[Series] Lyla’s Notes on Acoustic Spaces (Vol. 1): Should Anechoic Chambers and Soundproof Rooms Really Be Considered Separately from the Start?

Nice to meet you.
My name is Lyla Shinkai, and I serve as the official image character and technical guide for Sonora Technology.

Through daily consultations on anechoic chambers, soundproof rooms, and acoustic measurement facilities, I often encounter the same underlying assumptions:

• An anechoic chamber is a room that eliminates reflections.
• A soundproof room is a room that prevents sound from leaking out.

These definitions are not wrong.
However, in real-world acoustic measurement and evaluation, they are often not sufficient on their own.

In this series, rather than listing standards and terminology, I would like to organize the practical way of thinking required to make measurements and evaluations truly reliable, from an on-site engineering perspective.

Anechoic Chambers and Soundproof Rooms Are Not Opposing Concepts

In design discussions, I am often asked:
“Should we build an anechoic chamber, or is a soundproof room enough?”

In many cases, this question is asked a little too early.

This is because what truly matters on site is not the name of the room, but whether:

• Measurement results are stable
• Test conditions can be reproduced
• The acoustic field is suitable for evaluation

Even a room called an “anechoic chamber” can produce inconsistent results if its design is inappropriate.
Conversely, a soundproof room can be perfectly adequate for evaluation if the internal sound field is properly controlled.

Three Key Perspectives When Designing an Acoustic Space

At Sonora, before deciding on labels such as anechoic chamber, soundproof room, or anechoic box, we first focus on organizing three fundamental elements:

1. Absorption

Reflected sound acts as noise in measurement data.
Depending on how strictly a free field must be realized, the thickness and geometry of the absorbing structure—such as wedge-shaped absorbers or flat panels—are determined.

2. Insulation

If background noise is high, measuring low-level sounds becomes impossible.
This applies both to preventing external noise from entering the space and to preventing high internal sound levels from leaking outside.

3. Structure & Reproducibility

This includes physical factors such as floor vibration control, temperature and humidity management, and specimen mounting methods—all essential for ensuring repeatable measurements.

These three elements are not independent.
In real acoustic spaces, they interact simultaneously.

The True Starting Point Is “What Do You Want to Measure?”

The most important step in acoustic space design is to first clarify the following:

• What kind of sound source is being measured?
   (Size, frequency characteristics, directivity)
• Which frequency range needs to be evaluated?
   (Primarily low-frequency or high-frequency?)
• What level of accuracy is required?
   (ISO precision grade or internal comparative testing?)
• Is this a one-time measurement or a continuous evaluation process?

Only after these points are defined can meaningful decisions be made, such as:

• Whether a full-scale anechoic chamber is required
• Whether a high-performance soundproof room (or semi-anechoic solution) is sufficient
• Or whether a different configuration, such as an anechoic box, is more appropriate

In other words, “anechoic or soundproof” is the result of design—not the starting point.

Avoid Being Constrained by the Term “Anechoic Chamber”

The term anechoic chamber often carries a very strong image:
a large space, walls covered entirely with absorbing wedges, and specialized infrastructure.

However, in essence, an anechoic chamber is simply
one possible configuration for realizing a free-field condition.

When the objective changes, so do:

• The required size of the space
• The approach to sound absorption
• The necessity and level of sound insulation

Through this series, I hope to help you find the most appropriate way to measure sound, rather than the most conventional one.

Next Issue

**Vol. 2 – How to Create a “Measurable” Sound Field:

Understanding the Inverse Square Law and K2**

In the next installment, we will take a more technical step forward.

What does a free field mean from a physical standpoint?
And on what basis can we judge that a space is truly “measurable”—through concepts such as the inverse square law and the environmental correction value K2?

I will explain these ideas from a practical perspective that is directly useful in design and evaluation work.

— Lyla Shinkai