Q I have a Yamaha RX-V990 and a Sony SDP-E800 Dolby Digital Decoder. I am getting ready to purchase a subwoofer, but am a little confused on how I should hook it up. The Yamaha is Dolby Digital ready, but I there are input jacks for only the front, center, and rear speakers. How should I hook up the LFE channel coming out from my decoder? Can I plug it straight into the sub from the decoder? If I do this, it will only give me subwoofer output when playing my DVDs. I would like to use the sub with regular music as well as DVDs.

A This is a common problem with last year's generation of receivers. They only had 5 of the 5.1 pre-in jacks to pass DD or DTS through. They way I get around it is to connect the LFE output from the DD decoder to one line-level RCA input jack on the subwoofer, and the subwoofer output RCA jack from the receiver to the other line-level RCA input jack on the subwoofer. This way, you get bass sent to the subwoofer regardless of whether you are using the receiver's surround sound decoding (Pro Logic) or the DD decoder's output. In the case of DD, you will get the LFE from the DD decoder plus the subwoofer output of the receiver both going to the subwoofer at the same time, but I never experienced any problem with this. The latest generation of receivers with pre-in jacks have a subwoofer input (total of six jacks instead of five), but the older receivers only have five.

Q I have a question on Acoustic Room Treatments. My Home Theater room is extremely bright and reflective. If I clap my hands, I hear a discernable ring and echo. I have done everything I can do as far as carpeting, oversized couches, drapes, etc. but still have problems. I have seen acoustic treatment kits like Room Tunes and others and was wondering if you have had any experience with them or if you could offer any comments on acoustic treatments?

A There are two factors to utilize with room treatments: diffusion and absorption (see diagram on the left). I think your problem may be reflections from the ceiling, and you probably should consider adding absorbers there. I am getting ready to do this in one of our labs, because I can hear the reflections coming from the ceiling when I clap (clapping is a good test for room reflections as you obviously have discovered). This can be done with commercial room treatment products, or you can make them yourself using an egg carton mattress pad available at bed linen stores. They are very inexpensive (about $30 for king size), but they are not very attractive. I have a dedicated room for audio, and my wife does not care what I put in there in terms of the appearance. If you have the same situation, then you can just cut the mattress pad up in sections and mount them on the ceiling with push pins. Otherwise, your spouse may object to what this looks like. In that case, the commercial absorbers, although much more expensive, will look presentable. If you add too much absorption, the room will sound "dead". Diffusors will keep some of the "live" sound of the room but will improve the soundstage. If you feel you have the right amount of "liveness" in your home theater room, then you might think about using diffusors (which look a little more high tech, and can be attractive) instead of absorbers. The mattress pad idea is a way you can try it out without spending a lot of money, and then make a decision about whether or not to buy the commercial room treatments.

We get a lot of questions about room treatments, and if you have some DIY projects for constructing various types, please contact our DIY editor Ralph Calabria about them.

Q I am currently using my A/V reciever to power my B&W CDM7SEs and am in
the process of deciding on an amp and some new speaker cables for my L/C/R. Does bi-wiring actually do anything and how?

Secondly, in my search for an amp, I want to know if bi-wiring (with a three channel amp) is enough or if I should buy a six channel amp and
bi-amp? If so, should I by two amps of the same power or should I buy a smaller (less power) amp for the tweeters? What would bi-amping do
better than bi-wiring?

A I have never found bi-wiring to be of any benefit. Bi-amping works nicely, but is of value only when you really want to change the relative amount of sound coming from the tweeter vs. the woofer without using EQ or tone controls. For the majority of speakers, bi-amping is not really necessary because they are designed with the proper balance between the output of the various drivers. I would suggest putting your money into a good three channel power amplifier rather than a smaller six channel power amplifier, and using just one set of cables for each speaker (no bi-wiring).

Q I have read in your Q&A section that with good speaker cables there is not much to gain from bi-wiring over single-wiring. I have a pair of B&W 603 speakers bi-wired with Tara Labs Phase II TFA. After reading your statement on the issue, I replaced the bridges between the speaker terminals so it now was single-wired. Well there was a difference in the sound. Bi-wiring gave a much cleaner and controlled sound (not just brighter sound), it just sounded more right when bi-wired. I know that the Phase II TFA not are the best cables money can buy, but the amount of wire to my speakers was equal in both single and bi configuration, so if you are correct then why is there still a significant change in sound? The reason I am asking this is that I am planning to upgrade my speaker cables, but this got me wondering if I just should keep my current cables.

A The fact that you heard a difference, while others have not (such as in my case) is why bi-wiring is so controversial. The results depend on the output impedance of the amplifier, the resistance, inductace, and capacitance of the cable, and the impedance of the speakers. These are too many variables to make any concrete statements about the universal application of the technique. If you are happy with the sound, using bi-wiring with your specific cables, then there is no need to look for an upgrade. If you are not happy, then look for the upgrade, but it might turn out that less expensive cables will give you the results you prefer rather than more expensive. An upgrade does not always mean more expensive.

Q I wanted to know if you know of and/or could recommend a cable to connect a 5 channel preamp to a 5 channel amp? For now, I am using 5 individual monster ILR-2 interconnects but this causes quit the mess of cables. Does anyone make a 5 pronged cable of high quality? FYI, I am using the Sunfire Theater and Cinema Grand.

