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What Is a Standard Ruler for
Annoyance by Sound?
Up to now in this article, the goal has been to provide a foun- dation as to what goals should be set for STC or IIC. Pos- sible failures in achieving those goals have been highlighted. The question remains: What is a disturbance? Annoyance by sound is a response to auditory experience. The standard acoustic ruler is that any noise that exceeds the background noise level by 5 dB(A) or more has the potential to be an annoyance. This applies to all forms of sound from people’s conversations and automobiles passing on the street imping- ing on the street side of the house to mechanical noise to footfall from the floor above.
lapping of successive syllables or tones, excessive reverbera- tion reduces the intelligibility of speech and music within a room. People with a hearing impairment require a low re- verberation time of about 0.4 seconds. Because an acoustic wave is a pressure wave, an acoustically correct space has a positive physical effect. I have had clients say to me, “I don’t know why, but this room is my favorite. It feels so good.” On the other hand, too little reverberation will make the room “dead.” The ideal reverberation time for a room varies con- siderably and depends on several factors, such as personal preference, volume, or auditory constraint requirements.
Clearly, reverberation treatment is critical in rooms intend- ed for any type of audio application, such as a home the- ater or media room, but tuning reverberation should also be addressed in dining rooms, large volume foyers, and even bedrooms. In fact, any room intended for sleeping, read- ing, learning, working, conversation, or any focused activ- ity should receive reverberation analysis so that correction and optimization are incorporated in the final design. Ideal reverberation not only improves productivity and concen- tration but also provides a positive living and working en- vironment.
The reverberation in a room should be corrected by math- ematically modeling a room and positioning and applying acoustic material at precise locations on the surface bound- aries of the room. Too little acoustic material will not make a noticeable difference and too much material will make the room feel uncomfortable and is a waste of money.
Conclusions
Quietude is one of the most grand and yet achievable trea- sures a person can have in his/her life. This quietude should begin in the residence of that person. Although definably subjective for every person, it begins with a properly engi- neered space.
This article was written to clarify some of the misunder- standings of ASTM laboratory tests and field conditions and the tests performed in the field for the full team involved in the design of a residential home. With clarification, the construction process can assuredly be engineered and then tested to make the process more successful. Some of the methods by which expectations can be adjusted for each so- lution will help make a step forward toward providing true quietude, whatever that may be for each individual, achievable.
The doubling of the volume of a sound only shows a 10-point increase in decibels. For example, one TV set at a normal
LE 1 Article #5 Schnitta Residential Quietude
conversational level is about 60 dB. Ten TV sets at the same volume will sound twice as loud and register about 70 dB (Table 1).
Table 1. Subjective perception of actual sound energy change
Change, dB
Subjective Perception
Sound Energy Change, %
0-3
Barely perceivable
50
4-5
Perceivable and significant
69
6
Double sound pressure
75
7-9
Major perceived increase
87
10
Double loudness, 10× power
90
What does this really counsel us to do? On one hand, it is telling us that if your noise is 20 dB above background, a solution that takes care of 90% of the problem, as good as it may sound, still leaves a terrible problem. Additionally, it shows that if we can bring the noise to within 3 dB of the background sound levels when there is no noise, we may not need to spend a tremendous amount of money for total iso- lation. This perspective brings us full cycle as to the impor- tance of putting great effort into inhibiting flanking.
Acoustic Environment
I want to conclude this article not with the problems and so- lutions for direct noise and vibration in a residence but with the importance of creating an appropriate, or hopefully ide- al, acoustic environment. Once any intruding noise has been negated, this is often defined by the reverberation or decay time within a room or what distinguishes a vibrant sound- ing room from one that is offensively noisy. Reverberation is sound persistence due to repeated boundary reflections even after the source of the sound has stopped. Due to over-
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