Acoustic acoustic analysis: sound, diffusion, reverberation treatment

[Home Cinema Network]


With the continuous expansion of the home theater custom installation industry, good acoustic design is getting more and more attention from architects and architects. Indoor acoustic design is particularly important, including the choice of room size and volume, optimal reverberation time and its frequency characteristics, the selection and determination of the sound absorption material, the combination of sound absorbing materials and the appropriate reflective surface, etc.

Decibel decibels

Decibel refers to one tenth of Bell and is usually used to express volume. Dibebery does not express all things, it is just two energy levels. Because we rely on the sound of the sound, these compliance with the ratio of the logarithmic curve is expressed in the decibels make many things simple.

Here are some decibels worth remember: the minimum volume unit that can feel changes in normal conditions is 1 decibel; the speaker power is doubled, and the result is a significant increase in 3 decibels, the volume is doubled. 6 decibels; if you want to double the volume, we need to increase the power of the amplifier to the original four times.

Frequency frequency

The source of the sound is vibration, the vibration has the frequency (symbol F), that is, the number of vibrations per second, the unit is Hertz (Hz) people’s ear can be listened, only the vibration frequency is 20 Hz (one Say 16 Hz) ~ 20000 Hz sound, human vessel can have a sound.


20Hz or less, 20000 Hz is ultrasound, less than 20 Hz and above 20,000hz sound people do not sound, the most sensitive frequency of people is 100 ~ 3150Hz. In architectural acoustics, the sound of 200 to 300 Hz or less is generally referred to as a low frequency, and claimed to be an intermediate frequency, 2000 to 4000 Hz or more claims.

Absorption sounds

In terms of acoustic, the sound absorption refers to the sound, and the sound waves are absorbed when the soft material is encountered. The absorption capacity of the various materials is determined based on the absorption coefficient, which is determined based on the relative acoustic energy absorbed by the material when the sound hits the surface.


Absorption Coefficient sound absorbing coefficient

The sound absorbing coefficient is measured by the relative sound energy absorbed by the material when the sound hits the surface of the object, which is usually a value from 0 to 1, which multiplied by the number of object surface area is the percentage of sound absorbed by the surface of the object. This percentage unit is Sabins, originated from Harvard professor, the name of the acoustic Wallace Sabine.


The absorption coefficient is 1 means that the sound hits it. It is completely absorbed after the surface of the object, and there is no reflection. If the absorption coefficient is 0, the sound is completely reflected, and there is no absorption. Of course, the phenomenon of factor is obviously impossible, and the coefficient is 1 situation rarely. In addition, since different materials have different absorption characteristics at different frequencies, the absorption coefficient changes as the frequency changes. Acousticists often use absorption coefficients to determine RT60 and resonance time in the room, in fact, many building materials have been measured in acoustic coefficients for use with reference.


BASS TRAP low frequency trap

Each closed space will have different restriction frequencies with different size, so the size of the size directly affects the generation or disappearance of each different corner specific frequency of the space. The low frequency sound absorbing board is a low frequency sound absorbing apparatus for reducing the influence of indoor retention sound, which is generally mounted along the wall or in the corner.


The sound absorbing features of the low-frequency sound absorbing panel effectively prevents the low frequency sound from interfering with each other indoors, so there is a more accurate response in the hearing area. The bass sound absorbers have a lot of shapes and sizes, and there are also many techniques when installed, you can install it according to your needs.

DECAY attenuation


In terms of audio, attenuation is a method of taking sound termination. Any sound signal or a waveform envelope of an electronic instrument can be said to be composed of many elements, such as internal dynamics, delay, release, and attenuation, which can define features of a signal or waveform envelope. All signals or waveform envelope attenuates can vary depending on the variations such as time and attenuation amplitude.

DECAY TIME attenuation time


Attenuation time refers to the reconiality level of 60 dB (one million) levels that fall from the original length, sometimes it is called a reverberation time. If you carefully set up the attenuation time, you can make the mix to make the mix and moisturize it, and the sound will not become turbid or unclear.


Diffraction diffraction


The sound wave is called diffraction when encountering an obstacle or when it is to pass through the small hole (acoustic wave, electromagnetic wave or optical wave). Relative to obstacles, the shorter wavelengths are more likely to be more reflected, and they are scattered to the surroundings. Sound waves can also bend the open space over the back of an object (which can explain why when the door is open, you can hear him even when the door is said, but you can’t see him).


Diffusion diffusion

In terms of acoustic, proliferation is a key consideration, as it may cause serious problems due to the destruction of continuity reflection, and he also leads to a closed space to sound than actual. In fact, in terms of acoustic processing, diffusion is a good alternative or complement to absorption because it does not reduce sound energy, that is, he can effectively reduce reflections in space or on-site performance venue.


REVERB reverberation


The sound source stops vibration after the vibration is called a reverberation, sometimes people mistakenly call them echo. In a larger closed space, you can hear the reverberation if you clap your basketball. All rooms can have a reverberation, but sometimes we can’t find it. Reverbery is one of our main criteria for the subjective evaluation of the room. Our brain will make a judgment of the surrounding environment based on the reverberation.


