Source Contribution Analysis and Acoustic Transfer Function (ATF) Measurement — Optimized Methodology Using HBK & Sonora Technologies

Introduction

In the field of acoustic measurement, understanding how much each specific source contributes to the total sound field is essential. This evaluation process is known as source contribution analysis, and at the heart of it lies the measurement of the Acoustic Transfer Function (ATF).
By accurately measuring ATFs, engineers can identify individual noise sources and optimize product designs for noise control and sound quality.

High-performance anechoic and semi-anechoic environments are essential for minimizing environmental influences during ATF measurements. This article introduces the basic concepts of ATF, practical measurement methods, and how HBK’s measurement technologies and Sonora Technology’s chamber and absorption systems can be used to create the ideal acoustic testing setup.

What Is the Acoustic Transfer Function (ATF)?

The Acoustic Transfer Function (ATF) defines how sound energy propagates from a source to a receiver, typically represented in the frequency domain.
ATF measurements provide critical information such as:

• Influence range and directivity of sound sources
• Reflection and diffraction characteristics along the propagation path
• Environmental correction values like K2 (per ISO 3745/3744)

With accurate ATF data, industries including automotive, electronics, audio, and building acoustics can perform high-level noise control and acoustic optimization.

Basic Methods of ATF Measurement

Two primary methods are used to measure ATFs:

(1) Impulse Response Method

• Emits a short impulse (e.g., click or spark) and records the response at the receiver
• Frequency response is obtained via Fourier Transform
• Suitable for broadband measurement, but requires strong impulse signals

(2) Frequency Sweep Method

• Sends a swept sine signal from a speaker and records the response
• Offers high accuracy and robustness against background noise
• Highly compatible with HBK’s source and acquisition systems

High-Precision ATF Measurement Using Sonora Anechoic Chambers

(1) In Anechoic Chambers

Sonora’s anechoic chambers are designed to meet ISO 3745 standards and use proprietary Broadband Fractal Wedges (BFW) as wall absorbers.
This results in K2 ≤ 0.5 dB, enabling highly accurate ATF measurements.

Advantages

• Eliminates reflected sound for pure ATF data
• BFW offers wider frequency absorption compared to conventional wedges
• Ideal for integration with HBK systems like LAN-XI and 2270-S analyzers

(2) In Semi-Anechoic Chambers

Semi-anechoic chambers designed per ISO 3744 use reflective floors to simulate real-world conditions while minimizing ceiling and wall reflections.

Advantages

• Equipped with Broadband Fractal Board (BFB) for effective low-frequency absorption
• Enables realistic propagation modeling while maintaining K2 ≤ 4 dB
• Suitable for in-cabin vehicle testing and home appliance acoustic development

Recommended HBK Acoustic Instruments for ATF Measurement

(1) Microphone Arrays

• HBK Type 4942: Omnidirectional measurement microphone
• HBK Type 4944: High-precision reference microphone

→ Enables directional and spatially resolved ATF measurements in Sonora chambers

(2) Handheld Analyzers

• HBK Type 2270-S: Two-channel handheld analyzer
• HBK Type 2250: Advanced sound level meter

→ Ideal for rapid testing in semi-anechoic environments

(3) ポータブルインピーダンスメータ

• HBK Type 9737

→ Measures absorption performance of BFW/BFB panels and supports environmental correction

(4) Data Acquisition Systems

• HBK LAN-XI: Multichannel DAQ platform

→ Supports simultaneous ATF capture across multiple source/receiver points
→ Fully compatible with Sonora’s test rooms

Use Cases for ATF Measurement

Using HBK instruments in conjunction with Sonora acoustic chambers, ATF-based source contribution analysis delivers major benefits in fields such as:

Automotive	Road noise and engine/motor sound source identification
Audio Devices	Evaluation of speaker and headphone output characteristics
Home Appliances	Acoustic optimization of washing machines, refrigerators, air conditioners
Architectural Acoustics	Room design for concert halls and auditoriums
Medical Devices	Acoustic performance assessment of ultrasound systems

Conclusion

ATF measurement is a fundamental tool in accurate source contribution analysis.
By combining HBK’s state-of-the-art instruments with Sonora Technology’s anechoic environments and absorption systems, users can achieve highly precise and repeatable acoustic measurements.

• Anechoic chamber testing with BFW for high-frequency precision
• Semi-anechoic testing with BFB for real-world simulation
• Full synergy with HBK instrumentation for complete acoustic analysis workflows

• << Major Manufacturers of Acoustic Measurement Instruments and Anechoic Chambers
• Why Is Acoustic Testing Important for Home Appliances? >>