First, the impact of indoor acoustic environment
In the multi-channel sound system, the Dolby Pro Logic four-channel is the most representative, and it is still the most popular multi-channel sound system. Since the surround channel uses two surround channels, two surrounds are used. Speakers, so the system requires five speakers. Since the advent of the Dolby AC-3 digital multichannel system, the discrete 5.1 channel has quickly become the new multi-channel standard for home theater.
The indoor acoustic environment has a certain influence on the indoor sound field created by the multi-channel speaker. Different room sounds have different spatial acoustic characteristics. The multi-channel sound system uses multiple speakers to represent the sound image and create a surround sound effect. This is not an easy task. If there is no ideal indoor acoustic environment to match, then the comprehensive sound effect will not be good. According to the theory of acoustic psychology, the early reflection sound of less than 1ms in the interior is delayed. Significant interference with direct sound will make the sound become more turbid, which will affect the sound image localization. The early reflection sound between 1~30ms will have less interference to the direct sound, and it will be combined with the direct sound. It helps to increase the loudness, but it may change the tone of the direct sound. As for the reflected sound after 30ms, the human ear usually thinks it is a reverberation sound. For the above reasons, we must do a good job of sound absorption and diffusion in the audio-visual room. Acoustic processing such as sound insulation, otherwise, excessive reverberation will reduce the clarity and consistency of the sound and affect the playback sound.
In order to illuminate the grand stereo field of the theater, the room for audio-visual use should not be too small. If possible, sound-absorbing materials should be added.
Second, the speaker is placed
Under the premise of a good indoor acoustic environment, the more accurate the sound image localization, the more realistic and natural the sound, the more it can show the realistic effect of the sound and sound combination. First look at the placement of the speakers in the theater. The picture below shows the speaker layout for each channel of the actual theater with surround sound.
The left and right channel front speakers are separated from each other by almost the same distance as the movie screen. The front speakers are usually discharged behind the movie screen, and they can pass the sound to the audience through the small gap of the screen. Therefore, this speaker can be placed at half the height of the screen.
The subwoofer is not necessarily placed in a symmetrical position in the front speaker cluster; the standard theater has a number of surround speakers that, together with the front speakers, really "surround" the audience.
After referring to the above examples of speaker placement, let's go back and see how the speakers should be placed for the best sound. Here, we have to pay attention to the problem that the indoor play space we encounter may be much smaller than the real theater. Below, we will discuss the placement of three front (left, center, and right) speakers, then surround the sound box, and finally study the placement of the subwoofer.
1, the placement of the center channel speaker
The front center speaker is usually placed as close as possible to the center of the image screen. The center channel speaker has the greatest influence on the sound quality of the movie dialogue. In order to ensure that the dialogue is accurately positioned in the center of the screen and the sound is clear, the center channel should be used exclusively. A separate speaker is designed instead of an ordinary bookshelf speaker or a speaker inside the TV.
Most of the center channel speakers use a horizontal horizontal box, the best place for the top of the TV (if the front projection display screen is placed behind the screen), it should be as close as possible to the screen. If it is limited by the space of the room A more economical placement scheme can be used, that is, no center speaker is provided. However, the working mode of the AV amplifier should be placed in the "phantom" channel mode, so that the information of the center channel is from the left and right speakers. Balanced release, the sound is exactly in the center of the screen, which is suitable for small listening rooms. Of course, it is best to set the center speaker.
2, the left and right channel main speakers are placed
The placement of these two speakers has a certain relationship with the position of the center channel speaker.
In order to ensure the smoothness of the left and right movement of the sound image, they should be placed on both sides of the center channel speaker, and the three speakers should be at the same distance from the position of the best listener in front of the screen. In general, the center speaker should be placed a little longer than the left and right speakers until the sound field can be completely combined to create a truly unified sound image. The distance of the back is related to the size of the space, the listening position and the speakers used, which can be determined by experiment. In addition, the vertical height of the left and right channel speakers is preferably not higher or lower than the center speaker's axis by 0.3m (preferably slightly lower), otherwise the left, middle and right three The height difference of the speakers is too large, and the front sound image gives a sound jump when it is laterally displaced. Generally, floor-standing speakers can meet the above requirements. If you use a bookshelf speaker for the left and right speakers, you should attach them to the speaker stand so that it meets the above requirements.
