why are cardboards not used in cinema theatre to control noise pollution?
912713
Cardboard is not the good material for managing sound, but it's cheap.  The acoustic design of a theater aims for excellent sound insulation between adjacent theaters and to the outside.  Within a theater, the objective is providing the best movie sound to the audience.  That requires allowing some reverberation, but managing reflections and assuring that the sound is good at all seats.  Some thought is given to reducing audience-generated noise, but that's not primary.  The best way to minimize that is to attend a theater with a well-behaved audience.
377683
Litter.\n\nI know it is probably not as dangerous to our health as Air Water or Noise but it is such a simple thing for people to take control of.\n\nDrives me nuts to see someone just toss there garbage out the car window or to the gutter when they are walking. \n\nPigs.
436127
depends on what you want to do with the sound, but generally they use geometry to create sound friendly environments. (feedback reduction,  good resonance reverb, noise reduction, and others)
695807
To buffer and reduce the noise of people talking, moving, dropping popcorn and using cell phones.
198771
Well, the Smell that They really Dislike is "Fluffy", the Kitty Cat! But, since You want Them to Fly [away, leave] and not Die, That's not an Option for You, right? Okay, would you Consider a Non-Lethal Audio Approach? The Right type of Sound, Inaudible to You, would solve the Problem. Go to www.amazing1.com  They have some of the Coolest High Tech Gadgets anywhere. Do You have a Friend that's into Electronics? It would be much less Expensive to Mail Order whatever Rodent Router Device You need in Kit Form. Just Remember, by not putting "Fluffy" to Work, You'll be passing Your Problem off to Someone Else!
998764
You have to be more specific in your questions.  It seem people are thinking of movie halls rather than in the screen.   To be more specific, cigarette smoking by any character in a movie like hero, heroine, villian on screen has been banned.   I am against it.  Eventhough i am not a smoker and don't like smokers, but sometimes it is inevitable in some scenes..  So censor should come into play and they edit those scenes if found unnecessary.
221473
Yes cuz they don't like noise.
624605
You can start your search here  http://www.noisecontrol.nl/en/persluchtgeluiddempers_en.html
4137
going to the movies were it is quiet
167027
Acoustics deals with the creation, control and destruction of sound energy which consists of vibrations of a wide range of wave lenghts through air and other materials.  It is important in designing fine concert halls that they be well balanced between dead and too much resonation or echo.  The shape of the auditorium and the capability of walls, seats and the  audience (simulated by sand bags?) are tested for sound properties.  Special baffles may be installed to absorb excess sound.  Because sound can reflect from surfaces and focus or disperse, dead and live spots must be avoided.\n\nOne of my physics professors was an accoustics hobyist and build an anechoic chamber in the basement of his house.  The walls, etc. were coated with long sharp angles to absorb all sound for his experiments.  He said that he could tell when his son borrowed the sound chamber to play his rock-and-roll guitar because the entire house shook but he couldn't hear a thing.
300173
Most plastic "pollutes" because it doesn't degrade quickly.  Thus it forms unsightly litter, and sometimes kills small animals that might get caught in the bag.
253685
My first reaction is to suggest some noise cancelation earphones, but you say you do not want a device specific answer.  That walks us back from active to passive and we are talking insulation technigues to absorb sound and structural methods to scatter and reflect sound.  A masonry wall between your house and the tracks may well prove to be the most cost effective approach.  Try lookng over the Wikepedia articles referenced below.  Noise suppression and control is not a simple thing.
278787
in waves, therefore, in order to be transmitted it requires some medium to transmit the waves in. That's why sound can't travel through a vacuum such as outer space, for example
696293
A reel of film still passes through the projector.  I suspect that some cinemas will go over to a digital projection system soon. \n\nI have seen this method a few years ago at a festival and it was nowhere near the quality of the old system, particularly as it was  a large 2000 seat cinema.  But I am sure the technology will get better.
1135708
C\n\nBecause soundwaves are not really particles. They use any kind of medium (solids, liquids, gases) to propagate unlike light which is actual particles of energy which is why light can travel through a vacuum (sun to earth) but Sound cannot
517190
There is usually a lot of noise in a train station, and the buildings are usually quite large, which induces an echo factor and distorts the sound. Add in the sound of people walking, talking, dragging baggage etc. and you have a lot of background noise to overcome.
94716
One of the previous people who answered is correct in that the old-fashioned type of overhead projector is pretty much an obsolete technology.  However, with that said, many schools till use the old ones for the simple reason that they have them, and there is no money to buy the newer technology.  They also lend themselves to use by students in that they are less expensive, so less is lost if the kids cause damage. \n\nThe old projectors had a few problems in that for sure when you were in the middle of your presentation the light bulb would burn out.  The other problem was preventing the image from being "skewed" on the screen - there is a term for this but I've forgotten what it is.  Sometimes the mirror broke because of being handled roughly, but they are pretty sturdy machines.  Some of them were quite noisy because of the cooling fan - the bulbs get quite hot.  The room needed to be quite dark for them to work well, so that, combined with the continuous buzz of the fan and the stuffiness caused because the curtains were closed, tended to put the audience to sleep. \n\nThey have other advantages in that they are fairly simple to use and require no particular techincal skill.  You just write or draw your information on pieces of plastic called acetate or transparencies, using special markers made for overhead projector transparencies, and lay the plastic on the projection surface to project the image.  It was easy to get confused about the correct way to lay the acetate on the projector!!  YOu can use the acetate the same way as a chalkboard or whiteboard and write on it as you are teaching - the advantage being that you can face the class whie doing it - you don't need to turn your back to them.  Theoretically, you can use your computer to make "overheads" and print them.  However, in my experience, printing the transparencies often fouled up the printer!!\n\nThe newer projectors, no longer called "overhead projectors", are connected to a computer when in use, usually a laptop, and offer a much more sophisticated repertoire.  YOu can use Power POint to prepare presentations and have everything stored on  your laptop.  If you are using a video, Internet, or a TV segment in your presentation you can route it through the projector.  These projectors are smaller, lighter, more compact, definitely more trendy.  Today a professional presenter who showed up with the old type of overhead projector would be considered a bit behind the times.  You can incorporate the use of a laser pointer, remote control, etc. with these new projectors.   However, though they are getting cheaper, they are still much more expensive than the older models and require considerably more technical know how for operation.  When something goes wrong, it is often beyond the presenter's expertise to fix it so you often have to call in the IT person!!!\n\nThere is a device called a "palette" you can buy to sort of transform one of the older models into a model that will work like the newer ones.  I wouldn't recommend it.  If you are going to move to newer technology I would recommend skipping the half-way measure.\n\nI hope this is informative and of some help.