Acoustic Properties of Glass

The sound attenuation of any material depends on its mass, stiffness and damping characteristics. With a single glass pane, the only effective way to increase its performance is seemingly to increase the thickness, because stiffness and damping cannot be changed. The sound transmission loss for a single glass pane, measured over a range of frequencies, varies depending on glass thickness. Thicker glass tends to provide greater sound reduction even though it may actually transmit more sound at specific frequencies. Every glass pane thickness has a weak frequency value; that is, a frequency for which that glass is less 'noise absorbent' than for others. That value is known as critical frequency.

An 1/8” glass pane is rather transparent with poor attenuation measured in dB for high frequencies at the range of 4800 Hz. A 3/16” glass pane is poor for frequencies around 3600 Hz. A 1/4” thick glass pane performs poorly at 2400 Hz. Insulated glass units built with two panes of the same thickness are perceived to have good attenuation. They experience the issue of critical frequency as well, with the two panes vibrating (resonating) together at that frequency, thus reducing the overall acoustic performance of the glass.

The solution: Laminated Glass. A laminated glass pane will attenuate sound transmission more than a standard pane of glass (monolithic glass) of the same mass. A 1/4” laminated glass pane reduces sound at high frequency considerably more than a monolithic glass of equal thickness (8 to 10 dB of additional attenuation). Why? Because the critical frequency effect disappears due to the sound damping provided by polyvinyl butyral (the soft interlayer used to permanently bond the glass panes together, dissipating energy).

Further broadening this line of thinking, insulated glass does not preform as well as laminated glass because the air space between the two panes resonates easily transferring the noise without any loss directly through the seemingly insulative air space. IGU’s are not recommended for noise reduction glazing.