This page explains how ceiling speakers (SP) should be placed.

The effect of the Ceiling Speaker (SP) is that the SP interferes with the interior to a minimum. This is the biggest advantage for interior designers. So, are there any benefits for sound designers?
The advantage is that by providing a uniform volume, it is possible to provide background music that can certainly be called a "background" (the effect of a uniform volume will be discussed later). Therefore, one of the ideal designs is to achieve uniform volume using multiple SPs.

First, it will be explained how ceiling SP diffuses sound.

Connecting the areas around the ceiling speaker with the same sound pressure creates a balloon-like surface. This is called an "isosonic pressure surface."

This "isosonic pressure surface" is difficult to call, so in this explanation we will refer to it as a "balloon."
The picture on the right shows a 70dBspl balloon.
(The picture on the left is viewed from above.)

What is the sound pressure inside the 70dBspl balloon?
It would be easy if it were uniformly 70dBspl, but unfortunately the inside is not the same 70dBspl. The closer you get to SP, the higher the sound pressure will be. So there's an 80dBspl balloon inside, and a 90dBspl balloon.

In other words, the balloon with low sound pressure is on the outside, and the balloon with high sound pressure is on the inside.

Consider changing the volume with AMP or attenuator.
The image on the left shows the volume turned down, and the image on the right shows the volume turned up.
For someone listening directly below the speaker, the situation shown on the left may not produce enough sound, while the situation shown on the right may be too loud. 

​​Ceiling speakers are often designed based on their potential, but in reality they are often used at a reduced volume. The problem and solution in this situation will be explained.

Designers often arrange speakers based on their maximum potential. If the target sound pressure is 70dBspl, the designer will be satisfied with the arrangement shown in the image above on the right.

But in this case, the volume is turned down because it's too loud for the user.

​This will make it difficult to hear the sound at the middle point of the Speakers.

This is an acoustic problem that often occurs in real facilities. These designs are problematic if your design philosophy includes having announcements or background music heard no matter where the user is in the area.

​With this in mind, how should we consider speaker placement?​

It should not be too loud for the user, so first consider the maximum sound pressure that the user can tolerate. Let's set this to 95dB for this tutorial. (Actually, the maximum permissible volume varies depending on the purpose. For background music, it may be more lower.)

For practical purposes, it is necessary to reduce the volume to this maximum level (photo on the left). In other words, even if a speaker can produce a volume higher than this value, it will be useless.

Next, decide on the minimum target sound pressure you want to secure. (Earlier we thought about the maximum allowable sound pressure, but this time we will think about the minimum desired sound pressure.)

This is determined by the background noise at the site. This time, let's assume that the background noise (ambient noise) is 70dBspl, and set the minimum target sound pressure to be 80dBspl, which is 10dB higher than that.
Please refer to this page for information on ambient noise.

If you place the speakers using this 80dBspl balloon as a guide, you can secure 80dBspl. This means that we are able to maintain the minimum target sound pressure of 80 dBspl while keeping the maximum allowable sound pressure below 95 dBspl.

​
​Simulation

Designers can easily determine the installation location by performing simulations using tools based on the above information.

The simulators are famous for EASE EVAC and EASE Address, and TOA also provides data for EASE (.gll file).

​>> EASE Evac | Ahnert Feistel Media Group (afmg.eu)
>> EASE Address | Ahnert Feistel Media Group (afmg.eu)
​>> TOA EASE data dowmload (TOA DATA Library)

Even in the same distribution on the plan view, the distribution of sound pressure will be different if the ceiling height is different.
Therefore, an elevation chart is always required for simulation.

Even if the distribution is the same on the floor plan, the sound pressure distribution will be different if the ceiling height is different. In particular, the uniformity is different. Therefore, elevations are always required for simulation.

Ceiling heights may vary even on the same floor. In this situation, the volume will vary depending on the location. It is necessary to consider dividing the SP into different SP groups or using an attenuator or the like to adjust the volume of each SP individually.
　　　　　　　　　　　　　　　　　　　　　　　>> SP line grouping                   >> Attenuator

EASE Eavc and EASE Addtess can display histograms. Using this histogram, you can check the uniformity of the sound pressure component. The upper figure shows a state where the distribution is uniform, and the lower figure shows a state where it is not uniformly distributed.

Effect of uniform volume on BGM

The ideal background music would be one that provides the perfect "background" for shoppers. In other words, shoppers won't pay much attention to the background music, but it will give them the mood the store wants them to feel (fun, cool, calm, ... etc.). 

Shoppers move around the store, so if the volume of background music is not uniform from place to place, shoppers will pay attention to the background music due to changes in volume. It makes them pay attention to the background music whether they want to or not. In other words, the BGM becomes independent from the "background". The ideal is for many SPs to provide music evenly and at a low volume. This way, the background music can become the perfect "background" without causing any changes in volume for shoppers.

​Also, although it is not as accurate as simulation, the BIM/Revit data provided by TOA can display the sound pressure distribution range. Please see Tutorial and download them if you are interested.