ACOUSTIC

ACOUSTIC

What is acoustic related to architectural / construction

Acoustics is the interdisciplinary science that deals with the study of all mechanical waves in gases, liquids, and solids including topics such as vibration, sound, ultrasound and infrasound. A scientist who works in the field of acoustics is an acoustician while someone working in the field of acoustics technology may be called an acoustical engineer .

The application of acoustics is present in almost all aspects of modern society with the most obvious being the audio and noise control industries.

ARCHITECTURAL ACOUSTICS

Architectural acoustics (also known as room acoustics and building acoustics ) is the science and engineering of achieving a good sound within a building and is a branch of acoustical engineering. The first application of modern scientific methods to architectural acoustics was carried out by Wallace Sabine in the Fogg Museum lecture room who then applied his new found knowledge to the design of Symphony Hall, Boston.

Architectural acoustics can be about achieving good speech intelligibility in a theatre, restaurant or railway station, enhancing the quality of music in a concert hallor recording studio, or suppressing noise to make offices and homes more productive and pleasant places to work and live in.

Architectural acoustic design is usually done by acoustic consultants. Building skin enveloped. This science analyzes noise transmission from building exterior envelope to interior and vice versa. The main noise paths are roofs, eaves, walls, windows, door and penetrations. Sufficient control ensures space functionality and is often required based on building use and local municipal codes. An example would be providing a suitable design for a home which is to be constructed close to a high volume roadway, or under the flight path of a major airport, or of the airport itself.

The science of limiting and/or controlling noise transmission from one building space to another to ensure space functionality and speech privacy. The typical sound paths are ceilings, room partitions, acoustic ceiling panels (such as wood dropped ceiling panels), doors , windows , flanking, ducting and other penetrations. Technical  solutions depend on the source of the noise and the path of acoustic transmission, for example noise by steps or noise by (air, water) flow vibrations. An example would be providing suitable party wall design in an apartment complex to minimise the mutual disturbance due to noise by residents in adjacent apartments.

Diffusers which scatter sound are used in some rooms to improve the acoustics. This is the science of controlling a room's surfaces based on sound absorbing and reflecting properties.

Sound reflections create standing waves that produce natural resonances that can be heard as a pleasant sensation or an annoying one. Reflective surfaces can be angled and coordinated to provide good coverage of sound for a listener in a concert hall or music recital space.

To illustrate this concept consider the difference between a modern large office meeting room or lecture theater and a traditional classroom with all hard surfaces.

ACOUSTICS RELATED TO  ARCHITECTURAL  DESIGN / CONSTRUCTION

The Acoustic Nature of Materials

When we choose the materials that will make up the structure of a building, we are making decisions that will affect the nature of sound within the building. Many are the times that an acoustical designer has been called in to “fix” the acoustics after the building has been completed, and we always wish that we had been consulted before ground was ever broken.

It is possible to make improvements after the fact, but when the building has been

built we’ve lost the ability to affect the acoustics in two important ways. The first is having the ability to shape and dimension the rooms, and this we covered in the

handout for the previous class “Acoustical and Musical Scales in Sound Room Design”.

The other major problem with starting to build before designing the acoustics is that little or no consideration is given to the acoustic nature of the materials that make up the structure.

The following are some commonly used building materials and their acoustic properties, and ways these materials can be used for sound isolation and acoustic treatment. Sound isolation is the branch of acoustics that deals with keeping sound where you want it – in or out of the building, for instance, or keeping sounds in one room from invading another room.

Sound treatment, on the other hand, is the branch of acoustics concerned with the perfecting the quality of the sound we hear, and using the proper combinations of materials and shapes to create pleasing, musically accurate sound.

1. Concrete, stone, and other masonry materials

Masonry materials are great for sound isolation, especially when used in floors and walls where the masonry material is quite thick. A solid concrete wall 1 ft. thick will rarely cause clients to complain about sound isolation, for two reasons. One is the material’s rigidity, meaning that it will not flex and create sound waves on the quiet side of the wall. The other is concrete’s mass. Nothing stops sound waves quite like massive materials, and they are especially capable of stopping the critical low frequencies that are so hard to stop with less massive materials.

2. Stone and brick are very similar to concrete in mass, and concrete masonry units, although they are lighter, can do a very good job when they are fully filled with concrete, instead of just filling the cells that contain the rebar.

3. Concrete slabs also do a good job of isolating sound between floors – something that is very difficult to do any other way.

4. Wood, and wood products: Wood is much less dense than masonry, and provides much less in the way of sound isolation for that reason.

Wood products like MDF, on the other hand, are somewhat more massive, and are sometimes used in interior walls to add mass. OSB is less dense than MDF, but can be useful as well, as part of an integrated system. Plywood comes in varying densities, and again can contribute something to the equation in a multi-layer wall.

Wood’s real beauty lies in its ability to reflect sound in a pleasing way, meaning that it is a useful material for sound treatment. Since wood resonates easily, it has a way of absorbing some of the sound energy as it vibrates, letting some of the sound pass through to the other side, and reflecting some of the sound back from whence it came. This genteel quality of wood is one reason it is widely used in the making of musical instruments, and wood has a major role to play as an interior finish material in good sounding rooms.

