Building a Home Theater - Part 1: Introduction and Planning
Basic Design Goals - Room Dimensions
What is the size and shape of the room you plan to use? Both the size and shape of the room are important. The size of the room will help establish the seating arrangement and will greatly influence the optimum selection and placement of the audio/video equipment.
The size of the room will help determine:
• Optimum size of the TV or projector screen
• Seating arrangement and distance
• Speaker configuration
There is no one perfect size for a home theater but a room that is at least 15 feet wide and 20 feet long with 8 foot ceilings is a good place to start. A small room is typically 1,000 cubic feet or less and a medium to large room is 2,000 cubic feet or more. Ideally you want a room that is large enough to accommodate the video display of your choice, provide room for comfortable seating and allow locating speakers away from the main seating area without being placed too close to the walls.
Small Room: 10' Wide x 12' Long x 7' High = 840 cubic feet
Medium Room: 12' Wide x 20' Long x 8' High = 1,920 cubic feet
Large Room: 16' Wide x 24' Long x 9' High = 3,456 cubic feet
Obviously the size of the room will help dictate an approximate seating capacity and seating arrangement. In general, the main seating should be clustered around the primary listening/viewing area or "sweet spot" in the middle of the room. Each seat should have a clear line of sight to the TV/projector screen and all the speakers. Be sure to leave adequate spacing around the main seating area for the multi-channel surround sound to work.
Home Theater – General Layout:
• Cluster main seating around the primary listening/viewing area or "sweet spot" in the middle of the room
• Center the TV/projector screen on an end wall (long axis of the room)
• Leave space around front left and right speakers to let them "breathe" (2'~3' from side walls)
• Leave space behind the main seating area if you plan to use back-surround speakers (5' or more)
The shape of the room is very important as it will affect how sound propagates within the room. The physical dimensions of the home theater will have a significant effect on the basic acoustics of the room, particularly in the lower frequency, bass region (200 Hz and lower). Selecting the proper ratio of room dimensions will help minimize standing wave resonance. Sound travels as pressure waves that radiate out from the source (speaker) and reflects off the walls, ceiling, floor and other hard, flat surfaces. Standing waves can result when sound pressure waves travel back and forth within a room. At certain frequencies, the waves traveling in one direction will combine with those reflecting back in the other direction and produce areas of high and low sound pressure in the room. Areas of high pressure will sound unusually loud while areas of low pressure will sound unusually soft. If you have the option, it is much easier to minimize standing low frequency waves by designing the room with optimal dimensions rather than trying to fix the problem later (adjusting seating, moving speakers, and/or room equalization).
The worst shape for a room is a cube where all the dimensions (width, length, height) are equal. While there is no one perfect shape for a home theater, a good rule of thumb is to keep the width of the room at least 1.6 times the ceiling height and the length of the room at least 2.3 times the ceiling height. A lot of study has been done in this area and published over the years. L. W. Sepmeyer was the principal researcher who came up with the "golden room ratios".
When designing a new home theater start by defining the ceiling height (H) and then use one of the "Golden Ratios" to establish the width and length of the room. For example: if you have 8' ceilings making the finished room 12.8' wide by 18.6' long would be ideal for minimizing standing waves and for creating an optimum sound field. The main goal is to insure that no two room dimensions are the same or are multiples of one another.
If you are contemplating using a large room with a complex shapes and are serious about sound then a professional custom installer could be very helpful in getting it right from the start.
How much of the work are you planning to do yourself? As we just mentioned, the larger and more complex the home theater project, the more likely you are going to need professional help. You should have a pretty good idea of your capabilities before you start a project like this. Know your strengths and weaknesses. Building a home theater may be a great opportunity to learn something new but don't be afraid to ask for help or hire a professional when needed. Two of your best resources are professional builders and installers. A local builder can help take care of all the construction details that may be beyond your capabilities and they should know how to do the job right, safely, and to code. You may also want to enlist a custom installer to help with the initial design and later with the installation, setup and calibration of equipment.
Hiring an ISF trained custom installer will help insure they have the experience and equipment necessary to properly calibrate your home theater.