Q&A - #18 - July 1, 1997
Q 1) Do both Dolby AC-3 and DTS incorporate full frequency response in all five channels?
2) How good are the Marantz MA-500 mono block amplifiers and if they're not that great what's wrong with them (not enough power, distortion, timbre, color, etc.) and what would you reccommend in mono amps (I'm a university student who will be building his hi-fi system over a span of many years, expensive piece by expensive piece). I don't think I want to spend over $1,000 for one channel of sound.
3) Could you do a feature on Canadian speaker companies, PSB, Paradigm, Energy, etc.?
4) In 5.1 sound, is the subwoofer channel (LFE) used for general bass? Or is it usually bass from the front speakers? I know you're not supposed to be able to localize it, but then why would incorporating bass into the rear channels be different from the sixth's channel bass? Is the sixths channel's bass identical to the bass coming from the two fronts? What should I look for in a preamplifier or processor so I can add a subwoofer for the rear channels (i.e., my rear speakers can't really handle the bass).
This is all so confusing, I just want a great sounding system and I'd appreciate it if you could help. Oh yes, one more question (I know, I know I'm greedy, but hey).
5) I would like to test some of my developing electrical engineering skills, so are there any books or publications you'd reccommend on building hi-fi amps and/or speakers?
A Both AC-3 and DTS incorporate full spectrum sound in 5 of the 5.1 channels, and a limited bandwidth in the .1 channel (LFE or Low Frequency Effects).
The Marantz MA-500 monoblock amplifiers have received good reviews, and one of the reasons they perform well is that each amplifier module has its own power supply. It is rated at 125 watts into 8 Ohms, and 180 watts into 4 Ohms. The MA-700, rated at 200 watts into 8 Ohms would probably be a better choice for building a system over the next few years. There is also the choice of getting a good stereo power amplifier now (another brand), and then adding a three-channel amp later, for surround sound.
We have reviewed Canadian products already, and will be reviewing some more, but not because they are Canadian. Rather, because they are good products. We have requests in for Paradigm and PSB. Stay tuned.
In 5.1 sound, the sixth channel (the .1 channel) is for low frequency effects (LFE), but right now it appears most digital surround movies use the .1 channel as a duplication of the bass in other channels. I would imagine that soon there will be distinct effects in that channel routinely. Although bass is non-directional, it is only this way for the really low frequencies. Depending on your perception skills, you can begin to pick up the direction at somewhere around 60 Hz - 80 Hz. The directionality works based on the difference along the waveform that each ear hears the same sound. The brain interprets this as direction. The full spectrum sound in the surround channels will allow some direction cues to come from the rear, with frequencies in the 60 Hz region and above. As to adding a subwoofer to the rear channels, there are several ways. You can run the speaker cable to the sub in the rear and then out to the rear speakers from the sub. This will produce a high pass sound to the rear surrounds while the sub handles the low frequencies. You can also run a pre-out from the receiver to a power amplifier, and split the pre-out so that a coax cable also goes to the rear sub line-level input. Or you could run a coax from the pre-out to the sub, and another coax from the sub to the power amplifier, which, again, would send high pass to the surround speakers and low frequencies to the sub.
Go to the bookstore, like Barnes and Noble, and check the magazine rack for some of the amateur electronic publications, for example, "Speaker Builder", and "Glass Audio". Buy the issues that have projects in them you are interested in. Books take a long time to get published (I published six textbooks), so they are almost out of date when they hit the store shelves. Magazines will give you more of what you are looking for. You might try one of the many kits that are available as a first project, since all the parts are supplied (the only thing I don't like about kits is that there are always a few odd pieces left over, and I can't figure out where they were supposed to go).
Q I plan to upgrade my system to Dolby Digital (AC-3). I have a Nakamichi AV2 Receiver(Dolby Surround). It has pre-outs and pre-ins for 5 channels (only a pre-out for a powered subwoofer). I want to buy a DVD player and a processor for Dolby Digital. Please tell me what I need to know when I go shopping. Could you give some recommendations about brands and models?
A I'm glad you are thinking "digital". When you shop for the components, make sure that the processor has inputs that will accept the output from the DVD player. I don't think you will run into a problem with this, but it should be on your checklist. Most likely, the DVD player will have a digital coaxial output for the digital audio and an S-Video output for the video. S-Video connections will give you a much better picture than composite video. The audio outputs from the AC-3 decoder will consist of analog RCA jacks to which you connect the pre-ins on your receiver. There will also be a subwoofer (LFE) output on the AC-3 decoder. You can connect that directly to a powered subwoofer. I prefer doing it this way rather than routing the LFE channel sound through the other channels and extracting it from the subwoofer output on the receiver.
Q If I purchase a television with a good comb filter (3D digital) and use S-Video inputs (not component
inputs), will the visual and audio result be significantly inferior to
a system where component inputs are utilized? My understanding was
that a good quality comb filter would reduce some of the advantages of
component input. True, false, or somewhere in between ?!?
