Q&A # 233 - June 8, 2001

Staff

Q Your article at http://www.hometheaterhifi.com/volume_3_1/v3n1k.html seems to be incorrect as describing the speaker as a push pull. It's a push push or a pull pull, if anything. At least from all the other sites I've read that describe them. Pressure is supposed to be exerted (push) by one cone while it is simultaneously released by the other (pull). In the speaker in that article you have two cones pushing into the internal space simultaneously.  According to the diagram you essentially have two drivers in a sealed design. One is turned around and has some kind of pseudo-port. But other than that it is the same as putting two drivers in a sealed enclosure, but move out of the box simultaneously.

A Although the air in the enclosure is compressed by both drivers at the same time, one driver (the one on the front of the enclosure) is "pulling" inward, while the other driver (the one mounted in the slot on the bottom) is "pushing" inward. In other words, the cones are moving in opposite directions with respect to their baskets, but they are both compressing or decompressing the air in the enclosure simultaneously. Soundwise, this results in the cancellation of even-ordered harmonic distortion.

Q I have the following home theater system: DVD player optical connected to the DTS Millennium decoder (manual mode), which is connected by 6 RCA to a Denon AVR 3200 Dolby Digital receiver. I would really like to upgrade the sound (still having the DD and DTS sound) by connecting either a) a 5 channel THX or b) a combination of 3 channel (to power the front left/right/center) + 3 channel amplifier (to power the rear left/right/center) THX both. The brand will be Denon or Rotel and power of 125 Watts each channel. What will be the cheapest solution between a) or b) regarding power and sound quality? What will be the advantages and disadvantages for a) and b)? What will be the connections in each case? (Use the pre-outs of the Denon + use the rear outs of the Millennium?)

A The connections would be the same regardless of whether you have six channels of amplification in one chassis or have them spread out in two chassis. (There are some six-channel amplifiers out there.) The pre-outs of the receiver go to the Millennium, and the outputs of the Millennium go to the inputs of the power amplifiers. The disadvantage will be in the price for six equivalent channels in two chassis, since the cost of the chassis will be doubled with two of them. Since you are looking for the least expensive solution, get the five channel amplifier, and use one of the power amplifiers in the receiver to drive the rear center.

Q I'm buying my first home theater ever and was interested in purchasing a progressive-scan HDTV as well as a progressive-scan DVD player. The problem is I'm not sure they are worth it yet. Actually, I'm not sure WHAT I should  be looking for. I know progressive-scanning is better than interlaced displays, as evidenced by the computer world, but there don't seem to be many television displays supporting this yet. Also, all but one of the progressive-scan DVD players you've tested failed half of the tests in
your  December 2000 DVD benchmark.

Then there's THX, which I know is pretty much the audio standard a lot of people look up to, but also seems to have some video standards as well. The  Camelot Roundtable, the best progressive-scan DVD player you reviewed, doesn't support it. Should I care? I have a few THX DVDs and I know they work without THX gear since they play just fine on a DVD-outfitted PC, but how would I hear, or see, the difference? Would a THX-certified receiver work? Again, SHOULD I CARE?!?

I need help, quick! What to buy? What to do? There're so many options available and so little information I'm tempted to get a 27" with integrated VCR. And lastly, I need speakers! What can fill up a 17x30 space?

Here's the home theater setup I worked up! I won't say price is no object, but I'll pay for reasonably priced excellent equipment.

Pioneer Elite PRO-510HD projection TV, or Toshiba 55HX70, Camelot Roundtable DVD player, or Pioneer Elite DV-38A
Onkyo TX DS989 surround receiver, or Pioneer Elite VSX-29TX, or Integra  DTR-9.1

A Don't panic. You don't have to buy anything tomorrow. Relax. Setting up a home theater is a pleasure. Take your time listening and looking. I would suggest getting a progressive scan DVD player even if you don't get a progressive scan TV right now, because eventually you will get the progressive scan TV. There would not be any use in then having to replace your DVD player. Our latest Benchmark tests (last weekend) showed that none of the players (we tested 19) passed all of the tests, the Camelot included. One of the Panasonic players (price about $700) did very well. We are compiling the data now. It was exhausting for the staff. They went to bed typically at 3 am each night. Anyway, hold off buying the DVD player until we finish putting together the results. Integra kindly provided a DTR-9.1 for John Kotches to use in the audio tests of the DVD players, and it is the best receiver I (JEJ) have ever listened to. It is the only receiver I have ever seen that I would be perfectly comfortable having without an outboard power amplifier. I cranked it up with some intense 5.1 DVD-A music, and it just coasted along at 105 dB SPL, with no obvious clipping. It is a very fine product. I think you could comfortably buy the 9.1 right now, and you would be gloriously happy. As to the TV, I would suggest going ahead with a 16:9 HDTV model. They have really come down in price, into the $2,000 range. Getting one that is HDTV-ready (meaning no HDTV tuner is included) will still allow you to watch DVD movies in progressive scan, and it will be quite a bit less expensive too. Have the dealer connect a progressive scan DVD player to the various models you are interested in, and check out the image when the DVD player is outputting progressive scan vs. outputting interlaced. Different DVD players and TVs have different quality scalers.

