Lec.5 2021

Acoustics in Architecture Dr. Doha Mohammed

Acoustics in Architecture

Acoustics

Course objectives? Course importance? Course contents?

an example of books dedicated to the study of architecture and acoustics

‫مثال من الكتب لدراسة الهندسة المعمارية والصوتيات‬

‫‪Acoustics‬‬

‫‪Acoustics in architecture‬‬ ‫الغرض منها‪-:‬‬ ‫تصميم الفراغات الداخليه لالماكن وتوزيغ الصوتيات فيها‬

‫نبذه تاريخيه‪-:‬‬ ‫كان الصوت عامل حاسم الناس كثيره حيث كان يستخدم لرهبة الناس في المعابد وكانوا يقوموا بتضخم الصوت‬ ‫والوصول الي اقصي درجه من الرهبه عن طريق التدرج في المعابد الفرعونيه ابتداء بقدس االقداس مع التدرج‬ ‫في االرتفاع‪.‬‬ ‫تطور هذا النوع من الصوتيات حتي وصل الي االغريق حيث بدا التصميم حسب المعتقدات الدينيه الخاصه بهم‬ ‫والتطور التاريخي لهم حيث لديهم اكثر من حرفه او مهاره يستخدم فيها الصوت بشكل اساسي‬ ‫مثل‬ ‫المسرح او الكولوزيوم وشكله البيضاوي حيث يصل الصوت بشكل وطريقه مناسبه‬

‫‪Acoustics‬‬ ‫عند دراسة طباع هذه الفترات وجد ان االماكن التي تستخدم فيها االصوات توضع بالمناطق الريفيه حيث اتسامها بالهدوء‬ ‫حيث وجد ان االصوات تتالشي في بعض االماكن فقاموا بوضع مزهريات او فخار حيث انها تساعد علي وصول‬ ‫الصوت الي ابعد مكان‪.‬‬ ‫تم استغالل الصوت كاول استغالل كاستخدام ديني او عقائدي وتكرر في العصور الوسطي في الكنائس والمساجد‪.‬‬ ‫في العماره االسالميه تم التدرج في تصميم المساجد ثم التدرج في مستويات الصوت دون احداث اي نوع من الضوضاء‬ ‫في المسجد‪.‬‬ ‫تطورت الصوتيات حتي وصلت الي االوبرا حيث كان يصمم المكان بطرق خاصه لتوزيع وانعكاس الصوت بطريقه‬ ‫مناسبه‬ ‫ملحوظه‪ -:‬يرجع تدرج الصوت الي انوع االسطح فهناك اسطح تعمل علي تجعيد الصوت واخري تعمل علي تشتيت‬ ‫الصوت حيث تتوقف نوعية السطح الي طبيعته او مكوناته الفيزيائيه فيجب مراعاة انواع االسطح الموجوده في المكان‬ ‫لتفادي االضطرابات الصوتيه‬

Acoustics

During the antiquity, open theatres were mainly used for staging drama theatrical performances so that their acoustics were tuned for speech intelligibility allowing very large audiences to hear clearly the actors and the singing chorus. During this era, smaller sized roofed versions of these theatres, the “odeia” (plural for “odeon”), were also constructed, often at close vicinity to open theatres .The odeia had different acoustics qualities with strong reverberation and thus were not appropriate for speech and theatrical performances but instead were good for performing music functioning somehow similarly to modern-day concert halls.

Open amphitheatres

Roofed odeia

Acoustics

The ancient open amphitheatres and the roofed odeia of the Greek-Roman era present the earliest testament of public buildings designed for effective communication of theatrical and music performances over large audiences, often up to 15000 spectators. However, the known amphitheatric form appears during the age that saw the flourishing of philosophy, mathematics and geometry, after the 6th century BC. These theatres were the birthplace of the classic ancient tragedy and comedy plays fostering theatrical and music activities for at least 700 years, until their demise during the early Christian era. After a gap of 1000 years, public theatres, opera houses and concert halls, often modelled on these antique buildings, reemerged in Europe during the Renaissance era.

roofed odeia

open amphitheatres

Acoustics

History of Architectural Acoustics

The Herodes odeion at its current state and via computer model of the current open and its antique semi-roofed version. Very recent archaeological evidence indicates that the roof covered fully the building,

Evolution of the shape of open theatres. Roman period theatres had semi-circular orchestra and taller and more elaborate stage building.The red lines indicate the koilon / orchestra design principle as described by the ancient architect Vitruvius.

