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The Difference the Cavity Makes

The cavity or gap between an existing primary window and the secondary unit can make a significant difference to the level of noise insulation.  Unlike sealed units where the two pieces of glass are rigidly coupled together, the primary and secondary windows act as independent barriers to the transmission of noise.  The greater the cavity between them, the better the dampening effect of the combined window.  A minimum of 100mm is recommended.

Avoid the Gap

Gaps around window frames representing just 1% of the frame area allow the passage of airborne sound that can reduce noise insulation levels by as much as 10 dB.  Selectaglaze secondary windows are tailor-made with very effective seals to shield the whole window opening and minimise leakage.

Choice of glass

The ability to select a wide range of glass types to ensure optimum performance.· The inner and outer glass should have different mass to avoid the phenomenon of sympathetic resonance which will increase noise transmission at higher frequencies· Thicker glass has greater mass and improves performance particularly at lower frequencies· Acoustic laminate glass has a special interlayer that helps improve high frequency performance and is particularly suited to dealing with aircraft noise.

Acoustic Liners

Absorbent lining materials can be fixed between the window frames raising insulation levels by 1-3 dB.  These are most effective at higher frequencies.

• Reasonable Noise Levels
• Rw dB values for Selectaglaze Secondary Glazing Systems