The distance between the left and right channel speakers leaving the screen is related to the size of the screen. If you use a large, medium-sized screen color TV in a small room, the left and right channel speakers can be placed close to the sides of the screen. If the screen is small, you can make them a little further away from the screen to get a wider stereo field. But don't go too far from the screen, so as not to give people a false feeling because the sound image position is too far from the picture. From this point of view, there is a shortage of "innate" - the environment is too small. In summary, the sound directivity of the left, middle and right three-channel speakers is heavier than the diffusivity, that is, the radiation angle range of the three channels should be oriented toward the optimal listening position. This reduces the effects of reflected sound from the floor, walls and roof, and properly ensures the clarity of the sound image.
3, the placement of surround sound speakers
Surround speakers are used to create an atmosphere that plays an important role in the entire speaker system.
A, the type of surround speakers
Currently, there are two types of surround speakers, one is a common unipolar small speaker, which is usually placed on the speaker stand or hung on the wall. Another type of surround speaker is the THX recommended dipole type. Speakers, each speaker has two back-to-back speakers, which are connected in reverse phase. The speaker is composed of high-frequency sound only in front and rear and can not produce low-frequency sound (even if it is input low frequency signal) Why can't you make a bass because of the offset?) Why is this? Let's look at the working process of the dipole speaker. Two speakers are placed back to back in the speaker, and the two speakers are fed with opposite signals. At a certain moment, the A speaker inputs a positive polarity signal, and the paper cassette moves forward, compressing the front air (increased density). At the same time, the B speaker inputs a negative polarity signal, and the low box moves backward to make the front air sparse (density Reducing) The direction of the sound wave in front of the two speakers is reversed. If the two speakers feed in the full-band signal, the low-frequency is strong because of its long wavelength, so that the low-frequency sound from the A speaker is diffracted to the B-speaker. And being Weak (offset); while the medium-high frequency signal has a low diffractive power due to its short wavelength, the mid-high frequency sound on both sides of the speaker is small, so the offset effect in front of the speaker is not obvious, so that the two speakers are only issued to the front and rear. The high-frequency sound can't produce low-frequency sound. The purpose of using the dipole-type speaker is to avoid too significant directionality.
For the audio industry, the dipole speaker is a very strange type. This kind of speaker needs to be developed to mature. This kind of speaker is not full frequency band, because the frequency below 100MHz has been cut off. Therefore, the speaker is used because it only sounds forward and backward at the same time and never sounds to the side where the listener is located, and the sound is heard before the listener is filled with the listening room, so that a hearing habit can be created. Surrounded by the sound.
B, the placement of the surround speakers
The arrangement of the loop speakers should be different depending on the listening environment (room conditions) and the type of loop speakers. The speakers of the left and right surround channels should be more diffuse than the directional, which is beneficial to create a rich atmosphere. Surrounding atmosphere. When placing dipole-type speakers, we must consider two factors: resonance and self-fading. The best anti-resonance is 20% of the indoor space from the ceiling (or ground) (such as indoor height) 2.5m, the best position is 50cm above and below).
In order to make the frequency response smoother, a new device called low frequency "trap" (absorbing low audio) can be added to eliminate the reflection that causes the sound to decay.
For direct-radiation loop speakers, there are many options to consider. For example: fixed on the walls on both sides and pointing them to the rear corner; fixed on the rear wall, making them open and upward in an inverted figure-eight shape and Towards the junction of the side wall and the ceiling; placed on the floor against the wall on both sides, pointing upwards to the junction of the wall and the ceiling, etc. Many other options can be designed according to the specific conditions of the room. The surround sound field of the home theater is mainly indoors. Each anti-sound is shaped by the acoustic reflection and refraction of the surround speakers, and the room acoustic conditions of different rooms vary widely. As long as the patience test and careful comparison, the best placement plan will be found.
4, the placement of the subwoofer
Usually put the subwoofer near the front corner, preferably more than 1m from the corner, which can reduce the interference of standing waves. You can also put the subwoofer on both sides of the best listening position, keep the proper distance, because people The ear is not sensitive to the directionality of the subwoofers from both sides, so the subwoofer will not interfere with the original sound image localization of the front three channels. Of course, the best placement position should be determined by experiment. .
The method described below may be helpful in finding the best placement of the subwoofer. Place the subwoofer in the best listening position (temporarily remove the nearby debris), connect its speaker cable and play a strong bass repeatedly. The effect of the music, then carefully around the room to listen. Listen, ask the ear to stick to the ground, roughly at the height of the subwoofer. When listening, find the most stable, deepest, clearest point of the bass, that is super The best placement of the subwoofer.
Guangzhou Ehang Electronic Co., Ltd. , https://www.ehangmobile.com