The abbreviation of REVERB TIME-60DB, which is often used to represent a given reverberation time. The time in which the reverberation dissipated in a larger space is often up to 15-20 seconds. This means that in practice, the reverberation needs to pass the length of the length to dissipate to ambient noise.

Increase the environmental noise 20dB, the reverberation is reduced accordingly. The purpose of RT60 is to provide an objective measurement method for reverberation. This parameter illustrates the length of time required for reverberation to dissolve with ambient noise, or the reverberation reduces the length of the original volume of one million.


Critical distance critical distance

When the volume of the sound source is the same as the volume reflected from other surfaces, that point is a critical distance. These reflection volume and time control are a very important factor when creating a precise listening environment.


STL (Sound Transmission Loss) Solid Transmit Loss, Sound Sound

It is a sound insulation effect that can be reached in a particular hierarchy or 1/3 scale in a certain specification. For example, the 1/2 inch sound insulation wall is from 125 Hz to 15dB. A variable-sounding material is compared to a comparison is that the sound loss, in fact, the sound loss value measured in the real environment is certainly different from the laboratory measurement. But there is a sense that it is certain that even if a concrete wall is compared to the test results of the laboratory, it will be better than a simple single-layer soundproof wall.

SPL (Sound Pressure Level, Sootpress Level)

Decibel is a unit that measures the relative size of sound intensity. The physicist introduces the SPL sound pressure level to describe the size of the sound: the pressure generated by the vibration of the air is called the sound pressure, referred to as a sound pressure, and the effective value of the sound pressure The number indicates the strength of the sound, which indicates that the value of the sound is called the sound pressure level, and the sound pressure level is represented by the symbol SPL, and the unit is decibel (DB).

In general, the minimum sound pressure that the human ear can feel is 20μPa = 0dB SPL, which is hearing threshold; when the sound pressure reaches 20 Pa, that is, when the sound pressure level is 120 dB SPL, people’s ear will feel pain, so In acoustic or medicine, 20PA = 120 dB SPL is defined as pain threshold, and it works for a long time in this environment, which will cause harm to the auditory system.


NC CURVE / Contour NC Curve / Contour Noise Standard

The NC curve refers to still noise and environmental noise in space such as the auditorium. Curves or contour are the mechanism of human ear feel sounds, in short, human ear, different sense of sound of different frequencies. When the noise volume changes, the sensitivity will change. The NC curve is being used to explain the mechanism, which can objectively characterize the environmental noise level.

Since the ambient noise in most auditoriums is caused by a ventilation system, the frequency of its noise is maintained at a lower level, and the human ear is relatively irritating. The NC curve can effectively measure the environmental noise standard of the entire spectrum, and the numerical range is generally between NC-15 and NC-70. NC-15 represents a more quiet environment, which is in line with the standard, generally 30 dB SPL, noise frequency is less than 80 Hz, NC-20 is even more noisy, but it is still relatively quiet, and NC-25 ~ NC30 is for hearing. It is too noisy.

NRC (Noise Reduction Coefficient, Digare Coner)


NRC is an abbreviation of the noise reduction coefficient noise reduction coefficient, usually as a specific parameter indicates the sound absorbing efficiency of the noise absorbing material. It is usually indicative of a mean for a material for a 125Hz-4kHz band Sabine coefficient. The higher the value, the better the sound absorption effect. It is a more general standard, compared to other noise reduction coefficients, it cannot represent sound absorption effects on a particular frequency band. For example, the blanket in the home is better to high frequency band noise sound absorbance, and the low frequency segment is uncomfortable.

Standing Wave standing wave

Technically this is determined by the room mode, that is, the vibration mode of the air in the room. Sound interference interferes with each other, resulting in higher SPL values ​​in some areas, and low in other regions. The above areas have become vertices and nodes, respectively. The standing wave is easy to appear in a space of the integer multiple of half the frequency wavelength of the frequency. For a given distance, there will be a lot of frequencies that may generate a standing wave. The spatial sound of the standing wave on the room will have an adverse effect, but this can be avoided through the design of the house and the installation of sound absorbing plates.

Stand in wave

When the standing wave occurs, there are some specific points in the room to become a node, because the sound of the sound and the rigor are completely offset, there is no sound wave in this point. The node is approximately half-wavelength distribution, and there is a vibration abdomen on both sides of each node. Alternating distribution of the lumber, so the sound wave is similar to a sine wave. The same node can also be used to indicate the intersection of the cable, and the strip cable is often distributed in two points and intermediate points.

FLUTTER Echo vibrating echo

The sound caused by multiple reflection between two parallel reflective surfaces, and the distance between the two surfaces is large to the listener to hear the echo. This sound effect is often manifested as a fluttering sound in many cases because the time intervals between each other is very short. In a small room, since the interval between these echoes is so compact, it reflects the sound of a tubular echo.

More fresh and fun home theater information, please pay attention to the home theater network (WeChat: cnhifi), the nationally influential home theater audio player interactive media website.

About the Author

You may also like these