Q&A # 58 - April 7, 1998

Staff

Q The speakers I have, have the following frequency response:

The DD and DPL decoders have the following speaker settings: None/Small/Large for front, center, and rear channels. When set to large, the signal is sent to the speakers as is. When set to small, 80 Hz and below is redirected to LFE. I have bypassed the crossover in the subwoofer. The subwoofer output is set to be in phase and the volume control is set to 5 (range 0 - 9 ). With this configuration, 1) It is obvious that center and rear channel settings should be small. What should the front channel switch be set to? Wouldn't   the subwoofer be overwhelmed trying to reproduce the low frequency info from all channels and the LFE if the front is set to small? When the front channel setting is set to large, wouldn't there be information loss?; 2) I have calibrated the channel outputs to 75dB using an SPL meter. How should the LFE be calibrated? What should the volume control on the subwoofer be set to? 3) Calibration with an SPL meter yields the following settings: Left -1dB, Center 0dB, Right +1dB, Right surround +7dB and Left surround +8dB. The 2 dB difference in the L/C/R is due to the room geometry and acoustics. But, I can't quite figure out the 7dB difference in the fronts and the rears. Since all channels are driven by identical mono-block amplifiers can it be because the rears are rated at 4 Ohm and the fronts are 8 Ohms? 4) In stereo mode, left and right channels are at 0dB. What should the subwoofer channel be set at? 5) How do I determine the ideal settings for the subwoofer and the decoders in DD, DPL, and stereo mode so that the information is reproduced faithfully without creating dips and bumps in the overall frequency response?

A The front left/right should be set to "large", but the center may have to be set to "small". This will route all front left/right signals to the front left/right speakers, but < 80 Hz for the center will go to the subwoofer. Use of the SPL meter is great for front left/center/right and rear left/right, but it is not so easy with the subwoofer since our ears are not very sensitive to low frequencies, and we like to have potent bass with action films. I generally set the subwoofer to a level that just feels good and sounds right. Your rear speakers are set to a different level on the preamplifier for several reasons: their size, placement, sensitivity, and impedance, although 4 Ohm speakers would produce more volume than 8 Ohm speakers, all other things being equal, including the volume setting on the preamplifier. But don't worry about the different settings. That's normal for home theaters and is why we need SPL meters. However, you won't be able to correct peaks and valleys in the room response with just an SPL meter. You would need an equalizer too. We use the AudioControl Rialto and Bijou for that purpose. Very often, it is the center channel that needs a bit of tweaking, since bass loading in the 80 hz - 160 Hz region from the front of the TV screen is common.

Q Exactly how durable are CDs? Everybody knows scratches are bad, but errors due to this can be corrected by players' software. But how much? Is it true a lot of small scratches do more harm than a few big ones? What   about invisible scratches and sticky dirt? The pits and lands on CDs are so microscopic, aren't they affected everytime we put a CD on the player's tray? Philips' website also says to avoid bending CDs as this may cause unseen cracks (I'm not sure on the plastic or on the binary pit and land coded aluminium). It's very hard not to bend CDs when you try to pluck them out of very tight jewel cases (the center rim that grips the center hole of the CD). It would seem then (at least to me) that CDs, if used often, will not maintain their original fidelity as was envisioned. I say this because it seems to me my CDs sound lousier than when I first bought them. How much of this is due to damage and how much is due to psychologically getting bored with them I don't know. I do try my best to take care of my CDs, but I rented LDs with all their scratches and dirt, and they don't seem so badly affected. Then again, movie sound is not as picky as music. Sometimes I wonder why they didn't design CDs like Mini-Discs with the disc integrated into a hard case with an oblong hole for play back. That way, it would be much more durable without compromising portability as you need the jewel case to store your CD anyway. With DVD here and higher bit/sampling rate audio formats coming, how will these discs withstand scratches and dirt (especially DVDs for rent)?