Acoustics

History of Architectural Acoustics

structure of the Hellenistic period open theatre. https://www.whitman.edu/theatre/theatretour/glossary/glossary.h tm

Acoustics

History of Architectural Acoustics

Acoustics

History of Architectural Acoustics It is now clear that the “good acoustics” of these amphitheatres and especially of Epidaurus, is due to a number of parameters: sufficient amplification of stage sound, uniform spatial acoustic coverage, low reverberation, enhancement of voice timbre, all contributing to perfect intelligibility even at seats 60 meters away, provided that environmental noise is low. These acoustically important functions are largely a result of the unique amphitheatrical shape: for any sound produced in the stage or the orchestra, the geometric shape and hard materials of the theatre’s surfaces generate sufficient reflected and scattered sound energy which comes first from the stage building (when this exists), then the orchestra floor and finally from the surfaces at the top and back of seat rows adjacent each listener position and which is uniformly spread to the audience area .

Acoustic wave propagation 2D model for the Epidaurus theatre. The blue curves show the direct and reflected waves at successive time instances indicated by the red dotted lines. Along with the forward propagating wavefronts, backscattered and reflected waves from the seating rows are produced

Acoustics

Introduction: Late 1700s-early 1800s • Acoustics developed as part of physics and applied mathematics • Broad outlines not specific details

1800s 1856: Prof. Joseph Henry “Treatise on Acoustics Applied to Public Buildings” 1877: Lord Rayleigh “The Theory of Sound” 1895: Wallace Clement Sabine Fogg Art Museum, 1895-1905

Acoustics

Introduction: By the 1920s • Precise measurements became possible • Individual design and fabrication 1920s+ • Radio, television, amplified sound/music, motion pictures fostered greater demand for analysis/design Today Research to improve conditions for • Industrial noise • Hearing risks • Construction noise • Public health

Acoustics

Introduction: Buildings 1870: Der Grosse Saal der Gesellschaft der Musikfreunde, Vienna 1879: Central Music Hall, Chicago 1887: Chicago Auditorium, Chicago 1888: Concertgebouw, Amsterdam 1900: Boston Symphony Hall, Boston 1900-1948: None of note 1948: Royal Festival Hall, London 1961: Lincoln Center, New York

Acoustics

Acoustics ‫الصوتيات‬ • “a science that deals with the production, control, transmission, reception, and effects of sound.” •

definition from the Merriam-Webster Online Dictionary

• ‫ وآثار‬،‫ استقبال‬،‫ ونقل‬،‫ ومراقبة‬،‫العلم الذي يتعامل مع اإلنتاج‬ ‫الصوت‬." • ‫تعريف من ميريام وبستر قاموس على االنترنت‬

Acoustics Definition of Architectural Acoustics and its importance in Buildings

Acoustics “a science that deals with the production, control, transmission, reception, and effects of sound.” definition from the Merriam-Webster Online Dictionary

‫علم يتعامل مع إنتاج الصوت والتحكم فيه ونقله واستقباله وتأثيراته‬ Deals with the production, propagation and detection of sound waves ‫يتعامل مع إنتاج وانتشار واكتشاف الموجات الصوتية‬

Acoustics Definition of Architectural Acoustics and its importance in Buildings

Definitions of SOUND • •

•

•

physical wave in an elastic medium, usually air the sensation stimulated in the organs of hearing by mechanical radiant energy transmitted as longitudinal pressure waves through the air or other medium a vibration in an elastic medium such as air, water, most building materials, and the earth ‫اهتزاز في وسط مرن مثل الهواء والماء ومعظم مواد البناء واألرض‬ physically, sound is a rapid fluctuation of air pressure

