Q&A # 267 - December 12, 2001

Staff

Q I am planning to buy a A/V receiver with at least 100W of power. I am confused that some of them have high current with less watts and some with less current but with more watts. What are the difference between these two types of receivers? And which of them is better?

A If a receiver is rated into 4 Ohm speaker loads, they will often be marketed as "High Current" because 4 Ohm loads need more current at the same voltage. In general, the better products are rated into 4 Ohms, and are therefore, high current.

Q I have a 40 inch direct view Mitsubishi 507. To date I have been satisfied with my Pioneer Elite 97 for laser and CD playing. However, the boys want DVD. I use a Counterpoint solid state 200 watt amp into a Citation 7.0 processor. Which of the DVD players would you recommend for best video quality? I will not be using Progressive Scan as the TV cannot handle this feature. Do you get better quality in viewing interlaced feed if the unit has progressive scan? Is there a particular chip I should be looking for to insure excellent video quality? I will not be using the DVD player for audio.

A In your situation, an inexpensive DVD player will do just fine. Perhaps the Toshiba SD-K600 or SD-K600, which are stacked in large piles right now at CostCo and available for about $189 or less. There are also some nice inexpensive Panasonic players ($139), and they do not have the chroma bug, although it is not so visible with interlaced video anyway, because the scanning lines get in the way.

Q Is there any advantage to using a single multi-channel amplifier (e.g., 4 channels at 45 watts) to bi-amplify over using bridged (e.g., 2 channels at 100 watts) mode?

A Bridging an amplifier reduces its ability to drive low impedances, so if you have the budget, use more single amplifiers to bi-amplify. Using a bridged amp with more power to bi-wire will not be as effective, in my opinion.

Q I am wanting to install two subwoofers in my home theater setup merely because I am an "addict" for low bass. I have two subs that I want to utilize. Here is my equipment: 1. NHT SUBONE i - 250 watts; 2. NHT SW1P - 85watts; 3. Onkyo 85 watts/channel DD receiver with one SUBOUT connection; PREOUTS for fronts/center/rears, but NO MAIN INS. So, given the above "toys" what is the best way I can connect both of the subwoofers?

A I would suggest using a Y connector at the main left/right pre-outs and connect one leg of the right pre-out to the right subwoofer and the other leg to the right main-in. Do the same thing with the left pre-out and a Y connector. That way, you will have stereo subwoofers. Placement may be more difficult than making the connections. You can end up with less bass if you are not careful.

Q  In a lot of ads for DVD players and DTV sets you always see them stating that they do 3-2 pull down. This does not seem possible to me. From reading your article it is clear that 3-2 pull down is a process used to create a 60 field per second mpeg file which is stored on DVD. Or in case of broadcast it is used to create a NTSC video signal. Once on DVD or transmitted via cable the source format of 24 frame per second is lost. So it is not possible to do a 3-2 pull down anymore.

Is this correct? If so then perhaps their statement of 3-2 pull down really means that they are looking for the 3 2 3 2 sequence up duplicate fields to create the progressive scan image. If this is true it really should not be called 3-2 pull down but rather cadence decoding.

A Welcome to the world of non-standardized marketing terms and buzzwords. Sounds like you've pegged it: When they say a TV has "3-2 film mode" (or any other variation of the term "3-2"), they are saying that when receiving an interlaced signal, their built-in deinterlacer does 3-2 cadence detection and builds the progressive image in the fashion described in my (Brian Florian) article.

Q I've seen some pro installers use 75 ohm coax (RG-59 or RG-6) for line-level audio and composite video signals (the cables had Type-F to RCA adapters on each end). What are the reasons or advantages for using coax vs. standard line-level cabling?

A For the megahertz frequencies of video signals, 75 Ohm cable is necessary. They probably use it for audio signals (audio frequencies) too because that is what they have in the truck, and it is cheap. I would be more worried about the RCA adapters. They should be 75 Ohm as well, and most RCA plugs and jacks are 50 Ohm. For audio frequencies, 50 Ohm cables are fine, but for radio frequencies, such as video and digital audio signals, 75 Ohm cables and connectors are important.

Q I recently acquired a Citation 7.4 passive sub and would like to add it to my home theater. The front end is currently a Denon 2400 receiver with a sub pre-out among others. My questions are 1) How do I find out if the Denon has a crossover setting(s) associated with that pre-out or whether it sends a full signal that would require a separate crossover? 2) How much amplification should I be looking for? What are the important factors? 3) Are there any advantages to monoblock amps vs. bridged stereo amps?

A Subwoofer pre-outs always have a crossover frequency. It is usually fixed at around 80 Hz  - 120 Hz. You will have to look in the instruction manual to see which frequency. But in any case, you will likely need a separate crossover in the subwoofer to adjust it further. Even 80 Hz is too high. It needs to be more like 50 Hz or 60 Hz. There are commercial electronic (active) crossovers available, such as the Paradigm X-20. In fact, you can get subwoofer amplifiers with the crossover included. Get as much power as you can afford (400 watts or more), and don't use bridged configurations. Bridging reduces the ability to drive low impedances.

Q  I have a Paradigm Servo-15 Subwoofer and its companion X-30 crossover. My question is, if I use my receiver's 80 Hz crossover and then put it through the X-30, am I not daisy chaining the crossovers? Also, I cannot find anywhere if the sub itself has a built-in crossover? (The X-30 comes with the sub.) I swear I heare a timing error as the music seems ever so slightly out of time.

A Yes, you are daisy-chaining the two crossovers, and that can really throw off the timing, but the X-30 has a variable phase control, so try adjusting it until the timing sounds correct.

� Copyright 2001 Secrets of Home Theater & High Fidelity
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