A When CDs first came out, it was implied that they would not be affected by scratches. Now we know different. However, the music is encoded with all sorts of information that help the player decode it properly, with a minimum of errors. In fact, only about a third of the data on a CD is the music. The rest is overhead and error correction information. I have found that checking out CDs from the public library works just fine, even with a few more scratches than I have on my own collection. However, a broad deep scratch will cause the player to skip. Small bits of dust don't cause a problem, but dots of glue or other debris will also cause player skipping. Just as with LPs, you can wash your CDs with cool water and a little liquid detergent. This will get finger grease off as well as the dirt. Light flexing of the disc during removal from the jewel case probably does no harm. However, if you bent a CD into a cup shape, it could fracture the very thin aluminum coating that forms the reflective surface for the laser beam. With DVDs, scratches will be somewhat more of a problem since the tracks are so much smaller. This is one of the fears that the rental stores have, and originally, mechanically retracting sleeves were considered for DVDs. Unfortunately, it would have added too much expense. As far as the sound of the CD changing, I think this is a psychological factor. You obviously handle your CDs carefully, so I don't think you are causing any physical damage that is audible. Over time, you remember all the general features of the music and begin to pick up the details. I find this true each time I listen to a CD. I hear a little more than the last time. Maybe a triangle in the background, or someone's breathing, or whatever. Also, boredom will set in if you listen to the same CD over and over too often. Take your favorite food. If you ate it every day, how long would you continue to enjoy it? Try playing a CD that you wish you hadn't bought. After that, then the others will sound better. Fine music has to be savored.

Q You recommend a Carver AV-705 amplifier with the Yamaha 992 receiver on your recommended systems page. Since there's a powered sub with the system, I'm not sure what the role of the outboard power amplifier is.   Also, how do the B&Ws compare to the Polk RT800s which were reviewed in Secrets? From my interpretation, it sounds like the B&Ws are preferred when a subwoofer is available.

A We recommend an outboard power amplifier with every receiver that has a set of pre-out jacks. This is because the built-in power amplifiers of receivers just don't have the punch that outboard amplifiers do. As consumers, we have demanded so many features from the manufacturers, at a good price, they have cut back on the power supplies because that is the most expensive part. As for subwoofers, every system benefits from one, even if the speakers are full range. A good subwoofer is built to put out substantial signal at 20 Hz. "Full range" speakers really won't do that. So, whether the speakers are floor standing, like the RT800s, or bookshelf monitors, like the B&W DM-602s, a subwoofer makes a big difference. Also, you can adjust the volume of a subwoofer separately from the rest of the system, to get the kind of slam that many of us prefer with action films. Lastly, if you really like deep, deep bass, the AudioControl Phase Coupled Activator creates sub-harmonics that really shake the room. It's one of the best "gadgets" I've found to boost the home theater experience, but you need a big sub to use this. Something that will go below 20 Hz and not flinch.

Q I read in the DTS home page and many other articles (including some of yours) that in order to reproduce the DTS sound track accurately, one should use identical speakers for all channels. I've just bought five B&W DM-603 speakers for front left/right, center, and rear left/right channels. I wonder if I made a mistake or overkill buying a full range speaker for the center channel. Should I have bought the CC6 (B&W center speaker) instead, or I've made a good decision? Also, I'm considering to buy a preamp and an amp (say a B&K 3090 and a Sunfire Cinema Grand), but I've noticed that Yamaha just came out with the DSP-A1 with everything built-in. Do you think it's worth it to consider the Yamaha, or is it better to buy separates? Are you reviewing the Yamaha anytime soon? One last thing, the B&K 3090 doesn't have an RF input for laserdisc. If I buy an LD player, I have to get a separate converter box (also made by B&K) that will convert the RF signal to 6 channel inputs to the amp. Do you know of any way around this or should I just forget about that unit and look into something else?