Acoustics

• ACOUSTICS: branch of physics concerned with sound deals with the production, control, transmission, reception, and effects of sound 3 parts (elements): 1. Sound Source ( e.g. human speech, HVAC equipment) 2. Transmission Path (e.g. air, earth, building materials) 3. Receiver (e.g. humans, animals, sensitive medical equipment)

Acoustics

technology of designing spaces, structures and mechanical systems to meet hearing needs • effect of building design on the control of sound in buildings 3 Aspects of Acoustical Design in Buildings 1. Planning to keep noise sources as far as possible from quiet area 2. Internal acoustics of rooms 3. Structural precautions to reduce noise penetrations •

Acoustics

Wanted Sound (speech, music) – heard properly; considered desirable Unwanted Sound (noise) – annoyance; not desired or objectionable Characteristics of Sound • Audible • Inaudible

‫‪Acoustics‬‬ ‫‪Definitions of SOUND‬‬ ‫ماهية الصوت‬ ‫هو اإلحساس الذى يتم استقباله من االذن السليمة والناتج عن موجات طبيعية‬ ‫او اهتزازات ميكانيكية او سلسلة من التغيرات في الضغط المنتشر خالل‬ ‫وسط له خاصيتي الكتلة والمرونة يعرف باسم الوسط المرن‪.‬‬

Acoustics Definition of Architectural Acoustics and its importance in Buildings

Definitions of SOUND The human ear is capable of hearing sounds within a limited range. .‫األذن البشرية قادرة على سماع األصوات في نطاق محدود‬

Acoustics

TERMINOLOGIES Generation - sound is generated when an object vibrates, causing the adjacent air to move, resulting in a series of pressure waves radiating out from the moving object Wave – a disturbance or oscillation that transfers energy progressively from point to point in a medium or space without advance by the points themselves, as in the transmission of sound or light Sound Wave – a longitudinal pressure wave in air or an elastic medium esp. one producing an audible sensation

‫‪Acoustics‬‬ ‫يحتاج الصوت إلى ثالثة عناصر لحدوثه وهي‪:‬‬ ‫‪ .1‬المصدر الصوتي‬ ‫‪ .2‬وسط النتقاله‬ ‫‪ .3‬المستقبل‬ ‫والمصدر هو جسم فيزيائي يهتز بفعل مصدر طاقة خارجي‪ ،‬أما الوسط‬ ‫الالزم النتقال الصوت قد يكون وسطا غازيا (الهواء) أو وسطا صلبا‬ ‫(الحديد)‪ ،‬أما المستقبل فهو عبارة عن أذن اإلنسان أو أي جهاز الكتروني‬ ‫يستخدم الستقبال الصوت‪.‬‬ ‫المستقبل‬

‫المصدر‬

‫انتقال الصوت عبر الفتحات المعمارية‪.‬‬

Acoustics Animals have varied hearing ranges

‫وقد اختلفت الحيوانات السمع؟ نطاقات‬

Acoustics

Acoustics Many animals hear a much wider range of frequencies than human beings do.

•

‫• العديد من الحيوانات سماع مجموعة أوسع بكثير من الترددات من البشر القيام به‬ For example, dog whistles vibrate at a higher frequency than the human ear can detect, while evidence suggests that dolphins and whales communicate at frequencies beyond human hearing (ultrasound).

•

،‫ صفارات الكلب يهتز على تردد أعلى من األذن البشرية يمكن الكشف‬،‫• على سبيل المثال‬ ‫بينما تشير الدالئل إلى أن الدالفين والحيتان التواصل بترددات تفوق السمع البشري‬ ‫(الموجات فوق الصوتية‬ Frequency is measured in hertz, or the number of sound waves a vibrating object gives off per second. The more the object vibrates, the higher the frequency and the higher the pitch of the resulting sound.

