Q&A # 191 - July 21, 2000

Staff

Q With regard to the reader's question in the last Q&A column about the tape squeaking in his open reel tape recorder, tapes do deteriorate with time. I do volunteer work at an organization that tapes for the blind. Masters are on open reel tapes. We are meticulous in equipment maintenance. Some of our old (8+ years old) have gotten "sticky" and must be re-duped onto new tape. They literally bounce as they are pulled across the heads and tape guides!

A Thanks for the info.

Q I would like to ask a question regarding preamps. I currently am using a Yamaha receiver with 5 channel inputs as a preamp connected to a Sunfire amp. I have a DVD player with a built in decoder connected to the Yamaha. I was interested in DTS decoding, and better bass management. The question is, do you think it would be to better to A) purchase a similar receiver for under $1,000, but with DTS decoding, and continue the similar set up that I have now, or B) purchase a more expensive preamp ($2,500 to $3,500)? Specifically, I was wondering if you thought that a noticeable difference could be heard from the decoding between a built-in decoder in a DVD player vs. an expensive preamp? I also noticed that most preamps in the high price range do not have 5.1 channel inputs. Do you think this could a big problem (i.e., something in the near future in which DD or DTS decoding would not do the job, and require a separate decoder), or do you think that DD and DTS would do the job for the future? And finally, if you think the preamp route is the way to go, could you recommend some in the above price range?

A For DTS, you would need the decoding in the preamp or receiver anyway, since DVD players don't offer 5.1 analog out for DTS. Secondly, it is better to use the DD decoding in the preamplifier or receiver since you will then have access to all the DSP modes that they offer. The reason the high-performance processors don't usually have 5.1 analog inputs is that they offer hardware upgrades for new formats. The Meridian, for example, has room for additional circuit boards that you just slide into the chassis. They are also have upgradeable software through the Internet. The mass market products are just now beginning to be released with upgradeable features through RS-232 connections, and such things as IEEE-1394 jacks that can be added later. A few years ago, $2,500 meant the high-performance products. Now, you can get mass market items in that price range, and it takes $4,000 - $15,000 to get the high-performance units. Perhaps the most important thing a preamp/processor can have is a top notch power supply, so you should look to see if it has a good sized transformer and power supply capacitors. There are lots of very good processors out there, spanning huge price ranges. The Theta Casanova appears to be very upgradeable and has superb sound. But, it's expensive ($6,000). I think in your situation and budget, you should just go for a nice receiver that has pre-outs, like the Yamaha you mentioned, and use it with your Sunfire Cinema Grand amplifier. All the receivers now have DD and DTS decoding built-in.

Q I am presently researching a setup of a high end home theater in my unfinished basement and I would like to have a THX system. Nowhere can I find an answer to this question, so your help is welcomed. Is there an "ideal" size of room for a home theater? How high should the ceiling be? Is there a preference to finished ceiling or drop ceiling with insulation? I have the equipment in line: the new M&K Select 750 THX, Parasound Processor (AVC2500 Processor with 5x Amplifier) and one of the new HDTV 60+" sets from Pioneer or Mitsubishi. I want to make sure the room area I have selected will accommodate such.

A The conventional "ideal" ratios are 0.6 (H):1 (W):1.6 (L), more or less, but THX offers a graph that resembles an amoeba of other ratios that will work to spread out the room modes and offer the most likely environment for good bass response. In terms of imaging, aside from careful absorption and diffusion placed to kill the primary reflections, the absolute size of the room is not an absolute kind of call. The M&K's THX Select system is, in my experience, absolutely a joy. Take into consideration, though, that it was designed to accommodate rooms of roughly 2,000 cubic feet in terms of output, subwoofer frequency response, and dispersion patterns. The conventionally wide vertical dispersion pattern requires either ceilings and floors that do not reflect very much, or relatively nearfield listening (meaning the speakers are close to the listening position) to achieve pinpoint imaging. This suggests that the best distance in most environments from the front speakers will be within 12 feet or so. The use of an outboard amplifier was a good choice, as with most of the M&K satellites, the THX select system appreciates generous servings of clean power into 4 Ohm loads.

Q I have an Onkyo TX-SV646 receiver, Polk RT5 Left and Right speakers, a CS225 Center, and a PSW150 Sub woofer. I have been having problems with the drivers going bad, especially in the RT5s. Polk has replaced them with no questions asked. One day, I noticed while playing music that the receiver auto-protect mechanism was kicking in (this was with the volume at the 9 position)! I found that one of the drivers was again bad. I wrote a letter to Polk and got a call from a Customer Service guy who finally offered to replace the RT5s with their RT3 model. I said I would take them, since I would be getting a new warranty on them. My question: Am I doing something wrong that is causing these drivers to go bad? This guy seems to think I am, but they are giving me the speakers anyway. I never turn the volume up past 12 as suggested in the Onkyo manual (which is usually more than loud). The Onkyo has Bass and Treble control knobs, so how should I have these set? It also has the 3DB bass button, so should I be using that function? I guess what I want to know is: How should I optimally set my receiver so I can listen to it at high volumes (up to 12 position) without damaging these speakers?

