Instructor: M Sc. Eng. Nagham Ali Hasan 2 nd semester 2008/2009 University of Palestine College of Applied Engineering & Urban Planning Department of Architecture, Interior Design & Planning“Acoustic”

Acoustics Acoustics is the science concerned with the production, control, transmission, reception, and effects of sound. Research was done to look into the many aspects of the fundamental physical processes involved in waves and sound and into possible applications of these processes in modern life.

Main objectives are of sound control: 1. Space acoustic. 2. Noise control “vibration”

Historical summary:

What is Sound? It is a vibration in an elastic medium-air, water, metal, building materials ( physical) It is an auditory sensation that is felt by ear as a result from rapid changes in air pressure (physiological) Physical Properties

THE NATURE OF SOUND A vibrating object will produce a sequence of compressions and rarefactions in the air surrounding it. These small fluctuations in air pressure travel away from the source at relatively high speed, gradually dying off as their energy is absorbed by the medium. What we call sound is simply the sensation produced by the ear when stimulated by these vibrations.. Physical Properties

A Sound Wave: If you were to graph the pressure maxima and minima at a given instant. It should be noted that air cannot sustain any form of shear stress so sound can only be transmitted as a longitudinal wave. Thus the graph showing a sine wave refers only to variations in pressure or compression, not to the actual displacement of air. Physical Properties

Audible Range The ear can hear sounds ranging from 20Hz to 20kHz. It is most sensitive to frequencies which corresponds almost exactly to the speech band. between 500Hz and 4000Hz,

PROPERTIES OF SOUND The wave motion of sound can be described in terms of Amplitude, Frequency, Velocity and Wavelength. Frequency (ƒ) Refers to the number of peak-to-peak fluctuations in pressure that pass a particular point in space in one second. For human “can hear sound ranges Hz ƒ= c/s cycle/second

PROPERTIES OF SOUND Periodic Time (T) Periodic Time (T) Refers to the needed time to complete one cycle. T = 1/ƒ (second) Wavelength (λ) Wavelength (λ) : Refers to the physical distance between successive compressions and is thus dependant on the speed of sound in the medium divided by its frequency. It ranges between 17mm to 17m. λ= C/ƒ (m) Where C= speed f sound

Velocity (V) Velocity (V) Refers to the speed of travel of the sound wave. This varies between mediums and is also dependant on temperature. Assuming air acts as an ideal gas, its velocity (V in m/s) relates to temperature (T in °C) as follows; V = (0.6 T) (m/s) Where T: temperature MaterialSpeed of Sound (m/s) Air343 Steel6100 Timber5260 Brick3650 PROPERTIES OF SOUND V = λ * ƒ [Velocity = Wavelength * Frequency]

Sound power(W): watt sound intensity (I): watt/m 2 Sound power(W): watt هي معدل صدور الطاقة الصوتية من المصدر قدرة صوت محاضر تتراوح بين ميكرووات sound intensity (I): watt/m 2 معدل سريان الطاقة الصوتية خلال وحدة المساحة المتعامدة مع اتجاه الصوت I=W/A (watt/m 2 ) Sound pressure (P): pascal Sound pressure (P): pascal هو التغير في الضغط الجوي الناتج عن الصوت ( نيوتن / م 2)

Decibels (DB) used to measure this ratio between two: Sound Power, or Sound Intensity, or Sound Pressure Power W o 20 Hz - 20,000 Hz Intensity: I o to 10 W/m² Pressure: P o 2* to 200 Pa SPL= 10 log P/P 0 SPL= 10 log W/W 0 SPL= 10 log I/I 0 1 Bell = 10 Decibels (DB)

TUNES Pure Tune: Pure Tune: هي النغمة التي لها سعة وتردد ثابتين نتيجة تغير الضغط بها كحركة توافقية بسيطة كالناتجة عن الشوكة الرنانة. تعبر السعة عن خاصية الجهارة Loundness وهي درجة الإحساس السمعي الناتج عن الصوت بشدة معينة 1.Harmnic Tune 2.Nonharmnic Tune Complex Tune: Complex Tune: المحركات, مكبرات الصوت, الأصوات الآدمية, الآلات الموسيقية

Inverse Square Law

If a point source in a free field produces a sound pressure level of 90 dB at a distance of 1 meter, the sound pressure level at 2 meters is 84 dB, at 4 meters is 78 dB, and so forth.

Sound pressure level (SPL): هو الكمية التي يمكن قياسها عملياً عند وضع ميكروفون في مجال صوتي هو قيمة العلاقة بين الصوت المقاس عمليا إلى مستوى صوت استنادي ويقاس بجهاز مقياس منسوب الصوت P 0: منسوب ضغط الصوت العياري ويناظر أقل ضغط صوت يمكن للأذن سماعه في وسط هادئ = 2*10 -5 P rms: جذر متوسط مربعات الضغط SPL= 20 log P rms /P 0 Sound Power Level (SWL) Sound Power Level (SWL) refers to the magnitude of that power relative to a reference power SPL= 2SWL

Sound level (SL): Phone: وحدة قياس الجهارة Soune

Sound & Distance: 1.Spherical wave 2.Cylindrical wave 3.Plane wave

ATMOSPHERIC EFFECTS Wind Temperature The speed of sound is dependant on temperature, the higher the temperature, the higher the speed