•

‫ أو عدد من الموجات الصوتية كائن تهتز يعطي قبالة في الثانية‬،‫• ويقاس تردد في هيرتز‬ ‫ وارتفاع وتيرة وارتفاع الملعب الصوت الناتج‬،‫ أكثر الكائن يهتز‬.‫الواحدة‬

Acoustics 0 The softest sound a person can hear with normal hearing ‫أنعم صوت يمكن للشخص سماع مع السمع‬0 ‫التنفس الطبيعي‬10 normal breathing 10 ‫ أقدام‬5 ‫يهمس في‬20 whispering at 5 feet 20 ‫الهمس الناعم‬30 soft whisper 30 ‫هطول األمطار‬50 rainfall 50 ‫محادثة عادية‬60 normal conversation 60 ‫الصراخ في األذن‬110 shouting in ear 110 ‫الرعد‬120 thunder 120

•

• • • • • • • •

Acoustics 130dB - Jack Hammer (at 5ft) FT)5 ‫ جاك المطرقة (في‬- ‫ معاوقة‬130dB 120dB - Rock Concert / Pain threshold
 ‫ ألم عتبة‬/ ‫ حفلة لموسيقى الروك‬- ‫خارقة‬120dB 110dB - Riveter or a Heavy Truck at 50ft FT50 ‫ المبرشم أو شاحنة ثقيلة في‬110dB 90dB - Heavy Traffic (at 5ft) FT)5 ‫ حركة المرور الكثيفة (في‬-‫ و‬90dB 70dB - Department Store or a Noisy Office ‫ متجر أو مكتب صاخبة‬-‫ و‬70dB 50dB - Light Traffic ‫ إشارة المرور‬50dB 30dB - Quiet Auditorium DB30 - ‫ 
 قاعة هادئة‬30dB 20dB - Faint Whisper (at 5ft) FT)5 ‫الهمس خافت (في‬ 
 20dB 10dB - Soundproof room / anechoic chamber - ‫ غرفة كاتمة للصدى‬/ ‫ غرفة عازلة للصوت‬10dB

• • • • • • • • • • • • • • • • • •

Acoustics The speed of sound versus the speed of light

‫سرعة الصوت مقابل سرعة الضوء‬ • sound travels at 1130 feet per second at normal room temperature.

‫ قدم في الثانية في درجة حرارة‬1130 ‫• الصوت ينتقل في الساعة‬ ‫الغرفة العادية‬ • light travels at 299,792,458 meters per second, which is roughly 974,325,489 feet per second (974 million feet per second!!)

،‫ متر في الثانية الواحدة‬299،792،458 ‫• يقطعها الضوء في‬ ‫ قدم في الثانية‬974325489 ‫وهو ما يقرب من‬ !)‫ قدم في الثانية‬974،000،000(

‫‪Acoustics‬‬ ‫هناك قيم لمستوى الصوت تعتبر مؤذية لإلنسان وهي ما تسمى بعتبة األلم وال يستطيع اإلنسان أن‬ ‫يتحملها وتساوي ‪،150db‬وأيضا فان تعرض األذن لمصدر صوتي مقداره ‪ 140db‬لمدة دقيقة واحدة‬ ‫يسبب الما ً لألذن‪.‬‬ ‫ويبين الجدول التالي مستويات‬ ‫الصوت التي يتعرض لها اإلنسان‬ ‫يوميا لمدة ‪ 5‬ساعات بحيث ال‬ ‫يتعرض لخطورة فقد السمع‪.‬‬ ‫ومن الجدول يتبن أن الضجيج‬ ‫يعتمد على التردد حيث تزداد‬ ‫خطورته كلما قل التردد ويعتبر‬ ‫قيمة الضجيج المقبول هو ‪80db‬‬ ‫لمدة ‪8‬ساعات يوميا‬

‫التردد(هيرتز)‬

‫القيمة بـ ‪db‬‬

‫‪37.5-150‬‬ ‫‪150-300‬‬

‫‪100‬‬ ‫‪90‬‬

‫‪300-600‬‬ ‫‪1200-2400‬‬ ‫‪2400-4800‬‬

‫‪85‬‬ ‫‪80‬‬ ‫‪80‬‬

Acoustics

Introduction: Definition of Architectural Acoustics and its importance in Buildings

ARCHITECTURAL ACOUSTICS Building acoustics or architectural acoustics deals with sound in the built environment. • • • • •

Structures with acoustic implications:‫منشات تحتاج الى التصميم الصوتى‬ Airports Churches Theatres Concert and opera halls Educational structures, including class rooms, lecture halls, libraries, music practice rooms etc.

