Knowledge inventory about "stereo"

                                         Knowledge inventory about "stereo"

On many sound system projects, the question is often asked: "Should our system be mono or stereo?" On this topic, we provide a reference point for discussions of mono, stereo, and binaural sound systems .

Description of a mono system: All audio signals are mixed together and sent through a single audio channel. There can be multiple speakers in a mono system, even multiple speakers spaced far apart. The point is that the signal does not carry any information that reproduces or simulates the original position of the sound, such as differences in signal levels, time of arrival/phase information, etc.

Common types of mono systems include:

1. Mono center speaker group

2. Mono separation speaker group system

3. Distributed speaker system (with or without delay speakers)

Although mono, the system still delivers full frequency response, high fidelity, and is effective at amplifying speech and music.

The great advantage of mono: everyone hears the same signal, and, in a sensible system design, all listeners hear essentially the same system SPL. This makes mono systems ideal for speech reinforcement, as they are relatively easy to produce with excellent speech intelligibility.

stereo system

Description of the stereo system: A real stereo system has at least two independent audio signal channels, and the reproduced signals have a specific sound pressure level and phase relationship with each other. When the sound source is played through the playback system, it will be the same as the original sound source. obviously reproduced. Stereo is used when there is a need to reproduce the sense of auditory orientation and the position of instruments on a stage or podium, which is a common requirement in performing arts venues.

This also means that a mono signal that is only panned between two channels does not have the necessary phase information for stereo and is therefore not a true stereo signal; although there may be a difference in sound pressure level between the two channels, the position can be simulated difference, but this is only a simulation. A discussion of this point could take several pages.

Another requirement for a stereo playback system is that the entire listening area must be equally covered by the left and right channels, with essentially identical sound pressure levels. For this reason, in a home stereo system there is a sweet spot ("emperor position") between the two speakers, where the difference in sound pressure level and arrival time of the left and right channel sounds is small enough to preserve the stereophonic quality. Sound image and sound source position.

The sweet spot is within a fairly small area between the two speakers, and when the listener is outside this area, the sound image is lost and only one channel or the other is heard. The sweet spot in a living room may not be a problem, since the sofa can be placed there; but in a larger venue, such as a church or theater auditorium, the sweet spot may only include a third of the auditorium, The other two-thirds of viewers wonder why only half of the source is heard.

In addition, a stereo playback system must have the correct absolute phase response from input to output on both channels. This means that if the input of the system is a signal of a positive pressure waveform, the output of the system must also be a signal of a positive pressure waveform. So, taking a drum as an example, when the drum is struck to produce a positive pressure waveform at the pickup microphone, it should also produce a positive pressure waveform in the listening room. If you don't believe this has a huge effect, try inverting the polarity of your Hi-Fi speakers and listening to a source with a strong center image, such as a soloist. When the absolute polarity is flipped wrong, you won't get a solid center channel image, it will wander away from center and you can hear both speaker positions.

two-channel system

Many people misinterpret this as a stereo system because there are two channels, and a "stereo" mixer is connected before the system, and stereo amplifiers and equalizers are used throughout the system. What these systems lack, however, is uniform coverage of the entire listening area with very little variation in sound pressure level and phase response for each channel.

We might call this type of system a partition coverage system. To achieve proper sound coverage in large venues to reproduce the stereo image, it is necessary to have a sound system that can provide the signal of each channel with the ability to cover the entire listening area evenly, while maintaining the sound direction. Such systems sometimes require more budget, or because the listening zone is too wide for smooth overlapping coverage.

If a two-channel system plays a stereo signal and does not provide smooth sound overlapping coverage, then half the people in the listening area will only hear half of the audio program content, which makes a two-channel system a poor choice for music sound reinforcement s Choice. Most listeners hear a completely different mix of music than everyone else. This is an oversight that is all too common in music and entertainment venues, even in advanced venues that should have better system designs. Thinking that a binaural system is the same as a stereo system is a common misconception among people with a background in touring or live sound systems.

The most important things to pay attention to in the application of two-channel system in voice reinforcement:

When using a two-channel system to amplify a mono speech microphone, seats in the centerline of the room, just between the two channels, will also experience dramatic changes in frequency response and coverage uniformity, which is The result of acoustic interference and signal cancellation caused by the arrival of the same signal from two channels at the listening position at different times.

Left/Center/Right System

Sound systems described as Left/Center/Right (LCR) configurations have their own special applications. It combines the best of both systems, and importantly, when using an LCR system, the mix engineer understands which signal has to go to which cabinet, and which signal routing can cause problems. Additionally, LCR systems are not suitable for all room shapes or listening area layouts.

LCR systems are common in theaters and large churches where monophonic speech reinforcement is required, along with music or surround effects or mixed in a special sense of direction, with stereo or stereo-like imaging. Each channel of such a three-channel system should provide coverage over the entire seating area, while maintaining consistent sound pressure levels and sound orientation, as in the mono and stereo systems described above. There are a number of ways system designers can extend the stereo coverage listening area that involve the use of fill speakers.

fill speaker

Fill speakers are used to provide coverage for areas of the floor that are difficult to reach from where the left or right channel cabinets are installed.

In the example above, the left/right fill speakers and the center speaker cluster are separate and fed through a signal delay; The signal from the sound box will arrive at the same time as the signal from the left channel speaker group, if the signal from the left channel speaker group can reach here. For someone sitting near the front right, they will still hear the program coming from the left channel to get the full program content, although the stereo image will be compared to that experienced by a listener seated in the center of the room A little skewed, but the final stereo effect is quite satisfactory.

Speaker model selection, as well as speaker SPL and delay settings, are critical to the successful integration of fill speakers; if the volume is too loud and the delay is too long or too short, the fill speakers will detract The sound image heard by other listeners. If you want to try to study the Haas effect at home, then it is recommended that you first set up the sound pressure level and delay, and learn how to use the time domain measurement system.

It is also possible to use some of the speakers in the center stack as fill speakers, especially as DSP matrix systems become cheaper and it is extremely simple to set up individual delay processing for each speaker. This method is especially effective when the center channel cluster has similar speakers to the left/right channel clusters.

Which sound system is best?

As with many questions about sound systems, there is no single right answer to this one. More people will be satisfied with a well-designed mono system than a poorly designed or incomplete two-channel system. The important thing to remember is that the best sound system design for a facility is the one that works effectively within the constraints of the program source, room architecture, and acoustic conditions.

This means (to paraphrase the Rolling Stones): "You can't always get the system you want, but you'll find that sometimes you get the system you need." For effective stereo playback or sound reinforcement systems, it is important that the sound system be designed to be as efficient as possible, even if it means forgoing the ideal requirement of stereo sound as required by the program source.