Q&A # 179 - May 24, 2000

Staff

Q I am looking to improve my music/home theater (65%/45%) system. My current speakers are Snell KIIs for mains, and a Snell CC1 center channel, but I am looking to replace them with Thiel CS2.3s and one of the Thiel center channels. The rest of my system consists of a Yamaha RX-V990 with a DDP-1 as a preamp, using the main channels for the rear surrounds only, a Rotel RB980BX as main power, a Marantz MA-500 for center channel power, and a Definitive Technologies PF15TL subwoofer. The rear setup consists of Boston Acoustics Micro 90s with a Klipsch SW-8 to balance things off. Everything I have read about the Thiels says that they are very sensitive to the equipment driving them, so I was considering upgrading my electronics to a Rotel RSP-985 preamp with a Rotel RB-1090 as main power, which would handle the minimum impedance of the Thiels and give me DTS and THX. The RB980BX would then be used for rear surround power, and the MA-500 would remain as center power. Would this setup offer an improvement over my current system for driving the Thiels? Are there other components I should consider in the same price ranges? Should I be concerned that the main power will be 380 watts and the center and rears will be only 125 watts (I never turn the Yamaha above 1/3 while listening)?

A In your circumstance, I think you would be better off with a Yamaha RX-V995 and a Sunfire Cinema Grand (200 watts x 5 into 8 Ohms). This gives you DD, DTS, and low impedance driving capabilities with equal power for all channels, and plenty of it. Even at low volume, an amplifier can be taxed with a low impedance load when a peak comes along. The Sunfire will handle it with no problems.

Q I would really appreciate some information on the ideal or recommended speaker set up for a THX EX system including the use of rear/side subwoofers. I understand that it is recommended/suggested that both the side and rear speakers be dipolar speakers. My question is to do with positioning of the speakers. I have read where some recommend positioning the side speakers slightly forward of the listening area for EX playback as opposed to directly to the side of the listening area. Are the rears recommended to be mounted on the rear wall and closer together than the fronts? I believe the height is still the same two to three feet above seated ear level, so is this correct? Are both the side and rear channels full range in an EX or ES decoded soundtrack? If I were to hook up two rear subwoofers, should I hook up one for the side channels and one for the rear channels? Or alternatively, should I hook up one for the right side surround channels (both right side and right rear channels) and one for the left side surround channels (again both left side and left rear channels). I would do this by putting both rear subwoofers in the rear corners on opposites sides of the room, and run the right side surround output into the right input on the right sub and running the right rear surround output into the left input on the right sub and visa versa. So I would have the right side surround channel and right rear surround channel running to the sub in the right rear corner and the left side surround channel and left rear surround channel running to the sub in the left rear corner. What do you recommend? In addition, what would be the best way to hook up these subs? Using speaker line in and out or preamp in and out?

A Now that Surround EX is here, we are getting a change in the suggestion for where the rear surround speakers for 5.1 should actually be placed, namely, slightly in front of the sitting position and to the sides. The EX channel is mono, but it will work best with two speakers in the rear rather than one, because otherwise, you would have a speaker right behind your head. So, the EX is now the rear channel, and what used to be the rear surround channels in 5.1 are now the side surrounds. The problem with having more and more channels, is that the sweet spot becomes smaller and smaller. No listening room is perfect, so placement becomes a trial issue. And, putting speakers on the sides and slightly in front of the couch can be a real problem with the aesthetics of the room. You could very well have to start walking around speakers to get to the doorway.

We have a new model receiver now, with EX built-in, and two channels to drive it, so we will test all these issues out and report on them soon. Remember, EX is mono, and like the rear surround in Dolby Pro Logic, it will have a limited bandwidth, because it is derived in matrix form through the left and right DD or DTS rear (now called the sides) channels. So, EX is not a discrete channel. This makes me a bit nervous as to how it will affect the overall sound. With 5.1, all channels are discrete and can contain full range information. With EX, information is removed from the rear (side) channels, and put into the EX speaker(s). This means that the sides will now have less information than before (because mono info between left and right sides has been removed).

As to your subwoofers, in my experience, putting subs on opposite sides of the room decreases the bass at the listening position, because the subs are pushing air at each other and some of it cancels out. So, use a low pass setting on each sub of around 50 Hz, and put all your subs at one wall (they can be at opposite ends of the wall, just not facing each other like they would be if they were on opposite sides of the room). That is what I do, and it works beautifully.

