1.
If there is noise in the stereo, you can turn the volume of the stereo to the maximum without input signal, and listen to whether there is any sound, what kind of sound it is and whether it is acceptable.
2.
The sound quality mainly depends on the ears, including treble, alto and bass.
3.
In the bass part, the bass effect can be said to be a very important part of the overall sound quality, which is directly related to the shocking effect of sound fullness. For the performance requirements of the bass unit used in the loudspeaker, the following tests can be carried out. Put a glass of water next to the speaker. A speaker with good bass effect can cause the vibration of the glass. The better the bass effect, the more obvious the effect, the longer the time, the more realistic the weapon sound and explosion effect, and the better the shock effect.
4.
In the midrange part, it is difficult to distinguish the sound quality for most speaker products. Its main function is to produce a sense of reality, and you can watch multi-channel movies during the test.
5.
In the high-pitched part, the high-pitched effect of the speaker is generally intuitive, such as singing and some special electronic sound effects, and even some extreme sounds beyond the hearing range. You can feel it with some high notes, such as Vesta's CD.
How to audition when buying a speaker?
1\ Listening to noise other than music. The volume increases from small to large, and the maximum volume does not exceed the power of the speaker.
2. When the speaker is outputting high power, the surface vibration of the speaker is very small.
3. A pair of speakers should have the same loudness and sound symmetry. Use mono channels to listen to a pair of speakers in series or in parallel. Listen to the audition at a certain distance.
How do we test the sound system?
Lead: Friends who are new to the fever circle may be vague about the concept of evaluating the sound system. What aspects are evaluated? How to make an accurate evaluation? Solve problems for everyone here.
In fact, to put it bluntly, sound quality evaluation = "objective technical parameter measurement"+"subjective listening experience". Here we mainly talk about subjective aspects.
Evaluation of a system is sound, mainly in the following three aspects.
Three elements of sound system evaluation
First of all, loudness
Refers to the intensity of sound in decibels (dB). The sound pressure that the human ear can bear is between 0- 120B, and 120B is an auditory pain valve, which will instantly damage hearing!
The distribution of sound pressure is listed by the phenomena in real life:
10-20 dB: the sound of the clock.
80- 100 dB: truck noise on the street.
20-40 dB: speak in a low voice.
100- 120 dB: the strongest sound of the symphony.
40-60 dB: Window air conditioner
120- 140 dB: jet plane takes off.
60-80 decibels: noisy office
Second, the tone
Refers to the high and low frequency of sound. The frequency that the human ear can hear is called audio, which is about 20Hz-20kHz, and the unit of use is Hz. The seven common parts are as follows:
20-40Hz: Subbass
40- 160 Hz: bass
160-3 15Hz: alto.
3 15-2.5kHz: alto
2.5-5kHz: tenor.
5- 10kHz: treble
10-20kHz: ultra-high pitch
Third, timbre.
That is to say, the sound characteristics, usually pitch, are different from the intensity of overtones. This sound element can be understood as the sound made by piano, violin, guitar and other musical instruments.
A simpler understanding is that timbre depends on different overtones. The sound produced by every musical instrument, different people and all objects that can make sounds is accompanied by many overtones of different frequencies in addition to a pitch. These overtones determine their different timbres.
How to make an accurate evaluation
A set of sound system, its sound quality effect is based on the comprehensive embodiment of the above three elements of sound, in order to accurately evaluate sound, we should do the following three steps:
The first step is the basic speaker positioning.
▲ regular triangle method
This is the way to hear the most, the most direct and the clearest details, and many people like to use this way when evaluating the sound system.
In this way, the distance from the sound to the left and right ears is equal, and the position of the characters on the screen is the best listening position, which is what we call "the mercy position".
If you want to achieve the emperor's throne effect in the car, the situation is much more complicated than the above picture. With the help of the DSP audio processor that Sima will soon launch, the distance from the left and right channels to the ears can be made the same through the delay function.
The second step is to play the music at the correct volume.
Adjust the volume of the power amplifier to 80-90dB, which is slightly higher than the ordinary call level, but it will not be too laborious to avoid the sound quality deterioration caused by too small or too large sound pressure.
According to the data of sound quality evaluation, the sound pressure level of 80-90dB when playing music is the most beautiful for human hearing, which is also the sound pressure standard for sound quality evaluation at home and abroad.
The third step is to select tracks:
Male and female voices
The most familiar and sensitive part of the human ear, whether the timbre structure of this part is reasonable or not, is related to the quality of the sound, and can also show the distortion of the sound system, that is, the sound is round, full and transparent.
Enthusiasts strongly recommend the audition of Chinese female song "Cai Qin", which is widely recognized.
percussion instrument
It is used to evaluate the transient response ability, volume sense and frequency dive degree of the bass effect of the speaker with the lowest sound quality in the sound system.
In the sound system, low frequency is an important foundation of HiFi, and the loss of high-quality bass effect will greatly reduce the fun of music appreciation.
