HC sound lighting network reported the importance of sound field like a speaker box. A good sound field will fully exert the advantages of the audio equipment, and appreciate the pleasing to the eye; and an unreasonable sound field will greatly reduce the performance level of the equipment and affect the sense of hearing. Of course, due to the level of architectural decoration and the user's understanding of the sound engineering, many projects were contacted with the sound construction unit very late, so that the design of the sound field could not be completed completely, which led to the lack of sound field design in many audio projects.
A basic sound field design includes: sound insulation treatment, reduction of on-site noise, requirements of building structure, realization of sound uniformity, avoidance of problems such as acoustic vibration, focus, feedback, etc., indoor calculation.
01 sound insulation treatment
In order to create a quiet sound field and avoid affecting the units and residents in the surrounding environment, at the beginning of the sound field design, the sound insulation should be considered first to provide a good innate condition for the sound field. The sound insulation involves the construction. Sound insulation from the outside world, sound insulation in each room in the building. The sound insulation includes: sound insulation of the partition wall, sound insulation of the doors and windows, and sound insulation of the ceiling of the room connected to the top.
For the sound insulation with the outside world, the general building structure can achieve the basic sound insulation requirements, but if the architectural design does not consider the need of sound engineering at all, it is necessary to conduct an investigation of the sound insulation, and if necessary, should design the building. The unit conducts consultations and knows the local noise restrictions from the public security organs. Usually do not use the height of the floor as sound insulation for the sound insulation between the rooms. If the wall is too thin, it will bring some difficulty to the project. This time, in consultation with the decoration unit, add a layer to the wall during decoration. Intermittent to solve the high and medium frequency sound insulation.
It is more difficult to completely solve the sound insulation of the low frequency band, because there is no more effective way than increasing the weight of the sound insulation body.
Doors and windows are the weak link of sound insulation treatment. For their sound insulation, it is recommended to improve the quality of the door and window. If necessary, use leather door and double glazing, or add isolation channel outside the door and heavy hanging on the window. Double curtains, etc.
It is also crucial for the ceiling of the ceiling in the room to communicate with each other. Especially in some large entertainment venues built in recent years, the sound of the hall has a great influence on the surrounding rooms, and some of the interference is from the top of the ceiling. Some of the sound insulation schemes cannot be proposed too late, otherwise it is difficult to implement, so the sound designer is required to ask questions to the decoration unit as soon as possible to coordinate a feasible solution. For example, cover the ceiling with a layer of fire-resistant sound-absorbing cotton or add a layer of ceiling to the top of the ceiling.
In short, the sound insulation treatment of the project is of great significance, which not only improves the quality of the project but also facilitates the normal use of the user. At the same time, it should be carefully considered whether the sound insulation treatment is necessary and whether the processing method is feasible, otherwise it will increase unnecessary work and expenses.
02 reduction of on-site noise
For the background noise of the scene, many people do not pay attention to it, but in the relevant national standards, they all put forward corresponding requirements, such as: the first-level karaoke should be less than 35dB, the first-level disco should be less than 40dB, the reason is: the increase of background noise Large correspondence reduces the signal-to-noise ratio of the sound reinforcement system and affects the quality of the project. To effectively solve this problem, the above-mentioned sound insulation is limited, for example, whether the air outlet noise of the central air conditioner allows the installation unit to help solve the problem; The noise, size, installation location of the fan, etc.
03 Building structure
The general sound is incapable of letting the building structure be designed according to its own intentions. However, for the part where the engineering quality is strict and the construction project is processed on the reconstructed structure, it is necessary for the sound designer to make corresponding requirements as much as possible. Here mainly talk about some local structural conditions:
First of all, it is necessary to obtain the approval of the building unit for the load-bearing capacity of the wall or roof that needs to be hoisted in the sound engineering. Especially when the weight of the light shed is large, the safety of lifting is more important;
Secondly, it is necessary to have a more detailed understanding of the room structure in the existing building, the location of the embedded pipeline, and the exit, in order to facilitate the possible insertion and wiring construction;
The other is to understand the weak links in the internal structure of the building, to find out what landlords can change, and where not.
04 sound uniformity realization
The concept of sound uniformity is generally not very clear. There is not too much consideration in the project. Is it not important? No, it is very important.
To give a simple example: When you go to an entertainment hall, you find that the sounds are different everywhere. Some places are very beautiful. Some places are like shortcomings. The sound is erratic. This is the effect of poor uniformity.
In the relevant national standards, it is generally required that the deviation of the field pressure level test value at each point is less than 2 dB.
How to achieve a uniform sound field?
First of all, there should be no obvious defects in the building structure. For example, there should not be too many columns in the room, and the walls should avoid arcs with traps, especially the wall on the side of the stage should not have a large structure; there should be no large shadow areas in the sound reinforcement range. However, since a large number of modifications cannot be made to meet these requirements after the completion of the construction of the building structure, it is necessary to use the experience in the sound engineering, skillfully arrange the sound reinforcement area, avoid the large defect structure, and bring them The impact is minimized;
Secondly, it can provide some simple solutions to improve the sound diffusion effect to the decoration unit in a timely and effective manner. For example, all concert halls have good sound diffusing effects because they use a large number of sound diffusers of various shapes, and these structures can be completed by some simple decoration methods, so as long as the method is right, it should be achieved. Good results, of course, it is not easy to make reasonable and appropriate design of the shape, position and quantity of the diffuser. Generally, the economically feasible method is to use the wall cement to pull the hair, although this method is relatively old. And not very beautiful, but it can play a very effective role in the sound diffusion of the hall.
