A very effective way to minimize noise is to control it at the source, or “Turn down the volume!” Not unexpectedly, some noise sources are easier to control than others, or are outside the control of the person receiving the noise, so simply turning it down is not always possible. In this chapter we examine ways to control noise along the path of its transmission where a wide variety of means are available, often involving the architecture of the spaces in which we live, work and play.

If the sound is desirable, favorable conditions are provided for its production, transmission and reception. In a theater or worship space the talker is elevated on a stage or platform with respect to the listener. The transmission path (air) is made more effective by the use of reflective surfaces or a sound system, and thus, the receiver is provided with excellent listening conditions.

If the sound is undesirable such as noise from a neighbor’s television set or noise from machines in a workplace, for example, conditions may still exist for it’s production, transmission and reception. However, measures can be taken to suppress the noise at the source. The effectiveness of the transmission path can be reduced, often by use of partitions, barriers or enclosures that are adequately soundproofed. Thereby, the people subjected to the cacophony are protected or made tolerant of the disturbance. All sound sources other than a pulsating sphere have a certain amount of directionality or directivity. That is, they radiate sound more effectively in one direction than in another. An important example of this is the human voice. It’s much easier for someone to hear you if you are facing directly toward them. This is especially important when you’re speaking to someone with a hearing loss. So a solution in communication is to be aware of directivity and manipulate the environment to your advantage . . .

The voice is most directional for the higher frequency consonants that are most important for intelligibility. It’s the least directional for the lower frequency vowel sounds, as shown in Figure 11-2. If one were to measure the sound pressure level of a person speaking, one would find that for the lower frequency vowels, such as /a/, there would not be much difference whether measured from in front or behind the person. By contrast, there would be a greater loss of power for the higher frequency sounds such as the consonant /s/.

When the wavelength of sound is large in comparison to the body of the radiating device, it tends to radiate uniformly in all directions. That’s why you can put your subwoofer just about anywhere in the room, including behind a couch. Subwoofer wavelengths are longer than 10 feet, and they radiate in all directions. When the wavelength of sound is small in comparison to the body of the radiator it tends to beam like a flashlight or even a laser, for the very high frequency sounds. That is why you have to aim your bookshelf loudspeakers toward your favorite listening location!