Q&A # 110 - April 6, 1999

Staff

Q I have a Parasound HCA-2205A five-Channel high current amp. It's rated at 220 watts x 5 at 8 Ohms. The power requirements state: 110VAC-120VAC, 2200 Watts. What line conditioners can withstand the power requirements of my amp, along with other components?

A The power handling capability on AC line conditioners is sort of like the rating on your circuit breaker. It may be 20 amperes, but for a short time, more than 20 amps can flow. It is unlikely that you would ever be outputting 220 watts in each of the five channels. More likely, you would be sending maybe 20 watts to each of the channels, and every once in a while, with a kaboom or crash, you might get 150 watts in two or three of the channels for half a second or so. As a result, the line conditioner can be rated lower. I have several Rotel RLC-900 line conditioners that have turn-on delay for the power amplifiers, which is a feature I really like. This unit retails for about $200 and is rated at 1,300 watts for the power amplifier sockets. I have used it with two 750 watt monoblocks, plus several other small components plugged into it at the same time, and never had a problem.

Q You mentioned that balanced components have low noise as a benefit. My unbalanced audio system has very low noise, so wouldn't it sound just as good as a balanced system?

A The effects of a balanced component on the sound are not fully understood. Some feel that it is really just a matter of lower noise. Music has lots of fine detail that can be buried in hum and hiss, and even though these musical details are subtle, their absence can make a big difference in the listening experience. The ability to reduce noise in balanced circuits is a result of Common Mode Rejection, or CMR. This means that noise which is common to the + and - portions of the signal path is "rejected" to a measurable degree. Both balanced and unbalanced circuits have CMR, but balanced circuits just have an easier time doing it. I think that most of what balanced circuits do for the sound quality is probably because of very low noise. The fully balanced amplifiers that I use here in the lab are absolutely dead quiet when the CD is in the pause mode. I cannot tell that the amplifiers are on, even with my ear right up against the speaker, and the preamplifier turned half way up. So, "low noise" is a relative thing. Try setting your preamplifier volume half way up, with all your components on, but nothing playing. If you hear any hum or hiss, then a set of fully balanced components will likely improve on that situation.

Q I am playing around with building a sub/sat system using the Manger MSW (Bending Wave Tranducer, frequency response of 80 Hz - 33 kHz, for more info see www.techmdb.com). The recommended crossover is 150 Hz, which is too high to cross over directly to a sub. I'm looking for ideas which would allow me to cross over directly to a sub. I am going with an active crossover and my understanding is that, by using a very steep slope like 48 dB/octave, I can come closer to a driver's cutoff. I also think that using a sub that is along the same plane as the sats and which also fires in the same direction as the sats would mask a higher crossover point. Any other ideas or suggestions would be greatly appreciated.

A The problem with subwoofers reproducing frequencies at 90 Hz and above is that they tend to sound boomy. At 120 Hz, they can sound "chesty" (meaning that voices sound like the singer has been smoking 3 packs a day for a long time). The reason is they are large drivers in large boxes with very little or no damping material. This makes them resonate. I never use a subwoofer at a crossover frequency above 70 Hz. A smaller subwoofer, such as the Veloldyne HGS-10 or Sunfire, would be better for this task because they have smaller enclosures (yet plenty of power). That could reduce the boominess, but you would likely still encounter chestiness. You can try it and see if it works. If you get chestiness, then you might use a 5" driver in a single enclosure (one for each channel) to handle 70 Hz - 150 Hz, and a separate subwoofer for the < 70 Hz signal. In this case, you would need an additional two-channel power amplifier to drive the 70 Hz - 150 Hz speakers, and the necessary active crossovers between the preamp and power amps. Keep in mind that bass is omnidirectional only below 50 Hz. Above that frequency, you can begin to detect where it is coming from.

Q I'm in the market for purchasing a multi-channel receiver. One of the receivers I am considering is the Marantz SR-96. I am concerned that this receiver was manufactured in 1996, thus using older technology. Should I be concerned? Also, this receiver offers THX and DPL processing with a 5.1 input, so if I were to get an outboard processor for DD and DTS, would the THX processing further enhance DD and DTS?

