Now it’s time to head to the fridge for a cold one, kick off those shoes, and see how many decibels you can make from the MI3 sound track before the neighbors come over for an intervention.

Home Theater Design Part 9 - Adjusting for Peak Performance

Steve Faber | Home Theater Design and Automation

Click here for Part 1
Design Considerations
Click here for Part 2
Construction
Click here for Part 3
Speaker Placement
Click here for Part 4
Room Acoustics and Lighting Design
Click here for Part 5
Time To Start Shopping 
Click here for Part 6
Component Features and Performance 
Click here for Part 7
Component Features and Performance 
Click here for Part 8
Wire Management Labeling and Connections

Now it's time to head to the fridge for a cold one, kick off those shoes, and see how many decibels you can make from the MI3 sound track before the neighbors come over for an intervention.

by Steve Faber
 Home Theater Design and Automation


Hey, you're doing fine. Now your gear's hooked up and you've got sound coming out of your speakers. There's a nice looking image on your video display too. Just head upstairs, put a few bags of Orville's in the microwave and grab a cold one! Hold on! Not so fast there. You may have sound issuing forth into your theater, and a blaze of light coming off your screen, but how does it look and sound, really? What do you think the chances are that the equipment is adjusted just the way it should be for your environment? If you're thinking about the same as my Cougs have of landing in the Final 4, well you're not too far off. At least they made the tournament, Bucko!

Most manufactures ship their video products to look bright and beautiful on the showroom floor, where most consumers tend to confuse bright with right. Just as might doesn't make right, bright doesn't either. Sure, it's great to have a bright picture, but not at the expense of image fidelity. There are other things to consider as well, like the darker areas of the picture, or proper color rendition. Unless you spend all your time viewing videos of stadium lights, you'll want to ensure all factors are considered and you have a beautiful picture with richly saturated, accurate colors and deep, yet detailed grays and black.

Step one in this process is to track down a signal you can use to calibrate your TV or projector. Just grabbing that new Casino Royale DVD you picked up and looking at the faces to see if they look right doesn't cut it. You need a disc with actual test patterns on it you can use to determine what your TV really looks like. Two old favorites are Digital Video Essentials and Avia Guide to Home Theater. Both have the proper test patterns to properly adjust color, tint, black level (brightness), sharpness, and white level (contrast). Correctly setting these controls will do wonders for your TV picture. You'll now have the deep, rich picture you paid for when you blew up your Visa card for five grand.

Sadly, although your image will look much better by calibrating it using the aforementioned test DVDs, you can, and probably should, go even farther. Hiding behind that fantastic, HDTV color tapestry you see every night is a grayscale image waiting to be set free. If it's wrong, your whole picture will be wrong as well. Digital video has more detail in the luminance information than the chroma (color) information. NTSC digital video is actually subsampled to reduce required bandwidth and storage space. It uses 4:1:1 subsampling, meaning there is only color information for every 4th pixel (feel cheated?). This points to one of the reasons why proper grey scale rendition is so important. Color resolution of a DVD and HDTV is only half the luminance resolution. Poor color resolution will lead to smearing or blurry color transitions.

This all leads to one other way to ensure you're really getting the proper image; have the gray scale of your display calibrated. It won't give you added color resolution, but it will make sure your image looks correct. The information on color resolution served only to illustrate you shouldn't neglect the grey. It's awfully important. Many video displays are shipped form the factory with horrible grey scales. Basically, the set should give you grey with correct amounts of red, green and blue for all luminance levels. This is essential for proper shades of gray, white and black. In addition, proper grayscale calibration can help your pricey, new flat panel last longer, since many sets are incorrectly adjusted too high from the factory. Adjusting the grayscale usually requires a trip to the factory service menu, although there are some sets that allow access to the proper controls from the consumer menu. If you see controls labeled "drive" and "cut" or "cutoff" for each of the colors red, green and blue, congratulations, you've won the "I can calibrate my grayscale" prize. Be careful, you can mess up things almost beyond repair, especially if you found a way into the factory service menu. Usually setting grayscale is reserved for factory trained technicians or ISF certified personnel.

Now that you can see what you're supposed to, you may want to get the same satisfaction from your audio system. Calibration of your audio system entails adjusting the room out of your system and compensating for inaccuracies inherent in your electronics and speakers. You're trying to hear what the sound engineers and directors heard on the sound stage and in the studio when the recording was created. If you've got ears like them, after calibration you'll hear what they heard what they did when they crafted the masterpiece you're now enjoying. This assumes you've got no equipment related problems or inadequacies. Face it, you're just not going to get flat frequency response to 20Hz with an 8" subwoofer, unless your theater's the size of your neighbor's garden shed, and even then it had better be a pretty good 8" sub.

If you did your homework during the design phase and implemented the results of your research, most of the interior acoustic work, such as wall treatments, will be completed already. Furthermore, you'll know where to place your seating, subwoofers (you are using more than one, aren't you?) and other speakers for the best sound. Now you'll be doing mostly just electronic adjustments and minor position tweaks.

Don't forget to correctly balance the output from all the speakers. The easiest way to accomplish this is to use the internally generated test tone from your receiver or surround processor. The noise will play from each of the speakers in your system, on at a time. You can then adjust the volume so that each speaker plays at the same level. To measure the level of each speaker, don't try to use your ears. Most of us don't have ears that are quite talented enough for that. Instead, go to Radio Shack and grab one of their analog SPL meters. Use it instead of their digital one. It's cheaper and easier to use. Set it flow slow response and "C" weighting using the switches on the front.

At this stage, it doesn't hurt to do a review and take acoustic measurements of your room to verify you met your design parameters. During this process, make sure you check that all speakers are actually in phase. It's possible one of them is actually not. Don't laugh, it's happened before, and it'll happen again. Check the frequency response at the listening position and also the room's reverb time. Low frequency anomalies can be fixed, to an extent, with an equalizer. Do yourself a favor and pretend your's doesn't have boost, only cut controls. Some receivers and surround processors, such as those from B&K Electronics, have parametric equalizers included. These let you precisely target problem resonant frequencies in the bass region and attenuate them. You'll lose much of that boom / flab bass, and be rewarded with smoother, tighter bass that sounds real, not like that $99 swap meet wonder in your friend's rec room.

If you're using separates and have an equalizer in your system, you can work on the other speakers in your system too. The lion's share of the calibration gold will be dug in the lower frequencies though. Fix problems there and you'll be rewarded with some pretty outstanding soundtracks in your theater.

Now it's time to head to the fridge for a cold one, kick off those shoes, and see how many decibels you can make from the MI3 sound track before the neighbors come over for an intervention.


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