I want to set up a simple recording studio in my room. What should I do to reduce the reverberation on the wall?

in the recording place of film production. In the film production process, in addition to the simultaneous recording in the studio and location, the pre-recording, post-recording, music recording, commentary and effect sound recording and mixed recording all need to be carried out in a special recording studio. Due to the different contents and requirements of various recordings, recording studios can be divided into two categories: the first category is dialogue recording studios. Mainly in recording language, it can be used for dubbing the dialogue of feature films and translated films, recording the commentary of news documentaries and science and education films, recording the sound effects of various films, and can also be used as a mixed recording studio. There are 1 ~ 4 actors in the shed. The second category is music recording studio. Large-scale recording for large and medium-sized bands and choirs with 8 ~ 12 people; Medium-sized bands and choirs with 2 ~ 4 people can record; Small-sized recording rooms for soloists and soloists are recorded under the accompaniment of bands in large-scale music recording studios. This studio can also be used for small ensemble and effect sound recording for less than 8 people, so it is not necessary to set them up separately, but a small room is set up in a corner of the large-scale music recording studio, separated by a viewing window. For studios with large output, the mixed recording studio can be set up separately.

The basic body shape of a studio plays a decisive role in the sound quality of the studio. Choosing a suitable body shape will lay the foundation for good sound quality. See Table 1 for the dimensions of general recording studios.

Table 1 Physical dimensions of recording studios

In order to obtain a uniform normal vibration frequency distribution in the low frequency range, the size ratios of different types of recording studios are different. The ratio of length, width and height of a large music recording studio can be controlled at 3:2:1, that of a medium-sized studio at 2.5:1.5:1 and that of a small studio at 1.6:1.3:1. The plane geometry of the recording studio includes: rectangle, trapezoid, trapezoid at the front end and rectangle at the back end or other irregular shapes. Section shapes include: horizontal ceiling, inclined ceiling with low front and high back, and ceiling with inclined front and flat back. No matter what shape, it should create conditions for good sound quality and avoid all kinds of acoustic defects.

the sound quality is the main sign of the quality of the recording studio. The sound quality design of recording studio is based on the law of sound propagation in the room and the relationship between sound and hearing, which includes the following aspects. ① Reverberation time. It is the main index to evaluate the sound quality of recording studio, but it is not the only index. The best reverberation time varies with the purpose and volume of the recording studio; The reverberation time of music recording studio is long, which can make direct sound and reflected sound blend together, thus making the sound full; The reverberation time of the dialogue studio is short, so as to avoid the confusion of the voice before and after the speech and improve the clarity of the language. In the same kind of recording studio, the reverberation time of large volume can be slightly longer than that of small volume. The best reverberation time of intermediate frequency in recording studios with different uses and volumes is shown below. It gives the allowable range of the optimal reverberation time. The reverberation time in the figure is the best value of the intermediate frequency, the low frequency can be slightly higher than the intermediate frequency, and the high frequency should be kept flat with the intermediate frequency. The reverberation time of the recording studio is also different due to different recording techniques. The above optimum values refer to mono recording under natural reverberation conditions. In the multi-channel recording process under the condition of strong sound absorption, the reverberation time of the recording studio must be greatly shortened, generally between .4 and .6 seconds. In order to meet the acoustic requirements of different recording techniques and different uses, we can build a multi-purpose recording studio that can adjust reverberation time and change other acoustic parameters to improve the utilization rate of the recording studio. Changing reverberation time mainly depends on adjustable sound absorption structure. Adjustable sound absorption structures can be generally classified into three types: rotary, push and flip. The maximum adjustable area of the three structures is more or less. Generally, the adjustable area of the wall is about 2% of the total area, and with more than 2% of temporary adjustable sound absorption materials, such as carpets, curtains, acoustic screens, etc., the range of adjustable reverberation time can reach nearly 1 second. ② Early reflection sound. In addition to direct sound, the sound entering the microphone is also reflected from various surfaces in the shed. The early reflected acoustic energy within 5 ~ 8 milliseconds enhances the loudness of sound, language clarity and music fullness, so the early reflected acoustic energy at the microphone positions in the shed is increased to obtain good sound quality. The shape and material of the recording studio have a direct impact on the early reflected sound. Various diffusers with different shapes are arranged on the inner wall of the shed and various diffuser structures are arranged on the ceiling in order to generate more early reflected sound. In a large-scale music recording studio, only relying on the diffusion structure of the wall and ceiling can not obtain enough early reflected sound, and it needs the help of the reflective surface of the movable acoustic screen to supplement it. ③ Sound field distribution. The uniform sound field distribution in the recording studio is convenient for the sound engineer to choose the best position of the microphone, and also enables the performers and singers to correctly grasp the dynamics, thus making the music and sound balanced and mixed. Therefore, the wall and ceiling in the shed are configured with asymmetric reflectors and reflecting surfaces with different shapes. The sound field distribution is expressed by the decibel difference between the maximum sound pressure level and the average sound pressure level at each point in the shed. In general, this difference does not exceed 3 decibels, and the maximum and minimum values do not exceed 6 decibels. ④ Diffusion. Good diffusion can ensure the sense of space, fullness and activity of the sound, and maintain the naturalness of the tone in the shed. Irregular or protruding surfaces can reflect acoustic energy in many directions, so it is an important means to arrange diffusion surfaces and diffusers everywhere on the wall and ceiling to obtain good diffusion.