Q I am considering adding an external amp to my Denon 3300 receiver (105 w/ch), either monoblocks or a 5-channel amp that will be a good match for the Denon. I have in mind the Carver 705x (if I can find one), the new Parasound monos or the Marantz MA-500 monos. The reason I am looking for a new amp is because I am getting noticeable distortion at high playback levels (0 to +5 or about 85 dB). Also, the Denon is a little bright/harsh at this level. I have all Paradigm speakers - Monitor 7s for the mains, CC-350 center, Monitor 5 surrounds. Should I look for more power than 125 w/ch, bigger speakers, or something else? It's just that mass market receiver's typically don't have the greatest amps, so I thought I'd start there.

A The AV-705x should be fine, but if you really like to crank things up, you probably will indeed want even more power, say, around 200 watts per channel. One little trick that I use occasionally, is to turn the overall volume down, so that it is not harsh, but turn the subwoofer up. This gives a gut sensation of loudness, without the teeth gritting hardness that some movie soundtracks have.

Q I'm currently in the market to replace my Yamaha 2090 for a pre/pro for less than $2k. I auditioned several pre/pros from ACT3/ B&K20/ Marantz P9000/ Rotel 985. I currently have an ATI 1595 5 channel amp, a Velodyne HGS15 sub, NHT 2.5is, and NHT center and surrounds. Should I purchase a new or old processor? I see lots of DC1 offers.

A Since you are a Yamaha fan, I would suggest looking for a DSP-A1. Now that the RX-V1 has been released, you should be able to find one easily in your budget. It has the pre-outs you will need to drive your ATI. The problem with older, used equipment, regardless of the good deal, is that they might not have the built-in decoders you will need for DD and DTS.

Q If I connect two sets of speaker cables to the same speaker outputs on my receiver, then run one set to the main speakers and the other set to the speaker level inputs on a powered subwoofer; how does this affect the impedance that the receiver "sees"?

A Since the input impedance of the speaker-level connections on the subwoofer is high, your receiver will see primarily the impedance of the speakers, which is low by comparison.

Q I've got a home theater system which I've recently upgraded to consist of a set of Klipsch speakers (KLF-30s in the front, KSP-C7 for the center, a KSW-12 sub, and four KSP-S6 surrounds for rear and front effects), all running off a Yamaha RX-V2095. The 2095 has A and B outputs for the main speakers, and the KLF-30s can be bi-wired. Would I gain anything by using the B outputs on the receiver to run a second set of cables to my speakers, or would the additional power drain be more of a problem?

A You can bi-wire just by using the two sets of cables connected to the same binding posts and using the Speaker A switch. If you use A and B switches and the two sets of binding posts, this might work as well, but some receivers put the A and B into series to keep the impedance from dropping too low.

Q I would first like to thank you for your site. It has been such a great tool to learn about the new technologies and to sort through some of the misconceptions. I am not an electrical engineer and I was reading a question that was in the Q&A # 166 about clipping with an outboard power amp. This has me concerned because I am going to purchase an outboard amp next month, and I do not want to have this same problem. I am going to use an older Yamaha RV-902 that I have as a preamp and get a Classe CAV75 power amp. The Yamaha has an output voltage of 2.2V, and the Classe has a sensitivity of 0.85V and an input impedance of 75 kOhm. Am I going to have clipping problems?

A The Yamaha specification means it has a maximum output of 2.2 Volts. It is not 2.2 Volts all the time. The Classe spec means that 0.85 Volts will drive it to full output (or some other specified output listed in the spec sheet). This is what volume controls are for. The input impedance of the Classe is high enough that the output stage in the Yamaha will be able to drive it without clipping (a low input impedance is like a low impedance speaker, as it stresses the amplifier). So, you should not have a problem.

Q I would appreciate it if you could advise me on what I am doing wrong with my AV setup. I have connected my Carver AV 705X to the pre-outs of my Denon AVR 3200, but when I connect my speakers to the outputs of the Carver I get no sound. I am driving five NHT speakers, and I realize the Denon does not allow you to further amplify the rear surrounds. Any ideas about what I may be doing wrong.

A The 705 has small potentiometers above each amplifier channel module on the back. Make sure they are turned all the way up, rather than all the way down. Try using a Rec Out jack or other pre-out jack on your Denon to make sure you are getting some output from your main pre-outs. You could also try a different component, like the adjustable level analog audio outputs from your TV, with the volume control set all the way down to start with. What you want to test is (1) whether or not you are actually getting output from the Denon pre-outs, and (2) whether the Carver has an output signal when there is an input signal.

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