Sound Proof Foam

The term sound proof foam is another one of those misnomers. There is no foam on the market that is soundproof. I know this to be true because I have been manufacturing foam for 10 years. Lets pull apart these terms “sound proof foam” and examine them individually.

The term soundproof means to keep sound from entering a room from any outside source and to keep sound in the room from leaving the room and entering adjacent structures. Foam does not possess the physical properties necessary to stop this type of sound transmission. Foam is not dense enough or rigid enough to provide the mass and structural stability to stop middle and high frequencies, let alone have any impact on bass energy. It would take a piece of foam 11 feet thick to absorb all the energy of a 100 Hz. wavelength.

The terms sound proof and foam should never be used together. Foam is not used to sound proof anything. There is no such thing as sound proof foam. Foam is an acoustical tool that can absorb energy within a contained room. It can be used to control unwanted room boundary reflections, so the listening position is free from unwanted reflections and our ears can focus on the direct energy from our loudspeakers. Foam can be used to absorb and minimize the unwanted energy from another individual who is telling you to turn your stereo down. A better approach would be to place that individual in a soundproof closet.

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Home Theater Room

What must our home theater room have in it to make it a home theater room? It must have a video display unit. It could be a projector with screen, a lcd or plasma flat screen, or simply a crt television. It must have a receiver to process audio from our dvd, amplify this audio and send it to numerous channels which are all represented by speakers. It must have a sub woofer to provide low energy output into the room as to try and acoustically recreate explosions and car crashes.

Our home theater room must also have the ability to control external light from out side, so as not to interfer with the video display inside. The room must be of adequate size in both width, depth, and height to allow for proper video display sizing. The room must also be large enough to be able to position side and rear channels to allow for this energy to be utilized correctly at the listening position. Low frequency energy from the sub woofer needs the most room volume it can get to be heard as realistic.

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Home Recording Studio

Home recording studios are prominent today. With the digital technologies available today, one can have most of the processing power of larger studios in a much smaller space requirement. A home recording studio is usually set up in a spare bedroom or some other space not utilized by the current occupants. The science of small room acoustics must apply here.

Our first consideration in a smaller space must be the low frequency or bass energy. Small room volumes play havoc with low frequencies, or should I say low frequency energy plays havoc with smaller home recording studios. A great deal of attention must be paid to bass energy whether recording, monitoring or playback is being used , so that the bass energy does not smother the mids and highs. Low frequency absorbers are a must.

Reflection control in recording rooms must be controlled, so that the microphones are “hearing” the music and musicians and are not recording the room sound. Our monitoring position must be a realistic balance of absorption and diffusion technologies to allow for more direct energy from our speakers to reach our ears first, before the relected energy from our room boundary surfaces. This greater direct/reflected wall energy at the mixing position allows for a more realistic sound balance and thus a better mix.

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Sound Proof Materials

Sound proof materials is a bit of a misnomer. There are really no specific materials that are labeled sound proof materials. There are materials that have good sound proofing qualities, but no material, no matter what it is called by itself is a sound proof material. Materials of different types must be assembled in a specific way to create a sound proof wall, door, etc.

Most sound proof materials have a high density or weight per square foot that is heavier than most other materials. If the density of the specific material, say drywall, is not enough, one can add multiple sheets to create a larger surface density number. One can also use MDF or other composites to achieve proper density numbers.

These multiple material sheets should be isolated from each other by some type of damping compound. It is customary when designing and building sound proof materials, to separate materials of different densities physically, with another material type, from each other. This arrangement reduces vibration transmission through the material being constructed and thus noise transmission.

It is the density of the materials used and the way in which they are assembled together that makes for good sound proof materials. Now, one must decide where to place the materials to achieve the desired acoustical objectives. That process is entirely another issue.

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How To Sound Proof a Room

I get asked everyday about the process of how to sound proof a room. It is a difficult question to answer because it has so many variables to consider. It is even more difficult to accomplish especially when the client sees the cost.

In order to answer the question of how to soundproof a room, first, we must define some parameters. Sound proofing a room means that we must build the room in a way that keeps the energy produced within the room from whatever source, speakers, music, voice, etc., inside the room itself and not let it “bleed” outside of the room or into adjacent spaces. Secondly, we must keep the sound energy created from outside sources, busses, airplanes, motorcycles, out of the sound within the room.

If we were going to write a book on how to soundproof a room we would use absorption technology inside the room to reduce the pressure levels of low frequency energy within the room. We would also use absorption technology for the excess middle and high frequencies within the room. To keep outside generated energy from entering our room, we have to use barrier technology in the construction of the room. We must create a “room within a room”, similar to the Russian toy doll which has a large doll with a series of littler dolls in side in incrementally smaller sizes. This process mechanically decouples each structure from the other and thus reduces the pathways for vibrations to travel and create noise.

