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

On the recording scene of film production. In the process of film production, in addition to simultaneous recording on the set and location, pre-recording, post-recording, music recording, commentary and effect sound recording and mixing 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: 1 is a dialogue recording studio. Mainly in the 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 of large and medium-sized bands and choirs with 80 ~ 120 people; Medium-sized bands and choirs with 20 ~ 40 people can record; A small recording studio for soloists and soloists, accompanied by a band in a large music recording studio. This studio can also be used for small ensemble and effect sound recording with less than 8 people, so there is no need to set it up separately. Instead, a small room is set in a corner of a large music studio with a viewing window in the middle. For recording studios with large output, a mixed recording studio can be set up separately.

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

Table 1 Overall dimensions of recording studio

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

Sound quality is the main sign of recording studio quality. The sound quality design of recording studio is based on the propagation law of sound indoors and the relationship between sound and hearing, including 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 in the dialogue studio is short, which avoids the confusion of sounds before and after the speech and improves the clarity of the language. In the same kind of recording studio, the reverberation time of high volume can be slightly longer than that of low 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 recording studio is also different due to different recording techniques. The above optimum values refer to mono recording under natural reverberation conditions. In the process of multi-channel recording under the condition of strong sound absorption, the reverberation time of the studio must be greatly shortened, generally between 0.4 and 0.6 seconds. In order to meet the acoustic requirements of different recording technologies and different uses, we can build a multi-functional recording studio, which 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 usually be divided into three types: rotary, push and flip. The maximum adjustable area of the three structures is roughly the same. Generally, the adjustable wall area is about 20% of the total area, and it is equipped with more than 20% temporary adjustable sound absorption materials, such as carpets, curtains, sound insulation screens, etc. The adjustable reverberation time range can reach nearly 65438 0 seconds. ② Early reflex sound. Besides direct sound, the sound entering the microphone will be reflected by various surfaces in the shed. The early reflected acoustic energy within 50 ~ 80ms enhances the loudness of sound, the clarity of language and the fullness of music, so it increases the early reflected acoustic energy at the microphone position in the shed 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 to generate more early reflected sound. In a large-scale music recording studio, it is impossible to obtain enough early reflected sound only by the diffusion structure of walls and ceilings, and it needs to be supplemented by the reflective surface of movable acoustic screen. 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, so that music and sound can be balanced and mixed. Therefore, the walls and ceilings in the shed are equipped with asymmetric reflectors and reflective surfaces with different shapes. The sound field distribution is expressed by the decibel difference between the maximum sound pressure level of each point in the shed and the average sound pressure level. Generally speaking, 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 sound, and maintain the naturalness of timbre in the shed. Irregular or convex surfaces can reflect acoustic energy in many directions, so it is an important means to arrange diffusion surfaces and diffusers everywhere on walls and ceilings 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. Sound mixer judged whether it was good or not according to the remixes he had heard in the remix studio. The electro-acoustic response characteristics of the hybrid recording studio-the frequency response characteristics of the sound pressure generated in the working area of the hybrid recording studio after passing through the monitoring amplifier, the frequency division network and the loudspeaker-should be consistent with the electro-acoustic response characteristics of the cinema. Therefore, it is necessary to unify the electrical and audio response characteristics and measurement methods of mixed recording studios and cinemas, so as to provide conditions for the consistent auditory effects of recording and playback. Because the electroacoustic 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 electroacoustic response characteristics of the hybrid recording studio are also divided into two types, one is the mixed recording conventional film vocal cords, which are called "N" characteristics, and the other is the mixed recording stereo vocal cords, which are called "X" characteristics.

Acoustic defects There should be no acoustic defects in the recording studio. The acoustic defects that usually appear in the recording studio are mainly echoes and vibration echoes, which interfere with the sound quality. Echo refers to the sound reflection of two sounds, which can be distinguished. When the reflected sound is longer than the distance of direct sound by 17m, that is, the arrival time interval is more than 50ms, an echo will be formed. The reflected sound of the front and rear walls of the recording studio has the longest distance and is easy to echo; Parallel walls often cause trembling echoes. Therefore, there are no parallel walls and ceilings in shape, no irregular and non-parallel reflecting surfaces and diffusers in acoustic structure, and proper arrangement of sound-absorbing materials is conducive to eliminating echoes and vibration echoes.

Noise controls the noise of the recording studio within the allowable range, which is an important index of acoustic design. The allowable noise level of the recording studio is shown in Table 2. When a higher standard is adopted, NC- 15 noise evaluation curve can be used, with a single value of 25 dB. When using a slightly lower standard, NC-20 can be used to evaluate the curve with a single value of 30 dB. Noise control in the shed includes sound insulation of enclosure structure and noise elimination and vibration reduction of air conditioning system.

Table 2 allowable noise level of recording studio

The enclosure structure of sound-proof recording studio should have certain sound-proof ability to isolate the external environmental noise and make the allowable noise level in the recording studio reach the above standards. The wall is made of solid brick, with a thickness of 490 mm and an average sound insulation of 60 decibels. The roof adopts reinforced concrete roof panel and aerated concrete insulation layer, which can achieve the same sound insulation effect as the wall. If double-layer overhead slab can be used, the impact sound can be isolated. The recording studio and the auxiliary room should be separated by a 370 mm thick double wall with a gap of 120 mm between the walls to prevent solid sound transmission. Pipes passing between the two walls should also be treated to avoid the formation of acoustic bridges. The recording studio should adopt double-layer sound-proof 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 the suite form a voice-activated lock. The sound insulation capacity of this structure can reach 50 ~ 55 decibels. The soundproof door is a multi-layer composite door made of plywood, tongue-and-groove wood, rock wool board, felt and steel plate. The door crack between the door leaf and the door frame should be sealed with rubber gasket, and a door lock that can press the door leaf and the door frame 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 ~ 12 mm thick glass. The thickness and spacing of the three layers of glass are not equal, and their positions are not parallel, so as to avoid the resonance of the two cavities. Window frames around the cavity should be coated with sound-absorbing materials, and glass and window frames, window frames and walls should be sealed. The sound insulation capacity of this kind of window can reach 50 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 be completely separated from the building structure. All machine bases that generate noise and vibration should be spring vibration damping bases. Before entering the shed, the fan room should be treated with sound absorption, and the pipes connected with the ventilator should be treated with noise elimination, such as broadband impedance muffler and "chamber muffler". In the air supply duct and the return air duct, a sheet-type aerated concrete muffler, a slag expanded perlite resistive composite muffler or a "labyrinth muffler" can be arranged. Each air outlet can also be equipped with an acoustic muffler to reduce the regenerative noise caused by airflow generated by wind speed.