Acoustics: Some Frequently Asked Questions
Acoustics is the science that explains behaviour of sound in a given space. Being not a very familiar term, one may have a lot of questions, queries and doubts about this term. Here we have tried to answer a few commonly and frequently asked questions in simple vocabulary. General understanding of these basic concepts will go a long way in identifying and deciding on you acoustic needs and solutions. Hope you will find this useful.
Acoustics: Some Frequently Asked Questions.
1. Why do I need acoustics in my space?
Ans.: Unwanted sound is noise. Noise can be very irritable and sometimes hazardous. This necessitates the implementation of acoustics in any given space. Audibility increases the quality of music or lectures or any other audio environment.
2. How is Acoustics implemented?
Ans.: Acoustics is implemented with the use of various acoustic materials and techniques. The right material has to be used based on the space and purpose for which the space is used.
3. Will Acoustics work in restaurants?
Ans.: Yes. That is actually an ideal place for implementing acoustics. In fact, any closed space that is vulnerable to noise needs acoustic treatment. We can have a whole list of places where acoustics works and improve the levels of audibility.
4. Can I use Acoustic panels to address outdoor noise?
Ans.: No. Acoustic panels help reduce the noise within and the noise that seeps through thin walls. To control outdoor noise, Outdoor Sound Curtain Applications have to be used.
5. At what level does sound become unsafe?
Ans.: Damage from loud noise to hearing is cumulative and irreversible. Unprotected exposure to sound pressure levels above 100dB(A) must be avoided where ever possible. When exposed to levels above 85dB(A), use hearing protection, especially if you expect prolonged exposure.
6. What is reverberation time?
Ans.: The reverberation time, T, is defined as the time taken for sound energy to decay in a room by a factor of one million (i.e. by 60 dB). It is dependent on the room volume and its total absorption.
In metric units
0.161 x room Volume
T = ——————————————————————-
sum of Surface areas x absorption coefficients
7. What is sound absorption coefficient?
Ans.: The sound absorption coefficient is the fraction of the incidental sound power which is absorbed, or not reflected. There are often variations in the results depending upon the method of measurement. The sound absorption coefficient measured at the preferred octave frequencies over the range of 125Hz – 4kHz.
8. What is the difference between insulation & absorption of sound?
Ans.: There is often confusion between sound insulation and sound absorption. There are many instances where the use of sound absorbers improves sound insulation.
Sound insulation is to eliminate the sound path from the source or to reduce unwanted external noise inside a hall or room.
Sound absorption is to pass the incident sound energy through the absorber or convert some or all of the incident sound energy into heat. Good sound absorbers do not always make good sound insulators.
9. What is Active Noise Control?
Ans.: Active Noise Control is an electronic method of reducing or removing unwanted sound. A pressure wave of equal amplitude opposite to the unwanted sound is produced.
10. How do sound levels add?
Ans.: If there are two sound sources in a room, the combined sound level cannot be more than 3 dB above the higher of the two sound levels. However, if the sounds are phase related there can be up to a 6dB increase in SPL.
11. How is sound measured?
Ans.: General noise level is measured by means of an instrument called sound level meter.
The reading on a sound level meter (aside from weighting considerations) indicates the sound pressure, p, as a level
referenced to 0.00002 Pa.
Sound Pressure Level = 20 x lg (p/0.00002) dB
During any given time-interval peak levels will be numerically greater, and often much greater than the (rms) sound pressure level.
12. What is sound intensity?
Ans.: This may be defined as the rate of sound energy transmitted in a specified direction per unit area normal to the direction. With good hearing the range is from about 0.000000000001 Watt per square metre to about 1 Watt per square metre (12 orders of magnitude greater). The sound intensity level is found from intensity I (W/m^2) by:
Sound Intensity Level = 10 x lg (I/1.0E-12) dB
Sound intensity meters are becoming increasingly popular for determining the quantity and location of sound energy emission.
What is the size of the room that is optimum for room acoustics?
Acoustics may not give required results in very small rooms. Again it depends on the purpose for which the room is used.
In acoustics, the energy of sound waves is being taken in and trapped within the material rather than being bounced off or reflected. Materials are rated in terms of their ability to absorb sounds.
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