Q&A # 56 - March 24, 1998

Staff

Q I own a Mirage MC2 center channel speaker, and in home theater use, I find that during dialogue sometimes there is a bit of distortion. It sounds fuzzy or raspy, especially in very deep or screaming voices. Is this considered clipping? If it is, could you explain why because I own a HK AVR80 and it claims to be a high current receiver, and the volume setting is only at -10db. Would one of my solutions be just to buy a separate amp? Would it better to buy just one 5 or 6 channel amp or three 2 channel amps? I was thinking towards Parasound because they offer both routes at about the same price. It will be used primarily for music then secondarily for home theater. Could you also recommend any other amps at this level and price of the Parasound?

A With just about any mass market receiver, clipping occurs when in home theater mode and with high impact movies at high volume (which, from your description of "screaming voices", it sounds like you are watching). In particular, the center channel gets lots of use. That raspy sound is the buildup of harmonic distortion, the primary component of clipping (which is defined by many as the point at which there is 1% harmonic distortion). So, yes, you should consider an outboard amplifier, and I would suggest a five-channel unit rather than six-channel. From the type of movies you apparently like, I would suggest at least 100 watts per channel into 8 Ohms, and probably more. I like action movies too, and if I were getting ready to buy an outboard amplifier, it would be something like the Carver AV-705 or Sunfire Cinema Grand. I understand ATI 505 is supposed to be very good too, but we haven't reviewed it yet. In any case, get the most power you can afford.

Q I finally bought a home theater system, including a DVD player. The problem is, I don't like the widescreen versions of the movies. My wife doesn't either. So, we end up watching the full screen version on the other side of the disc, even though some of the picture appears to be chopped off. Is there something wrong with the way our TV is showing the widescreen movies?

A Assuming you have a 4:3 TV, just be sure the option on the DVD player menu is set for 4:3. If you have one of the 16:9 TVs, then you need to set the option for 16:9. Other than that, no, there is nothing wrong with your TV. In fact, it seems many people prefer the full screen version (called Pan & Scan, or P&S). There is something bothersome about those blank areas at the top and bottom of the screen. Also, widescreen movies are designed for movie theater screens that are physically wider than the screen on which 4:3 movies are shown. But, at home, the movie is shown on the TV screen at the same width regardless of the aspect ratio (width of the image divided by the height), and after watching a 4:3 image, switching over to a 2.35:1 widescreen movie produces a strange sensation, like something is missing. In the early 1950s, when widescreen movies (CinemaScope) began appearing at movie theaters, the studios filmed the first CinemaScope movies in both formats, using two different cameras, and two different takes, just in case audiences didn't like widescreen. I managed to locate a rare segment of the non-widescreen version (4:3) of "Demetrius and the Gladiators", shown on the right, to compare with the CinemaScope version, shown on the left. This 4:3 version is not the P&S version but, rather, an actual filming of the movie with a spherical lens rather than the anamorphic lens. Notice how the CinemaScope image has more picture area on the sides, but less at the top and bottom. This is due to the way the image was composed in the camera viewfinder. The P&S image from the CinemaScope version of Demetrius would probably look like the picture shown at the bottom-left, enlarged to fit the TV screen, and it is similar to, but not identical to, the composition from the actual 4:3 spherical version. (Screen shots copyright Twentieth Century Fox.) Nowadays, directors use "Super 35" format for this purpose (to end up with widescreen versions for the movie theater, and non-widescreen versions for broadcast TV), but they do it with one camera. The image on the film is cropped to produce the final format (movie theater or broadcast TV). HDTV will probably change our preferences, since the TVs are all 16:9. Conventional 4:3 images will be shown in the center of the TV screen, with blank areas on the sides, while widescreen movies, and HDTV broadcasts, will occupy the entire width of the TV screen, and they will be physically wider than the 4:3 images.

Q I am in the market to buy an A/V preamp/processor. I am considering the B&K AVP-3090, Acurus ACT3, and EAD Theater Master Encore. They all have AC-3 and DTS. The only difference that I am aware of is the D/A converter. I am told that the B&K uses an 18 bit D/A and the others use 20 bit D/A. My question is which one is better? I guess the more basic question is : What is the difference between an 18 bit, 20 bit and 24 bit D/A? Will an 18 bit D/A handle a 20 bit or 24 bit encoded DVD/CD ?

A Although current CDs use 16 bit word lengths (1s and 0s in groups of 16) to code for the voltage on the waveform, there are various processes that "presume" 20 bit words, in that they try to reconstruct the way the original recording was made using 20 bit words. HDCD is that way, and so are a few others. Digital Audio Discs (DADs) on the DVD format use 24 bit words, and 96 kHz sampling (conventional CDs have 44.1 kHz sampling). DTS uses 20 bits. When the DAC resolution is less than the software (the recording), the least significant bits (LSB) are dropped. So, they can be played, but some of the low level detail will be missing. Go for one of the 20 bit components.

Q I have a bass problem. Any speakers I put near the front left and front right corners of my room, which are the ideal positions for the main left and main right speaker, cannot produce low bass at all. I see the drivers moving but no sound, and the phase is absolutely correct. I tried placing a 12" woofer in the corner, and the result are the same. The room dimension is 4.2 x 8.4 x 2.5 meters. Would you please let me know how to calculate for the standing wave for this room, and the way to solve this problem? In AC-3, I am forced to redirect bass from the main
speakers to the subwoofer next to the listening position despite the fact that they are 4-way full-range speakers. This puts unnecessary work to the subwoofers.

