Q&A # 48 - January 28, 1998

Staff

Q How much of a difference can a specialized CD transport make? I currently have a Parasound C/DC 1500 which I connect with coaxial digital connector to my Theta Casablanca, which contains the standard D/A converter boards. I recently tried comparing this setup to a Theta Digital Jade CD transport with the same D/A converter. I could not hear any audible difference.

I have seen reviews of different transports in which the reviewer is able to characterize the individuality of each component under review. All my testing indicates that it is not this simple. It seems more likely that a specialized transport goes into the same category as high-end speaker wire, interconnects, treatments, and accessories.

A There is much more difference between a mass market CD player and the high performance players, than there is between the various high performance players, transports, and DACs. The Parasound C/DC and the Theta are both high performance components. Secondly, a reviewer usually has listened to so many components, that the subtle differences become apparent. In any case, the trend right now is a move back to high performance one-box players rather than separate transports and DACs. Sounds to me like you don't need to upgrade.

Q I have a mid-bass hump in my listening room. Can you tell me the preferred method of equalization? If it is active EQ could you recommend a model that would work well with both music and home theater. If it is passive can you tell me how to make a bass trap or direct me to a source of plans as I am pretty handy. The bass traps I have seen are fairly expensive and seem like they would be easy to duplicate. My budget is about $1,000. Thanks for what I consider the best home theater site on the net.

A The BEST way to reduce the mid-bass hump would be to use bass traps, since an active EQ puts additional items in the signal path. However, the EASIEST way is to use the active EQ. This is especially so with low frequencies, which are more difficult to attenuate with traps than higher frequencies. So, start by experimenting with bass traps. You can do this by putting large pillows in each corner of the room, stacking them about 5 feet high (that's a lot of pillows, but bed pillows, rolled up blankets, and couch cushions should work for the experiment) and adding pillows or subtracting pillows until you get the effect you want. If it works, you can make permanent traps by rolling up an egg crate mattress pad (available at linen stores for $30) and putting it into loosely woven material that has been sewn into a cylindrical cover about 20" in diameter and 5 feet high. If that does not work, then you can go with an active EQ. AudioControl and Rane make very good ones, and if you are going to use it with home theater, you should get an EQ with enough channels for that. A unit such as the AudioControl Rialto or Bijou will do it. You might find that EQ will be useful in some of the other channels as well, such as the center, where bass loading off the front of the TV screen is common.

Q Following your oft-recommended advice, I have added a Carver AV-705x to serve as an external amplfier for my Yamaha 2090. My question is this: do I still have to worry about turning up the volume knob too loud? Can the receiver be overdriven as a pre-amp?

A Any amplifier can be overdriven, but the Carver AV-705x is very powerful, and it is unlikely that you would overdrive it at humane listening levels. Generally, most amplifiers operate well within a volume control setting up to about the 12 o'clock position on the preamplifier. A reasonably loud situation, without distortion, occurs with the volume control at about 10 o'clock. Unless you had an input signal that was unusually high (some CD players do this), you would not overdrive the preamplifier in the receiver. A clue to an overdriven preamplifier would be a loud, distorted sound when the volume control were set at, say, 8 o'clock (with the 0 volume setting at 6:30). So, have fun and blast away, but be careful of your ears. The big amplifiers these days are capable of delivering SPLs that are not good for our hearing.

Q I am new to home theater and just purchased my equipment, which consists of an Energy Take 5 speaker system, Denon AVR-1400 receiver and Yamaha SW-2 sub. I've noticed on some Pro-Logic movies, there seems to be a huge variation between quiet dialogue sections of the film and loud sound effects. If I increase the master volume to allow me to hear talking in a quiet scene, I'm blown through the back wall during the next explosion or gunfight scene. I tried increasing the center channel volume only, but it seems that a lot of the louder effects come through the center channel. Also, per the suggestion of the salesman who sold me the receiver, and contrary to what the receiver's manual instructed, I changed the center mode from Wide to Normal. Not much change, though. Like I said, some, but not all movies are like this where I'm adjusting the volume a dozen times during the movie. "Contact" and "Mars Attacks" are among them. So my question would be, is there something I'm doing wrong on my end, or is this the way these soundtracks were produced and the blame lies there?

A Welcome to the world of large-dynamic-range movies. The fault is not yours at all. It is the way the sound track is mixed. This is why the dynamic range selection feature is present on some of the new receivers. Since most of the latest films are primarily mixed for DD, the huge dynamic range carries over to the Pro Logic mix. It shouldn't, but it does. Part of the "blown through the back wall" phenomenon you are experiencing is actually clipping of the receiver's amplifiers. This is characteristic of all the mass market receivers. The power supply is the most expensive part of the preamp/power amplifier, and in order to give the mass market a lot of features in a one-box package, the power supply is not very big. You could add an outboard amplifier to the pre-out jacks on the receiver (I am not familiar with all of Denon's models, but there are usually a set of pre-outs for the front left/right/center on Denons), and that would give you some improvement.

