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

Historical summary:

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

PROPERTIES OF SOUND FUNDAMENTALS of ACOUSTICS 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 = λ * ƒ [Velocity = Wavelength * Frequency] Material Speed of Sound (m/s) Air343 Steel6100 Timber5260 Brick3650

Sound power(W): watt sound intensity (I): watt/m 2Sound 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): pascalSound pressure (P): pascal هو التغير في الضغط الجوي الناتج عن الصوت (نيوتن/م2) Decibels (DB) used to measure this ratio between two: Sound Power, or Sound Intensity, or Sound Pressure spl= 20 log P/P 0 dB swl= 10 log W/W 0 dB spl= 10 log I/I 0 dB Power W o 20 Hz - 20,000 Hz Intensity: I o to 10 W/m² Pressure: P o 2* to 200 Pa

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 SPL= SWL

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

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

SOURCE CHARACTERIZATION Point Sources and Spherical Spreading Line sourcespoint sources are one-dimensional sound sources such as roadways, which extend over a distance that is large compared with the measurement distance. With this geometry the measurement surface is not a sphere but rather a cylinder Sources that are small compared with the measurement distance

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. Inverse Square Law for sphere source

Inverse Square Law for cylindrical source I= P / 2πr L dB

Example For a point sound source, If you measure a sound level I 1 = 60 dB at distance d1 = 3 m, then at distance d 2 = 5 m the inverse square law predicts a sound level?? I 2 = dB The answer

Reflection, Refraction, absorption, and Diffraction

Diffraction

Diffusion, refraction