The famous audition disc EAGLES Eagles can be said to be a comprehensive demonstration disc, and one of the opening songs of Hotel California has been playing drums for more than ten or twenty years, which can be proved.
the classical symphony
Because there are many musical instruments, it can show the layering of high, medium and low frequencies of the sound system, that is, the frequency characteristics.
Generally speaking, it is to listen to the instruments of each voice clearly. Because most classical music is played and produced in concert halls with good acoustic environment, it can also show a sense of space in the scene of sound system, which is of course related to the listening environment.
Electronically synthesized music
Represents the dynamic range of sound pressure and sound level of a sound system. Some famous electronic music is made of non-acoustic instruments, which can almost reach the limit of audio equipment. On the cover of the CD, sometimes it is marked "Pay attention to control the volume! Be careful not to burn the horn.
Because there is no point sound source effect when playing musical instruments, the sound stage (that is, the sound field) can be made very wide by the method of anti-equivalence.
jazz
Demonstrate the positioning ability of the sound system and the consistency of stereo speakers. Jazz tracks are played with fewer instruments, and there are solos by various musicians, which can get clear audio-visual positioning, and it is also the track that most easily reflects the charm of stereo music.
Solo instrument
Express the resolution, transparency and timbre structure of the sound system. Most musicians will use some difficult techniques to play complex songs.
Lead: At present, most professional stereos used in domestic dance halls are imported equipment, which should be said to be highly reliable. The main problem is that the professional quality of operators is uneven, and there are few units equipped with qualified Andhadhun. Therefore, improper operation often leads to poor sound effects and even damage to equipment. In this paper, the operating points of audio equipment in small and medium-sized dance halls are explained, which can be used as a reference for formulating operating rules. In addition, in small and medium-sized dance halls, the phenomenon of self-excited whistling caused by microphone sound feedback is a common headache for users, because frequent whistling will disappoint guests, the acoustic effect is impossible to talk about, and in serious cases, it will cause equipment damage. Therefore, the phenomenon of self-excited howling is an important problem in the sound of ballroom, which is described separately below.
First, the audio equipment on and off sequence
Boot should start from front to back, that is, from the sound source equipment (CD player, ld player, DVD player, tape recorder, video recorder) and audio processing equipment (voltage limiter, exciter, effector, frequency divider, equalizer, etc.). ) to audio amplifier to TV, projector and monitor. Turn off the power amplifier in reverse order. This operation can prevent the impact of switching equipment and prevent the power amplifier and speaker from being burned.
Second, preparation before singing-debugging
1. The volume control potentiometer of the power amplifier should be set to the maximum position; The accompaniment music and microphone splitter on the mixer should be set on the 0dB mixer, and the gain input gain of each branch should be placed in the adjusted position; The fader of the total volume of the mixer is first placed at the minimum position (lower end); The sound quality compensation knob of the mixer is placed in the middle position.
2. Experiment with the accompaniment channel, that is to say, play songs and music with CD or LD, and jump the mixer to nearly -—6dB. At this time, the singing and accompaniment music are roughly at the normal working volume; However, it should be noted that the volume is moderate and pleasant, and excessive loudness is easy to make people tired. Andhadhun wants to listen to the effect in different positions in the hall. Such as stereo audio and video, music quality and so on. The music you play should be familiar with. You can adjust the volume repeatedly (adjust the shunt gain) to compensate the shunt sound quality until the sound effect is satisfactory. The requirements for music effects should be strong and aesthetic, the high notes should not be harsh, the low notes should not be muddy, and the singing should be clear, for example, the female voice's teeth sound is clear and audible, but not too heavy. Set the shunt fader at 0dB and the total volume fader at 0dB. Adjust the shunt gain input gain button to make the AU meter indicate about 0dB. At this point, the system reaches the rated output power. However, in normal operation, the total volume fader is generally adjusted below 6dB or-10dB, which is less than the rated output power.
3. Test the microphone channel. Generally speaking, at least two microphone channels should be prepared. Try the sensitivity and dynamic performance of the microphone first, and then add reverberation and accompaniment music to sing. The sound after reverberation treatment is rounder and fuller than the original sound, with a sense of hierarchy and scene. Adjustment of microphone volume: The shunt fader is set to 0dB, and the microphone volume is adjusted by the shunt gain input gain button. It is better that the indicator light of shunt peak level flashes occasionally, and the measurement of total output power depends on AU meter.
4. The audition adjustment of small bands is to audition the microphone lifting and electrical signals of various musical instruments and balance the sound proportion according to the music style.
5. Adjustment of video images, that is, projectors and color TVs should make their images clear and colorful by adjusting knobs such as brightness, contrast and color saturation. The sound engineer should be proficient in using DVD player and song ordering device, and be familiar with the disc position on the song ordering list. Note that when singing formally, you should press the D/A key on the DVD player. Eliminate the original song.
Thirdly, the adjustment of audio processing equipment.
Room equalizer. The room equalizer has two functions: one is to adjust the sound quality and make up for the unbalanced frequency response caused by the reverberation time in the hall; Another important function is to depress a certain frequency band and suppress the howling caused by acoustic feedback. The room equalizer should keep the position set during the debugging of audio engineering at ordinary times.
