Ground-Reflection Test Room for Automotive NVH & Appliance Noise
Hemi-Anechoic Chamber
Hemi-anechoic chambers with anechoic walls and ceiling and a hard, reflective floor — the standard acoustic environment for automotive NVH testing, household appliance noise rating, and ISO 3745 sound power measurement. Reflective ground plane replicates real-world product operating conditions.
Technical Specifications
Applications
- Automotive NVH testing (interior and exterior)
- Vehicle pass-by noise simulation and analysis
- Powertrain, engine, and transmission airborne noise testing
- Household appliance noise rating (IEC 60704)
- Power tool and garden equipment certification
- Industrial machinery sound power (ISO 3744)
- Electric vehicle inverter and motor acoustic testing
Overview
A hemi-anechoic chamber replicates an infinite hard reflecting plane in free space — the most common real-world acoustic environment for products that operate on floors, ground surfaces, or mounting surfaces. Unlike a fully anechoic chamber, the floor of a hemi-anechoic room is hard and acoustically reflective; walls and ceiling are lined with sound-absorbing wedges that eliminate reflections.
This configuration is the reference environment for ISO 3745 (acoustic test methods for sound power in anechoic and hemi-anechoic rooms), IEC 60704 (household appliances), and ISO 3744/3746 comparisons for product certification. Automotive manufacturers use drive-in hemi-anechoic chambers as the primary facility for vehicle interior NVH characterisation, pass-by noise simulation, and powertrain airborne noise separation.
HEMU Acoustics hemi-anechoic chambers are designed to ISO 3745 Annex A qualification criteria. The reflective floor is polished concrete or steel plate achieving a reflection coefficient > 0.99 (NRC < 0.01). Free-field deviation ±1.5 dB is achieved above the chamber cut-off frequency (typically 100 Hz, or 63 Hz for large-volume rooms).
Background noise levels of NC-15 or below are standard. The room shell is typically a box-in-box construction: a floating concrete slab on spring isolators carries the anechoic wedge lining system, while the outer shell provides mass-law isolation from exterior noise sources. For automotive applications, drive-in access requires a recessed floor channel or low-threshold flush ramp maintaining the ground plane continuity.
Optional underfloor dynamometer foundations, rotating ground plane turntables, and four-poster NVH rigs can be integrated. Full acoustic qualification report per ISO 3745 is provided at commissioning.
Key Features
±1.5 dB Free-Field Deviation — ISO 3745 Qualified
Free-field condition above cut-off frequency verified to ±1.5 dB per ISO 3745 Annex A criteria. Verified by acoustic measurement at a 3D array of microphone positions spanning the test volume. Qualification report issued with ISO 3745 pass/fail criteria at all one-third octave bands from cut-off frequency to 10 kHz.
Hard Reflective Ground Plane
Floor surface is polished concrete (power-floated and sealed) or 6 mm steel plate, achieving NRC < 0.01. No floor treatment is applied in the measurement area. Continuous reflective plane extends from the drive-in threshold across the full room footprint. Floor maintains continuity within ±1 mm level tolerance across the test area.
Drive-In Access for Vehicles and Large Equipment
Low-threshold flush ramp or recessed floor channel maintains ground plane continuity at the chamber entrance. Standard opening widths 3.5–6.0 m, height 3.0–5.0 m. Electric-powered acoustic door slides clear without disrupting the test area. Available with remote door control from the control room.
≤ NC-15 Background Noise
Box-in-box floating construction: outer concrete shell provides mass-law isolation; inner floating slab on spring isolators (5 Hz natural frequency) carries the wedge system. All mechanical services isolated. Background noise measured at commissioning at all one-third octave bands from 63 Hz to 10 kHz and reported against NC-15 curve.
Wedge Lining System for ≥ 100 Hz Cut-Off
Wedge geometry is determined by the target cut-off frequency. Standard 300–600 mm wedges achieve 100 Hz cut-off. For 63 Hz cut-off, 900–1,200 mm wedges are required and room height must increase accordingly. Wedge material options: melamine foam (lightweight), fiberglass (durable), recycled PET (sustainable alternative).
Automotive NVH Integration Options
Underfloor dynamometer foundation (up to 500 kW road load), rotating acoustic turntable with ground plane continuity, four-poster NVH rig mounts, and exhaust extraction with silenced ducts are available as integrated options. Cabling routes and service penetrations are coordinated with the acoustic design to maintain SE and background noise performance.
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