A Receivers with a set of 5.1 input jacks for outboard receivers tend to bypass all DSP when using those 5.1 inputs so that all you really have is the volume control and power amplifiers. Now that very affordable receivers with DD and DTS processing built-in are available, I would not recommend getting a "DD-ready receiver", i.e., a receiver with a set of 5.1 inputs for use with DD and DTS outboard decoders, unless it is at substantial discount. This does not include components that are upgradable internally with optional cards or software. Such units are designed so that the upgrades will go through whatever DSP circuits that they have, as well as THX. The various DSP modes available on receivers will do what THX does, but they are not called THX for copyright reasons.

Q Did you have chance to test the "newer" version of the ACT-3 after they solved the hissing problem? I have about US$1800-2000 to spend on a DAC/preamp/processor. Should I get the ACT-3 for an all in one or go for separates? What would you recommend for the separates?

A Unfortunately I haven't had the pleasure of hooking up with the revised model. But, even the first version was very respectable as a DAC/preamp. As a surround processor, I can't seriously fault it. All around, it's very refined-sounding. You can do better, either with a separate DAC/transport or even a very high-quality CD player running straight into a dedicated two-channel analog preamplifier. However, then you still need a processor. You could also get a better processor/preamp such as the Lexicon DC-2/MC-1 or Meridian 565/861, all of which are awesome in two-channel performance (only if using the digital input with a good transport, as any analog input simply converts to digital which adds an unnecessary step of conversion). Either way it costs MUCH more for a little improvement, and some additional useful features. Unless you've got literally many thousands invested in speakers and amplifiers, I wouldn't recommend taking that path, but rather staying in your allotted budget.

When I made the comparison with my CD player, one needs to remember that CD players have an inherent advantage compared to outboard units in that the master clock controls the transport and the output of the digital bit-stream from the ring buffer to the DAC. Outboard DACs, whether in an outboard DAC or in a digital surround processor, are receiving an inherently compromised signal in terms of jitter, and have only an imbedded clock to work with, and then must reclock the signal before conversion. Some are better at attenuating jitter than others, and some transports can spit out the signal with less contamination than others, but in essence, it's a different issue to address. So, a $600-$700 CD player from a company with very efficient manufacturing can sell an item merely for the sake of bolstering a reputation as opposed to actually making money, and they have an incredible advantage in straight two-channel performance compared to a unit which must not only accommodate a more difficult chain of conversion, but also provide more channels of conversion and output, processing, and level control.

The advantages of the ACT-3 are that you get all the necessary components of a complete system, and because the architecture of the processing makes it upgradeable, you're not going to be left out in the cold if things such as Firewire (IEEE1394) become common. At least, that's the idea. Though not formally reviewed, B&K's Ref 20 (roughly $2500) is another excellent, somewhat future-proof product, which I think offers a slightly more open top-end like the JVC CD player, but also lacks the ultimate performance of dedicated two-channel playback systems. Both the ACT-3 and the REF-20 are REALLY close though, a far better value, and altogether a good investment in the long-run as far as digital/processing technology goes. At the same time, they're bare bones when it comes to features such as lots and lots of DSP modes.

For those who want a less costly temporary fix, some of the better receivers for $999 or less offer lots of inputs, DD and DTS processing, and very respectable audio performance. Ironically, because they're so inexpensive, they usually have power supplies which make them more suitable as preamplifier/tuner/processors. And, over 3 years, they've only cost you as much as cable TV.

Bottom line, if the ACT-3 has eliminated the background noise issue, and the features accommodate your needs, though there are many options that may approach or meet the performance level at or near the price, I know of none that definitively surpass it. Factor in that it's one of the least expensive processors that can actually incorporate evolving formats, and it's got a real edge in the long-term picture. Plus, it's a brick (as in heavy duty build quality). Sound is a subjective evaluation, and you're going to take the ultimate responsibility. I know, too many choices. If I hadn't blown my A/V budget for the near future recently, I'd have the same problem. I'm just thankful that companies lend us this stuff for review.

Q I am building a home. Should I prewire for IEEE1394? What about signal type, speaker type, and gauge? Should I install acoustic insulation within the walls of the home theater room? If yes, what type and how much? Hopefully, you know if someone like THX (or any other reputable company) provides home theater construction guidelines?

