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New Home Theater Set Up Approach Using Diffusion

MikeSorensen April 30, 2012 No Comments
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Home Theaters Today

Our home theaters are complicated set ups from an acoustical perspective. In a 5.1 system set up, we have 5 separate channels plus the .1 which stands for our low frequency effects or in more common nomenclature, our sub woofer channel. We have a left and right channel which we are all familiar with because most of us started with stereo systems. We also have a center channel added which produces the vocals and dialogue that are critical to our movie presentation. Lets don’t forget about the rear channels in our 5.1 system. They are there to provide us with ambient information that is present and occurring behind us just as in a real life.

More Channels

To add more realism to the home theater scenario, we are now introduced to 7.1 home theater presentations. This means that in addition to our rear channels present in a 5.1 system, we have added two side channels. The addition of our side channel speakers is an attempt at more real life representation of the audio that we hear in real life situations. Some will argue that the addition of two more channels is just an attempt by audio manufacturers to sell more speakers and add an additional two channels of amplification to home theater receivers. Lets take the high road and work from the premise that we are trying to duplicate real life acoustics and add to the sonic realism of our home theater presentations. We even have 7.2 systems which can add another sub woofer to the mix and generate more low frequency energy for bigger explosions and larger sounding car crashes. Future configurations can even include 10.2 sound with 10 channels of individual energy and two more channels for low frequency energy.

Real Life Acoustics

In a real life scenario, we have audio and video coming at us from every direction. We have video that we see using our 50mm lens in our head. Our eyes see many things that may or may not have audio signals attached to them. We have sounds coming at us from the sides and back of our heads. We have sounds that emanate from our normal horizontal viewing, such as an airplane flying overhead. Most of this energy is reflected energy that is bounced off of many surfaces before it reaches our ears. Some of it we pay attention to and some of it we do not. The audio energy we pay attention to usually is the audio that has the most amplitude or volume and is the more direct energy that travels the shortest distance from the source creating the energy to our ears. We listen to the direct energy but hear the rest. In our home theaters, we pay attention to the direct sound from our left, right, and center channels because that sound is coordinated with the video presentation directly in front of us. The sides and rear of our home theaters represent the ambient or non localized audio which is blended with the home theater front sound.

Current Installation Practices

How do we install all of these multiple mono sources that represent these side and rear channels, so that they acoustically represent real life? Most installations that we observe have the speakers mounted on the side and rear walls and pointing at the listening position. Granted some side and rear channels are configured differently with speakers pointing in different configurations such as is the case with dipoles, but for the most part, side and rear channel speakers are direct firing and are aimed at the listening positions. Is this really how we hear or listen in real life? Is our real life acoustic a blend of multiple mono sources firing at us from every direction, or is our acoustic a blend of direct energy and reflected energy reaching our listening position in varied dimensions.

If we have a video screen in front of us, we need to have the audio correspond with the video. If an actor is speaking on the screen, the vocals must appear to emanate from the screen and not behind us. If a car drives from the left side of our screen to the right side, the audio presentation must track with the video and move from left to right in sync with the video. The left, right, and center channels do a good job of moving the audio signal around to achieve the necessary realism that our ears and eyes demand. Does the same hold true for the rear and side channels? Does the current side and rear channel configurations really acoustically present real life sound experiences?

Side And Rear Channels

Since the side and rear channels are really about secondary or ambient information that is heard in combination and laced with the direct sound from our left, right, and center channels, we need to recreate this phenomenon acoustically. Current home theater speakers and their respective installation positions do not accomplish this. Since most of the information we receive from the sides and rear channels is secondary information when compared to the direct signals from the front of the theater speakers, we need to present this information in the same manner as real life sound sources present it to our ears. The signal from the sides and rear channels needs to be a non localized signal and presented in a manner that creates a field of energy that is spread out evenly across the rear and sides of our listening position. To achieve this, we can use a time tested and acoustically proven blend of two dimensions of quadratic diffusion.

No More Wall Mounts

This new set up does not involve mounting speakers of any configuration to any wall surface. Speakers that are wall mounted, never sound realistic. There are too many acoustic anomalies that go with wall mounted speakers. It is never a good idea to position a energy producing device next to a room boundary surface. The speaker should be allowed to free stand on its own and not have room boundary surfaces to deal with. Instead of mounting our speakers to the side and rear walls, lets mount two dimensions of quadratic diffusors on those walls. Lets mount vertical and horizontal diffusors on both our side and rear walls, so that any sound energy that enters our diffusors is spread out in both horizontal and vertical directions across the listening position in our home theaters. This two dimensions of sound is more in tune with what we hear in real life acoustics.

Freestanding Side and Rear Speakers

To make sure we have the necessary information entering our diffusors, we position our side and rear channel speakers with the speakers firing into the diffusors and not at the listening position. Our speakers are facing the diffusors with their backs to the listening position. This configuration allows for the side and rear channel information to be non localized since the speakers have their backs facing the listening position in our home theaters. It also allows for the side and rear channel information to be spread out evenly in time and phase across the listening position with the more realistic and life like two dimensions of sound diffusion.

More Space Please

Obviously, this configuration requires more physical space than current home theater set ups. Side and rear channel speakers must be placed on stands at ear level just like the left, right, and center channels and have at least 6′ of space between the front of the speakers and the diffusors. The back of each speaker must be at least 5′ from the listening position. This front and back distance is necessary to allow the diffused waveform from our diffusors to properly form at the listening position.

With this new home theater rear and side channel diffusor blend, we have a more realistic acoustic than current wall mounted scenarios which direct fire the information at the listening position. Side and rear channel information is non localized and does not compete with the direct energy from our left, right, and center channel information, just like real life acoustics. Side and rear wall information is blended and laced in the correct balance with the front channel information.

Current home theater side and rear channel speaker mounting configurations do not realistically duplicate real life acoustical information sources. By using diffusion and a freestanding side and rear speaker set up we can achieve a sonic presentation that is more real and lifelike.

MikeSorensen

I am a structural engineer as well as a master furniture maker. I design cabinets for low frequency, activated carbon absorbers. Connect with me on Google+

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