A The only multi-connector available (in the USA) is the DB-25, which is also used on computers. I had hoped this connector would be adopted for general use, but it is present on just a few processors and power amplifiers. The use of IE1394 interfaces in the future will make our cable mess obsolete.

Q With all the trouble some people are having getting proper timbral and phase match, refraction, relflection, and placement problems with centre speakers, I was wondering if in fact it was worth the trouble at all?

If you have good quality front speakers that image well left to right, the centre speaker should not be necessary at all. I have tried using a Pro Logic setup (using a Yamaha DSP E1000 as the decoder) in all modes, and I found that the phantom mode provided the most natural panning of sound. I still get rock solid centre localization of sound, but the sound no longer seems to have a slight discontinuity across the front.

I found that Pro Logic downmixes from DVD were even more noticeable (especially in "The Right Stuff", chapter 5 when the sound barrier is broken and the X1 flies left to right, front only).

For DD or DTS, can you see this being more of an issue since the centre is a discrete channel? Or would the phantom mode mix the centre well enough into the front mains to work fine as well?

Have any of your staff experimented with this? Ribbons such as the Newforms with their excellent horizontal dispersion would be an ideal choice I would think.

To me, the centre speaker would be more relevent for systems with front speakers that don't image that well.

A The most likely situation where you would notice a tonal matching problem with the front left/right and the center is where the front left/right speakers are markedly different than the center. Such would be the case with very large front left/right speakers since most of the time, we have to use a small center speaker that can sit on top of the TV. DD and DTS have increased the problem because the front left/center/right and rear left/right all have full spectrum sound, so not only is the center an issue, but the rear as well (compared to the tonality of the front left/right). However, the center channel still is used mostly for dialogue rather than sound effects, even with DD and DTS, compared to Pro Logic. Using Phantom mode (or "None" for the center channel speaker seletion in some receiver menus) works fine as long as you are seated at equal distance from the front left/right speakers. And, this applies to movies only. With DD and DTS music, the center channel's discrete placement of instruments in that channel would be lost in the phantom center channel speaker mode.

Q After reading a review on your website Aug/97 for a 40" Toshiba RPTV, I took a look at their website. I read some press releases that indicated they were making improvements on some TVs that are yet to be released. One such improvement is Progressive Component Video. They are also releasing their third generation DVD player which will have PRO Component Video out. How much more benefit will there be between standard RGB/component video and PRO RGB/component video? Will I see a difference? Will it cut back on the thin black horizontal lines on RPTVs currently?

How soon are HDTV's coming out? Some of the new Toshiba RPTVs are supposed to be DTV ready when utilizing a RGB/Component video converter. Would you please share your thoughts on this issue? I guess if I could wait (yeah right!) for HDTV, I would be better off and not have to deal with negatives of Projection TVs.

What type of connectors will HDTVs have? Inputs/Outputs?

A Standard component or "Colorstream", as Toshiba is calling it (I wish companies would dump the marketing lingo because it does nothing but confuse people), is what most high end DVD players output, which is the native signal format.

Colorstream Pro or Progressive Video is line doubled. Most movies are stored on the disc in their native 24 frames per second format. Your TV runs at 30 FPS so the DVD player must convert the signal using a process called 2-3 pull down in order that the 24 frame per second movie is shown on a 30 frame per second TV. At the same time they must also interlace the picture to work with the NTSC system.

The picture is actually stored in the progressive format, but this requires a TV capable of scanning at a higher rate to show it as such, like a computer monitor or data/graphics grade projector. The latest Toshiba TV will actually play back the original 24 fps image as is off of the disc. This will eliminate most shimmering artifacts that you see on blinds, bricks, and striped t-shirts.

There is a PC version on the market that uses the Mpact decoder chip which takes the 24 fps and triples it to 72 fps, then outputs the signal.
Do the black lines go away? Not on a graphics grade projector! The problem is that the projector can scan faster than 31.5 kHz and that is the rate that progressive DVD outputs. These projectors like to run anywhere from 40 kHz to 62 kHz. Hence the need for a line quadrupler or
Tran Scanner or Interpolator.

The new Toshiba TVs will up convert any HDTV image to 1080i. That means they will take a 720p picture and modify it up by interlacing it! I consider this to be a mistake on their part and I believe it will hurt them in the long run. It is important for TV manufactures to display the signal as is coming in, whether it is 480p, 720p, or 1080i. I look forward to the day we get 1080p because interlaced formats are the reason for many artifacts that we see.

I don't know what type of connectors HDTVs will have, but probably the backwards compatible ones such as RCA, S-Video, and probably some sort of digital connector.

Q In responding to the first question of Q&A #69, you said that driving a pair of 92 dB/2.83 V speakers would require 10 W, while a pair of 95 dB/2.83V would only require 5, and a 89 dB/2.83 V would require 20. While my guess is that you are using simple numbers in order to illustrate the idea of 3 dB = double the power, I am a little confused. I surmise that the 80 dB would be measured from a listening position (not many people do their listening from 1M, after all), which is how 10 W into a 92 dB/W/M speaker would not be 102 dB, but my memory of physics fails me -- what is the rate of dropoff in dB for distance?

A The volume drops off as 1 over the square of the distance between one measured position and another. So, if it is 92 dB at 1 meter, it would be 1/4th that volume at 2 meters, which is 89 dB, and 1/16th that volume at 4 meters, which is 80 dB.

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