The mixed recording studio with electro-acoustic response characteristics is a recording place where various vocal cord materials (language, music and various effect sounds) are mixed into a sound structure and sound technical requirements that meet the film creation intention. The mixed sound engineer judges whether it is good or not according to the mixed sound he has heard in the mixed recording studio. The electro-acoustic response characteristics of the mixed recording studio-the frequency response characteristics of sound pressure generated in the area where the mixed recording artist works after passing through the monitoring power amplifier, frequency division network and loudspeaker-should be consistent with the electro-acoustic response characteristics of the cinema. Therefore, it is necessary to unify the electrical audio response characteristics of mixed recording shed and cinema and their measurement methods, so as to provide conditions for the consistent auditory effects of recording and playback. Because the electro-acoustic response characteristics required by the conventional film vocal cords with narrow frequency band and the optical stereo vocal cords with wide frequency band are different, the electro-acoustic response characteristics of the mixed recording shed are also divided into two types, one is the mixed recording conventional film vocal cords, which is called "N" characteristics, and the other is the mixed recording stereo vocal cords, which is called "X" characteristics.

there should be no acoustic defects in the acoustic defect recording studio. The acoustic defects that usually appear in the recording studio are mainly echoes and vibrating echoes, which interfere with the sound quality. Echo refers to the acoustic reflection of two sounds that can be distinguished. When the reflected sound is 17 meters longer than the distance of direct sound, that is, the arrival time is more than 5 milliseconds, an echo will be formed. The distance of reflected sound between the front and rear walls of the recording studio is the longest, which is easy to echo; Parallel walls on both sides often cause trembling echoes. Therefore, it is beneficial to eliminate echoes and vibrating echoes without parallel walls and suspended ceilings in shape, irregular and non-parallel reflecting surfaces and diffusers in acoustic structure, and proper arrangement of sound-absorbing materials.

Noise controls the noise of the recording studio within the allowable range, which is an important indicator of acoustic design. The allowable noise level in the recording studio is shown in Table 2. When a higher standard is adopted, NC-15 noise evaluation curve can be used, and the single value is 25 dB. When using a slightly lower standard, NC-2 can be used to evaluate the curve, and the single value is 3 dB. Noise control in the shed includes sound insulation of enclosure structure, noise elimination and vibration reduction of air conditioning system.

table 2 allowable noise level in the recording studio

the enclosure structure of sound insulation recording studio should have certain sound insulation ability to isolate the external environmental noise, so that the allowable noise level in the shed can reach the above standards. The wall is made of solid brick wall with a thickness of 49 mm, and the average sound insulation can reach 6 decibels. The roof adopts reinforced concrete large roof slab and aerated concrete insulation layer, which can achieve the same sound insulation as the wall. If double-layer overhead slabs can be used, the impact sound can be isolated. The recording studio and the auxiliary room should be separated by a double wall with a thickness of 37 mm, with a gap of 12 mm between the walls to prevent solid sound transmission. The pipeline passing between the two walls should also be treated to avoid forming an acoustic bridge. The recording studio should adopt double-layer sound insulation doors, and the wall of the small suite between the two-layer doors is coated with sound-absorbing materials, so that the double-layer door and suite form an acoustic lock. The sound insulation capacity of this structure can reach 5 ~ 55 decibels. The sound insulation door is a multi-layer composite door made of plywood, tongue-and-groove wood, rock wool board, felt and steel plate, etc. The door gap between the door leaf and the door frame should be sealed with rubber gasket, and a door lock that can make the door leaf and the door frame press tightly should be used. The observation window between the recording studio and the auxiliary room, and the projection hole between the recording studio and the projection room need to be soundproofed with 2 ~ 3 layers of 8 ~ 12mm thick glass. The thickness and spacing of the three layers of glass are not equal, and the positions are not parallel, so as to avoid the vibration of the two cavities. The window frames around the cavity should be coated with sound-absorbing materials, and the glass and window frames, window frames and walls should be sealed. The sound insulation capacity of this kind of window can reach 5 decibels.

the air conditioning and ventilation system of anechoic recording studio must be treated with noise reduction and vibration reduction. The air conditioning and ventilation room should keep a certain distance from the recording studio and make them completely separated from the building structure. The base of all machines that produce noise and vibration should be a spring vibration damping base, and the fan room should be sound-absorbed Before entering the shed, the pipes connected with the ventilator should be silenced, such as broadband impedance muffler and "chamber muffler". Chip aerated concrete muffler, slag expanded perlite resistive composite muffler or "labyrinth muffler" can be set in the air supply duct and return duct. Each air outlet can also be provided with an acoustic muffler to reduce the regenerative noise caused by the airflow generated by the wind speed.