From a PA Engineer’s Perspective, “A Room Should Be Well-Absorbed” — But Does That Work for Acoustic Measurement?

This comment came from a seasoned PA engineer during a casual conversation.
For live sound, studios, and temporary PA setups, this idea is completely natural.

• Reflections cause feedback.
• Reflections blur localization.
• Reflections make mixing harder.

From a PA engineer’s point of view, a good room is one where sound disappears quickly.

But here is the key question:

Does the same logic apply to an anechoic chamber used for acoustic measurement?

What a “Good Room” Means in the PA World

In PA applications, the ideal room typically has:

• Minimal wall and ceiling reflections
• Short reverberation time
• Little sound returning to microphones

In other words, a room where sound stops as soon as it is produced.

This “deadness” is not just preference—it is a practical requirement for stable and controllable sound reinforcement.

From a listening and operational standpoint, this evaluation is absolutely correct.

Anechoic Chambers Are Not Designed to Be “Quiet”

An anechoic chamber is often described as:

• Extremely quiet
• Sound-absorbing
• Uncomfortable or “ear-ringing”

However, quietness is not the true objective of an anechoic chamber.

The real purpose is simple: To realize a free sound field.

A free field is a sound field where:

• Sound propagates without reflection
• Sound pressure decreases according to the inverse square law
• Distance doubling results in a 6 dB reduction

ISO 3745:2012 defines this requirement quantitatively using the environmental correction factor K₂ ≤ 0.5 dB.

“More Absorption” Does Not Automatically Mean “Better Measurement”

Here is where PA intuition and measurement reality begin to diverge.

A typical PA-oriented approach

There are reflections → add more absorption.

What sometimes happens in measurement spaces

• Absorption becomes uneven
• Directional reflection characteristics appear
• The sound field loses spatial uniformity
• The inverse square law no longer holds consistently
• K₂ increases instead of improving

As a result, the room may feel more dead, yet become worse as a measurement environment.

This is a critical point:

What Changed with ISO 3745:2012

Earlier standards (ISO 3745:2003) specified detailed construction rules, such as:

• Normal-incidence absorption coefficient ≥ 0.99
• Wedge length ≥ λ/4

These were design prescriptions.

In ISO 3745:2012, these annexes were removed.
The focus shifted decisively to one criterion:

In other words:

• Material type
• Absorber shape
• Visual “deadness”

are no longer the evaluation target.

Only the resulting sound field matters.

Sonora’s View: Absorption Is a Means, Not the Goal

At Sonora, we do not reject the PA engineer’s instinct to control reflections.
Instead, we redefine its role.

• Absorption is a tool, not an objective
• Quantity is less important than uniform effectiveness
• Spatial consistency of the sound field is essential

This philosophy underlies the design of Sonora’s Broadband Fractal (BF) absorber series, which emphasizes:

• Broadband and stable absorption
• Reduced directional reflection bias
• High sound-field uniformity

The goal is not simply to “kill sound,” but to ensure a verifiable free-field condition.

Bridging PA Intuition and Measurement Physics

The statement

is not wrong.
It is simply incomplete when applied to acoustic measurement.

In PA work, the question is:

In anechoic design, the question becomes:

“Does this room obey acoustic physics correctly?”

An anechoic chamber is not a space designed to feel comfortable or impressive.
It is a space designed to be objectively correct.

Understanding this distinction is where PA experience and measurement engineering finally meet.

Key Takeaways

• PA environments favor strong absorption for practical control
• Anechoic chambers prioritize free-field validity
• Absorption amount alone does not guarantee good measurement
• ISO 3745:2012 evaluates inverse square law performance, not structure
• Sonora designs spaces where sound fields, not materials, are optimized