Moreover, the reasonable arrangement of the sound system, especially the placement of the speakers must be strictly required. If you can use the computer design software provided by some speaker manufacturers to simulate the sound field in the design, it would be better if it is not, it should be adjusted in practice until the sound field is the best.
05 tremor, focus, feedback avoidance
For the problem that the sound vibration, sound focus, and sound feedback bring poor sound reinforcement, some people blame all the reasons on the audio equipment, which is not appropriate, in fact, they should belong to the field of sound field.
Usually these problems do not happen from time to time, so they often do not attract enough attention in general engineering. Even if these problems occur, many people do not realize that this is caused by the unreasonable sound field, or that it is the sound field. Reasonable, there is no way to solve it.
Acoustic vibration, for example: the sound system work is generally normal, but occasionally suddenly on the scene can hear rhythmic pulse-like "bashing" or "beep" sound, usually somewhere in the low and medium frequency bands Most likely to happen. When the hall is large, the sound is far from the direct sound, which makes people feel very uncomfortable. This is a sound.
The reason is that the sound is reflected back and forth between the parallel walls in the hall, and the reflection of the wall is very strong, and the sound energy is hard to be weakened. Therefore, it is required to check whether there are two reflective objects in the hall at any time during the decoration. Large area parallel surface, there are not too many glass, stainless steel structure. These things that seem normal to the decorating unit can cause problems.
The curved surface where the sound focus occurs is placed on some large decorative items or hanging curtains, curtains, etc. to reduce the possibility of sound focusing.
Pre-stage prevention of acoustic feedback is difficult, and the frequency of feedback occurrence cannot be accurately predicted during design. However, the prevention of acoustic feedback is more important for practical application. Therefore, it can be analyzed at different frequencies when designing decorative materials in the early stage. The sound absorption coefficient of the point is roughly judged by referring to the calculation of the reverberation time, providing necessary reference for construction and commissioning.
Of course, if we want to completely solve the above problems, we should rely on the later equipment debugging to improve. 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. Make up for the lack of sound field.
06 Calculation of reverberation time
Reverberation time is the most controllable quantitative indicator in the design. The importance of this is that if properly designed, the performance of the sound system is very good, 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 front sound field design can be satisfactorily satisfied, and the reverberation time can be well controlled, the sound effect can be greatly enhanced. Before calculating, you must first select a reasonable reverberation time target value. The selection of this value is generally based on the volume and purpose of the hall.
In terms of specific values, 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 natural sound of the hall will be more and more dry. Well, I hope to add artificial reverb to the system to achieve reverberation requirements during debugging and use.
At the same time, in recent years, the interior decoration materials are increasingly updated, and materials with high sound absorption coefficient are widely used, which makes the reverberation time of a large number of halls generally small. It can be seen that the starting point of this design principle and the influence of objective conditions There is no need to doubt, but it should be known that the reverberation sound in the sound field is the natural reverberation sound produced by the sound source. It is based on the direct sound to show its particularity and is an important characteristic in the sound field.
Adding artificial reverberation when the system is used is equivalent to adding the direct sound in the signal to the reverberation. At this time, the sound played by the speaker has no direct sound from the sound engineer. Although recording a program often adds different levels of reverberation, which is equivalent to destroying the source (sound source), this method not only disturbs the good relationship between the direct sound and the reverberation, but also violates the sound field reverberation. Make the room have the right purpose of "the hall". This point I think can be put forward for the engineering designers to discuss.
Brief reverberation time calculation formula
General engineering can be carefully calculated at home 500Hz or kHz. The sound absorption coefficient of various materials should be strictly in accordance with the data provided in the product parameters or building materials manual, otherwise the calculation results may be larger. Reverberation time requirements are not a specific absolute value, as long as the disparity is not too great, the calculation should also consider how much the audience has an impact on the reverberation time.
Best reverberation time reference for each hall
At the end of the 07 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, in order to facilitate their safe and correct use of equipment, to create a healthy listening environment, but also to provide a basis for electrical design in sound engineering. The selection of the model provides a reference.
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 curves indicate the loudness values ​​at the corresponding frequencies and sound pressures. The human ear responds differently to sounds of the same sound pressure and different frequencies. The sound 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; The loudness produced in the human ear is basically the same. If there is no shortage of hearing in some frequency bands, the sound pressure must be sufficient to achieve the sound pressure level. This is the basis for the selection of the reference sound pressure in the sound pressure calculation.
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 take 70~80dB;
For sound engineering for general music playback, this reference sound pressure can take 85~90dB as the basis for calculation;
At the same time, it leaves a peak of 12~18dB peak and 1~3dB of ambient noise margin for the system's sound reinforcement.
Then, at the average listening distance, the designed sound level of the sound reinforcement should be:
P amount = (85~90) dB+(1~3)dB
Then, according to the actual sound reinforcement range of the hall, the average listening distance L is determined, and the rated sound pressure level should be the actual sound pressure level at this position, and then the sound pressure level P of the speaker can be calculated by the calculation. :
According to the aforementioned: the relationship between the change of the distance 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
At this point, the design of the sound is basically over, and the subsequent work is to work closely with the architectural decoration unit to put the design requirements into practice.
Responsible Editor: Intern Reporter
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