That '70s HD Advisor

Posted Fri Aug 13, 2010 at 12:00 PM PDT by

Editor's Note: Each Friday, High-Def Digest's own HD Advisor will answer a new round of questions from our readers. If you have home theater questions you need answered, send an email to

If you've already sent a question and don't see it answered yet, please be patient as we work our way through them. To browse through previously answered questions, visit the main HD Advisor page.

Answers by Joshua Zyber

Passive vs. Powered Subwoofers

Q: I finally broke down and bought a new receiver, a Yamaha RX-V565. I can use my old speakers from my previous Home-Theater-in-a-Box for now until I save up enough money to upgrade those as well. My question is about the subwoofer. On the subwoofer output on the receiver, it says "Subwoofer (Pre-Out)." I am assuming this means that the sub is amplified in the receiver, rather than me needing a pre-amp. Also, it has what looks like a standard RCA plug for the sub, but my current subwoofer has the old bare wire plug. Can I use my current subwoofer, and can I simply go out and buy a connector?

A: There are two basic types of subwoofer in a home theater system: passive and powered. As with any speaker, the audio signal sent to a subwoofer needs amplification before you'll hear any sound. A passive subwoofer relies on that amplification to be performed in the A/V receiver or in some form of intermediary amplifier placed between the receiver and the sub in your signal chain. A powered subwoofer has the amplification built right into it, and requires nothing more than the raw audio signal.

If your old subwoofer only has binding posts for speaker wire, but has no RCA input and doesn't plug into your electricity directly, it's a passive model. You'll note that the rest of your speakers are also passive. (You connect them straight from the receiver by speaker wire.) While your receiver is probably built with plenty of amplification to run your main five (or seven) speakers, the subwoofer traditionally needs more power to drive the low frequency audio at loud volumes. Even if your receiver offered standard speaker wire outputs for a subwoofer (the RX-V565 does not), you'd really be better served with external amplification anyway.

The "Pre-Out" connection on your receiver is a pre-amplified output. Meaning, it outputs the audio signal before amplification. The receiver expects you to do that amplification elsewhere.

You have two options at this point. The easiest is to buy a new powered subwoofer. Connect the Subwoofer Pre-Out from the receiver directly to the sub and turn it on. Your other option is a little more complicated. You can buy a dedicated subwoofer amp that will accept the signal from the Pre-Out on the receiver, amplify it, and then connect to your subwoofer by speaker wire on the other end.

If your passive subwoofer came from a Home-Theater-in-a-Box system, odds are that you'd be best off replacing it altogether with a new powered sub that's designed to dig deeper and play louder anyway.

Ugly Blu-ray Cover Art

Q: Although this is more of an aesthetic question, I was wondering if you could explain to me why many Blu-ray releases use alternate box-artwork for the covers as opposed to using the original poster-artwork. The recent release of 'National Lampoon's Vacation' is a perfect example where the original classic movie poster artwork is replaced by some cheesy cover-art that looks as if it should be at the back of the box! Maybe it's just me, but I find this a bit disappointing.

A: I happen to be annoyed by this as well, and that 'Vacation' cover is a real eye sore. The simple answer here is that the studios' home video divisions rarely care about the aesthetic values of movie poster art. They just want to move product. The easiest way to catch a potential buyer's eye as he or she browses the racks at Best Buy or Walmart is to design a cover with a big photo of the main star's face on it. The hope is to inspire a reaction of, "Oh hey, that's [insert famous actor's name here]. I like him [or her]. Let me see what that movie is."

Meanwhile, the more attractive artwork designed to be displayed on large posters in movie theater lobbies typically isn't as immediately eye catching when shrunken down to DVD or Blu-ray size.

Some studios care more about the look of the cover art than others. Discs from the Criterion Collection almost always feature very tasteful artwork. On the other hand, major studios frequently give us abominations like that 'Vacation' cover, which was probably thrown together in half an hour by a college intern marginally proficient with Photoshop.

Dropped Frames

Q: So I just bought a new TV, a Sharp Quattron LC-40LE810UN, and I love it. However, on some movies it will flicker black very quickly for about a second. It seems to only happen when I am watching Blu-rays at 24 fps. I assume this is because it is dropping frames, but I am not an expert on this stuff. If it helps, I am using a PS3 as my Blu-ray player, and I generally have the motion interpolation (called "Motion Enhancement" and "Film Mode") set to on, often high. It is an awesome TV, so I will not get rid of it for this, but any advice would be appreciated

A: My first immediate suggestion is to turn all frame interpolation off. These so-called "motion enhancement" settings may make motion look superficially smoother, but they do so by generating artificial frames that were not originally contained in the source signal (i.e. the movie you're watching). The TV creates these new frames by averaging the data from frames in the source and essentially guessing what something in between those frames might look like.

Movies are photographed at 24 frames per second. 1080p Blu-ray discs are encoded at that original rate. The Sharp LC-40LE810UN is a 120 Hz model, meaning that it refreshes its frames 120 times per second. The easiest and best way to convert a 24 Hz source to display on a 120 Hz screen is simply to multiply the original frames so that each repeats four additional times. This is called 5:5 Pulldown, and the result should be seamless to your eye.

When you turn frame interpolation on to the maximum setting, the TV generates four fake frames for every one original frame in the source. Only a fraction of what you're watching on screen was actually photographed by the movie's director or cinematographer. Give that some thought.

When the TV has to generate more fake frames than real frames, it should not seem at all surprising to find that it will occasionally glitch and cause the flicker you're seeing. I have a feeling that simply turning all this artificial processing off will solve the problem.

Homework Assignment: You Be the Advisor

The HD Advisor knows many things, but he doesn't know everything. Some questions are best answered with a consensus of opinions from our readers. If you can help to answer the following question, please post your response in our forum thread linked at the end of this article. Your advice and opinions matter too!

HD Advisor Column Title Suggestions

JZ: It's time once again to put the call out for assistance coming up with HD Advisor column titles that fit the numerical theme. Basically, I've got next to nothing after this week. Help me out!

Check back soon for another round of answers. Keep those questions coming.

Joshua Zyber's opinions are his own and do not necessarily reflect those of this site, its owners or employees.

See what people are saying about this story in our forums area, or check out other recent discussions.

Tags: Joshua Zyber, HD Advisor (all tags)