Acoustical Design in Modern Architecture Part III

This is a snippet from our Acoustical Design in Modern Architecture course. This course is approved for HSW credits nationwide. 

Using basic concepts of acoustics, there will always be three basic ways to attenuate or reduce sound.

  • If possible, we can replace sources of sound with others that produce less noise. In a similar approach, we can locate sensitive spaces further from generators of noise, to lessen the acoustic impact on them.
  • We can block sound from reaching a receiver with heavier, more massive materials and barricades that are less affected by the kinetic energy of sound waves.
  • We can interrupt the path from source to a receiver with light and absorbent materials to absorb the energy of sound waves.

Those three basic principles form the foundation for specific design strategies that follow, which apply equally to controlling sound in every building type. (Part III of III | Read Part I | Read Part II)

  • Resisting transmission of noise from the exterior into the interior of a space
    • Exterior noise still coming through the roof by vibrating membrane materials like metal roofing, will easily transfer through, since such materials are usually directly fastened to supporting structural members. Isolation clips can be used to allow movement between roofing membrane and structure and absorb some kinetic energy trying to pass through. This is good practice anyway, since those two components tend to expand at different rates due to solar exposure, and need to be able to move slightly differently anyway.
    • Noise will transfer through the weakest link in the acoustic envelope, whether it be a door, a window, or an air vent.
    • If air can get through a closed door, so can noise. Seal doors well and use airlocks to prevent direct transmission through open doors.
    • Windows are very poor blockers of sound. Glazing vibrates when struck by the acoustic energy of site noise, and that vibration passes the energy inward. Multiple panes, with air space between them, absorb some energy. Separated frames resist sound transfer by reducing structure-borne sound. But by far the most effective way to mitigate leakage of sound through glazing is to design buildings so noise sensitive spaces inside do not have to glaze directly facing sound waves generated by exterior sources of noise. If possible, minimize or eliminate large expanses of glass facing site noise sources.
    • All the problems mentioned above are still present, but two more can be added when windows are operable. Necessary clearances for windows to operate, also allow sound in through the gaps. If air can enter, so can sound. And of course, when the windows are open to the source of exterior noise, that is the largest acoustic gap possible.
    • If exterior noise cannot be eliminated and is still distracting, its impact can be minimized by adding a water feature to the site, thus masking the sound

 

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Acoustical Designs in Modern Architecture

This is a snippet from our Acoustical Design in Modern Architecture course. This course is approved for HSW credits nationwide. 

Using basic concepts of acoustics, there will always be three basic ways to attenuate or reduce sound.

  • If possible, we can replace sources of sound with others that produce less noise. In a similar approach, we can locate sensitive spaces further from generators of noise, to lessen the acoustic impact on them.
  • We can block sound from reaching a receiver with heavier, more massive materials and barricades that are less affected by the kinetic energy of sound waves.
  • We can interrupt the path from source to a receiver with light and absorbent materials to absorb the energy of sound waves.

Those three basic principles form the foundation for specific design strategies that follow, which apply equally to controlling sound in every building type.  (Part I of III)

  • This seems extremely simplistic, but while selecting a site for a project, some attention should be given to what is nearby, what kinds of sounds can be expected due to proximity to what generates them, and whether such sounds are acceptable or would need to be blocked or lessened.
  • If the site is large enough, locate structures far enough from noise generators, that sound waves have time to spread out and weaken before striking the enclosed spaces. Each doubling of distance from a source of noise lowers its sound level by 3-6 dB.
  • If possible, lessen or block the objectionable noise at its source. An example would be an enclosure, built around an auxiliary power generator on site.
  • Use dense screens of evergreen vegetation to help dissipate and absorb the kinetic force of sound waves entering the site. While these are not highly effective, they help somewhat and are aesthetically pleasing.
  • Use low walls or earth berms to deflect or totally block the kinetic force of sound waves entering the site. Redirect kinetic energy up, over or around the building. This is the function of concrete walls used to separate highways and high traffic streets from adjacent neighborhoods. Such barriers may not have openings and must block the line of sight between noise source and receiver, to be effective. The best that can be hoped for from such barriers, is lowering the sound level by 10 dB.
  • Block exterior noise that transmits sound by using the wall as a diaphragm. Use enough wall mass that it uses up a great deal of acoustic energy to vibrate the outside enclosure assembly. For example, tilt-slab concrete exterior walls block far more sound from nearby trains, than sheathed steel stud framing.

More sound solutions next week!


 

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