Acoustics Structures with acoustic implications

Thank You

Acoustics Assignment (1) Research about: History of Architectural Acoustics Buildings designed acoustically

Research format: 3 paper

Lec.2 2021

Acoustics in Architecture Dr. Doha Mohammed

Acoustics How does sound work? Sound travels as a longitudinal wave - a wave that causes air to compress and expand in the same direction as it travels. A sound will vibrate the particles in a material, whether it is a gas, liquid or solid, losing a little bit of kinetic energy with each further movement. The most effective method of stopping sound from travelling is by putting some kind of vacuum in its path. Sound works by compressing and vibrating matter, and in a vacuum there's nothing to compress or vibrate. This is why in space, no-one can hear you scream! Any given material will pass on a small amount of the wave to some extent, and the greater the distance it is passed, the less noisy the sound is on the other side of the material. The frequency of the sound wave, without getting technical, is the measure of how high or low the sound appears to the listener. Deeper sounds like bass from a stereo are low frequency, higher sounds such as speech are around the mid to high level frequency range.

Acoustics

https://study.com/academy/lesson/what-is-spl-sound-pressure-level-definitionexamples.html

Acoustics Measuring quantities of Acoustic energy

Acoustic measurements are the obvious prerequisite of acoustic investigations, in research as well as in applied acoustics. They are an important tool for the analysis of acoustical problems or for creation of experimental references in theoretical and numerical approaches. Sound Energy Density ‫كثافة الطاقة الصوتية‬ Sound Intensity ‫كثافة الصوت‬

Sound Speed

Sound Pressure

‫سرعة الصوت‬

‫ضغط الصوت‬

Sound Power level (SWL)

Decibels

‫مستوى الصوت‬

‫ديسيبل‬

Acoustics Characteristics of Sound waves ‫خصائص الموجات الصوتية‬

‫‪Acoustics‬‬

‫تعبر عن قوة‪ ،‬الصوت‪ ،‬أو ضعفه وهذا يتوقف على سعة الذبذبة الصوتية وتقاس شدة الصوت بالديسبل ‪.‬‬ ‫أقل شدة صوت يمكن لإلنسان العادي سماعها هي ‪ 20‬ديسبل ‪ ,‬تتحمل االذن أقصى شدة صوت حتى ‪ 150‬ديسبل •‬

‫‪Acoustics‬‬

‫الترددية‪:‬‬ ‫وهي استمرار سماع الصوت بعد انقطاع الصوت‬ ‫المباشر من المصدر ويكون ذلك بسبب‬ ‫االنعكاسات التي ال تزال تتردد في المكان المغلق‬ ‫وعلى ذلك يستمر تالشي الصوت تدريجيا‪,‬‬ ‫ويطلق على الزمن الالزم النخفاض مستوى‬ ‫الصوت – بمقدار ‪ 60‬ديسبل بعد انقطاع المصدر‬ ‫األصلي‪ -‬بزمن االرتداد‬ ‫ويتوقف زمن االرتداد على كل من االمتصاص‬ ‫وحجم المكان المغلق فكلما زاد مقدار االمتصاص‬ ‫الكلى بالمكان المغلق كلما زاد االرتداد‬

Acoustics Characteristics of Sound waves ‫خصائص الموجات الصوتية‬ All waves have certain properties. The three most important ones for audio work are shown here: Wavelength: • The distance between any point on a wave and the equivalent point on the next phase. Literally, the length of the wave. Amplitude: :‫السعة‬ • The strength or power of a wave signal. The "height" of a wave when viewed as a graph. • Higher amplitudes are interpreted as a higher volume, Hence the name "amplifier" for a device which increases amplitude. Frequency: • The number of times the wavelength occurs in one second. Measured in kilohertz (Khz), or cycles per second. The faster the sound Source vibrates, the higher the frequency. • Higher frequencies are interpreted as a higher pitch. For when you sing in a high-pitched voice you are forcing your vocal chords to vibrate quickly.

