Q&A - #9 - April 21, 1997

Q What does it mean when an amplifier is advertised as "High Current"?

A This is a marketing term that is used by some manufacturers to designate that the amp can handle low impedance loads. With any given rail voltage, the amount of current drawn by the speaker load increases as the impedance drops, as per Ohm's Law I = E/R. Amplifiers with hefty power supplies will double the maximum rms watts that they can deliver when changing from an 8 Ohm speaker to a 4 Ohm speaker. The really big ones will further double when going to 2 Ohm loads. Of course, it is really a matter of semantics. One could say "High Current" even if the amp were not capable of doubling its wattage with 4 Ohms compared to 8, as long as the amp is stable into 4 Ohms (not overheating).

Q I just wanted to comment on Stacey Spears' Toshiba SD-3006 DVD article. The statement was made regarding component video versus S-Video and composite video: "(S-Video and Composite are restricted to a 3.58 MHz bandwidth limit, while DVD does not have this limit.)"

This statement is not correct. While the color carrier is at 3.579545 MHz, luminance information goes well beyond this frequency. Broadcast video extends to about 4.2 MHz and non-broadcast composite video can go much higher. Otherwise, you would never be able to get 330 lines of resolution from broadcast and 425 lines from laserdisc. Both of these formats are composite. Comb filters play a significant role in separating these components from one another. Motion adaptive (3D) comb filters work the best and do not limit the luminance frequency response to 3.58 MHz.

A Yes, that 3.58 was a typo, and the paragraph in the article has been corrected. The Y of LD goes out to 5.3 - 5.6 MHz, then rolls off from there. The 3.58 MHz is the sub carrier frequency. Sorry about that.

The 'Y' (luma) of DVD is 6 MHz, and the 'Y' (luma) of Laser is 5.3 - 5.6 MHz.

There is a question going around as to what the Cr and Cb of DVD is after MPEG-2 encoding. Before MPEG-2, 'Y' is 6 MHz, Cr is 3 MHz and Cb is 3 MHz. "After" is somewhat of a mystery. I am now hearing that 'Y' is still 6 MHz, but the Cr and Cb are now 1.5 MHz.

The 'C' Chroma is in a matrix format which gives 1.3 MHz to 'R-Y' and 0.5 MHz to 'R-B'. 'R-Y' is converted to 'I' which is 0.877(R-Y), and 'Q' is 0.493(B-Y). I and Q are modulated onto a carrier at wt, where wt=3.579545 MHz (3.58 for short). The formula for NTSC = Y + [Q Sin(wt + 33) + I Cos(wt+33)]

It gets confusing!

There was also another correction to that article, in that DVD players don't have comb filters, so component video is the best connection to use, followed by S-Video, and finally composite video. Therefore, for DVD, S-Video connections will be better than composite video connections, regardless of the TV. For LD, it still is true that composite video will be better than S-Video, if the the comb filter in the TV is better than the one in the LD player. The S-Video connections will be better if the comb filter in the LD player is better than the one in the TV.

Q I have read the comments about the DVL-700 not being a very good DVD player. I have also read several articles saying that as a LDP it compares with the Elite models. Have you had a chance to test it as such? If so, do you think as a LDP it compares at least to the 704 (which is suppose to compare to the Elite models)? I have been thinking about getting this model if it is a better LDP than my 505 and at least I could start getting into DVD.

A I have not tested it as a LD player yet. I will be getting one and looking at it with real DVD software, and as a LD player. I know that the DVL-90 (Elite Version) uses the CLD-79 LD transport and adds DVD to it. I do not believe they are using the 704 for the DVL-700, because of the cost. They are probably using the 505 or 604 as the LD section. I would keep the 505 for LD only and add a separate DVD player. This will save you money because the DVD-only players are cheaper than the combi players. Both the RCA and Toshiba have DVD players starting at $499.

Q I need some advice -- I AM DESPERATE!!! Can I get a decent pair of speakers for under $1000 for the pair? I have been looking at Paradigm 7se. What do you think?

A We have not had the chance to test Paradigm's line yet but hope to soon. However, from the ones we have tested, I would suggest the B&W DM-602 or the NEAR 10M/15M. All of these are in your price range and provide solid clean sound. There are lots of fine speakers at < $1,000, but these would be a good place to start. I think it will soon be time for us to publish a "Secrets Recommends . . ." page.

Q I just spent a lot of money on a receiver that has AC-3 built in, but now I want DTS too, and the receiver has none of the 5.1 inputs you mentioned. What can I do?

A Some, but not all receivers can be upgraded by MSB Technologies. It depends on the type of chips in the receiver. They have a website at http://www.msbtech.com/. Prices are $699 for a DTS upgrade to your receiver. The Yamaha 3090 and Denon 5600 can be upgraded. They can also put an AC-3 output on your LD player, or you can do it yourself (see DIY # 3 next week).

Q Hello from Iceland. I have many hobbies, one of them is my stereo. I have Sony STR-D911 Pro Logic A/V Receiver I use for for my home theatre system and CD. I have two old Pioneer 70w front speakers, one 100w Senett Concept SH44 center speaker and two old 16 ohm 60w Pioneer surround speakers. I also have an old Normende 25" stereo TV, two VHS VCRs, an old Sanyo hifi, and a new Panasonic hifi. I do not like the sound of my home theatre system. I think it lacks a lot of bass, and the rear speakers I hate. The sound from the rear is too low and I do not get the cinema feeling when I am watching movies. I know I do not have the most expensive system, but this will have to do for now. To fix the theatre sound should I buy a new subwoofer, new rear speakers or a new center speaker? I want to buy it all but cannot afford it. I have listened to the Jamo 200 center speaker and love it. Is the center speaker only for dialog or does it have some surround effects? If you suggest I should buy a new sub how big should it be and does it work to connect my 70w to it?

