Q I have an older Bose Lifestyle 12 system that is analog only. I would like to upgrade to a digital amp, and would like to know if I could use the (installed & wired) Bose cube speakers, and add a subwoofer? What type of 5.1 amp and sub would you recommend? The room is about 18x20.

A The Bose satellites are so small, they cannot handle anything below about 200 Hz. The bass management in most receivers does not have a low-pass that high, so you would need to wire them through the speaker-level outputs of the subwoofer. However, that will only work for two of the speakers, because subwoofers only have two speaker-level inputs and outputs. You will get better results by scrapping your old system and getting not only a new receiver, but the speakers to go with it.

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Q I have a small amount of hum from my speakers and subwoofers in my home theater setup. I have a variety of other equipment all connected in the set-up, including satellite/TiVo receiver, DVD player, Parasound processor and Parasound amplifiers. I also use a BPT isolation transformer. How much hum can one eliminate? It's most noticeable when I turn the subwoofer volume controls higher. Using an adapter to eliminate the ground plug for the amplifier makes a difference (I never directly touch the amps when they're plugged in), but there remains a definite residual hum that also comes from the satellite speakers. Is there a way sure fire way to get rid of all of this?

A Ground loop hum is a big problem for home theater because we have so many components all connected together. The BPT does not isolate the ground. The ground is passed through from the input to the output, because that is code, and it would be against the law for them to sell it without that ground pass-through. If your subwoofer is grounded, you can eliminate the ground prong by using one of those adapters, but this bypasses the safety mechanism that the ground supplies. If it is an ungrounded subwoofer, you can try reversing the plug, but you would need the adapter there too, because plugs are polarized and so are the sockets.

Another solution here, aside from running an additional ground connection between the AC sockets that supply the subwoofer and the equipment rack, is an isolation transformer before the subwoofer input (Iso-Max Sub-1RR made by Jensen, for example http://www.jensen-transformers.com/sub1rr.html). The other alternative is to try to minimize the noise by setting the subwoofer output level as high as possible on the receiver or preamp, and then attenuating the level more on the subwoofer input.

I have also noticed ground loop video problems, using a projector across the room from the DVD player, and using component video. Jensen's VBH-3RR component video isolation transformer might be useful in solving that problem. http://www.jensen-transformers.com/iso_vid.html.

Lastly, Jensen also makes an isolation transformer for reducing ground loop hum caused by cable TV connections.

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Q I am wanting to buy my husband a nice home theatre system for Christmas. I know NOTHING about these . . . spending around $1000 (+/-). I have looked at the Onkyo LSV950, Bose Lifestyle 8 and 12 (I do have a DVD player) and Kenwood 705DV. Any suggestions, comments?

A There are lots and lots of these home theater in a box (HTB) systems out there. Look for one that has a subwoofer with a cone that you can see, either on the side, front, or bottom, rather than the ones with just the port (an opening that looks like a funnel). Also, you should be able to connect the speakers directly to the receiver rather than going first to the subwoofer, and connecting all the other speakers from the subwoofer. Other than this, they are all pretty similar in terms of quality.

Here is an HTB with the subwoofer. Notice that it has a driver facing to the side (red arrow) and a large port (green arrow). Some HTB subwoofers only have the port. This would indicate a small driver inside the enclosure.

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Q Is the 700 ANSI Lumens of the new Marantz 12VS2 DLP projector not too low, offsetting the benefits of its 2600:1 contrast ratio? Why did they only use a 150W SHP lamp and not a 200W?

A It is difficult to guess why anyone designs a product a certain way. The bottom line is always whether or not the product does what you want it to do. For me, however, 700 ANSI Lumens is not enough, especially when you consider that we would probably calibrate the projector, which would undoubtedly mean a reduction in the final brightness. I prefer something that starts out at least 1,000 ANSI Lumens to give some room for calibration.

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Q I read your table which gives recommended gauge v. length of run for speaker wire. I'm using 12 gauge for approximately 40'. I've got extremely high efficiency speakers, and clean power to spare. What, if anything, am I losing by not using 6 gauge or so, and what do I stand to gain?

A If the gauge is not thick enough for the length, you might end up with attenuated high frequencies, which would be independent of your efficient speakers and high powered amplifier. However, 12 gauge is probably good enough. Going to 6 gauge would mean some very thick stuff.

