Environmental Systems in Architecture

1. Environmental Systems in Architecture Instructor: M Sc. Eng. Nagham Ali Hasan “Acoustic” 2nd semester 2008/2009

2. Acoustics Acoustics is the science concerned with the production, control, transmission, reception, and effects of sound. Environmental Acoustic • Main objectives are of sound control: • Space acoustic. • Noise control “vibration”

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7. 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.

9. 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 20-20000Hz ƒ= c/s cycle/second

10. PROPERTIES OF SOUND 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 Periodic Time (T)Refers to the needed time to complete one cycle . T = 1/ƒ (second) 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]

11. Sound power(W): wattهي معدل صدور الطاقة الصوتية من المصدرقدرة صوت محاضر تتراوح بين 25-50 ميكروواتsound intensity (I): watt/m2 • معدل سريان الطاقة الصوتية خلال وحدة المساحة المتعامدة مع اتجاه الصوت I=W/A (watt/m2) • Sound 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/P0 dB • swl= 10 log W/W0 dB • spl= 10 log I/I0 dB

12. 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 • SPL= 20 log Prms/P0 P0:منسوب ضغط الصوت العياري ويناظر أقل ضغط صوت يمكن للأذن سماعه في وسط هادئ= 2*10-5 Prms: جذر متوسط مربعات الضغط SPL= SWL

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

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

16. SOURCE CHARACTERIZATION • Point Sources and Spherical Spreading

17. Inverse Square Law for sphere source 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.

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

19. Example • For a point sound source , If you measure a sound level I1 = 60 dB at distance d1 = 3 m , then at distance d2 = 5 m the inverse square law predicts a sound level?? I2 = dB The answer

24. Reflection, Refraction, absorption, and Diffraction

25. Diffraction

26. Diffusion, refraction