Q I recently put together a system that uses a Yamaha RX-V596 and a Mission FS2-AV speaker system. The Yamaha does not have an option for multichannel output of a purely stereo source. Is there a way that I can output audio to more that just one pair of speakers? I have an old Sonance Amp selector - Speaker switcher/distributor and have thought of running the rear channels as well as the b speaker set from the amp through this. What do you think?

A The 596 has Pro Logic as well as numerous DSP modes that will convert two-channel stereo to sound that comes from all the speakers. This is not 5.1 discrete, but it begins to approach it. However, taking two-channel stereo and turning into surround sound does not always sound very good. I have found that piano in particular sounds terrible when surround sound DSP modes are applied. I think what you are referring to is just having stereo in the rear as well as the front, but un-processed. If you use the A and B speaker selectors both on at the same time, the two left channel speakers and the two right channel speakers will be wired in series to prevent amplifier overload. This will work, but you need to have all the speakers the same, i.e., impedance and sensitivity.

Q I have an audio system with a Sherwood 6090 receiver and some older Acoustic Research speakers (model # unknown). I recently bought a Sony Wega 27" TV - most basic model - hoping to achieve better sound by using my audio system and speakers. A local audio salesman told me that the simplest way to do this would be to run cables from the audio out section on the back of my TV to the Auxilliary audio in section of my receiver. He then suggested turning on the TV, using the built in speakers on the TV for what amounts to a center channel and using my audio system speakers for left and right sound, and then adjusting the TV volume and the receiver volume until I got the sound I wanted. (I know this isn't an ideal system, but it seemed to make sense using the components I have). I have done this, and it seems to work.  The problem is that the audio speakers are putting out an irritating hissing sound in addition to the TV sound. They do not make this sound when I am listening to CDs. Do you have any suggestions as to the source of this problem and a solution? Is the problem with the way I have setup the system or something else?

A Audio from TV programs contains lots of hiss, and the audio system in TVs is usually less than terrific. That is where your hiss is coming from. You hear it in the other speakers because they are much better than the speakers in the TV. The only way to reduce it is to turn the treble control down a bit on your receiver when you watch TV programs using your receiver.

Q I have an Onkyo 676 receiver, Celestion C-3 front speakers, Celestion C4-C center, and Celestion MK rear speakers. I have the front three speakers bi-wired to the receiver. When I play the THX intro on my DVDs, as the volume increases, the sound begins to shudder. It's a low vibrating sound. I was wondering if you can give me any advice on how to fix this problem. The speakers sound fine during the films at high volume. I believe they are positioned correctly. Also, I have hardwood floors, so could this contribute to the problem?

A The THX intro has some very intense, deep bass, and I suspect that you are just setting up some room resonance. Every room has them. At certain frequencies, the studs in the wall will pop and snap, glassware will tinkle, etc. The shuddering is because it is like you are sitting inside a big drum. Low frequencies are more difficult to tame with such things as wall treatments, but "Tube Traps" are available to help. However, they are expensive. Here are some links: http://www.silentsource.com/basstraps-tubetraps.html    http://www.tubetrap.com/.

Q I have a question for your editors regarding crossover frequencies. I own a Sony DA555ES receiver that has a fixed crossover of 100 Hz. My problem is that when I bypass my Velodyne's crossover and use the Sony's, it sounds horrible. When I use my sub's internal crossover and set it to 70 Hz, it sounds great. My question is when I use my sub's crossover, am I missing everything between 70 -100 Hz? How do I solve this problem?

A The Sony's 100 Hz is a low-pass, meaning that everything below 100 Hz is sent to the subwoofer. So, by setting the Velodyne subwoofer crossover (also a low-pass) to 70 Hz, you are eliminating 70 Hz to 100 Hz from being reproduced in the subwoofer. It sounds bad when you turn off the Velodyne crossover because that 70 Hz - 100 Hz sound is very localizable, and it also sounds boomy due to the large box that subwoofers occupy (they all have that problem). Assuming you have your other speakers set to "Large" in the bass management menu of your receiver, you are not missing anything. If you have them set to "Small", then yes, you would miss the 70 Hz  - 100 Hz sound. Try setting at least the front main left/right speakers to "Large", and your Velodyne to 70 Hz or even lower (50 Hz).

Q In terms of sound, what are the advantages and disadvantages to using a mass market A/V receiver as a preamp and processor? For example, would $1,800 for an Onkyo TX-DS696 mated with an Outlaw 750 5-channel amp outperform a $3,000 Denon AVR-5800?

A The advantage of using a mass market receiver as a preamp/processor is that you get lots and lots of features that are not present on high-performance processors (many DSP modes). The disadvantage is that the power supply is usually weak on the mass market product, and they tend to use inexpensive op-amps at the pre-out stage. This compromises the capability of a good outboard power amplifier. However, the emergence of the $3,000 and above mass market receiver is changing this. These products sound really good, even with their enclosed power amplifiers. The above mentioned Integra 9.1 receiver is a good example. But, it is $3,500. That is a lot of money. I would say that, for the choices you mentioned, the Denon AVR-5800 would deliver the better sound.

� Copyright 2001 Secrets of Home Theater & High Fidelity
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