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Surround Speakers

What are surround speakers? They are the part of our home theater system and their purpose is to “surround” us with sound energy in the sides and rear of our video presentation. The left, right, and center speakers fill up the front of the room. The sunwoofer provides the “bang”

Surround sound speakers take the airplane that is flying over from the screen to the rear of the room and follows the video image with sound to produce the acoustical sound trail needed to fool our brains. As the plane flies overhead, the sides and rear channels are “handed” the signal from the front speaker system and move it from side to rear or even side to side as in a car crash. In order for this image to track correctly, the surround speakers must have their amount and rate of room reflections controlled though proper room treatment techniques.

A balance of sound diffusion and sound absorption techniques are needed to creat the correct ambient sound “image” at the viewing/listening position from the surround speakers. One must minimize room boundary reflections, so that the surround speakers can have a defined image across a wider surface area than is required from the front channel speaker system. Once we have used the correct amount of absorption and in some rooms over absorption, we add diffusion to spread that more defined signal out across a wider area along the sides and rear of our rooms without any more energy loss.

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Home Theater Design

Home theater design must take into consideration the electronics, which includes the video producing system, the amplification, and the speakers. The seating system and the room acoustics must be given more weight and concern than any other component when home theater design is considered.

The listening and viewing area serves two masters. First, it must be at the proper distance from the video monitor or screen in order to view the image correctly and without fatigue. Secondly, the listening and viewing position must be at the correct distance from all the speakers, so that all information is processed correctly by the ears and brain.

The video distances are easy to calculate in any home theater design. The size of the video screen will define the distance parameters used. The audio from multiple mono sources, the rear, sides, and front channels must be dealt with correctly in order for all sound sources to blend together and become balanced and un noticed as to their positions in the room. In the audio side, room distances, room boundary surfaces acoustical treatment, and subwoofer placement are critical and are often not given the consideration they deserve in most home theater designs.

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Listening Room

If you have a dedicated listening room, you are surely fortunate. A listening room is a portal through which one can enter many worlds.

In a dedicated listening room, all the energy of the room is controlled, so that it arrives at the listening position at the correct time. The sound at the listening position is a blend of the direct sound from our loudspeakers and the reflected energy from the room’s walls. Our acoustic goal is to achieve the correct blend and balance of both the direct and reflected energy. This balance, once achieved, provides for a sound stage that can allow someone to connect with the music. It can truly transport one to a different time and place.

With a proper soundstage, there is a height, width, and depth to the musical presentation that can bring an emotional connection to the music. It is this emotional connection we all strive so hard to achieve. One can “see” the vocals and instruments on the stage. There is a separation between the instruments and vocals and all sounds are heard clearly. One can even hear the breaths of air the singer takes. You are transported from the audience to the stage..

I love my listening room and could not imagine life without it. I hope I never have to. I wish the same for you.

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Home Theater Speakers

Home theater speakers come in many different flavors. First, we have the standard right and left channel speakers which we are all familiar with. Most of our musical information is present in the left and right channels. Movement on the screen, which goes from left to right, should begin at the left channel speaker and move to the right channel speaker in synch with the on screen presentation.

The center channel speaker is an integral part of any home theater speaker system. The center channel speaker is for dialogue. Most center channel speakers are positioned below or above the screen, so that the dialogue appears to be located on the screen. Some center channel speakers are positioned directly behind the screen. Obviously, the screen would have to have perforations in it to allow the sound energy from the center channel to pass through the screen.

Side and rear channel speakers are usually a blend of left and right channel information which is then spread out along the sides and rear of our home theater systems. This process is termed matrixed. Some source materials have discreet information recorded in them for the side and rear channels which means the engineer actually recorded separate tracks of data for the sides and rear channels instead of “borrowing” from the left and right channel data. The side and rear channels provide non – localized, ambient energy which if properly positioned and acoustically treated can add to the realism of the presentation.

The most important part of any home theater speaker package is the sub woofer. Its job is to provide the low frequency energy for explosions, car crashes, and the like. Most sources have a separate channel that contains this low frequency data. This is where the designation 5.1, 6.1, and even 7.1 comes from. The number to the right of the decimal point indicates that there is one channel for LFE or low frequency effects.

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Home Theater Receiver

A home theater receiver is an amplifier, preamp, video processor, and possibly a tuner to receive AM and FM signals. Another way to bring all of these functions into your home theater is to use separate components for all of these functions. Separates allow the end user to control the quality level of each component more accurately.

A home theater receiver manufacturer will design a receiver that will be sold for a particular price point in a certain market segment they are targeting. They will mix and try to match a video processor, amplifier, preamplifier etc. and make their quality and costs fit into a targeted pricing framework. This will create a product that has multiple functions, but will usually lack the individual quality level found in separates.

A home theater receiver has everything under one roof sort of speak, and thus they are all sharing a common circuit board, chassis, and cabinet. Separates will usually have all these components but will not have to share functions with other parts. For example, each component in a video processor will be designed to focus and create a video image full time without sharing any other functions of their design with a preamp or tuner. A manufacturer of separates can maximize the performance of his unit because he can focus solely on one function and maximize its potential.

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