• Acoustic glass

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Acoustic Glass

This section provides only an introductory guide to control of noise using glass.

Did you know?

• sound reduction will improve with increased glass thickness due to the greater mass involved;
• sound reduction will decrease somewhat with increasingly larger glass areas but not enough to make much difference in the majority of architectural glass sizes;
• sound reduction will improve with the use of laminated glass due to the vibration dampening effect of the PVB interlayer. Laminated glass is particularly effective for interior partitions as it reduces the 'coincidence dip' attributed to monolithic glass in the 1000 - 2000Hz range, a range attributed to the human voice. The optimum PVB interlayer thickness for sound reducing laminated glass is 1.14mm but 0.38mm will generally suffice. Multi-laminates combine the mass effect of solid glass with the dampening effect of the interlayer for superior sound reduction;
• sound reduction will improve with the use of glass/airspace combinations, but the performance is critically dependent upon the width of the airspace. An airspace of 100mm is generally regarded as a minimum for reasonable benefits at medium to high frequencies. The optimum airspace is about 300mm, but for practical purposes 200mm is more acceptable;

What is STL & STC?

There are two fundamental considerations that come into play when measuring the reduction of sound through windows and selecting a glass for sound insulation:

• Sound Transmission Loss (STL) - indicates the effectiveness of a window or wall in reducing exterior sounds. In determining the ability of a window or wall in reducing outdoor sounds such as traffic noises, engineers usually figure STL in the frequency ranges of 100 - 150Hz (UK) or 125 - 4000Hz (USA). The STL is measured in decibels(dB) and thus the greater the STL value the better the glazing is for reducing sound;
• Sound Transmission Class (STC) - indicates the reduction of sound provided by an interior wall. This rating applies to interior partitions, walls, ceilings and floors, but not to exterior walls. In terms of glass this means office partitions, viewing windows for radio/TV stations and similar applications. The STC value is a number rating that is designed to correlate the effectiveness of sound insulation of elements against sounds normally sourced inside buildings (i.e, speech, typewriters). Before exploring the sound reduction capabilities of glass it is important to establish the fact that the best sound reducing glass cannot do its job if air leaks or cracks allow sound to travel around or through the glass.

What is coincidence dip?

This occurs where the panel vibrates in unison with the frequency of the sound. The result is that the sound insulation values of the glass panel are reduced at that specific frequency. The frequency at which the 'dip' occurs varies with the thickness and the stiffness of the glass. The thicker and stiffer the glass, the lower the frequency at which the 'dip' occurs. Where specific frequencies are targeted for noise reduction, an anaylsis of where the frequency 'dip' occurs for the glass type under consideration is important.