This is a little blurb that I have given to previous customers to read over.
Depending on the current construction of your existing windows, windows with laminated glass can net significant improvements. Laminated glass will usually add about 3-5 STC points over a double pane vinyl window.
Sound Control Principles
What is Sound?
Sound, which is defined as any thing the ear can hear, originates from something making vibrations. These vibrations spread out in all directions, much like the ripples created when a stone is dropped in still water.
When a sound is generated in air it causes air pressure changes. The human ear can hear such sounds in a range from 20 to about 20,000 air pressure changes per second.
The number of these air pressure changes emanating from the source of the vibration is measured by the number of cycles per second. In the field of acoustics, the international term for cycles per second is hertz (Hz). When a sound wave is said to measure 500 Hz, it means that there are 500 "ripples" of air pressure per second from the vibration. This 500 Hz is the sound frequency.
There are two fundamental considerations which come into play when measuring the reduction of sound through windows, walls, or other building components:
Sound Transmission Loss (STL) -- indicates the effectiveness of a window or wall in reducing exterior sounds and are measured in decibels. When measuring the ability of a window or wall to reduce outdoor sounds such as traffic noise, STL's are generally figured in the frequency range of 125-4000 Hz. STL's are frequency dependent.
Sound Transmission Class (STC) -- measured in decibels, is an average value associated with a material's effectiveness in reducing sound. An STC rating is a quick reference number for the entire frequency band, and is designed to measure interior noises at levels most common to human speech (500Hz-2,000Hz). The higher the value, the greater the reduction of sound.
Critical considerations when controlling sound
Sound transmission occurs whenever there is an air-space. It is important to note that sound reducing glazing systems are rendered less effective if air leaks exist around glass, doors, vents or other areas. In addition, it is important when increasing the effectiveness of one component or material in a structure, such as the windows, other building components such as the walls need to be brought to a similar efficiency level. Sound will always travel through the weakest component.
Factors relating to the effectiveness of controlling sound
There are three physical properties of glass that have a bearing on its effectiveness in sound reduction:
Mass - sound reduction will increase with increased glass thickness due to the greater mass involved.
Damping - the reduction of sound due to the ability of a material to absorb sound rather than allowing it to transfer through. Laminated glass, with its polyvinyl butryal interlayer, is an example of a material that is effective in absorbing sound.
Stiffness - refers to the ability of a glazing system to bend or wave with the sounds motion. 1/2" glass will bend or wave with sound where as 1/8 is likely to resonate or vibrate.
Sound Control Example
1/4" over 7/32" Laminated provides the following benefits:
1/4" provides the mass which reduces sound transmission.
The 1/8" lites which make up the 7/32" laminated glass have the ability to bend rather than vibrate. The polyvinyl butyral interlayer in the laminated lite provides the damping or absorbing of sound. This glazing option provides benefits of all 3 physical properties: Mass, Damping and Stiffness.
Sound Solution Ideas
Laminated Glass -- Best
1/4" over 1/4" -- Adequate for many situations
Lites of differing thickness
Insulated Glass -- a noticeable improvement from a single lite
Quiet Line Vinyl Windows -- multiple glass lites combine to reduce sound dramatically. Wider, multi-chamber frame further reduces sound effects.
Vinyl Windows -- hollows in vinyl frame help deaden sound.
WoodClad Windows -- hollows in pultrusion frame help deaden sound.
Air infiltration can affect the amount of sound that enters the home. Quick Guide for Applications for Adequate Sound Control (units only, does not include frame)
General neighborhood noises - 1/8" over 1/8" (STC 28)
Near a busy road or highway - 1/4" over 1/4" (STC 35)
Near Airport - Laminated over 1/4" (STC 39)
Near Train - Laminated over 1/4" (STC 39)
Near park or gathering place - 1/4" over 1/4" (STC 35)
Loud music from neighbor - Laminated over 1/4" (STC 39)
Laminated glass also provides great protection from UV and adds safety and security.
Use caution specifying differing thickness of glass. The wavelengths where this combination is effective are very specific.