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1. Module 1, Part 1 BUILDING SERVICES - IV WADIYAR CENTRE FOR ARCHITECTURE | MYSURU

2. Introduction to Sound: Origin and nature of sound, its characteristics and measurement– Amplitude, frequency, period, wavelength, velocity of sound, sound pressure, sound intensity, decibel scale, sound and distance – inverse square law. Humans and Sound: Human hearing, auditory range for humans (Frequency and Intensity – threshold of audibility and pain), pitch (association with frequency), tone, loudness (association with amplitude and intensity), Phon. Module 1, Part 1 WADIYAR CENTRE FOR ARCHITECTURE | MYSURU

3. INTRODUCTION Sound is energy that travels in waves through elastic media, causing pressure fluctuations and particle movement. It is an auditory experience resulting from the stimulation of hearing organs due to pressure changes in media. Sound can be r eflected, transmitted, or absorbed by different materials. Soft materials like textiles absorb sound waves , limiting their movement. In contrast, hard surfaces, such as ceramic tiles or wood, reflect sound waves, creating echoes. The term " reverberation" describes the reflection of sound waves off surfaces. Dense materials, like concrete , transmit sound waves through them . WADIYAR CENTRE FOR ARCHITECTURE | MYSURU

4. INTRODUCTION Sound waves are Longitudinal waves In a Longitudinal Wave the particle displacement is parallel to the direction of wave propagation . WADIYAR CENTRE FOR ARCHITECTURE | MYSURU

5. AMPLITUDE The extent of a vibration between the highest crest to the position of equilibrium in a propagating wave motion is called Peak –Amplitude. The extent of a vibration between crest to trough in a propagating wave motion is called Peak to Peak Amplitude. The time needed for one complete cycle of vibration to pass a given point is called Time Period. Amplitude and sound are directly proportional, implying that the amplitude of the wave determines the loudness of a sound wave. WADIYAR CENTRE FOR ARCHITECTURE | MYSURU

6. FREQUENCY Frequency describes the number of complete wave cycles that pass a fixed point in unit time. It is measured in cycles per second (cps) or hertz unit. The distance between two successive crests or troughs or the distance of a complete cycle of a wave propagation in the direction of wave motion is called wavelength. WADIYAR CENTRE FOR ARCHITECTURE | MYSURU

7. VARIATIONS IN AMPLITUDE, FREQUENCY & WAVELENGTH WADIYAR CENTRE FOR ARCHITECTURE | MYSURU

8. SOUND WAVE PROPAGATION IN AIR WADIYAR CENTRE FOR ARCHITECTURE | MYSURU

9. SOUND INTENSITY The amount of energy that is transported past a given area of the medium per unit of time is known as the intensity of the sound wave . The greater the amplitude of vibrations of the particles of the medium, the greater the rate at which energy is transported through it, and the more intense that the sound wave is. Intensity is the energy/time/area ; and since the energy/time ratio is equivalent to the quantity power, intensity is simply the power/area. Typical units for expressing the intensity of a sound wave are W/m 2 . WADIYAR CENTRE FOR ARCHITECTURE | MYSURU White Cheeked Barbet Call & Song

10. INVERSE SQUARE LAW The mathematical relationship between intensity and distance is sometimes referred to as an inverse square relationship, i.e., the intensity varies inversely with the square of the distance from the source. The inverse square law states that the intensity of sound decreases by approximately 6 dB for each doubling of distance from the sound source. This principle holds true to all energy sources. The figure to the right seeks to illustrate it graphically The formula to calculate sound intensity at different points using the inverse square law is WADIYAR CENTRE FOR ARCHITECTURE | MYSURU