Acoustics Behavior of Sound Waves

https://rionAcoustics

sv.com/support/st_sound_en.aspx

Behavior of Sound Waves

Acoustics

Behavior of sound waves in enclosures: Factors that affect the behavior of sound in an enclosed space: • Edge diffraction of sound - Edge diffraction results in the curvature of part of a sound wave around the edge of a barrier. This causes the obstacles to scatter the sound waves making it behave like a source of sound. • Sound shadow - Any barrier interrupting a sound wave will create a shadow, synonymous to light rays. However, because of edge diffraction some sound will creep into this but such penetration is frequency dependent - high frequencies are less diffracted than low frequencies. Such problems can occur in auditorium with balconies.

Acoustics Behavior of Sound Waves

The experience of sound depends on: • The sound level. • The frequency. • The type of sound, if it is constant or intermittent. • If it is noise or nice music.

https://rion-sv.com/support/st_sound_en.aspx

Acoustics Behavior of Sound Waves

Acoustics Behavior of Sound Waves

BEHAVIOUR OF SOUND IN AN ENCLOSURE

Acoustics BEHAVIOUR OF SOUND IN AN ENCLOSURE: When sound waves come into contact with a solid material some sound is reflected back into the room, some sound is absorbed by the wall and finally the sound energy / vibration travels through the wall by vibrating it and then passes through to the other side. Sound also travels by direct and in-direct means. An example of direct sound would be hearing your neighbours TV through the wall, no surprise the noise is travelling directly through the wall. When sound travels indirectly, think of it much like water, it will always find a path, often via indirect methods. Travelling around, under and over any obstacles in its path. Noise which reaches a room in this way is also referred to as flanking noise.

Acoustics

Behavior of sound waves in enclosures:

• When the sound waves strike the surface of room three things happen (1) Some of the sound is reflected back in the room. (2)

Some of the sound energy is absorbed by the surfaces and listeners of the room/hall .

(3) And some of the sound is transmitted out of the room through vibrations of floors, walls and ceilings.

Acoustics BEHAVIOUR OF SOUND IN AN ENCLOSURE sound waves are likely to behave in the following ways:

• Reflection

•

Absorption

•

Refraction

• Diffusion

•

Diffraction

• Transmission

Acoustics

Behavior of sound waves in enclosures: On encountering barriers posed by the enclosure, sound waves are likely to behave in the following ways: • Reflection • Absorption • Refraction • Diffusion • Diffraction • Transmission

Acoustics Behavior of Sound Waves -On encountering barriers posed by the enclosure, sound waves are likely to behave in the following ways: 1- Reflection: This occurs when the wavelength of a sound wave is smaller than the surface of an obstacle. In the case of an enclosed space, the sound waves hit every side of the enclosure continuously until the sound energy reduces to zero. The amount of waves reflected depends on the smoothness, size, and softness of the materials of enclosure. The angle of incidence of sound rays is equal to that of the reflected rays only if the surface of the reflector is flat. But when it is curved, the angles are different.

2- Absorption: When sound waves hit the surface of an obstacle, some of its energy is reflected while some are lost through its transfer to the molecules of the barrier. The lost sound energy is said to have been absorbed by the barrier. The thickness and nature of the material as regards its softness and hardness influences the amount of sound energy absorbed

3- Refraction: This is the bending of sound when it travels from one medium into another medium. The difference in the composition of the two different media bends the sound i.e. the angle of incidence changes into an angle of refraction as it travels into the new medium.