A Most consumer video sources, such as laserdisc players, will not have as good a comb filter as is present in top notch TVs. In such cases, the composite video input should be used, so that you can take advantage of the comb filter in the TV. The audio will be the same in either case, since the S-Video and composite video connections carry the video signal only, not the audio. Component video is the best (outputs available on some DVD players and inputs on some newer TVs), because it contains the color in its original uncombined form, along with the separate luminance. So, component video has three signals, two of which are color, and the third is the luminance (brightness), while S-Video has two signals, one of which is the combined color and the other is the luminance, and, finally, composite video has the color and luminance combined into one signal. The comb filter separates out the color and luminance. Because they overlap in frequency, there is an artifact that results, called dot crawl. This appears along the edges of contrasting colors, such as yellow and blue. It looks like a moving escalator. When you go to the TV store, look at the inexpensive ones compared to the top of the line. The better the comb filter, the less the dot crawl. So you should use the device with the best comb filter to separate them, whether it is in the player or the TV.
Q I bought an HK AVR20, two 8 Ohm main speakers, and two rear speakers. Can I connect a 6 Ohm center channel speaker to my amplifier? How will it influence my main speakers?
A I would say that you will probably have to turn the volume of the center channel speaker down somewhat more than if you were using another 8 Ohm load for the center channel. If the speaker is a different brand than your front mains, there might be a tonality difference. You can adjust this with an equalizer (EQ). We have surround sound equalizers on hand routinely, since the center channel speaker is affected by reflections from the front of the TV picture tube. A typical problem caused by TV tube reflections is "chestiness", which is a peak in the 120 Hz - 160 Hz area. Other problems we like to correct with EQ are 80 Hz "boominess", 800 Hz - 1 kHz "nasality", and 4 kHz - 6 kHz "sibilance". They can be present in any speaker, except subwoofers, which often have the boominess problem, but usually not the others. Speakers can have dips or peaks at any frequency, of course, but these are ones that we particularly don't like.
Q I have had a Forte model 4 pure class A (50W into 8 ohms) and the Forte F44 preamp for a number of years; my speakers are a pair of Martin-Logan Aerius. I've loved the performance of this setup as listening to high quality music has been my focus and still is primarily. I am now trying to decide whether to integrate this equipment into a home theater setup that will allow me to
do both, or to keep it as a separate system. Not only would the latter
approach be potentially more expensive, but I'm afraid that if future CDs are
encoded with surround sound, then I would be missing out on that. What
equipment suggestions would you have for additions toward my goal of
developing a home theater?
As a corollary to that, I have to decide which orientation to use in a future
media room that hasn't been built yet. The room is 14' x 19', and I'm
struggling with whether to put the TV on the long wall in that room (which is
fairly dark and in the basement) or on the short wall in another similarly
dimensioned room (the latter room however has sloping ceilings on both sides
and has alot of windows). I've never found anything in my reading that helps
to make this decision from an acoustic standpoint. Would my electrostatic
speakers function better if they were placed on the long wall in the basement
room? The manual recommends that "the best side wall is no side wall", which
seems to be a reference to the dipolar configuration of the speakers and the
need to avoid any side waveform reflections.
I realize this is a longwinded question, but you don't realize how much this
is perplexing me. I don't want to make any stupid decisions, and want to
choose both the right equipment and the right room. If you can help me,
thanks in advance. I've made little headway with reading materials and local
salespeople.
A Electrostatic speakers are great in home theaters. We heard the Martin Logans in San Francisco at the Hi-Fi '97, using them all the way around, including an electrostatic center channel. Although most of the surround sound CDs (DTS) that we have heard, result in putting you in the middle of the orchestra, it is only a matter of time before the recording engineers get the technique down. Probably something like discrete three channel stereo in the front, and discrete ambience in the rear. Pure Class A amps usually have huge power supplies, so your power amps will probably be fine for home theater. Perhaps get another stereo Class A power amp for the rear, and maybe a Class A monoblock for the center. Another pair of Aerius for the rear will do just fine. You should look into their electrostatic center for tonal balance. Because of your power amps, I would suggest getting a top quality processor, such as Meridian, Lexicon, or Theta. Electrostatics do perform best when not near the walls. However, the 14' wall may be sufficient since your speakers can be about 7' apart, leaving 2.5' between each speaker and the side walls (taking into account the speaker itself). But, you should experiment with the room you already have, putting the speakers closer and closer to the walls until you hear objectionable reflections. That will be the limiting dimensions on which you can base your decision.
Q I have a home entertainment system in my basement that's used mostly for movies and sometimes for music. It consists of a Pioneer VSX-D704S A/V receiver, two Cambridge Soundworks model 8 bookshelf speakers, a Cambridge Soundworks Center Channel Plus that's placed on top of a 35" RCA TV, two Cambridge Soundworks rear dipolar speakers, and a Cambridge Soundworks Powered Subwoofer in the front left corner of the square room. I'm not completely satisfied with the sound when it comes to movies. If you have any comments and recommendations I would be grateful.
A Probably the most dramatic improvement you can make is the addition of a more powerful subwoofer. Something that will play really deep and clean, and move a lot of air, like a Velodyne F-1500R. That runs about $1,600. Then, get an AudioControl Phase Coupled Activator, at $299 (reviewed in February, 1996, in Secrets), which goes between your receiver and subwoofer. That will allow you to get 20 Hz - 30 Hz sounds, even when the movie sound tracks only go down to 40 Hz. Powerful, deep bass is very important to the home theater sound experience. The combination I mentioned above will make your entire home theater room shudder, and give you what I think you are missing in your present system.
� Copyright 1997
Secrets of Home Theater & High Fidelity
Return to Table of Contents for Q&A.