A I see two problems. One is that you have speakers that are not tonally matched. Even expensive speakers will often not sound right in a home theater if they are mixed between brands. Secondly, a subwoofer is extremely important. The low frequencies are felt as well as heard. Probably half the home theater experience is due to a good subwoofer. Therefore, I would suggest you get a sub first, then a new center channel speaker. The sub should be as good as you can afford. Something like the Velodyne F-1500 would do the job. Your front left/right speaker outputs from the receiver can go to the sub, then the speaker outputs from the sub go to your front left/right speakers. A line level subwoofer or mono output from the receiver would be better if you have it. Most of the movie sound comes out of the center channel speaker, so that is next on the list of new purchases. Keep in mind that whatever brand of center channel speaker you get, should be the same brand that you eventually replace your front left/right and surround speakers. The main thing to look for in a center channel speaker is that it sounds natural with voices. That is where most of the dialog comes out, and slightly unnatural voicing is very noticeable. Some of the sound effects come through the center channel too.

Q I am in the process of recycling some 2-way monitors. I found the drivers, but I have a hard time choosing a 2nd order crossover network. My question is: How do you differentiate a Bessel network from a Linkwitz-Riley or Butterworth? What are their qualities/weaknesses?

A All crossovers have the same basic components: an inductor that provides low-pass signal to the woofer, a capacitor that provides high pass signal to the tweeter, and a resistor for balancing the output of each driver so that they are matched. If there is one set of these components, it is first order, with a 6 dB/octave slope. Two sets give a second order, with 12 dB/octave slope. Three sets gives a third order, and four sets gives a fourth order, and so on. They can be in parallel or series. Depending on the phasing that is required, i.e., where the drivers are in relation to one another in the enclosure, and other factors, the value of each component is selected. It is a very complicated process. There are lots of different types of crossovers, including Butterworth, Linkwitz-Riley, Bessel, Chebychev, Legendre, Gaussian, and Linear-Phase. The Linkwitz-Riley, sometimes called Squared Butterworth, are second or fourth order all-pass filters (phase shifting and flat magnitude response). If you are recycling the drivers, and putting them in an enclosure that is the same size and driver placement as the original, the safest bet would be to use crossover parts that are the same values as the original. Otherwise, get a copy of "The Loudspeaker Design Cookbook" by Vance Dickason or one of the computer programs that helps design the crossover.

Q I own a Harmon-Kardon AVR 80 receiver that has 6-channel direct inputs for AC-3 or DTS upgrade. Which units would you recommend and would you go AC-3 or DTS?

A An outboard AC-3 decoder such as the Yamaha DDP-2 would be fine. The Millennnium DTS decoder can also be used. I would go for both AC-3 and DTS. Each has its use, and not all movies will be released in both formats.

Q In the DVD movie review in Secrets, it was mentioned that "Goldeneye" has anamorphic/letterbox and pan & scan. In the review itself, it was mentioned, "you are prompted with a screen that asks you if you would like a widescreen image (layer 2) or pan & scan (layer 1)." So my question is this: where is the letterbox version? Surely it must have been embedded SEPARATELY on either layer 1 or 2. The letterbox format can't be the same as widescreen/anamorphic. There must be at least 3 different options for the format, not 2, right?

A You must tell the DVD player what type if TV you have, i.e., 4:3 or 16:9. If you have a 4:3 TV, then the DVD player will "unsqueeze" the anamorphic picture and format it for your TV. If you have a 16:9 TV, you will be shown the anamorphic image, and your TV will have to unsqueeze it using the "Full" mode.

Some DVDs do not contain the anamorphic image, just the standard letterbox version. In this case, when using a 16:9 TV, you will have to use the "Zoom" mode. A good example of a DVD that is not recorded in the anamorphic mode is "Mortal Kombat."

Q What is the difference between bipolar speakers and Bose's direct/reflecting designs? Both seem to rely on direct as well as reflected sound. I need to know which is really better for home theater as I want to build up a good system.

A "Direct Reflecting" is Bose' trademark name for a variation on bipolar speakers. Usually, the Bose speaker has drivers on the side as well as the front. The side drivers are not at 90⁰ to the front, but at some angle in between. Bipolar speakers have drivers on the front and back, or they may be arranged side to side. They are in-phase, meaning that each driver is moving out of the enclosure at the same time. This compares to dipolar, where air is moving out of the front at the same time it is moving into the enclosure at the back (out of phase). This can be done with two drivers, or one driver that is open at the back. None is necessarily better than another. It depends on your audio tastes. Monopolar is more focussed than bipolar or dipolar, but the soundstage of bipolar and dipolar is bigger. The manufacturers generally recommend monopolar for digital surround modes (AC-3 and DTS), but you really need to just listen to the various types and decide what you like.

Q Thanks for the interesting review of the DTS decoder. My question applies to people who are primarily interested in the >2 channel sound from CDs rather than cinema. How do I integrate a 5.1 system with an existing high-end hi-fi system without compromising the sound?. There must be some way to connect between the preamp and amp but I can't see how to do it without ALL sources running through extra links to the DTS/AC3 processors ALL the time. Purists would feel this will affect the sound.

A You can run the front left/right channels (two-channel stereo) through a tape loop. This will give you CD player to preamp to power amp connections when playing regular CDs, and surround sound when you want to have the CDs using the surround sound system. When the tape loop is turned off, the signal will not be passed through the surround sound decoders. When the tape loop is turned on, the front left/right of the surround sound output will be passed back through your preamp.

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