A Having bass from two speakers in opposite corners cancelling each other is common. This is one thing you have to be very careful with when using double subwoofers. In fact, there can be a 6 dB drop in some frequencies with two subs. When properly placed though, the effect is great. They have to be placed at unequal distances from all walls, and probably the distances from the walls for each speaker have to be a little different. One of the best ways to place speakers for the low frequencies is to put one speaker in the listening position, and then move around the area where you will be placing the speaker while some music or movie with deep bass is playing only through that speaker. When you find the spot where it sounds the best, put the speaker where you were standing, and then do the same thing with the other speaker. Sometimes, the best speaker placement for listening will not be the most convenient to the looks of the room, and that is a compromise that has to be decided upon as it arises.

Q I am trying to set up a home theatre and have some questions about using my existing speakers in a surround setup. Right now I have a
Yamaha RX-V592 receiver doing Pro Logic and I'll upgrade to DD this summer. I own one pair of B&W DM601s, one pair of KLH bookshelf 3-ways (which I know very little about), a Christmas gift center channel speaker made by JBL (approx $250 and sounds pretty good), an
Audiosource SWfour powered sub, and one pair of Cerwin Vega VS -150 3-ways. The question really concerns the Cerwin Vegas. I want
them in the mix but they sound so much louder than the other speakers that they dominate the room. I've had to turn up my center channel and surrounds (right now the KLHs) just to keep up. I'd like to use the 601s in the setup, but they're not sonically matched with the CVs. I'd hate to give up on the CVs, but everyone is telling me that the B&W's are better. Let me give you some specs on the CVs to help you with your
response. 400 watts max, 5 watts min, 27Hz-20Khz, 102dB sensitivity, 4 Ohms impedance, bass reflex, 15" driver, 6 1/2" mid, 1" polymer foam dome tweeter, 35 3/4" x 18" x 18 5/8" dimensions, 90lbs.

A The answer to your question is in the Cerwin Vega specifications. The 4 Ohm load will cause more current to be drawn than the other speakers. Also, 102 dB is a very sensitive speaker, and this means they will play much louder with the same power input to them than the other speakers, which are less sensitive. It is apparent you want to use the Cerwin Vegas. So, instead of turning the other channels up, turn the front left/right (Cerwin Vegas) channels down. This will help, but not totally solve the problem because the Cerwin Vegas will always be taking more current than the other speakers relatively, and this will lower the performance of your receiver. The 592 has pre-out jacks, so you should consider a more powerful outboard five-channel power amplifier later. Until then, you might try turning the CVs down just a little more than you would really like so that the power supply in your receiver can deliver enough current to the other speakers.

Q I have a DCM Sub 2 connected to my THX receiver's sub output. The DCM has no bypass switch for the crossover. I'm going to add a THX sub to the receiver's sub out and want to know if moving the DCM to the front left and right channels would work? I was reading over some of your past Q&As and read where you used "Y" connectors between pre-out and amp inputs to send audio to a sub. Would this work for the DCM or is all of the LF sent to the sub output? I know THX crossover is about 80 Hz, and I'm wondering if the upper sub LFs need a subwoofer also?

A The THX mode will send all <80 Hz info to the subwoofer. You could use a couple of Y connectors to send pre-out info from both left/right channels to the DCM when you get your THX sub for the subwoofer output jack, but, only >80 Hz info would go to the DCM. Unless you have really small speakers in the rest of the system, the DCM would be useless in this configuration. Two subs can be really nice, but as noted in another Q&A above, you have to be very careful in placing them. If you want to continue using THX mode, I would suggest putting a Y connector at the subwoofer output, and send one leg to the DCM and the other leg to the THX sub. The DCM would have two crossovers in its signal path, but it would still work.

Q When a set of home theater speakers are "THX" certified does that mean that they have been re-equalized as well as having tonal balance? What about laserdiscs with the "THX" mark? Have they been re-equalized or do you have to set an amplifier with THX re-equalization on THX mode?

A The THX surround processor does all of the re-equalization. In order to keep things straight, they do not do any re-eq in speakers, amplifiers, or videos. They know that if they applied re-eq to any or all of the parts outside the processor, there would be problems and confusion. THX labels on amplifiers, speakers, laserdiscs, and DVDs, mean that the item in question meets THX standards (power and fidelity). To take advantage of re-eq, you will need a THX processor. Some other companies offer their version of the THX re-eq, but they are not labeled as THX.

Q I am in the process of looking at home theater systems. I need information on RPTV and home theater speakers and components. I am looking at spending $6,000-$7,000. What products are the best out there in that price range?

A First, I will make a budget allocation suggestion: $2,000 for the TV, $1,000 for a DD receiver with 5.1 pre-outs, $600 for a DVD player, $1,000 for a five-channel outboard power amplifier, $1,400 for speakers, $1,000 for a powered subwoofer. That's a lot of money, so shop around and don't buy on impulse. There are many fine products that would do the job within your budget. An example kit would be the Yamaha RX-V992 DD Receiver, Toshiba 3107 DVD Player, Carver AV-705 Five-Channel Power Amplifier, B&W DM-602 Speakers (four of them), B&W CC6 Center Channel Speaker, and Sunfire Subwoofer. Several of these items can be found below MSRP. I did not make a TV model suggestion because the model numbers change so often, but I would suggest looking at something on sale, like a last year's model, and just make sure that it has at least one S-Video input.

� Copyright 1998 Secrets of Home Theater & High Fidelity
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