Common Myths In The Home Theater Hobby

There are many myths that can be found in common practice when it comes to home theater. Having excellent test equipment, standards knowledge and familiarity with the best studio post production environments gives me insight into what common practices are based less on science and more on myth. The following are some that I encounter.

• Bass Traps Are Required For Great Room Acoustics And Sound Quality – I find that bass traps are being overused in many home theaters. The affect that this can have on a room is that it will be too dead acoustically and a waste of money. The best approach to room acoustic treatment is to measure the reverberation characteristic of the room with all of the furnishings in place and then calculate and install the treatments that are required to bring the room within specification or within budgetary or appearance limitations.
• Sound Isolation Is Required For Great Room Acoustics And Sound Quality – I find that sound isolated rooms with double drywall and other measures to minimize sound escaping from them are the most challenging rooms acoustically and tend to sound worse than those that are not isolated. The reason this is the case is that low frequencies typically escape at a high percentage from a room that is not isolated. Once you isolate the room problems like bass modes and bass reverberation become much more of a problem. Bass modes in these rooms can be improved with complex room dimension design and multiple subwoofers. Acoustically treating the bass reverberation tends to be very difficult at frequencies less than 100Hz without over treating the higher frequencies.
• All Subwoofers In A Home Theater Have To Be The Same To Have Good Sound – multiple subwoofers are commonly used in home theaters for two reasons. One is to add additional sound output capacity. Using subwoofers of similar low frequency extension for more capacity is a good idea. The other main reason to use multiple subwoofers is to fight bass modes. Bass modes are most problematic above 30Hz. Since that is the case a smaller subwoofer can be used to improve room modal response. The benefits of this are a smaller footprint and lower cost while maintaining similar sound quality. The keys are to use a smaller subwoofer that is of reasonable quality and sound output. Equalizing the larger and possibly the smaller subwoofer to blend them together smoothly with the smaller unit is also a good idea.
• Rooms With Ideal Dimensions Will Fix Bass Modes – while room dimensions can improve bass modes all rooms with parallel walls and ceilings will have relatively strong modal behavior at some frequencies. This is even more true when multiple rows of seating are involved. The most effective way to reduce bass modal behavior in a room are multiple subwoofers setup properly along with a room design that minimizes bass modes. The rooms I encounter with the best low frequency behavior do not have parallel walls and use multiple quality subwoofers.
• Automatic Audio Calibration Will Deliver The Best Sound – after measuring over one thousand audio installations I find that there is no simple route to great sound to be found by running the automatic calibration methods found in various preamplifiers and receivers. The simple truth is that many key parameters found in audio sources, subwoofers and speakers can ruin the sound and render all of the adjustments that the receiver can do moot. The other problem is that the microphones and the logic to be found in these units are not sufficient to resolve the issues to within the tolerance of even modest home theater equipment, much less high precision gear. If you want great sound someone must go through the effort of meticulously setting up the parameters in these products along with the other devices in the sound reproduction chain.
• Power Conditioners Fix Ground Loops – many people invest quite a bit of money in power conditioners attempting to fix ground loops. This in general does not work. The best approach is to ensure everything that is connected electrically to the audio preamplifier has the same ground potential and the outlets are wired correctly. This includes external ground sources like cable, satellite, telephone and wired Internet connections. Home automation systems that are wired into the system can complicate this greatly by extending the ground issues to all devices connected by wire to the automation system. Optical or wireless connections can help with this problem when fixing the wiring problem is difficult. There are products on the market that can isolate ground loops with intervening devices between RCA and XLR audio connectors or those specifically designed to isolate the ground on the electrical connection.
• Expensive Cables Are Required For Great Audio And/Or Video – contrary to what you might expect I find that expensive cables are more likely to have problems than ones that would be typically used in a good professional installation. I suspect this is caused by them having less quality control than larger companies that produce professional cables. The key is to use a reasonable level of quality and stopping with cables that would be found in a professional installation.