A Prewire for everything you can think of, running to one or two base locations, where you can hook into equipment or simply provide a junction between areas. Category 5 network cable might do the job, terminated to the IEEE1394 connector type. Category 5 cable is relatively flexible in terms of function. You can run it for phone, computers, and even use spare conductors, perhaps doubled up, to active contact sensors or voltage triggers in different locations. I'd suggest at least two runs of RG-6 coaxial cable (or its foamed counterpart CAC-6 which has better bandwidth due to a lower dielectric constant) to every location you think you might remotely want video equipment (TV, DTV, Cable, DSS) or digital audio equipment. In addition to two or four runs of category 5 network cable, which is relatively cheap, line level cable runs (shielded, twisted pair will accommodate both balanced and unbalanced operation) and speaker wire, you might consider fiber optic cable in choice locations as well as long as you've got the walls open. You don't have to terminate it until possible future use, and it won't corrode, though you might want to make sure water doesn't get inside it by putting silicone on the end. There are some proprietary wires that AMX, Lutron, and a few other companies use, but unless you're looking into comprehensive home systems like that in the near future, I wouldn't get too worried about it, though it couldn't hurt other than possible wire tangle at the base locations.

It makes things much easier if you label the wires as you go, either with a permanent sharpie marker or preferably wire labels that don't smear. It will save a lot of work later on when the walls are sealed up and you're trying to find a specific set of conductors. Also, try to group the wires by type and function, perhaps bringing them down or up into the stud bays though separate holes, or even into separate stud bays. General wiring tips, be gentle and patient. Be careful about drilling through your house, and don't yank on the wire too hard. Speaker wire and heavy duty coaxial cable can take a lot of abuse, and line level cable's not too bad, but CAT-5 is fragile, which is part of the reason it's nice to have multiple runs, even if you don't think you will need them all. The stuff is pretty cheap, less than 10 cents a foot if you buy 1000 ft spools, so it's worth it. Stay away from AC electrical wire if you can do so (3 feet or so at least) and cross it at 90 degrees where necessary. Try to keep data wires away from the line-level audio/video wires. When running wires through walls, keep them away from the edges of the stud, or put up nail guards, to avoid getting your cables punctured when putting up sheet rock. In addition, try to keep the wires neatly wrapped with tie-wraps.

Under the house, keep the wire off the ground so that any possible rodents don't start chewing on it. In case you worry about forgetting something to key locations, you can also run a couple of Smurf tubes (blue accordion-looking tubes) with some pull-strings left inside. So long as you've got the walls open, try to avoid running wires directly under carpet. Run either under the house, through the walls, or in the attic, as cables under carpet can easily become pinched or pierced. Also, if possible, run the entire Home Theater on a single AC 20 or 30 amp AC circuit. This doesn't mean a single outlet, only that the outlets (including those possibly used for powered subwoofers) have a nearby common source from a single breaker. Even though an array of very large power amplifiers have the potential to bring an average 15 amp AC line to its knees, more importantly, the heavier gauge wire, and the common path to ground, will alleviate ground loop problems to an extent. Code usually requires that all circuits ground at the breaker box, although the AC outlets on the circuit can all be daisy chained. I wouldn't hop from one to the other too much, as it compromises the integrity of the ground a little. Perhaps run an additional heavy gauge grounding wire to a central location in the room ("star grounding"). Keep flourescent lights, dimmers, and motors on a different circuit. Make sure to ground the TV cable to the same ground or use an isolator (Mondial make an exceptional one, Jensen makes a very good and much less expensive model).

Speaker wire usually carries only low bandwidth AC, roughly 15 Hz -20 kHz. It is important, if only for the sake of meeting building code, that your wire is rated for in-wall use. Besides, wire designed for that purpose will usually stand up to more pounding, even if only because of the extra jacket. I like 14-4 (four conductor, 14 gauge) for all around use. If you only require a single pair, you can double up the conductors to make a low-inductance equivalent to eleven gauge in terms of resistance. Or, you can terminate it to a wall plate with four speaker binding posts which gives you the option of bi-amping, or driving two pairs of speakers, including passive subwoofers, with the regular speaker, or even adding side speakers not so far away from the rear channels. However, in that case, it would be better to just run a separate set of cables and put them into a box with a blank until they're needed. Plus, if the sheetrocker drives a nail through a couple of conductors, or grounds one of them, you're not out of luck. As for specific types of cable, Liberty and Belden both make durable, reasonably priced cables of this and other kinds. Monster Cable also makes a variety of cable, which is slightly more flexible, but at the same time, the soft jacket often catches edges which makes for an occasional problem. It's also more expensive. Nordost cable is great if you're going to put them under carpet.

