OTHER TECH

Black Bar Blues

Q. Will the image on the new Blu-ray and HD DVD formats fill the screen of a 16:9 display? I use an outboard scaler to do just that with widescreen movies that otherwise have black bars top and bottom. But since these discs are high-def, shouldn't they fill the screen fully the same way high-def broadcasts do? Joe Istre New York, NY

A. Al Griffin says: Depends what's on the disc. HDTV broadcasts such as network dramas and sports are produced in a widescreen 16:9 format that perfectly matches an HDTV's screen dimensions. But most movies have a wider aspect ratio than that of HDTV - either 1.85:1 or 2.35:1. That's why you see black bars at the top and bottom of the screen when watching widescreen DVD movies, and you'll continue seeing them with the new HD DVD and Blu-ray formats. Hang on to that scaler!

Power Rules

Q. For a home theater roughly 20 x 30 feet in size, is there a rule of thumb to determine appropriate amplifier power output in terms of, say, wattage per square foot? And would there be a separate equation for the surround speakers, which usually require less power? George Lane Jessup, MD

A. Ian G. Masters says: There's no such rule of thumb because there are too many variables to consider besides amplifier power. If, for example, you have speakers that have a sensitivity of 84 dB SPL, they will require twice the power of 87 dB SPL speakers to produce the same amount of sound. If your room has hard, reflective surfaces, whatever other acoustic problems those might create, you'll need less power (or less acoustic output, however you might achieve that) than if you had thick carpets and curtains plus overstuffed furniture. If you're using a powered subwoofer or two, you'll need lots less amplifier power for the other channels than if you were running them full-range. Size matters, too, and you have a rather large room - so it will require a lot of acoustic energy to fill. In the end, the best rule is to buy as many watts as your budget will stand.

As for the surround channels, while these do tend to drive smaller speakers, multichannel music and digital soundtracks can place high demands on them, so don't skimp.