Q&A # 284 - April 24, 2002

Staff

Q I've been hearing about edge enhancement (EE) and that "The Phantom Menace" DVD suffers from it. What is EE and why is it 'bad'? Is it located on the media itself? Do video processors/DVD players/monitors produce EE as well? How do you identify EE when evaluating hardware/software that you are about to purchase?

A Edge enhancement is in the software (the movie). It is an algorithm that is applied to the image so that edges appear sharper. While it might make the picture a little snappier on small screens (29"), it is very undesirable for large screen projectors (60"). Here is a simulation, shown below. The image on the left has no enhancement, while the image on the right does have enhancement. I enlarged the images from their originals to show you what they would look like if you were looking at them on a large screen. Notice the white edges around the blue and yellow. The enhancement gives a false impression of sharpness. There is no way to tell which DVDs have it and which do not, until you put the DVD in your player and take a look.

Q I run into a lot of debate regarding maximum lengths of various video cables and associated signal loss. Could you please offer some advice regarding the typical interconnections? Composite video, composite RGB, S-video, YPbPr, YCbCr, RGB/HV, Firewire and DVI are the most common concerns.

A I have used 25 foot component video cables (BetterCables.com) with no problems, but those are analog signals. With digital, long cables can be more problematic. DVI and Firewire are not really for cables longer than 12 feet, but I have tried 18 foot DVI connections, and it worked fine. The most important thing is probably the quality of the connector, which in the case of composite and component video, should be 75 Ohms.

Q I've read that low frequencies and a good placement for a sub is very difficult to obtain in a room with very high ceilings. Is this true? I currently have the same problem. When I do a frequency sweep I notice that when it comes to about 100 Hz the sound simply fades away and when it goes lower it becomes stronger again. My system consists of a Marantz SR-5000 amp and a pair of Mission M74 speakers. I don't have a sub at the moment. What could the problem be? My room which is 3m x 4m and 4m high or my system?

A When you play your audio system in a room, the sounds bounce off the walls, ceiling, and floor, and the reflected signals interact with each other. The result is that the sound coming from all the various surfaces augments each other (peaks) in certain parts of the room and cancels (nulls) in other parts of the room. These specific parts of the room are called nodes. The size of the room affects the frequencies that cancel or augment. So, as you run your sweep and stand in one part of the room, you hear the nulls and peaks as the frequency changes. Here is a series of spectra showing frequency response of a subwoofer with the microphone placed close to the main driver (green line) vs. with the microphone placed in other parts of the room (yellow, blue, and pink lines). The green arrow points out the spot where the main (active) driver loses response. The passive radiator is on the other side of the enclosure, and it fills in at this spot. Notice that the room response shown in the other three lines are similar except for a few places such as pointed out by the yellow and pink arrows. In the one place of the room where I recorded the pink spectrum, there is a null in that frequency range compared to the yellow spectrum. For these spectra, I used an inexpensive uncalibrated microphone to show that it does not have to be fancy to pick up these effects. You could detect them with the Radio Shack SPL meter, which is fifty bucks.

You can calculate the best spot to put your subwoofer by the following formulas (adapted from Cardas Audio):

The distance from the center of the woofer cone at its widest point (near the grille cloth) to the side wall = width of your room x 0.276

The distance from the center of the woofer cone at its widest point (near the grille cloth) to the wall behind the subwoofer = width of your room x 0.447

Q I have a Marantz SR-7000 receiver with Paradigm Monitor 7V2 mains, CC-370 center and PW-2200 sub. If I set the speakers to "small", bass info below 100 Hz is sent to the sub. The Monitor 7s supposedly have a flat response � 2 dB to 34 Hz. Should I designate the mains as small or large and what crossover should I use for the subwoofer?

A Set them to "Large" and use your subwoofer with a crossover of 40 Hz. This will give you full range sound in the main speakers, and some augmentation below 40 Hz since the subwoofer output jack will still get some low frequency feed. The rolloff of the sub above 40 Hz will likely coincide with the rolloff of the mains, but you will have to adjust the subwoofer volume carefully.

Q I've recently invested in a Marantz DV4100OSE DVD player and a Marantz SR4200 AV receiver. I intend to use the DVD player as my CD player too. I'm looking for a speaker system that can do justice to the music performance but still give a decent home cinema experience.

I'm currently using a 20 year old Celestion stereo pair which were outstanding when bought, but are now showing their age with my new kit. I am considering the Mission m72 home cinema system but I've got a small room so the speakers need to be quite close to the walls, and a rear ported front pair might not be the answer. I've also thought about the Bose Acoustimass range but I'm worried that the mid range performance may be disappointing.

A There are so many good speakers out there, it would be difficult to list some choices without listing them all. For your situation, though, I would indeed suggest something that is either front ported or sealed enclosure. I would also suggest speakers with 8 Ohm impedance and high sensitivity (> 88 dB/w/m) so that your receiver will have an easier task. This should narrow down the choices.

Q How do I connect two subwoofers to a receiver that only has one subwoofer output jack?

A There are a couple of ways to do this. One is to connect the left and right speaker outputs to the two subwoofers, and the speaker-level outputs of the subwoofers to your speakers. A second way is to use the left/right pre-outs (if your receiver has them) to drive the line-level inputs of the two subwoofers. A third way is to use the left/right tape rec-out jacks to feed the two subwoofers. These three methods will give you stereo subwoofers, and it assumes both subwoofers are the same or very similar. Otherwise, it might be best just to use a Y splitter at the subwoofer pre-out jack to feed both subwoofers the same signal, and you stack them one on top of the other.

Q I have an Elite 510 RPTV and have been putting off buying the HD satellite receiver until there is more content, but the blocky picture is really annoying. If I buy one, will I at least get some improvement in non-HD DirecTV signals simply by switching from S-Video output to component? Any other ideas on mitigating the "blockiness"?


A Blockiness or "pixelation" is a result of the digital signal not being strong enough. I see it occasionally on any satellite TV system, because the broadcasts for all the channels have to share a finite bandwidth limitation, but if it is happening often, it could be that your satellite dish has moved out of proper alignment with the satellite, but also, you can get this problem if you have two satellite TV receivers connected to a single dish LNB (Low Noise Block down-converter). Modern dishes have two LNBs.

Q  In general, do smaller speakers sound better in a smaller room compared to larger speakers in the same room? (A sub could be used with both comparisons, to remove the very low bass consideration).

A Smaller speakers won't sound better in a small room than large speakers, but small speakers will sound better in a small room than they would in a large room, because you would have to crank the volume up in the large room, and this puts stress on small speakers.

� Copyright 2002 Secrets of Home Theater & High Fidelity
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