As to room treatments and wall insulation, you're getting into an area which needs very specific attention. Fiberglass insulation works nicely, but just as important is the construction of the wall. If possible, it's good to decouple the inside wall from the outside wall, building an extra, suspended wall, where studs touching one side of the drywall don't touch the other. If you really want to get into this, you need an acoustician who specializes in small environments (not concert halls exclusively). To really do this right (a luxury I can't personally indulge in sense I rent) you should soundproof your room, disperse and spread out standing waves, and control initial reflections. If you don't mind spending the money, you might consider THX training for a quick and somewhat thorough course in acoustics. I went to a CEDIA mini-course on the topic recently, and learned a few things. I also got some modal analysis software put into Excel format. Of course, if you have specific questions, we're always glad to add our input.

Put insulation in the wall, on the wall, and use it as the wall itself, if possible. The last is kind of hard in many situations. You don't want to make the room too dead, but the general rule is to put absorption on the floor and side of the wall the screen is on, and dispersive items (like book shelves) along the rear and perhaps even ceiling. To decide locations for absorption, sit at the different listening locations, and have a friend move a mirror along the wall until you can see each of the speakers. Put some masking tape on each area, and know that's what you have to address. Also, walk around the room and clap your hands once the walls are up and you have most of the furniture in. When you get to spot that has a significant slap echo, put absorptive or dispersive furniture or treatment panels on one of the walls, staggering the treatment between two parallel walls if necessary (treatment on one side for a couple feet, then on the other) so that you don't have a lop-sided soundstage in terms of left to right. As a last step, consider equalizing the subwoofer in 1/6 octave or 1/3 octave increments. One octave increments or more won't do much good. Pull down peaks, but don't boost any dips more than a couple dB, as it's pretty much a lost cause to throw output into a canceling situation.

For a dedicated home theater, THX has a whole bunch of information, though I don't think it's available in any convenient, inexpensive method. You can either do the footwork yourself at the library or by asking questions at a variety of places, attend their dealer/installer training, consult with someone who has and hopefully paid attention (no guarantee of that) or hire an acoustician. None of these are inexpensive when it comes to either your time or money. I would take the first two, in addition to the last, if neither are of critical concern. If you're buying your equipment from a THX certified dealer, you might be able to milk them for information for "free." However, to really get in-depth would take hours, and they'd probably want compensation, which to be truthful is fair.

Q I currently have a Yamaha RX-V692 receiver with 5.1 analog inputs and a Yamaha DDP-1 Dolby Digital processor. Can I also connect an outboard DTS processor, such as the current Millenium model, with high quality Y-cables, or will that degrade the sound of both substantially? I know I could add DTS processing to my DDP-1 through MSB for about $700, but I have found discounted outboard processors for much less (plus I only paid $150 for the DDP-1).

A Yes, you can use two outboard processors with one set of 5.1 inputs, but the way to do it is with the pass through that is available on most DTS processors (the companies built them with that in mind). This lets you use one set of cables going to the 5.1 inputs on your receiver. Using Y connectors between two sources and one set of inputs on your receiver is not a good idea.

Q I have a Dolby Digital 5.1 speaker setup and use a Radio Shack sound meter to get all the speakers levels matched up. But since the subwoofer is in a whole different frequency range, I'm wondering what level I should be setting it at. Right now I'm adjusting it to what feels right, but I would like to set it to match the studio's mix.

A Setting the subwoofer to what feels right is exactly what you should be doing. Theaters at the Cineplex are too loud for my tastes, and I watch movies at home at a level that is pleasant to me. The subwoofer is part of the whole system, and I adjust that to my personal tastes too, which is generally turned up a bit to compensate for the lower volume of the main channels. There is no standard for studio mixes. It all depends on the producer's intent for each movie, and there are lots of different producers out there. And, if the mix doesn't suit me, I turn various channels up or down (or off it is a lousy movie) depending on my mood. Your SPL meter is fine for general setup, but after that, adjust the various knobs until it feels good, just as you are doing right now.

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