribs / reinforcing partitions, but these components are not indispensable for any speaker. The elements have only three parts: the speaker unit, the cabinet and the crossover.

The classification of speakers is:

The classification of speakers has different angles and standards. They are divided according to the acoustic structure of the speakers. There are closed boxes, inverted boxes (also called low-frequency reflection boxes), passive radiator speakers, and transmission line speakers. For their respective characteristics, see details. Related question and answer. Inverter boxes are the mainstream of the current market; judging from the size and placement of the speakers, there are floor boxes and bookshelf boxes. The former is relatively large and is usually placed directly on the ground. Sometimes, shock-absorbing feet are also installed under the speakers nail. The floor box has a large volume and is convenient to use larger and more woofer. Its low frequency is usually better, and the output sound pressure level is higher, and the power carrying capacity is strong. Therefore, it is suitable for large listening area or comprehensive requirements. For occasions.

The bookshelf box is small in size and usually placed on a tripod. It is characterized by flexible placement and does not take up space. However, due to the volume of the box and the size and number of woofers, its low frequency is usually not as good as the floor box, which carries power and output sound pressure. The level is also smaller, suitable for use in a smaller listening environment; divided according to the narrow bandwidth of the playback frequency, there are wide-band speakers and narrow-band speakers. Most speakers are designed to cover the widest possible frequency band. , Belongs to wideband speakers. The most common narrow-band speakers are the subwoofers (subwoofers) that have emerged with home theaters. They are only used to restore a low-frequency to a very low-frequency band; according to the built-in power amplifier, they can be divided into passive speakers and Active speakers, the former does not have a built-in amplifier and the latter has. Most home speakers are currently passive, but subwoofers are usually active.

Audio Introduction

Sound refers to sounds other than human language and music, including sounds of the natural environment, sounds of animals, sounds of machine tools, and various sounds made by human actions. The sound probably includes a set of amplifiers, peripheral equipment (including limiters, effects, equalizers, VCD, DVD, etc.), speakers (speakers, speakers), mixers, microphones, display devices, etc. Among them, speakers are sound output devices, speakers, subwoofers, and so on. A loudspeaker includes three types of speakers: high, low, and medium. There are three, but not necessarily three. The development history of technology can be divided into four stages: tube, transistor, integrated circuit, and field effect tube.

Audio components:

Audio equipment probably includes power amplifiers, peripheral equipment (including limiters, effects, equalizers, exciters, etc.), speakers (speakers, speakers), mixers, sound sources (such as microphones, musical instruments, VCD, DVD) display equipment Wait a moment to add up a set. Among them, the speakers are sound output devices, speakers, subwoofers, etc. A speaker includes high, low, and medium speakers, three, but not necessarily three.

Speaker sound principle:

To understand the principle of speaker sound, we first need to understand how sound is transmitted. The propagation of sound requires a medium (vacuum cannot transmit sound); the sound relies on all gases, liquids, and solids as media to spread out. These substances that are used as media for transmission are called media. It’s like water waves. When you throw a stone on a calm water surface, there is a wave on the water surface, which then spreads to the other side for 4 weeks. The sound wave is also formed like this. The frequency of sound waves is in the range of 20-20, 000 Hz, which can be heard by the human ear; below or above this range, the human ear cannot hear.

Water waves and sound waves travel in the same way. Through the propagation of media, human ears can hear sound.

Sound waves can propagate in gases, solids, and liquids

Let’s talk about the working principle of the speaker. A horn is a device that converts electrical signals into acoustic signals. It consists of coils, magnets, paper cones, and so on. The amplifier outputs a current of varying size (AC), which moves the coil under the action of a magnetic field through the coil. The coil is connected to the paper cone to drive the paper cone to vibrate, and the vibration of the paper cone pushes the air to make a sound.

The horn speaker is still widely used in some markets in rural and urban areas. Once the sound film of the horn speaker is lost, it is necessary to ensure the correct installation of the sound film. The following introduces a method that can easily solve this problem. Installation can be performed in two steps.

The first step is to select paper of appropriate thickness and cut two pieces of paper with a width of ~ 10mm and a length 20mm larger than the diameter of the center piece. Then place the two paper strips on the center piece perpendicular to each other (the position should be centered). To prevent them from moving, you can stick them with a little paste. Insert both ends of the paper strip into the magnetic gap. Align the voice coil on the sound film with the magnetic gap and gently press it down. Due to the existence of the paper strip, the position of the voice coil at this time is exactly in the middle of the magnetic gap without being deflected. Measure and apply universal glue on the edge of the sound film, and cover the top of the sound head. Align the screw holes and tighten the screws. And remember the relative position of the upper cover and the sound head in the appropriate position. Leave it for 8 hours. After the universal adhesive is completely dry, you can unscrew the screws and remove the upper cover. At this time, the sound film was stuck on the upper cover.

The second step is to solder the leads to the terminals. Remove the two pieces of paper, and then put the cover back on, paying attention to the mark made originally. At this time, you can use the multimeter R × block or 1.5V dry battery. While constantly touching the two terminals to make a “click” sound, tap the cover to the maximum “click” sound, and there is no friction sound. Gradually tighten the fixing screws. When tightening the screws, they should be tightened alternately, instead of tightening one screw, then tighten the second screw.

Microphone, scientific name is microphone, translated from English microphone (microphone), also known as microphone, microphone. A microphone is an energy conversion device that converts a sound signal into an electrical signal.

The classifications include moving coil, capacitive, electret and recently emerging silicon micro-microphones, in addition to liquid microphones and laser microphones. Most microphones are electret condenser microphones, which work by using a polymeric diaphragm with permanent charge isolation.