The speaker wire will cause frequency response deviations, though the extent and nature of which will depend as much on the impedance curve of the loudspeaker as the speaker wire. The speaker wire is mainly resistive, but also places a slight inductance component in series, which can attenuate higher frequencies. However, if the loudspeaker's tweeter's inductance is high enough, the speaker wire can actually accentuate the higher frequencies. Generally speaking, lower impedance speakers will suffer more from series resistance or inductance in speaker wire, but to truly understand what's happening, you need to get into voltage drop in series circuits, where the series impedance of the speaker wire is mostly flat, but may rise slightly at higher frequencies, and the loudspeaker's impedance is as variable as loudspeaker sound.

Essentially, the speaker wire interacts with the loudspeaker impedance to provide tonal alterations with a character similar to taking the loudspeaker's impedance plot and dumping it onto a high-resolution graphic EQ. This may often mean floppy bass and honky midrange, but the range of variation is unlimited. Using 6 gauge wire is impractical, and actually has more inductance than smaller gauge wire, which would lead to less high-frequency fidelity. Using 12 gauge is probably fine for 40 feet, but if you really wanted to, you could tie in two identical runs of 12 gauge (with any shorting straps left in) together to get the equivalent resistance of 9 gauge, and half the inductance of 12 gauge.  If you do this, it is critical that you keep + and - applied as such with both cables, not both conductors of one cable for the + and both conductors of another cable doubled up for the - terminal, lest the increased space between the + and - path actually increases the total inductance. This is one of those instances we have discussed, about bi-wiring, where using two sets of zip cord could improve the sound, whereas good high performance speaker cable, which may very well have low inductance to begin with, may not benefit in bi-wire configurations.

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Q I recently purchased a Sony DVD player, and I enjoy the benefits of clearer picture and sound. However, I've been noticing that more often than not there are digital artifacts that take my attention away from the films. For example, watching the DVD of 'Powaqqatsi', I noticed that on static shots with - for example - a sunset, the colour shading from the sun to the outer picture is accentuated by a digital line separating the steps in shading.  Is this the player, the original DVD transfer itself, or something else?

I've heard that sometimes cabling can be an issue, but this doesn't appear to be an RF-related problem. However, to be safe, I'm going analog-out from the DVD player, in to a Sony A/V receiver, and analog-out to the TV.

A This is called "Posterization" and is a problem with 8 bit images in DVDs. Here are two examples. Example 1 (on the left) has 256 shades of gray (color is superimposed on this), and example 2 (on the right) has 24 shades of gray. See how the gradation is all but eliminated by reducing the number of shades of gray. If DVD moves to 16 bit images someday, the issue will probably go away, but 16 bit might never happen. Even HDTV is 8 bit video. Newer players have 10 or 12 bit video DACs, but the image is still 8 bit unfortunately. Some players and projectors hide the problem to a certain extent.

Any one hue can have only 256 levels of brightness (2⁸). I ran an experiment keeping the hue the same but changing the brightness level a point or two, and put the two color swatches next to one another. I could easily see the borders when the brightness was 255 compared to 252 for yellow and green. It was more difficult with blue, and I could not see the boundary with red. However, on a bright projection screen, it may be easier to see boundaries with all colors and values closer together, such as 255 vs. 254. Also, it may turn out that between the DVD encoding, DVD playing, and projection, 8 bit video could get truncated to 7 or 6 bits, and then, gradations in color would be even more obvious. If such is the case, DVI connections between player and projector (or TV) will probably get rid of this issue, assuming the video DAC in the projector is high quality.

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Q I am a beginner in home audio, but with great interest in hi-fi. I am thinking of buying a subwoofer, and from your suggestions, Velodyne ranks among the best companies. I own a pair of bookshelf Bose 101, and an Acoustimass with two satellites, Bose too, driven by a Denon AV-2850.  The main idea is to grow with time by changing for a better pair of front speakers. In this direction, would a CT-150" or a SPL 10" - 12" be the better option?

A I have always been a fan of larger drivers (15" or 18"). They don't have to work as hard as a smaller driver (8", 10", or 12") to produce plenty of bass with lower distortion. I would go with the CT-150 (15" driver). The smaller subwoofers are for situations where you don't have much room, or don't like the look of a big box. If those are not issues, then get the largest subwoofer you can afford.

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Q I am trying to find a progressive scan DVD changer with equivalent performance and similar price to the Panasonic DVD-RP62. Specifically, I am looking for a changer that has the Sage/Faroudja chipset and is immune from the chroma upsampling error - but doesn't cost more than $500. I was hoping the Panasonic DVD-CP72 would fill the bill, but it
doesn't appear to use the Sage/Faroudja chipset. Any ideas?

A The new Yamaha DVD-CX1 is a killer player, with no chroma bug, and does DVD-A. It is similar to the Panasonic RP82, but it is a changer. MSRP is about $1,000, but I found it for $805  - $850 on various E-Stores.

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