3D PJs, Ground Loop, Width vs. Height

Projecting 3D
Just heard you guest-hosting The Tech Guy radio show, and you were talking about the JVC 3D projectors. Do you need active-shutter glasses to watch a 3D projector like the JVC at home?

Thomas Terry

The JVC and most other 3D home-theater projectors utilize active-shutter glasses to view 3D images. These projectors use an IR emitter that bounces its signal off the screen or is mounted above the screen pointing at the audience to synchronize the glasses to the alternating left and right images. The advantage of an active-glasses system is that it can be used with a normal projection screen; the disadvantage is that the glasses are very expensive at roughly $150 a pop. The flagship JVC DLA-RS60/X9 (pictured above) ships with an IR emitter and two pairs of glasses, but the RS50/X7 and RS40/X3 do not, so you must buy the emitter and glasses if you want to watch 3D on those models.

A few projectors use passive glasses—for example, the LG CF3D and Runco D-73d use passive-polarized glasses, which requires a special polarization-preserving silver screen that doesn't work all that well with 2D images. On the other hand, the glasses are much less expensive and lighter in weight. The SIM2 C3X Lumis 3D uses a technology called Dolby 3D, which employs passive glasses but not polarization, so no special screen is necessary. Click here for an explanation of Dolby 3D, here for a discussion of passive-polarized 3D, and here for some info on active-shutter glasses.

Getting Loopy
When I have my PC connected to my Sony Bravia KDL-32EX600 via VGA, I see lines going down the display, similar to what you see when you point a video camera at a CRT monitor. As soon as I disconnect the cable to the TV, the interference stops. Unplugging the HDMI cable connecting the TV to the digital set-top box also makes the lines go away. Any cable connected to the TV seems to show this interference. Do you know what is wrong? Is it just bad wiring in my house?


This sounds like a ground-loop problem to me. If the TV and source devices (PC, set-top box) are plugged into different AC outlets, their ground voltages might well be slightly different, which causes the effect you describe. Try plugging the TV and one of the source devices into the same outlet using a power strip or multi-outlet extension cord and see if the problem persists. If the interference goes away, keep the devices plugged into the same outlet or have an electrician rewire that room so all outlets are connected to the same ground.

If this does not solve the problem, there might be a grounding issue in the TV, which will require a technician to take a look.

Personal Preference
Which is better, adding a pair of width or height speakers to a 5.1 or 7.1 system? Should these speakers be matched to the main left/right pair or the surround left/right or surround rear pair?

George J. Perkins

In my view, neither is "better" than the other—it depends on your preference. Width speakers, which are placed at ±60 degrees from the center, create a more uniform lateral soundfield with smoother pans around the room, while height speakers are placed about 45 degrees above the main left and right speakers and create a more three-dimensional soundfield. Keep in mind that there is no commercial content with discrete information in these channels—Dolby Pro Logic IIz synthesizes the height channels, and Audyssey DSX synthesizes height and/or width channels.

As I've said many times, it's important to match the tonal characteristics of all the speakers in a multichannel system as much as possible. If you have floorstanders in the front left and right positions, it's easy to put two more of the same model in the width locations, but not in the height locations, in which case, matching them to the surrounds is perfectly acceptable.

If you have a home-theater question, please send it to scott.wilkinson@sorc.com.