Acoustics Behavior of Sound Waves 4-Diffusion: This is the scattering of waves from a surface. It occurs as a result of the texture and hardness of the obstacle is comparable to the wavelength of the sound. The direction of the incident ray changes when it strikes the surface of the obstacle. Satisfaction is achieved when sound is heard in all direction at equal level.

5-Diffraction: When the wavelength of a sound wave is smaller or equal to the size of the obstacle, the sound rays tend to bend round the edge of the obstacle thereby turning the edge to a sound source

6- Transmission: In this phenomenon, sound wave is carried by molecules of the obstacle through vibration and reemitted at the other side irrespective of the medium. It can be structure borne, air borne or impact sound.

Acoustics Behavior of Sound Waves

‫‪Acoustics‬‬

‫‪Acoustics wave behaviors in a vacuum‬‬ ‫سلوكيات الموجه الصوتيه في الفراغ‪-:‬‬ ‫طبيعة الموجات الصوتيه هي موجات كهرومغناطيسية‬ ‫تنتشر وسط مرن مثل الهواء والماء ومعظم مواد البناء‬ ‫واألرض‬

‫‪Acoustics diffusion field‬‬ ‫مجال انتشار الصوت‪-:‬‬ ‫التحول التدريجي من الفراغات‬ ‫الخارجيه الي الداخليه في قاعات االستماع‬

‫‪Acoustics‬‬ ‫سلوك الصوت فى الفراغ المغلق‬ ‫عندما تصطدم موجة الصوت بجدار ما‬

‫فان جزءا من الطاقة الصوتية ينعكس‬ ‫بينما يتسلل الجزء االخر الى داخل‬ ‫الجدران‪ ,‬حيث يمتص جزء منه ويفقد‬

‫الجزء الباقي الى الجانب االخر من‬ ‫الجدار ‪.‬‬ ‫وإذا ما قابلت موجات الصوت‪ ،‬حائل‬ ‫أو عائق فإنها غالبا تنحرف عن‬ ‫مسارها ‪,‬أو تتشتت‪ ،‬إذا كان السطح‬ ‫متعرجا‪.‬‬

Acoustics

Behavior of sound waves in enclosures: Factors that affect the behavior of sound in an enclosed space: The way in which sound behaves in an enclosed space depends on many factors which include: • Reduction in its intensity of sound – This can results due to the distance between its source and the receiver. • Absorption of direct sound by the audience – The listeners of the sound absorb some of the sound in the process of hearing. • Absorption of direct and reflected sound by The walls, ceiling and floor of the enclosure absorbs and reflect sound waves thereby controlling the way the sounds behave. • Reflection of sounds from right-angled corners - Sound incident to a right-angled corner of room will be reflected back towards source if surfaces are acoustically reflective. This can in turn produce echoes especially in large spaces. • Dispersion of the sides of an enclosure - Reflections can be controlled by making one surface dispersive i.e. not at right angle to each. This would have affected the reflection of the sound thereby affecting its behavior.

Acoustics

Behavior of sound waves in enclosures: Sound Absorption Amount of sound energy not reflected

Thank You

Acoustics Assignment (2) Research about: Acoustic measurements units Behavior of sound waves in enclosures

Research format: 1 paper A3

Lec.4 2020

Acoustics in Architecture Dr. Doha Mohammed

Week Lectures:

Lectures Topic

Assigienm ent topic

1

Introduction: -Definition of architectural acoustics and its importance in buildings -Measuring quantities of Acoustic energy -Characteristics of Sound waves

(Define Project)

2

Behavior of sound waves in enclosures

researsh

3

Sound Absorption waves

research

4

Sound Reflection waves

5

The effect of achieving acoustics requirements on theater formation

researsh

Quize1

6 7

The effect of achieving acoustics requirements on theater formation Midterm Exam

8

The Acoustical Defects The concepts and objectives of the successful acoustics design + about acoustic treatments

researsh

9

Design of music listening rooms - Types of music listening halls (advantages and disadvantages) -Acoustic defects in meeting rooms-

researsh

10

Paper Discussion - (Project Submission & Discussion)-Paper Discussion

researsh

11

Final Revision

(final Project)

Acoustics

Behavior of sound waves in enclosures: Sound Reflections Reflection This occurs when the wavelength of a sound wave is smaller than the surface of an obstacle. In the case of an enclosed space, the sound waves hit every side of the enclosure continuously until the sound energy reduces to zero.

