table of Contents:

The first chapter of the home theater audio debugging full analysis of the speaker wiring debugging

The second chapter of the home theater audio debugging full analysis of the subwoofer settings

Chapter III Use of Sound Analyzer for Full Analysis of Home Theater Audio Commissioning

The fourth chapter of the home theater audio debugging full analysis of the power amplifier configuration

The fifth chapter of the home theater audio debugging full analysis of the impact of the power supply

The sixth chapter of the home theater audio debugging full analysis of the two-line crossover

The seventh chapter of the home theater audio debugging full analysis of the top ten lies in the audio industry

Chapter III Use of Sound Analyzer for Full Analysis of Home Theater Audio Commissioning

What is the sound pressure level?

The sound pressure level is a measure of the magnitude of the sound vibration pressure at a certain point. It usually uses decibels to indicate the size of its value. Therefore, the unit of sound pressure level is dB SPL. The higher the sound pressure level, the louder the sound. The slightest sound we can hear is 0dB SPL. This is the lowest audible threshold mentioned earlier. We hear a variety of voices everywhere in our daily lives.

The concept of standard listening sound pressure level: Sound pressure level dB SPL Examples of sound pressure levels

Above 150 dB - take off at a nearby jet;

140 dB—near artillery launch;

130 dB—Rattle percussion at 15 cm, rock concert, pain threshold;

120 dB—symphony orchestra performance;

110 dB — small and medium ballroom;

100 dB—machine repair factory;

90 dB - subway;

85—Typical home high-fidelity audio listening volume, typical listening sound pressure level;

80 dB—busy road traffic;

70 dB—large and medium sized restaurant;

60 dB—face to face conversation;

50 dB — office average noise;

30~50 dB—room noise;

20~30 dB—stationary ambient noise in the studio;

0 dB — audible threshold, 0.0002 dynes/cm 2 , 4000 Hz, young people

Use process: Sound pressure meter (Hong Kong Xima AR824 noise meter / sound level meter / volume meter / noise meter AR-824)

Temperature range 30~130dBA (35～130dBC)

Measurement accuracy ±1.5dB

Frequency response 31.5HZ-8.5KHZ

Digital and resolution 5Digits & 0.1dB

Dynamic feature selection Fast/Slow

Microphone 1/2" condenser microphone

Frequency weighting characteristics A & C

Dynamic range 50dB

Sampling frequency 2 times/sec

In theory, the speaker is nominally the sound pressure value that can be released or expressed by the speaker. Generally, it is only for the moment, not for a long time. It depends on whether the power amplifier can give this power. However, the sound pressure value cannot be directly used. Measure the quality of the sound.

Test: adjust the total volume of the power amplifier to 0db, set the sound pressure meter to C weighting, slow gear, set the sound pressure gauge position to 80 decibels, and then measure the pink noise. The sound pressure meter reading should be at this volume. Measured, adjust the level of each channel, so that the sound pressure of each channel is maintained at 75, the center of the highlighting point can increase 1-2db, the bass channel should be larger than other speakers about 10db.

Test the wheat as far as possible from the back of the sofa, make sure that the test wheat 30 cm sphere is unobstructed, including your own, the sound pressure will drop in the front.

My Huiwei 6.3HT audio is matched with the Tianlong 3310 amplifier. The total volume of the amplifier is adjusted to 0db, and the sound pressure meter can't reach the value of 75. I think the power of the amplifier is not enough. The 9-1000-ton box is equipped with 6,000. The -7 thousand power amplifier is not good enough. The next chapter will talk about speakers and amplifiers.

Of course, as long as the sound pressure meter readings of each box are consistent, it is not necessary to entangle the 75db, 75db is the reference value.

After many attempts by the fans to change the settings and compare: "Kung Fu Panda in the Jaguar jailbreak and the finger pointing to the magical power; Ye Wen 2 in the scorpion Dan and Hong Jinbao contest paragraph; the final battle paragraph of the fuse line, etc. feel the speaker set large or small 5.0 channels The sound changes little, the sound details are similar, but the difference is not small, that is, after setting the small, the low frequency effect is stronger, the obvious low frequency volume and clarity is better than the effect of setting it to be large. Finally locked in the setting is small, come out The effect is personally satisfactory."

Sound system design theory, sound pressure level calculation formula to achieve the area space, sound power and area algorithm

Is the sound pressure level you want to achieve

After knowing the sound pressure level you want to achieve, you can use the following method.