Q Can you tell me the big differance between a high wattage, say 125W per channel amp, as opposed to a high current amp that has a wattage rating at 75 watts per channel, but sells for the same price or more than the amp that's rated at a much higher wattage? I want to upgrade my Dolby Pro Logic receiver to a Dolby Digital receiver, but I want to know what to look for, in terms of a high current amp or high wattage amp. My budget is around $1500.

A An amplifier that is designed for high current is one that is rated into 4 Ohm and sometimes 2 Ohm loads (speakers), while one that is not specifically high current is usually rated primarily for 8 Ohm speakers, but will do "OK" with 4 Ohm speakers. The term "High Current" can be just a marketing technique too, since high current is a relative thing. With any conventional amplifier, it will deliver higher current at 4 Ohms than it will at 8 Ohms, with the same voltage. "High Wattage" is also relative, since someone who has a 200 watt/ch amplifier might consider a 400 watt/ch amplifier as high wattage, while someone with a 125 watt/ch amplifier might consider the 200 watt/ch amplifier as high wattage. So, there aren't any definitions here, for high wattage or high current. If you want to keep your options open for future growth of your home theater system, I would suggest getting a receiver that has DD built in, and a set of pre-out jacks so you can add a larger five channel power amplifier later. If you want total upgradability, then get a receiver with a set of pre-in jacks AND a set of pre-out jacks, so you can add outboard decoders for DD and DTS, as well as the outboard power amplifier. Mass market receivers are primarily modest current products, for 8 Ohm speakers, so I would suggest, as compliant with your $1,500 budget, that you buy something like a mid-priced Yamaha (they have the pre-ins and pre-outs) and an outboard DD decoder. That should run you about $1,000 total, depending on discount availability. Later on, get a nice five channel amp like the Carver AV-705. 

Q I just bought a B&W CC6 and a pair of B&W 602 speakers, and the salesman mentioned that there was a 50 hour break-in period. Exactly what happens to the speakers in this break-in period and should I resist turning them up too loud until this time is over?

A Speakers have moving parts, and they change over time, with most of the change occurring early. Typical speakers are a bit "tight" at first, with the anticipation that they will loosen up to about the right point before they settle down. What I hear most often is a slightly laid back bass and, occasionally, an overly bright tweeter, until the break-in period is over. It will be perfectly alright to play them reasonably loud right away, and this will simply speed up the break-in period. What I do is turn the system on with a CD in the "Repeat" mode, at moderate volume, and then I do other work or leave the house. The system plays all day, so I don't have to wait for 50 hours of regular listening to get through the break-in period. However, it is never a good idea to play any system really, really loud, to the point you are gritting your teeth, no matter whether the system is new or "broken in".

Q Is it possible to use a splitter to distribute the digital signal from the LNB of a DSS satelite? I know for multiple TVs and different programs I need extra receivers. However, I don't see why even a raw coax digital signal can't be split just like cable. I mean it's still a voltage signal that can drive two or more parallel loads, right? Is there something I don't know or are they just charging $100 extra for a $5 splitter.

A There are some splitters out there that will split a DSS signal. I have used one from Monster Cable which has a wider bandwidth than the average Radio Shack box. If you use a splitter that does not have the bandwidth, you will end up with a terrible TV image.

Q Most recent high end RPTVs (Sony XBR and Hitachi SBX) list in their specifications 1000 lines of horizontal resolution (the number of vertical lines that can be displayed). Mitsubishi's 40" Diamond Line direct view TV lists 700 lines of horizontal resolution. Can we expect that future decoders for HDTV will allow their full utilization? If not, then what is the significance of this specification? Will the digital signals from the DBS satellites require new receivers to handle HDTV transmissions? What presently limits DBS's horizontal resolution?

A Manufacturers tend to fluff up the spec to be the leader in the "Spec Wars."  The Toshiba that I am using claims it has 700 lines of horizontal resolution. But when a signal generator is attached, the TV just barely does 480. There is no one standard that all the manufacturers use to determine the overall resolution. They use whatever makes their TV appear the best.

Not sure on the status of the new DBS receivers. When HDTV is launched, most of the broadcasts will come across UHF. Unity Motion, a rather new company, will have an HDTV satellite up and running in 1998. They will first begin broadcasting 525P (Progressive) then add the HDTV signal when it is ready.

The resolution is determined by how much bandwidth the signal has. DVD has a bandwidth of 6 MHz, which equates to about 480 vertical lines of horizontal resolution (80 lines/MHz). The lower the bandwidth of the signal on DBS, the more channels they can squeeze into the space. It's all about money, and currently they make more money by offering consumers lots of channels.

Q I'm currently using a regular RCA cable for connection on my CD player and new digital receiver. I am pleased, and right now the sound is great. So, is upgrading to an optical cable for connection worth another $40? If so what are the advantages?

A There are a couple of advantages to optical cable. One is that, since the connection is not electrical, no ground loops (hum) or noise introduced by the cable acting as an antenna can occur. Secondly, impedance matching problems are eliminated, also because the connection is not electrical. If you are using good digital coax cable to send the digital output from your CD player to the DAC in your receiver, and you are happy with the sound, no change is needed.

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