Brian Bollens | Acoustics

Before we go into any real detail about architectural acoustics and how it can be maximized within design I feel that it is important to define a few terms:

A mechanical wave is a wave that propagates as an oscillation of matter, and therefore transfers energy through a medium.

Acoustics is the interdisciplinary science that deals with the study of all mechanical waves in gases, liquids, and solids including vibration,sound, ultrasound and infrasound.

For our purposes as architects as we work on the Cinematek project we will mostly deal with:
Sound is a vibration that propagates as a mechanical wave of pressure and displacement, through some medium (such as air or water). Sometimessound refers to only those vibrations with frequencies that are within the range of hearing for humans or for a particular animal.

Here are some acoustic basics to know when designing:

• When sound strikes a surface, some of it is absorbed, some of it is reflected and some of it is transmitted through the surface. Dense surfaces, for the most part, will isolate sound well, but reflect sound back into the room. Porous surfaces, for the most part, will absorb sound well, but will not isolate.
• The best way to stop sound transmission through a building structure is to isolate the sound source from the structure before the structure has a chance to vibrate.
• Walls need to be isolated from ceilings and floors, usually by means of dense, pliable rubber.
• The main ways to minimize sound transmission from one space to another are adding mass and decoupling.
• Limp mass is most often better than rigid mass (actually, a combination of the two is really what you are after).
• Every object, every construction material has a resonant frequency at which it is virtually an open window to sound - kind of like a tuning fork that “sings” at its particular resonant frequency.
• Different materials have different resonant frequencies.
• Trapped air (a.k.a., air spaces and air gaps) is a very good decoupler.
• Airtight construction is a key concept. Sound, like air and water, will get through any small gap. (Sound can leak through openings as small as 1/32” – in some cases even smaller.)
• Sound bounces back and forth between hard, parallel surfaces.

Very often the shape of a surface can have an interesting effect on acoustic quality and clarity. Upon some research on that specifically I found the definition of a whispering gallery.
A whispering gallery is usually a circular, hemispherical, elliptical or ellipsoidal enclosure, often beneath a dome or a vault, in which whispers can be heard clearly in other parts of the gallery. Such galleries can also be set up using two parabolic dishes. Sometimes the phenomenon is detected in caves.

There is a whispering gallery just like this located in Grand Central Station in New York City for example.