The maximum sound pressure level (SPL) at a certain distance from the speaker = the maximum sound pressure level (dB) of the speaker - 20log distance (m)

For example; calculate the maximum sound pressure level at 10 meters above the speaker and substitute it into the above formula;

The maximum sound pressure level (SPL) at 10 meters from the speaker = 1010 (dB) - 20log10 (meter) = 90dB

The above calculation formula is calculated on the axis of the speaker. If there is an off-axis angle with the speaker, the function of the off-angle should be reduced. Generally, the estimation is not required. In the range of the radiation angle of the speaker, the speaker axis and the radiation angle are The edges differ by 6 dB and can be estimated from this. In the case of multiple speakers in a room, the maximum sound pressure level at a certain point (mono sound reinforcement, that is, the information of each speaker is the same) is more complicated, and is related to the indoor critical reverb (including room The sound absorption coefficient and space size) are related to the delay time of each speaker reaching this point. Simply put, the sum of the maximum sound pressure levels of each speaker from this point is added to the critical point of this point. The difference between the reverberation sound pressure level and the direct sound pressure level during the reverberation time (I wonder if this expression can be clearly stated), the maximum sound pressure level at a certain point = 10log (speaker 1 + speaker 2+....... ) + (reverberation sound pressure level - direct sound pressure level) The above calculation has two conditions; one is that the maximum sound pressure level of a speaker at this point is less than the maximum sound pressure level of other speakers at this point.

supplement:

The first indicator in the sound reinforcement system indicator is “maximum steady-state sound pressure level”. The sound pressure level is simply the sound size heard in dB (decibel). The sound pressure level differs by 3 dB in the equipment index. The output power is doubled, and the maximum sound pressure level of the speaker (that is, the maximum sound output from the speaker) is the function of the rated output power (non-peak power) of the speaker plus the sensitivity of the speaker. The calculation formula is;

Speaker maximum sound pressure level (SPL) = speaker sensitivity (1W / m) + 10log speaker rated output power

That is, the output sound of the speaker is determined by the rated power of the speaker and the sensitivity of the speaker.

For example; a speaker (100w, sensitivity 90 dB) is substituted into the above formula;

Speaker maximum sound pressure level (SPL) = 90 (1W / m) + 10log100 = 110dB

A speaker (200w, sensitivity 87 dB) is substituted into the above formula;

Speaker maximum sound pressure level (SPL) = 87 (1W / m) + 10log200 = 110dB

From the above calculations, it can be seen that the 100w speaker with a sensitivity of 90 dB is as large as the sound of a 200W speaker with a sensitivity of 87dB.

Above is the sound pressure level 1 meter away from the speaker

At the end of the sound field design, the calculation of sound pressure level should also be considered: avoidance of acoustic vibration, focus, and feedback.

For the problem that the sound vibration, sound focus, and sound feedback bring poor sound reinforcement, some people can only say that the sound effect is not good, and all of them are classified as equipment. This is not appropriate. In fact, they should all belong to the sound field. Category, usually these problems do not happen from time to time, so in general engineering, often can not attract enough attention, even if these problems occur, many people do not realize that this is caused by the unreasonable sound field, or that is known as the sound field The hospital is unreasonable and there is no way to solve it. For example, the sound system work is generally normal, but occasionally a rhythmic pulse-like sound or "squeaky" sound can be heard on the spot. Usually it is most likely to occur in some places in the middle and low frequency bands. When the hall is large, the sound is separated from the direct sound for a long time, which makes people feel very uncomfortable. This is a kind of tremor. The reason is that the sound is relatively parallel in the hall. The walls are reflected back and forth, and the reflection of the wall is very strong, so the sound energy is hard to be weakened. Therefore, it is required to check whether there is any in the hall at any time during the decoration. Two large reflective areas with strong reflexivity, there are not too many glass, stainless steel structure, because these things that seem normal in the decoration unit may cause problems; the arc surface of the sound focus occurs Xuan some large decorative items or hanging curtains, curtains, etc., to reduce the possibility of acoustic focusing; pre-prevention of acoustic feedback is more difficult, and the design can not accurately predict the frequency of feedback, but the prevention of acoustic feedback The practical application is more important, so the sound absorption coefficient at different frequency points can be analyzed by the selection of decorative materials in the early stage of design, and the calculation of the reverberation time can be roughly judged to provide necessary reference for construction and commissioning. Of course, the sound should completely solve the above problems. It should be improved by the later equipment debugging. Generally, after the completion of the project, the signal generator and the spectrum analyzer are used to detect the sound reinforcement area, and the equipment is repeatedly debugged. To make up for the lack of sound field.

