Duct Area Change Noise Attenuation

Overview

Engineering reference data for Duct Area Change Noise Attenuation in acoustics.

Key Formulas

Speed of Sound

$c = \sqrt{\gamma R T}$

Speed of sound in an ideal gas.

Sound Level

$L = 10 \log_{10}(I/I_0)$

Decibel level.

Wavelength

$\lambda = c / f$

Wavelength = speed / frequency.

Variables

Practical Example: Duct Size Attenuation

The attenuation formula calculates noise reduction when air passes through an abrupt duct area change. Here is an applied example based on the provided data.

For an area ratio of $\frac{A_1}{A_2} = 5$, the attenuation $\Delta L$ is calculated as:

$$\Delta L = 10 \log \left( \frac{(1 + \frac{A_1}{A_2})^2}{4 \cdot (\frac{A_1}{A_2})} \right)$$

Substituting the value:

$$\Delta L = 10 \log \left( \frac{(1 + 5)^2}{4 \cdot 5} \right) = 10 \log \left( \frac{36}{20} \right) = 10 \log(1.8) \approx 2.5 \text{ dB}$$

Note: This model is valid only for sharp, sudden changes in duct cross-sectional area, not for gradual expansions or contractions.

Source: engineeringtoolbox.com

References

• Original Source