• More Expensive Equipment Is Better Than Something Cheaper – as with cables more expensive anything in home theater is not necessarily better than something more modest in price. This does not mean that there are no products that deliver on their high price. There certainly are, but there are also many products on the market that deliver lower quality results than some other choices that can be as much as ten times less expensive in price. Amazingly, many people convince themselves once they have purchased one of these overpriced items that it is great and they go around posting on the Internet how everyone else should go buy it too. I have been very surprised myself to find out how poor some of these highly praised products fair when they are objectively compared to others on the market. That is why I have the manufacturers listed on the sides of this blog. They are the ones that I find consistently deliver reasonable value at various price points.
• My Projector Is Rated At X Lumens Which Will Easily Illuminate My Screen – The fact is that projector lumen ratings are frequently based on settings that have nothing to do with good image reproduction. When purchasing a projector try and find a review where the light output was measured with a D65 white point. Combine a projector that is 2-3 times dimmer than rated with a screen that is 30-50 percent dimmer than rated and you have a recipe for a very dim home theater.
• I Have THX Mode On My Display So It Is As Good As It Can Get – I find that THX modes in displays are rarely very close to right and frequently not even the best mode to achieve the most accurate image from a display.
• The Higher The On/Off Contrast The Better – I find there is a limit to what looks correct with respect to on/off contrast. Too low of on/off contrast and the image will look washed out and lack pop because the near black has too much gray mixed in with it. Too high of an on/off contrast and the image looks clipped with the near black information being too dark to see anymore. How much is too much is a function of the display ANSI contrast and the room environment, but in general over about 30,000:1 starts becoming a problem in even a very dark room and a display with high ANSI contrast. SMPTE for example specifies 2000:1 minimum for a reference screening room. I have also seen SMPTE documents for DCI warning of excessive on/off contrast causing these very problems.
• Projection Screen Light Levels Below The SMPTE Standard Are Fine If The Room Is Very Dark – I find this to be very false. The SMPTE standards for light output from a screen are carefully chosen and used to color grade the film. Once you go too dim the colors become lifeless and bright scenes lack the pop the image should have had.
• Automatic Irises In Projectors Are A Great Substitute For Native On/Off Contrast – I find that projectors with sufficient on/off contrast look much better than ones that use an automatic iris to boost the contrast range of the projector. The problem is that when the iris closes to enhance the black level it dims the scene too much resulting in muted colors and less pop in the image. Poor applications of this technology also introduce light level pumping and excessive projector noise.
• Accelerated Aging Of Plasma Displays Will Improve Their Image Quality And/Or Life – I find no correlation between the plasmas I work on and the fact that they ran a series of test patterns for numerous hours or used the display normally before calibration. If anything I find that the plasmas that run these procedures have more problems caused by the process being implemented improperly resulting in image retention from a menu that came on while they were gone.
• Projection Screen Gain Will Fix A Poor Room – A gain screen will reduce the impact of wall reflections on the image proportional to the gain. However, the closer the walls are to the screen the more difficult this is to pull off. The highest gain screens like a Da-Lite High Power are best at this, but require the projector to be mounted near the viewers head height. The best performing theater rooms using front projection all have dark surfaces and furnishings.
• Projection Screen Gain Is Without Problems – many people falsely believe that a projection screen with gain does not bring problems. A neutral gain screen is what is used for studio screening rooms. Gain screens will add image artifacts including sparkles, hot spots, different light output at different locations in the room and color errors. Their effectiveness of improving light output is also a function of the angle of the projector and the viewer with the screen. The further off-axis the viewer and/or the projector the dimmer the image will be. Gain screen manufacturers also frequently dramatically overstate the products gain bringing all of the problems for less improvement than published.
• You Can Use Almost Any Tools And Get The Good Calibration Results – I talk to numerous people who believe that whatever they do they can get good results for calibration. I find this to be false. For example, a projector I worked on recently had been done by a well known competitor. I was able to get 40% more light from it which will dramatically increase the effective light output. I also achieved much better color using my tools than he did with Calman and a Minolta CS-200. The following charts show some of the differences. Note the dramatic difference in gray scale tracking caused by sensitivity problems with the CS-200. The color gamuts were completely different because of better decisions on how to calibrate the gamut and the improved accuracy of the PR-670 that I use. The competitors blue was very purple and the green was very yellow. These levels of differences are common between AccuCal tools and others.

AccuCal Gray Scale Calibration

Competitors Gray Scale Calibration

AccuCal Tristimulus Calibration

Competitor Tristimulus Calibration