A My guess is that you are clipping the amplifier pretty hard, and that is blowing the drivers. This is very easy to do, and I have destroyed a few drivers in my time too. The tweeters are usually the first to go, but it can happen to any of them. If you want to use the tone controls, then turn the bass down a bit and compensate by using a good subwoofer. You can also turn the treble down, but bass reduction will help the most. Don't use the 3DB Bass control. The RT3s are smaller than the RT5s, and you will have the same problem if you continue to clip your amplifier. Mass market receivers don't have power supplies for cranking up to really high volume. You should consider something that can connect an outboard power amplifier through pre-out jacks on the receiver.

Q I have just purchased a B&W LCR6 S2 center channel speaker and am driving it and 2 X Polkaudio RT5 surround speakers with a Rotel RB-993 3-channel amplifier. At the moment, the B&W is bi-wired to the one output of the RB-993. I have an Onkyo TX-DS777 receiver driving the RB-993 from the surround left/right and center pre-outs (my mains pre-outs on the 777 are driving an RB-991 stereo amp). Here is my question. Can I connect the output of the RB-993 to the low pass input of the B&W and then connect the center channel amp output of the TX-DS777 to the mid/high pass input of the B&W thereby bi-amping the B&W with the Rotel amp and the 777's internal amp, or should I leave the setup as is?

A As long as your speakers are bi-wireable or bi-ampable, then using the Onkyo's power amplifiers in a bi-amping configuration with the Rotel power amplifiers should work fine. I would suggest using the Rotel to drive woofers and the Onkyo to drive the tweeters. The woofers will require the lion's share of the power.

Q In regard to DVD-Audio, why do we need to have 5.1 channel inputs also in our preamp section to take advantage of this so called better audio reproduction? Can't we just pop in a DVD-Audio disc in the player, press play, and let the 24/96 or 24/192 DAC in the player do its job of decoding and reproducing multi-channel audio that we presently hear with today's DVD movies? Why use the optical or coax cable connection? Isn't the decoding scheme with DVD Audio and DVD-Video the same?

A The problem stems from so many outboard DACs being on the market. It implies that the DAC in the player is inferior, which is not necessarily the case at all. In fact, many CD players have superb DACs and there is no need to add an outboard DAC. The advantage of using optical or coax with DVD 5.1 movie sound is that you only need one cable to connect the player to the DD/DTS processor/receiver, instead of 6 cables. With DVD-A, the same situation exists. The DACs in the players will be as good as any that might be in the processor, but because of copyright issues, the first players will only output the 5.1 analog, having already been decoded in the player. The sound will be excellent, but you will need 6 cables to connect the player to your processor/receiver. Also, you won't be able to use any of the DSP modes in the receiver, because the 5.1 analog inputs bypass them.

Q Video CD is quite popular here in Asia, and I'm using my Pioneer 525 DVD player to play CDs and Video CDs, as well as DVDs of course. I heard comments that playing Video CDs in the DVD player will harm the player as their playing speed is not the same. Is this true?

A Since the players are designed to handle Video CDs, any difference in speed is programmed into the player to begin with. It will not harm your player.

Q I will soon be adding a new five channel amplifier to my home theater system, using my DSP-A2 from Yamaha as the pre/pro for the time being. I have narrowed my decision to a few amplifiers, notably the Rotel RB-985 mkII and the Outlaw 750. My question relates to the difference in specs on these two amplifiers (and other amps, for that matter). To what degree can one amplifier be judged superior to another based on specifications? If there are important specs to focus on in comparing amplifiers, what would they be?

A The Outlaw 750 has received lots of accolades, and because it is sold direct, on the Internet, it is a heck of a bargain at $1150 (including shipping). Comparably priced units, such as the RB-985, deliver less power. The 750 is almost twice the weight of the 985, indicating a larger power supply. Remember though, you don't have a place to go listen to the 750, which you would do with the Rotel that is sold through dealers. Returning the 750 for repairs or whatever will cost money. You would take the Rotel to the store where you bought it. What I am saying is that the lower price of the 750 is not without its issues. However, power amplifiers are not like speakers, where differences between brands can include huge tonality changes. Power amplifiers don't have "features" as such. There is just the power on switch, input jacks, and binding posts. I would try the 750 between the two choices you have outlined. Spec manipulation is usually a problem with mass market products, where the power is sometimes specified into 6 Ohms instead of 8 Ohms. Or, it will give the power with only one channel driven. Or, it might give the power at 1 kHz instead of 20 Hz - 20 kHz.

� Copyright 2000 Secrets of Home Theater & High Fidelity
Return to Q&A Index.