1. What is an Anechoic Chamber?

An anechoic chamber (or soundproof room) is a specialized space where sound waves are almost entirely absorbed, creating an environment with minimal sound reflections. It offers a uniquely silent setting where a “free field” is established. Anechoic chambers are primarily used to measure small sound sources or sources without specific installation conditions.

#### Types of Anechoic Chambers:
– **Concrete-Based Chambers**: These have high sound insulation but are weak against low-frequency vibrations and susceptible to vibration transmission risks. Installation often requires digging pits in buildings, making relocation difficult.
– **Panel Assembly Chambers**: The current standard. They are easy to assemble and disassemble, making relocation possible. They overcome the drawbacks of concrete chambers and are more cost-effective.
– **Wood + Board + Veneer Chambers**: A cost-saving method but disadvantageous in safety due to flammable materials. Relocation is virtually impossible.

When designing an anechoic chamber, it is crucial to consider sound insulation, operational efficiency, ambient noise, and the measurement frequency range. Properly balancing these factors results in a high-quality measurement environment.

2. What is a Semi-Anechoic Chamber?

A semi-anechoic chamber is similar to an anechoic chamber but includes reflective surfaces, such as a floor. Sound reflects off these surfaces, allowing for the measurement of sound in a “semi-free field.” It is typically used for measuring heavy machinery or sound sources fixed to the ground, particularly those with reflective characteristics.

Semi-anechoic chambers require sound insulation comparable to anechoic chambers. The floor is usually made of hard, flat materials like concrete to prevent sound waves from vibrating and reflecting. Careful design of the acoustic environment is essential to minimize vibration effects.

3. What is Sound Power Level?

Sound power level is a fundamental metric for evaluating the noise emitted by machines and devices. It represents the total sound energy radiated by a source and is widely used for machinery noise assessments and noise predictions. Measurements follow international standards, such as ISO 3745.

#### Applications:
– Evaluating the noise reduction effects of machinery
– Noise assessment during procurement and inspection
– Providing essential data for noise reduction strategies

Sound power level is essential for understanding the performance of sound sources. Accurate measurement environments, like anechoic or semi-anechoic chambers, are vital for precise evaluations.

4. Distance Attenuation Characteristics of Sound Pressure Level

In anechoic and semi-anechoic chambers, the “inverse square law” applies, meaning sound pressure level decreases by 6 dB(A) each time the distance from the source doubles. Adhering to this principle is crucial for accurately measuring the attenuation of sound over distance.

#### Permissible Deviation:
– **Anechoic Chambers**: ±1.5 for 100–125 Hz, ±1.0 for 1 kHz–5 kHz
– **Semi-Anechoic Chambers**: ±2.5 and ±2.0 under the same conditions

These standards ensure accurate measurements of acoustic properties.

5. Measurement Methods

In anechoic chambers, a spherical measurement surface (sphere) is established around the sound source. The center of the sphere aligns with the acoustic center of the source, and the radius must be at least twice the source’s maximum dimension, or no less than 1 meter.

In semi-anechoic chambers, a hemispherical measurement surface (dome) is established based on the reflective floor, maintaining similar distance requirements. This setup ensures precise sound evaluations.

6. Ambient Noise Correction

To prevent ambient noise (background noise) and measurement device noise from affecting results, the difference in sound pressure levels between the operational and non-operational states of the sound source should ideally exceed 15 dB(A). If the difference falls between 6 dB(A) and 15 dB(A), ambient noise must be corrected. Measurements are deemed invalid if the difference is below 6 dB(A).

7. Measures to Prevent Reflections

Anechoic and semi-anechoic chambers must be meticulously designed to prevent sound wave reflections. For example, gridded floors or equipment cranes can act as reflection sources, affecting measurements. During tests, unnecessary equipment should be removed, and sound-absorbing treatments applied.

Lighting is another overlooked factor. Fluorescent lights can generate noise, so incandescent lights are recommended to minimize ambient noise. Additionally, wiring noise should also be carefully managed.

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Leverage Anechoic and Semi-Anechoic Chambers for Precise Acoustic Measurements!

Anechoic and semi-anechoic chambers, with their unique characteristics, provide optimal environments for various acoustic measurements. Utilize these quiet, reflection-free spaces to obtain accurate data and conduct advanced noise evaluations and solutions efficiently!