Machines Sound Level Reduction

Overview

Engineering reference data for Machines Sound Level Reduction 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

Symbol	Description	Unit
$c$	Speed of sound	m/s
$L$	Sound level	dB
$\lambda$	Wavelength	m
$f$	Frequency	Hz

Noise Reduction by Enclosure Type

The following table summarizes typical sound pressure level reductions achievable with different enclosure and isolation strategies:

Noise Reduction Due to Distance

The Inverse Square Law states that for a point source radiating sound in a free field, the sound pressure level decreases by approximately 6 dB for each doubling of distance from the source.

This relationship is expressed by the formula:

$$L_2 = L_1 - 20 \cdot \log_{10}\left(\frac{r_2}{r_1}\right)$$

Where:

• $L_1$ is the initial sound pressure level at distance $r_1$
• $L_2$ is the sound pressure level at distance $r_2$
• $r_1$ and $r_2$ are the distances from the sound source

Practical Applications

• Enclosures (Types 4 & 5): The most effective solutions. A rigid, sealed enclosure provides the base attenuation (20-25 dBA). Adding internal absorption lining and vibration isolation mounts can significantly increase performance to the 40-45 dBA range.
• Barriers (Type 3): Provide moderate noise reduction (~5 dBA) and are often simpler to implement than full enclosures.
• Vibration Isolation (Type 2): Primarily reduces structure-borne noise transmitted through the building structure, offering a small but important reduction.
• Combined Strategies: For maximum effect, combine distance attenuation with physical barriers and enclosures.

References

• Original Source