5. Steel: Steel is a quite dense material, but because of its expenseve it is rarely used as a sound isolation material. Steel’s density actually becomes a liability in structural uses where its dense nature causes it to carry sound vibrations for long distances. If you strike an I-beam with a hammer and place your ear to the other end –let’s say 24 ft. away, you’ll see that the sound carries quite well through the steel. This type of sound transfer is called structure-borne vibration, where sound is carried through some material other than air for a time. The other main type of sound transfer is air-borne vibration.

6. Drywall and plaster: Drywall is the poor man’s masonry, and for interior walls can provide a lot of mass for the money. But one ½” layer doesn’t do all that much. Multiple layers are used in sound studios and broadcast facilities where high mass walls are needed.

7. Roofing: Asphalt shingles are fairly massive, as you know if you hauled them up to the roof, but they are also thin. Installation with a large overlap, heavy felt, and even double layer sheathing can help quite a bit. Ceramic and clay tiles are more massive than wood shakes by far, and can do a reasonable job in residential applications. Metal roofing has mass but is thin, and requires that the underlying structure be fairly massive.

8. Glass and other transparent materials: Glass is quite massive – about three times as massive as drywall. So in a sound wall with three 5/8” layers of drywall on one side, one layer of 5/8” glass maybe inserted to create a window on that side , provided that it is properly sealed. A corresponding piece of glass would be required on the other side of the wall, at the appropriate thickness.

9. Insulating materials (fiberglass, foam, rock wool, etc.): Insulating materials have little mass, so they have limited uses for sound isolation. However, fiberglass has good sound absorption characteristics, and is very useful as a sound treatment material for sound room interiors.

Fiberglass and rock wool, which has similar acoustic properties, absorb sound by slowing the velocity of the air particles carrying the wave. Wood, on the other hand, absorbs sound best when in the pressure zone of a sound wave.

10. Fabrics and other soft materials: Fabrics, carpets, and other soft materials can be useful for sound treatment. Heavy stage type curtains are much more effective than thin fabrics. Carpets, although sometimes better than nothing, can soak up too much mid and high frequency sound while leaving boomy lower frequencies untreated. As part of an overall plan, carpet can be put to good use, but area rugs are much more versatile and adjustable.

QUESTION TWO

Why is empty building crack faster than building occupied by people.

INTRODUCTION:

Cracks can occur due to chemical reactions in construction materials, changes in temperature and climate, foundation movements and settling of buildings, environmental stresses like nearby trains, earth quakes etc. Faulty design, bad quality materials, wrong method of construction, weather effects and lots of wear and tear can create cracks in walls, floors and ceilings.

Here are given various reasons of cracks which is applicable to both occupied and un-occupied building. However we shall consider reasons why empty buildings (i.e. un-occupied) cracks easily compared to occupied one.

1)  Thermal Movement: All materials expand on heat and contract on cool. Thermal movement in components of structure creates cracks due to tensile of shear stresses which is particularly severe in an empty house. It is one of the most potent causes of cracking in buildings and needs attention which is not commonly attended to in an empty house

2)   Shrinkage: Most building materials expend when they absorb moisture from atmosphere and shrink when they are dry. Cement made materials shrink due to drying up of the moisture used in their construction. This is very severe in emty bulding as the rate of dryness and moisture absorbtion is reduced in an occupied house.

3)   The local trees put hundreds of pounds or leaves and seeds on the roof each year. If these aren't regularly mucked out, they flow downhill with the water to the drains, where they stop them up. The water, especially when it is snowing, weighs 8lbs/ gallon, and there can quickly be several tons of water on our roof which can easily  crack down the building

4)   A leaking Roof: Over the course of time the water leaches all the glue and materials from the plywood, causing the plywood or roofing to snag and snap, tearing the membrane of the roofing materials. It literally falls in, about years later. Now it's raining in side. It's also likely to be downhill towards the drain, so all the water flows towards it and into the interior of the building.

5)   People come in and steal the copper out of the building, ripping and tearing the walls and conduit. People hang out inside and destroy drywall for fun. Paint, feces, etc.

6)   The mold starts to grow. Tree seeds take root inside. The mold destroys the drywall and the wet-and-dry process begins to dryrot the walls. You wouldn't believe how fast everything would 'go back to nature' if the people weren't around. If there wasn't street cleaning, the years particulants and leaves would build a 2" dirt layer which would cover the pavement, and in a very short order of time tree roots would tear apart the pavement. Deadletter how brick row houses fall apart; the (flat) roof leaks, rotting the cross beams, allowing the walls to bow. gravity pretty much takes over after that.

7)   Buildings that are not abandoned are maintained. Wood is protected from rotting, iron and steel is shielded from the environment to slow down rusting, plants are prevented from growing and breaking apart concrete and mortar, etc. Basically, most man-made structures are not designed to be able to withstand the harsh effects of nature without intervention (maintenance).

8)   This is a significant factor: Once windows get broken, moisture, plant and animal life can effect ingress. Mould, decay, frost-shattering, animal damage and rot can then occur relatively quickly. All these have a big cosmetic effect and a brick or stone building may be relatively sound structurally but look in extremely poor repair for the reasons arble mentions above.

9)   Plants grow and find holes (or make their own) which destabalize infrastructure. Humans living there can prevent this manually.

10)               Humidity and massive temperature changes encourages rot and bacteria growth. Humans living there prevent this by having the heat on. Age and light tarnish things (paint, finishes, etc) and causes humans to react with improvements, and increasing standards in building maintenance forces them to fix things that are broken.