How “Silence” Has Been Redefined Over Time – The Evolution of Audiometric Room Standards in ISO 8253 and JIS T 1201 –

◆ Why Did the Definition of “Quiet” Change?

In audiometric room design, quietness is not a matter of perception—it’s defined by objective measurement criteria.
But these criteria themselves have evolved over time, in response to advances in medical precision, testing equipment, and spatial acoustics.

This article explores how international and national standards—ISO 8253 and JIS T 1201—have changed, and what those changes mean for modern test environments.

◆ ISO 8253: From Broad Guidelines to Frequency-Specific Criteria

◉ 1983: Original Publication (ISO 8253-1)

• Introduced unified global procedures for pure-tone audiometry

• Provided basic guidance on room acoustics and background noise

◉ 2010 Revision

• Added MPANL (Maximum Permissible Ambient Noise Level) for each frequency band

• Defined acceptable noise limits for 1/3-octave bands from 125 Hz to 8000 Hz

• Shifted focus from A-weighted values to frequency-specific noise management

▶ Why this change?
→ More sensitive audiometers required stricter control of low- and high-frequency ambient noise to ensure measurement accuracy.

◆ JIS T 1201: Aligning National Standards with International Precision

◉ T 1201-1:2000 (updated in 2017)

• Defined pure-tone testing methods and conditions for Japanese facilities

• Adopted 20 dBA or lower as the recommended ambient noise limit using A-weighted measurement

◉ T 1201-3:2017 (newly established)

• Incorporated 1/3-octave band evaluation, aligned with ISO 8253

• Provided design and environmental guidelines for sound isolation and room acoustics

• Reflected practical use cases in Japan (e.g., hearing aid testing, public health screening)

▶ Why was it split into multiple parts?
→ Because test method guidance alone wasn’t enough—comprehensive room design needed to be standardized.

◆ Why Were These Revisions Necessary?

The need for tighter control over room noise was driven by several key trends:

• Increasing use of audiometry for both children and seniors, who are more sensitive to noise interference

• Widespread adoption of high-performance audiometers with extended frequency ranges

• Regulatory requirements demanding clearly documented noise criteria for insurance, reimbursement, and subsidy applications

Result: Quietness now must be quantified and verified, not just assumed.

◆ Common Misalignments Still Found On-Site

Despite updated standards, outdated practices still persist:

• Evaluating only with A-weighted dBA levels (ignoring spectral content)

• Using NC values alone without 1/3-octave band analysis

• Measuring noise at floor level instead of at ear level where the patient sits

These mismatches can lead to noncompliance—even when designers believe they are meeting requirements.

◆ Enclosure’s Approach: Built on the Latest Standards

Enclosure follows ISO and JIS standards not just in design documents, but in execution:

• Designs are based on 1/3-octave ambient noise evaluation

• Interior soundproofing and acoustic structures are optimized for frequency-specific absorption and isolation

• Final verification includes in-room NC testing at ear level, with data to support certification

All of this is powered by core technologies from Sonora Technology, a leading expert in precision sound environments.

◆ Summary: Even Silence Evolves

The revisions of ISO 8253 and JIS T 1201 are more than just technical updates.
They represent a shift toward scientifically validated, repeatable acoustic conditions that support accurate hearing measurement.

At Enclosure, we don’t just respond to these standards—we help clients implement them through measurable design, verified performance, and fully integrated acoustic solutions.