A If you can figure out a way to place the 603 as a center speaker, then you did the right thing. Ideally, all the speakers, including the center, should be the same for DD and DTS. For Pro Logic, the front left/center/right should be the same. The problem is, for floor standing speakers, it is difficult to find a place for the center channel speaker. You should try placing the TV on a cabinet with the 603 below it, in a vertical position like the others. That will probably give you a more balanced tonality than with a center channel speaker laying on its side. For most of us though, we really don't have the option of putting a floor standing speaker in the center position.

Q I'm thinking about purchasing the new Sony VPH D50Q CRT video projector. I've seen it and am amazed at the picture quality. And considering the MSRP of $10,000 US or $14,995 Canadian, I strongly feel that this is by far, the best projector in the market within this price range. Sony claims that this unit is fully HDTV compatible, and their specs seem to indicate the same, but, since no HDTV sets have hit the market along with broadcasts, I'm not too too eager to become the early adopter and be stuck with a $15,000 hole in my pocket. What is your opinion on this unit, and do you believe this projector will NOT be history once HDTV starts and that it indeed will be HDTV compatible when it starts? Finally, would you spend $3,000 on a line doubler, considering HDTV does not require a line doubler?

A The Sony D50Q is a fantastic projector for its price. Two other projectors in the same price range to consider are the Zenith 500 and Dwin HD-500. All three are some of the "relatively" affordable data grade projectors. They all should be able to handle the proposed HDTV specs.  Until HDTV is truly here though, we will never really know for sure. Yes on the Line doubler! While HDTV will not support it, everything else will. If you want to watch NTSC TV, LD, or DVD, any of these will most definitely benefit from a line doubler. You should look at both the Sony and Dwin line doublers.

Q I currently own a Toshiba SD-3107 DVD player and now have a need to play PAL-encoded Video CDs. My thought was to buy a laserdisc player that would also play PAL encoded Video CDs to a standard NTSC television. Do you know of any laserdisc players that meet this criteria?

A Multi-format video players here in the US are scarce, but they are more popular overseas. Because of this, you rarely see anyone selling them here, and I have not personally ever used one. Not all LD players can play a video CD, and in fact, very few can. A lot of DVD players can play video CDs but again, you will either have to buy a PAL player or find a multiformat player.

Q Can anyone help me identify the problem with my Sony TV? There are faint jagged lines running from left to right near the top and bottom of the screen. I don't think the mirror or the suface of any of the lenses is the problem. Could it be something with the 'fluid' in the lenses that is used for cooling? My set is not the XBR model and is about 1.5 years old. The width of the lines is only about 1/8 inch and they seem to disappear when the set is viewed from some angles.

A It could be RF interference from the cable TV connection. Try disconnecting it and see if the lines disappear. Also, it could be an overscan problem. The beam is "blanked" when it finishes a line and returns to the left side to begin another line. If the blanking is turned off too soon, it bounces off the inside of the picture tube before it hits the front of the screen to begin the line scan. The stray electrons pass through the openings in the mask in such a way as to cause odd lines. This is probably something that can be adjusted by a repair person.

Q I presently own an HK AVR20 receiver which has preamp outputs. I am using the unit solely for stereo ( I am not considering home theater for another few years). I would like to add a more powerful amp to my system, but I have heard that it is best to have a dedicated preamp. Is the difference between a stand alone preamp and a receiver very big? I really cannot afford most of the preamps I see advertised, so if the difference is not major I'd prefer to use my receiver as a preamp to save money. If it makes a difference I listen to mostly classical, jazz, and gospel.

A There is a difference between the preamplifier in a receiver and dedicated preamplifiers, but that is partly because dedicated preamplifiers are generally quite expensive and they can afford to put higher quality parts and power supplies in them. In any case though, your HK receiver preamplifier will work just fine. Since you listen to gospel music, I assume there is occasional pipe organ. You should consider a good subwoofer if you don't already have one.

� Copyright 1998 Secrets of Home Theater & High Fidelity
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