Selection and placement of loudspeakers

Before the invention of the amplification system, a large number of people gathered in the auditorium to listen to speakers without amplification. The auditorium makes use of the geometric structure and sound processing of the room to provide natural sound enhancement for the sound source.

The ancient Greeks even added sound reinforcement canisters to the actors' masks to cover more spectators. But even with these tools, it wasn't really effective in solving the problem of speaking to a large number of people - until people invented the sound reinforcement system.

There are at least four reasons for the reinforcement system.

1. room size - it is hard for listeners to hear the natural sound of the sound source.

2. the geometric structure of the room the geometric structure of the modern auditorium is no longer competent for the natural sound reinforcement. The popular 180 degree sector room is at least 60 degrees wider than the unprocessed human voice coverage. As long as the speaker turns around, some audiences can not hear the speech clearly.

3. Ambient Noise - Background noise generated by people, traffic, heating and air conditioning systems obscures the sound source and makes it impossible for some or all listeners to listen clearly.

4. Architectural Processing - The processing required for natural sound reinforcement may be very expensive and not applicable to all musical styles.

Sound reinforcement is necessary when social activities require large numbers of people to stay in large spaces.

An analogy

When a room is illuminated with lights, people will use appropriate lamps to illuminate it where it is needed. This can be understood by everyone. The same is true for sound system designers when selecting and placing speakers.

If there is good room acoustics, some major sound problems, such as poor effective gain and poor speech clarity, can be directly attributed to inappropriate speaker selection and placement. The most common reason is that sound designers have to give up their preferred speaker type and location for aesthetic reasons.

Building and sound reinforcement

Architects often regard loudspeakers as objects other than buildings, which are not really "appendages" to the whole. The Institute of architecture does not teach the design of sound systems, nor does it have to teach itself. They emphasize the visual effects of the site, focusing heavily on the geometric structure of the space and the visual flow.

This is their mode of thinking and the responsibility of their work. Large and conspicuous speakers disturb their overall concept of space.

When designing a room, the architect does not know the type and number of speakers needed, so it is impossible to integrate the speakers into the design. Even if they can, we'll see that their efforts to camouflage and hide the speakers are likely to damage their performance.

For speakers, to accomplish their mission, they must occupy some of the most visually important parts of the room. It is no wonder that architects and sound system designers often clash.

Three variables

The job of the sound system designer is to make sure that everyone can hear the sound reinforcement. To achieve uniform coverage in the audience area, they have to deal with three variables.

Including: loudspeaker type speaker location - speaker number

If the system designer gets the power to control these three variables, the result will be the best. If a client or architect orders one or more of them, the workload of the system designer is reduced, but the effect of sound reproduction is greatly reduced.

Loudspeaker position

The ideal location of the loudspeaker is not possible. The ideal location is where the sound source is needed.

Imagine a small Troupe or classical orchestra performing at a small venue. Without any amplification, sound from each source can be heard, and the spatial location of other sources is accurate.

As the room size increases, musical instruments may need voice amplification. The band has been using localized amplification for years, and now the personal sound system is still on the market for small-scale venues - a contemporary reappearance of Grateful Dead's "sound wall" technology decades ago.

(Wall of Sound is a huge sound reinforcement system, designed in the 1970s by audio designer Owsley Stanley for live performances by the band that died of gratitude. )

The location of sound source is the natural location of sound. This approach is unrealistic and inflexible in many applications, so we need a compromise. The first choice is to place the speaker directly above the sound source that needs to be amplified, which takes advantage of the fact that human hearing can not locate sound well in the vertical plane.

If the speaker is on the left or right side of the speaker, the listener will obviously feel that the sound does not come from the speaker. If the speaker is placed above the speaker, the auditory system of the listener is obscured and the sound is assumed to come from the speaker. The eye effectively pulls down the sound to correspond to the vision. The speakers are placed above the room so that the sound can be projected to the back of the room without overhearing the front-row audience.

Considering these aspects, it is very reasonable to put speakers directly on the stage.

Size vs efficiency

The loudspeaker must be large enough to control the direction of the sound. Small speakers radiate sound in all directions.

As the size of the loudspeaker increases, its directivity increases. Directional control is absolutely necessary in all audio systems, and the more control you need, the bigger the speaker. This is the principle.

Another reason for choosing large loudspeakers is low frequency efficiency. In many religious settings, it is hoped that the system can produce extremely high sound pressure levels at extremely low frequencies.

This means that a large amount of air must be moved, which in turn requires larger piston surface area. Without large loudspeakers, it is impossible to achieve high sound pressure levels at low frequencies in large spaces. People often use more than one loudspeaker to achieve this.

The lower the octave, the more the radiation surface area is needed. If you want to play back the thunder of an Easter musical, or the bass pedal of an electronic organ, it's best to have a very powerful low-frequency speaker system. This must be a huge system and should be placed in the room.