11. SOUND PRESSURE Sound Pressure is the force of the sound wave (N) acting on the surface area (m 2 ) perpendicular to the direction of the sound. Sound is usually measured with microphones responding proportionally to the sound pressure. The lowest sound pressure possible to hear is approximately 2x10 -5 Pa (20 range,, 0.02 mPa) or 2 ten billionths of an atmosphere. This minimum audible level occurs normally between 3000 and 4000 Hz. For a normal human ear pain is experienced at a sound pressure of order 60 Pa or 6x10 -4 atmospheres . Due to this range, it is convenient to express sound pressure with a logarithmic decibel scale related typically to the lowest human hearable sound. WADIYAR CENTRE FOR ARCHITECTURE | MYSURU  

12. DECIBEL SCALE The human ear has the ability to handle an immense range of different sound levels. To express sound levels meaningfully in numbers that are more flexible, a logarithmic scale is used , rather than a linear one. This scale is called the decibel scale or dB scale. On the decibel scale, 0 dB is the smallest audible sound . A sound 10 times more powerful is 10 dB A sound 100 times more powerful than near total silence is 20 dB A sound 1,000 times more powerful than near total silence is 30 dB Sound can be measured with a device called decibel meter. It measures and samples sound. WADIYAR CENTRE FOR ARCHITECTURE | MYSURU

13. Introduction to Sound: Origin and nature of sound, its characteristics and measurement– Amplitude, frequency, period, wavelength, velocity of sound, sound pressure, sound intensity, decibel scale, sound and distance – inverse square law. Humans and Sound: Human hearing, auditory range for humans (Frequency and Intensity – threshold of audibility and pain), pitch (association with frequency), tone, loudness (association with amplitude and intensity), Phon. Module 1, Part 1 WADIYAR CENTRE FOR ARCHITECTURE | MYSURU

14. THE AUDIBLE SPECTRUM Humans are capable of perceiving sounds within a frequency range of approximately 20 Hz to 20 kHz. (While infants can hear frequencies a bit above 20 kHz, they tend to lose some sensitivity to high frequencies as they grow older; for most adults, the upper limit typically falls between 15 and 17 kHz .) The hearing threshold is the sound level below which a person’s ear is unable to detect any sound . A threshold shift is an increase in the hearing threshold for a particular sound frequency. It means that the hearing sensitivity decreases and that it becomes harder for the listener to detect soft sounds . Threshold shifts can be temporary or permanent. The human hearing range is a description of the pitches and loudness levels a person can hear before feeling discomfort. There are a variety of sounds in our environment, ranging from faint sounds like birdsong and rustling leaves to louder sounds like music, yelling, and industrial noise. This human hearing range is called the audible range . WADIYAR CENTRE FOR ARCHITECTURE | MYSURU

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16. PITCH, TONE & LOUDNESS Pitch is that characteristic of a musical sound by which a shrill sound can be distinguished from a grave one , even though the two sounds may be of the same intensity It is also defined as that characteristic of sound by which the ear assigns it a place on a musical scale . When a stretched string is plucked, a sound of a certain pitch sensation is produced. If the tension in the string is increased , the pitch (the shrillness) becomes higher. Increasing the tension, also increases the frequency of vibration. Therefore, pitch is intimately related to frequency. WADIYAR CENTRE FOR ARCHITECTURE | MYSURU

17. PITCH, TONE & LOUDNESS Tone is a musical or vocal or a melodious sound with reference to its pitch, quality, and strength/intensity . A sound of single frequency is called tone; however, its intensity can vary.  Two different types of voice tones are as follows: Simple tone: a simple tone as we know is a single frequency sound whose intensity varies accordingly. Complex tone: a complex tone is a mixture of several simple tones, also known as overtones . The tone of the lowest frequency is the fundamental overtone .  Additionally, the frequencies of the overtones can be whole multiples, i.e., 2nd, 3rd, 4th multiple. Therefore, we call these fundamental frequencies, second, third, and fourth harmonics of the fundamental tone, itself known as the first harmonic. Consequently, a combination of harmonic tones is pleasant to hear, and therefore, we call it a musical tone. WADIYAR CENTRE FOR ARCHITECTURE | MYSURU