Detailed Explanation of Acoustic Laboratories: Purposes and Structures of Reverb Chambers, Sound Ins

As the name suggests, the primary function of an acoustic laboratory is to serve as an experimental site for acoustic research or environmental acoustic studies. Additionally, companies such as speaker manufacturers and acoustic treatment firms require such an environment that meets relevant standards to test various parameters and indicators of new products during R&D.

So, how many types of acoustic laboratories are there? What are their purposes? The editor will provide an introduction.

Classification and Basic Structure of Acoustic Laboratories

Broadly speaking, acoustic laboratories can be divided into three main categories: reverberation chambers, sound insulation chambers, and anechoic chambers. Laboratories must have excellent sound and vibration isolation from the surrounding environment to avoid interference from external noise during experiments. Structurally, rooms are typically constructed as separate concrete boxes placed on spring foundations. Spring foundation methods include steel springs, air springs, cork, etc., selected based on practical needs. The resonance frequency of the room-mass-spring system must be strictly controlled, usually below 1/20 of the lowest test frequency used in the laboratory, ensuring external vibrations do not affect indoor testing.

Sound insulation typically employs double-wall construction, with the outer wall being plastered brick and the inner wall made of concrete. Specially designed soundproof doors with precise seals (e.g., wool-lined edges or inflatable rubber gaskets) ensure airtightness. Acoustic laboratories usually include a control room for test instruments and control devices.

Overview of Acoustic Laboratory Types

1. Reverberation Chamber

Reverberation chambers measure material absorption coefficients, airborne sound absorption, sound power spectra of sources/machines, and loudspeaker efficiency. They also conduct noise fatigue tests and generate artificial reverberation. Volumes range from 100-500m³. High-frequency reverberation time limits depend on molecular absorption, low frequencies on viscous wall absorption. Different sizes serve different purposes: e.g., the Institute of Acoustics (Chinese Academy of Sciences) has three chambers—425m³ for specialized research, 191m³ for routine absorption testing, and 100m³ for measuring wall/ceiling sound insulation.

Requirements: 1) Maximize reverberation time; 2) Ensure diffuse sound field.

2. Sound Insulation Chamber

Used to test sound insulation properties of floors, walls, doors, and windows. Constructed with vibration isolation pads (springs), soundproof panels, doors, windows, and ventilation silencers. Single/double-layer designs are chosen based on required insulation levels.

1) Vibration pads: Selected based on polarization coefficient/load (typically 4-5 sets).

2) Modular panels: Typically 50/75/100mm thick with galvanized steel outer layer, perforated inner layer, and rockwool/fiberglass core. Double-layer structures have ~100mm gaps.

3) Doors/windows: Require high insulation (30-40dB). Double-glazed windows (100mm+ thickness) are common. Overall insulation depends on component integration and sealing. Performance is rated by indoor-outdoor sound level difference (20-45dB), with double-layer needed above 35dB.

3. Anechoic Chamber

Anechoic chambers eliminate sound reflections via wall-mounted absorbers (absorption coefficient >0.99). They test electroacoustic properties like sensitivity/frequency response of noise-canceling devices (e.g., speakers/driver units). Graduated absorbers (fiberglass wedges/cones or soft foam) are used. Test objects are placed on central nylon/steel mesh (limited to lightweight items).

4. Semi-Anechoic and Trihedral Chambers

Trihedral chambers have three adjacent hard reflective surfaces and three absorbent walls. Placing sound sources/receivers at the reflective intersection creates a reflection-free path like semi-anechoic chambers (limited to fixed points). Semi-anechoic chambers use the floor as a reflector with absorbent walls/ceiling.

5. High-Intensity Sound Laboratory

Simulates high-noise environments and studies materials/structures under intense sound, large-amplitude waves, and metal fatigue. Includes a 160dB reverberation chamber and 170dB traveling-wave tubes. Sirens (efficient/fixed spectrum) or airflow speakers (adjustable random noise) generate sound fields.

6. Aeroacoustic Wind Tunnel

A low-noise, low-turbulence wind tunnel within an anechoic chamber with an open test section. Studies flight speed effects on fan/propeller noise and flow-induced noise. Combines aerodynamic ducts/controls (minimal energy loss) with acoustic free-field conditions (large dimensions, background noise <60-70dB). Contracting nozzles reduce turbulence; low-noise fans with silencers control noise.