The angle of incidence of sound rays is equal to that of the reflected rays only if the surface of the reflector is flat. But when it is curved, the angles are different.

Acoustics

Behavior of sound waves in enclosures: Sound Reflections

The Law of Reflection

• The direction of incidence and reflection is best described by straight-line rays • Incident rays and reflected rays make equal angles with a line perpendicular to the surface, called the normal • Angle of Incidence – angle made by the incident ray and the normal • Angle of Reflection – angle made by the reflected ray and the normal • Law of Reflection – the angle of incidence and the angle of reflection are equal

Acoustics

Behavior of sound waves in enclosures: Sound Reflections Reflection The amount of waves reflected depends on the smoothness, size, and softness of the materials of enclosure.

Acoustics

Behavior of sound waves in enclosures: Sound Reflections When a sound wave encounters a sharp discontinuity in the density of a medium, some of its energy is reflected. Reflective surfaces are typically smooth and hard. A few common acoustic problems caused by reflections are echoes and Reverbertion

Acoustics

Acoustics Some sound waves will reach the listener directly without interruption, whereas others are reflected back by surfaces. The paths shown in figure 1 are one of the many ways they can be shown. The physical and mathematical models used to give a more detailed picture are usually much more complicated.

Acoustics

Behavior of sound waves in enclosures: Sound Reflections • Reflection – some or all of a wave bounces back into the first medium when hitting a boundary of a second medium • When all the wave energy is reflected back instead of being transmitted, it is total reflection • If some energy is transmitted and some is reflected, the wave is

partially reflected

Acoustics

Acoustics

Behavior of sound waves in enclosures: Types of sound reflectors

Acoustics

Behavior of sound waves in enclosures: Sound Reflections

The reflected wave

WAVE FRONT

front from a flat

surface are also spherical and their centre of curvature is the image of source of sound.

SOUND SOURCE

FLAT REFLECTOR

Acoustics

Behavior of sound waves in enclosures: Sound Reflections •Sound waves reflected at a convex surface are magnified and are considered bigger. WAVE FRONT

•They are attenuated and therefore weaker. •So convex surface may be used with advantage to spread the sound waves throughout the room.

SOUND SOURCE

CONVEX REFLECTOR

Acoustics

Sound Reflections •The sound waves reflected at a concave surface are considered smaller.

CONCAVE REFLECTOR

•The waves are most condensed and therefore amplified.

•The concave surface may be WAVE FRONT provided for concentration of reflected waves at certain points. •The combination of rays creates acoustic foci that lead to a repetition of sound

SOUND SOURCE

Acoustics Sound Reflections An echo or amplification of reflection may occur when ( Echo ) ……. Echoes occur when Reflected wave of sound reaches the ear more than 0.1 seconds after hearing the original sound wave. If the time elapsed between the two sound waves' arrivals is more than 0.1 seconds, Then the feeling of the first sound will be over In this case, the second arrive Wave is perceived as a second sound, instead of a first sound prolongation. Instead of reverberation there'll be an echo.

Acoustics Sound Reflections An echo or amplification of reflection may occur when

(Amplification ) …….. The sound waves reflections off surfaces are often influenced by the surface shape. Flat surfaces reflect sound waves so that the angle at which the wave reaches the surface is equal to the angle the wave leave the surface at , But when the surfaces is curved leads to a phenomenon of greater interest. Curved, parabolic-shaped surfaces have the habit of directing sound waves to a point. Sound waves reflecting parabolic surfaces focus all of their energy to one point in space ; the sound is amplified at that point.

Acoustics

Reflection formula: A+B-C