Calculation of reverberation time

For the sound field design, the average person can understand intuitively, and the more contact is the reverberation time, because it is the most controllable quantitative indicator in the design. The importance of reasonable reverberation time is reflected in the design. The sound field will make the sound system perform very well, giving the impression that the sound is full and round, not dragging, and not disturbing. It can be said that if the requirements of the sound field design in the front can be satisfactorily satisfied, the reverberation time can be controlled. If you are good, you can add a lot of sound effects. You must first choose a reasonable reverberation time target value before calculation. The selection of this value is generally based on the volume and purpose of the hall.

On the specific value, most designers prefer to make the recommended sound field reverberation time smaller. The reason is: the sound field reverberation time can not be adjusted after a long time, so it is suggested that the hall should be more natural. The better, the better, in the debugging and use, the artificial reverberation is added to the system to meet the reverberation requirements. At the same time, in recent years, the interior decoration materials are increasingly updated, and the materials with higher sound absorption coefficient are widely used, which makes the mixing of a large number of halls. The ringing time is generally small. It can be seen that the starting point of this design principle and the influence of objective conditions are not doubtful, but it should be known that the reverb sound in the sound field is the natural reverberation produced by the sound source. It is based on direct sound to show its particularity. It is an important characteristic in the sound field. When the system is used, artificial reverberation is added, which is equivalent to the direct sound of the signal and the reverberation. In the sound that is played, there is no direct sound that the sound engineer wants you to hear. The professional audio usually adds different levels of reverberation when recording the program, which is equal to destruction. The source of the program (sound source), so this method not only disturbs the good relationship between the direct sound and the reverberation, but also violates the sound field reverberation in order to make the room have the proper "canton" purpose. Can be proposed for engineering design sales staff to discuss.

The brief reverberation time is calculated as follows:

General engineering can be carefully calculated at home at 500 Hz or kHz. The sound absorption coefficient of various materials should be strictly in accordance with the data provided in the product parameters or the building materials manual. Otherwise, the calculation results may be larger and larger, of course, with the recommended values. Based on the near calculation results, the designer does not need to ask the decoration unit to improve too much, because the reverberation time requirement is not a specific absolute value, as long as the disparity is not too large, the calculation should also consider the audience. The effect on reverberation time.

At the end of the professional sound field design, the calculation of sound pressure level should also be considered. The purpose is not only to provide users with feasible engineering electroacoustic parameters, so that they can safely and correctly use the equipment to create a healthy and listening environment. In order to provide a basis for the electrical design in the sound engineering, it provides a reference for the selection of equipment.

Before calculating the sound pressure level, it is necessary to select a corresponding appropriate environment for its quasi-sound pressure level, and the selection of the reference sound pressure level must understand the equal-acoustic curve of the normal human ear, namely the Fletcher-Munson curve.

The curve reflects the human ear's response to different frequencies and different sound pressures. The numbers on the curve indicate the corresponding frequencies and loudness values ​​under sound pressure. The unit is: Phono, the human ear's sound with different frequencies of the same sound pressure. The response is not the same. The sound level of the low-frequency sound of the same sound pressure level in the human ear is lower than the high-frequency sound of the same sound pressure level; if the sound of each frequency band is basically the same in the human ear, In the absence of hearing in certain frequency bands, it is necessary to achieve a sound pressure level of sound pressure, which is the basis for selecting the sound pressure of the sound pressure.

For the language sound reinforcement project, since the language signal is mainly concentrated in the middle frequency band, the equal response curve degree is less correlated here, so the reference sound pressure level can be 70~80dB; for the sound engineering of general music playback, this reference sound The pressure can take 85~90dB as the basis for calculation; at the same time, leave the peak of 12~18dB peak and the ambient noise margin of 1~3dB for the sound reinforcement of the system, then the rated spread of the design on the average listening distance The sound pressure level should be: P = (85 ~ 90) dB + (1 ~ 3) dB and then the average listening distance L needs to be determined according to the actual sound range of the hall. The rated sound pressure level should be at this position. The actual sound pressure level, and then the sound pressure level P of the 1m position of the speaker can be calculated by:

According to the above mentioned: the relationship between the distance change and the sound pressure correspondingly changed by 6dB, the sound pressure level that the speaker needs to provide at 1m is: P=P amount +6LogL, the design of the sound is basically finished, then The job is to work closely with the building decoration unit to put the design requirements into practice. More home theater knowledge, all in the home theater network WeChat cnhifi.

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