2. Pressure limiter. Voltage limiter is also an important equipment in audio engineering. Its functions are: first, to compress or limit the dynamic range of programs, to prevent overload or distortion, and to protect power amplifiers and speakers; Another important function is to improve the loudness of the program (which can be clearly felt by hearing).
The adjustment data of the pressure limiter are as follows: (1) Noise door: When the indicator light is on, the noise door is closed and the sound is low. Play the role of silencing. When the input signal drops to the threshold level, it starts to turn off, and the noise gate is generally placed between 0PEN and -—20dB. (2) Compression threshold level: Determine the level of starting compression, which is generally set to-10 to 0dB. At the beginning of compression, the gain decreases, and the gain decrease (dB) indicator light starts to light up. (3) Compression ratio RATT0: set to 2:1; (4) Action time attack: set to10 ms; (5) Release time: put it in O.3s
3. reverberator. At present, digital reverberator is widely used. There are many different reverberation effects solidified in this machine to choose from. Andhadhun wants to audition the reverberation effect of reverberator one by one, list the available sections, and use the keyboard in Andhadhun at any time.
Four, tuning point (mainly operating the mixer)
1. Andhadhun of karaoke bar works in the control room. When tuning, they should monitor the main channel and the return channel with the monitor box and monitor headphones respectively. Andhadhun should be familiar with the relationship between monitoring sound and live sound, and the adjustment of sound quality depends largely on personal hearing.
2. Use pressure limiter and exciter to increase the loudness and beauty of sound. The adjustment of the exciter mainly depends on hearing, and the sound should be adjusted to be full and pleasant according to the instruction manual of the equipment.
3. Beautify singing with reverberation. For non-professional singers, reverberation should be appropriately increased to cover up the noise and defects in their vocalization.
4. Pay attention to improving the low frequency and high frequency when the volume is low; When the volume is high, raise the intermediate frequency appropriately to enhance the brightness of the sound.
5. Tuning is mainly based on singing. When the song appears, the accompaniment gradually decreases to highlight the song. The low frequency should be attenuated by 3-5dB, the high frequency above 7kHz should be attenuated by 3dB, the intensity of middle and low frequency can be increased when it is raised around 200Hz, and the brightness of singing can be obviously felt when it is raised by 3-6dB at 2-4kHz. For disco or rock music, we should pay attention to greatly improve the low frequency (40- 100 Hz) and high frequency (7-20 Hz).
6. Don't turn the compensation button violently when raising the bass, so as not to damage the power amplifier and speaker due to excessive power output. Low frequency adjustment of the equalizer is also needed.
7. If there is whistling feedback, you should quickly pull down the fader of the total volume of the calling station to remove whistling, and then gradually push it up after finding out the reason.
8. When the main channel fails to play, the rotation angle of the echo speaker can temporarily replace the main channel, so that the singing can continue. The microphone for singing should be memorized. When the microphone is muted, it can be replaced by a backup. The DVD player should also have a backup, which can be replaced when the DVD player fails.
V. Suppressing acoustic feedback (howling)
1. Self-excited howling caused by microphone acoustic feedback is a common phenomenon in karaoke bars. Due to sound feedback, the gain of general public address system can't be very large. The causes of acoustic feedback howling are: (1) The microphone is too close to the speaker, and the microphone is facing the speaker; (2) The reverberation adjustment on the mixer is too large; (3) The microphone volume is adjusted too much; (4) The pressure limiter is not connected; (5) Auditorium acoustic design defects.
2. In view of the above reasons, the following measures can be taken:
(1) Define an approximate range for the singer's activity stage, and whistle should not appear in this range. In other words, the singer should not be too close to the main speaker, and the main speaker should be symmetrical on both sides of the stage; A singer should not stand with the microphone pointed at the speaker.
(2) The stage of the karaoke room should be acoustically treated, and sound-absorbing materials should be installed on the walls and sides.
(3) Connect the pressure limiter, the compression ratio should be set to = 2: 1, the action time is 10ms, and the release time is 0.3s.
(4) Don't turn up the reverberation and volume on the mixer.
(5) When the above measures don't work, we can adjust the equalizer to attenuate the frequency that is prone to howling. The specific operation method is as follows: firstly, record the position of each frequency point of the equalizer; Then, demonstrate it. Increase the volume (adjusted by the universal fader of the mixer) until the system just produces self-excitation, and lower the adjustment buttons on the equalizer one by one from the low frequency, which can effectively eliminate the frequency points of self-excitation howling. According to experience, there is generally only one self-excited resonance frequency (for example, 250Hz), which can be pulled down by 3-5 dB, and other frequency points should remain in the original recorded position. This method can effectively suppress acoustic feedback, but it can't give consideration to the music effect. Through adjustment, the stability margin of amplification gain can be 5-6 dB, which is necessary for the stable operation of the system.
(6) If the above measures are still ineffective, we can consider installing an acoustic feedback suppressor. For example, the frequency shifter can effectively overcome the acoustic feedback, so that the amplification gain can obtain a stable margin of 5-6. Only by doing the above can we ensure the smooth progress of the activities.