Sound field is a word often mentioned by HiFi enthusiasts. What we are pursuing when playing HiFi is real sound. The sound we hear is not only distributed in a two-dimensional plane, but exists everywhere in the space and can be perceived by people. Whether a system can accurately restore the distribution of sound in space is an important criterion for measuring the quality of a HiFi system. However, the sound field that HiFi enthusiasts often refer to in the "sound field" professional field is two concepts. The concept of sound field in the professional field is narrow, and often refers to the distribution of sound intensity in space, and the "sound field" that we enthusiasts often say is two concepts.
The "sound field" that enthusiasts often say is the comprehensive feeling of multiple indicators such as sound source localization, perceived source width, and sense of space. In this article, I will give a visual introduction to those factors that will affect the "sound field". We want to achieve a better "sound field" performance on which equipment should be worked hard.
The width of the sound field can be described by the perceptual sound source width (ASW). As shown in the figure below, the perceived sound source width is determined by the binaural auditory cross-correlation function (IACC) and the early lateral acoustic energy ratio. The binaural auditory cross-correlation function can be understood as the binaural energy similarity, which is a very abstract sounding concept. Its main meaning is the similarity between the sounds heard by our left ear and the sounds heard by our right ear. Generally, the smaller the IACC, the larger the ASW; it can be understood that the more stereoscopic the sound, the wider the sound field. But it is worth noting that the sound field is not as wide as possible, but as real as possible. Normally, if we listen to music with a speaker, the sound from the right channel speaker can be received by our left and right ears; when listening to songs with headphones, only the right channel can receive the sound of the right channel To. Therefore, the IACC of the speaker system is usually larger than that of the headphones, and the width of the sound field is moderate. However, because the IACC is too small, the width of the sound field is too large, which will give people a very false feeling. At the same time, the lateral sound energy of the earphone is much larger than that of the speaker, which further causes the sound field to be too wide.
At the same time, as mentioned above, IACC stands for binaural energy similarity, so for a given speaker or headphone system, the higher the channel separation, the more accurately the sound source width that the sound engineer wants to express. This is also the reason why monitor speakers and high-end HiEnd systems usually use left and right channel separation power and mono power amplifiers, because this can effectively reduce the crosstalk of left and right channels and improve channel separation. This is also a large part of the reason why our earphones feel that the sound field has changed after changing the amp. The difference between a balanced system and an unbalanced system is also largely in channel separation.
In addition to the difference between different music sources and recordings. The positioning of the distance by people basically depends on the ratio of the energy between the direct sound and the reverberant sound (late reflection) in the room.
The reverberation energy ratio is basically an amount that only the speaker system has, so only the speaker system can better restore the sense of depth and distance of the sound field. In contrast, the sound in the headphones is always like you. Issued in front of and close to the top of the head.
The reverberation energy ratio is related to the reverberation radius, and the space is limited, so I won’t go into details here.
3. Sense of space
Human perception of the size of space through sound depends on reflected sound, specifically divided into reverberation time and early reflected sound.
The reverberation time depends largely on the recording itself and the room's reflection, so even the headphones will have a certain sense of space, but this feeling will not change substantially with the model of the headphones. In general, only the speakers In order to restore a better sense of space.
At the same time, a paper published by TEAC in Japan on AES shows that the high-resolution audio source (Hi-Res) and ordinary lossless audio source will not have much difference in the sense of space. The recording mentioned here refers more to the recording size and post-mixing processing.
4. A sense of direction
For a single sound source, human perception of its direction depends on the binaural time difference, binaural intensity difference, binaural phase difference, and pinna effect; while for the stereo sound that we often listen to, it is the left channel and the right sound For a multi-sound source system composed of channels, more factors need to be considered at this time. (Note that the number of sound sources in this sentence is the number of sound sources in the playback system, not the number of instruments in the music)
Since a considerable part of the energy of the sound of the headphones is emitted from the side of the human head (after HRTF conversion), the sense of surround will be stronger than that of the stereo speaker system.
In general, the sound field of the speaker system is far superior to the headphone system.
For the speaker system, you can improve the channel separation of the decoder through the mono power amplifier, the dual-loop cattle power amplifier (the previous three look at the specific situation, and often the perception is not strong or exceeds the domain limit), reasonable speaker positioning and appropriate Acoustic decoration to obtain accurate sound field restoration.
For headphone systems, the best method is to use DSP-based sound field reduction algorithm, the amp itself has little effect on improving (not changing) the sound field.