Voice problem

Many typical faults of the sound system, such as low clarity, muddy, and poor sound localization, may be attributed to reflected sound. Most of these harmful sounds are caused by concealing and concealing loudspeakers.

Reflection sound exists objectively. We expect the reflected sound to make use of the reflected sound and the need for reflection. But not all reflexes are beneficial. Audio designers try to avoid two kinds of reflections, one from objects close to the speaker and the other from objects far away from the speaker.

The first reflex causes acoustic staining, and the second causes echo, which reduces the clarity of music and speech. Trying to mask the loudspeaker always produces early reflections, thereby changing the frequency response of the loudspeaker. These include meshes, covers, and holes, all carefully designed to make them visually more beautiful. In short, measures that make speakers more aesthetically sound may make voice worse.

It takes careful design to allow the speaker to remain acceptable while being masked. Unlike light waves, if time is not aligned, sound waves may cancel out one another. But this is not all bad.

Sound system designers make use of the length and cancellation interference to achieve the required coverage of the loudspeaker array. A good sound designer understands the role of interference and knows how to use it to improve system performance.

Let's look at some ways to visually reduce the presence of speakers.

Cover up - the net cover always hinder the sound. The only problem is "the degree of hindrance" and "whether it can be heard".

I've seen system designers spend a lot of money expanding the frequency range of the sound system to more than 20 kHz and hiding everything behind a mesh that can't pass through more than 20 kHz.

But even without a mesh, the sound energy above 16 kHz is seldom transmitted to every viewer because of air absorption, so it is acceptable to cover the speaker with some fabric in front of it.

Of course, fabric needs a frame. The frame has more hindrance than the fabric it supports. The frame members should be made as small as possible, so it is best not to put them on the main channel of the system's high frequency drive.

Cavity placement - the worst position for placing speakers is in the cavity. The speaker itself is a carefully tuned resonant system. The size, volume and opening are carefully chosen to produce the required response.

The essence of the cavity is "the box in the box", which will obviously change the response of the loudspeaker. Given the effort involved in designing loudspeakers, placing them in arbitrary-sized cavities always undermines the designer's ideal response.

Mesh cloth - do not paint the mesh cloth even if it is a thin layer. The paint will block the hole through which the sound waves pass. If the screen is not in the right color, replace it.

Please remember two points before choosing a suitable mesh cloth. Mesh cloth should be acoustically penetrating and should meet fire safety requirements. Unfortunately, these guidelines will exclude most of your first choices. It is very simple to test the audible effect of mesh cloth.

Just listen to some music and voice through a reliable speaker and cover it with a mesh sample. What you hear is the test results. If the mesh cloth changes the voice, do not use it. You'll find that the air passing through the mesh produces very low sound attenuation and is a good choice for masking the speakers.

Easy maintenance - sooner or later, it is necessary to repair loudspeakers. Please remember this point when assembling mesh cover. It should be removed as unit or module panel.
Go back to your position.

The loudspeaker can be placed in free space without placing any object next to it, so that these acoustic traps can be avoided. One noteworthy exception is that ultra-low frequency loudspeakers can be naturally amplified at room boundaries because of their long wavelength.

This arrangement can enhance the sound of ultra-low frequency loudspeakers, but if applied to medium and high frequency loudspeakers, it will cause very bad results, because medium and high frequency loudspeakers have short wavelengths and can not be well coupled with walls, roofs and other adjacent surfaces. A compromise would be for engineers to paint the speakers and install hardware, as well as a thin layer of metal mesh.

Most speaker manufacturers can provide no surface version of their products. The veneer can be used on the surface of the box, but please note that the adhesive will dry out over time, causing the veneer to fall from the ceiling, causing danger.

Loudspeakers are not the only devices in fully functional rooms. Others include ceiling fans, HVAC vents, lamps, structural beams and supporting columns. No one has doubts about their existence, and no one really cares if they are visible. We will not ask architects to completely hide ceiling fans, or even ask them to reduce the ceiling fan size. The same is true for loudspeakers.

Find a rule

I've been working in the sound industry for quite a long time, and I've found a pattern in installing sound reinforcement systems in public spaces.

The first design is always visually acceptable but not sound enough. Over time the system was upgraded and refurbished, and eventually the sound was great but the speakers were visually striking.

In a auditorium, the consideration of sound should end above visual considerations. Just as headphones are accepted for their sound advantages, so should visible large speakers.

The main component of the sound reinforcement system is loudspeaker. Just as a guide stands in a flat, open area to communicate with a group of people, the speakers in the sound enhancement system work best if they are visible.

This view helps to create an aesthetic view of architects and end-users. "Form follows function" is applicable here. In a venue, when deciding the type and location of the sound system, the sound quality of the sound reproduction should be fully considered.

It's natural to see where we hear the voice coming from. We have two ears because we can locate sound in space.