Q&A # 187 - July 5, 2000

Staff

Q I currently have an Onkyo 919 with B&W 604s for the front and Polk M5s for the rear. My sub is a Sunfire Signature. I will soon buy the new Onkyo Integra DTR-9 which is the Integra equivalent to the Onkyo 989. Since this is a 7.1 receiver, I will need to get another pair of rear speakers. I'd like to buy another pair of M5s, but they have been discontinued. The M3s are still available though. Since I'd be staying in the Polk line, do you think I'd be OK in getting the M3s (the little brother to the M5), as my 2nd pair of rear speakers?

A Yes, I think that would work just fine, since the rear center channel uses two speakers rather than one.

Q I think this was alluded to in a recent preamp review regarding the Audio Illusions line, wherein the 4 dB detents in the volume pot were replaced with 2-3 dB detents to allow lower listening levels. I have the Adcom GFA-5802 and am breaking in the VTP101I, and the sound, while fabulous, gets too loud by the 3rd or 4th detent - it didn't do this last week when i first got it. 1) is this an expected part of break-in for the preamp? 2) Is this indicated by impedance and/or sensitivity specs? The VTP101I output impedance = 300 Ohms.The 5503 amp manual online says Input Sensitivity for 1 watt..... 0.1 volts, for 200 watts..... 1.4 volts. Input Impedance..... 49.9kW (i assume the W should be an O).

A The break-in period should not be marked by a change in the output level of your preamplifier or the output of your power amplifier. The loudness of new speakers might change a bit, but not very much. If it is getting too loud by the third detent , and it did not do it the week before, the volume pot may have become defective or has gotten dirty for some reason. I would have it checked out by a service center.

Q Why is it that there are only 2 wires (black/white) and no ground wire in all the circuits in my house? I've noticed that the receptacles are "grounded" or connected together at the service entrance box. All of my electronics use a 3-prong plug. How do I ground them? Should I connect all of the chassis to the cold water pipe or just leave them as it is? Please help me because I don't want to get an electric shock.

A Older houses tend not to have grounded AC outlets. However, you can have an electrician ground the outlets in your audio room, and it is very inexpensive, assuming the ground wire is in the cable and has just not been connected. Ground is mainly for safety, and here is a link for reference: http://www.copper.org/pq/primer/#footnote-ref-3.

The diagram shown on the right indicates the way grounded AC outlets are wired in the USA. Although the ground wire is a separate conductor in grounded AC wiring, the neutral and ground are both connected together back at the circuit breaker box. So, if your house wiring does not have the third conductor, you can ask your electrician about just connecting the ground and neutral pins inside the AC receptacle. It is not the best way to have a grounded receptacle, but it works. I am not sure if this meets code though. Otherwise, you can connect the ground pin in your receptacles to a cold water pipe. I think this will be better than connecting all your hifi chassis to the cold water pipe directly.

Q I have bought a Yamaha Home Theatre system and have been having problems hooking it up. The manuals suggest at least 2-3 ways of setting up the system. The problem revolves around the fact that my subwoofer has two inputs, one for high level signals and one for low level signals. Do I use both or one? Secondly, one diagram from Yamaha shows the receiver using both A and B speaker outputs, with outputs A to satellites and B to subwoofer with the A and B buttons both depressed on the receiver. How should I hook it up?

A If your receiver has an RCA subwoofer output jack, use that. It will entail an interconnect going to the line-level input on your subwoofer. If you use the high-level (speaker-level outputs) to the subwoofer, use of the A and B outputs let you have two sets of speaker binding posts, one to the satellites and one to the subwoofer. However, you can also use just one set of binding post outputs to the high-level input on your sub, and the high-level outputs back to your satellite speakers. This will eliminate everything below 80 Hz to the satellites. If you have very small speakers, this (sub high level outputs back to satellites) may be the way to go. But, if your speakers are larger, then use the RCA subwoofer output from your receiver to the subwoofer, and just the A speaker output of the receiver to your speakers.

Q I've been considering the last piece of my HT system: the subwoofer, and I'm really confused about this whole high-pass/low-pass thing. My processor is a Yami RX-V2092, power amp Rotel 985MK-II (5 channel),  speakers Stratus Silvers (front), C5, and minis (rear). All five channels of the 2092 are pre-outed to the amp, and then on to the speakers. In bass management, I have declared as follows: Mains: large, Center: small, bass directed to mains; Rears: small, bass directed to mains; Sub: none; LFE bass directed to mains. Now, it seems to me that I should be able to just plunk the sub (like an HGS-10 or Sunfire) down in between the main pre-outs and the power amp using low-level connects, set the sub crossover to about 45 Hz, and pass 46 Hz+ on up to the power amp. Right?? But then I come to this high-pass (80 Hz) thing. What is that all about? Does that mean I have a hole between 45 Hz and 80 Hz where the signal just goes into hyperspace?

A You won't have the 46 Hz - 80 Hz hole because that info is going to the mains. If you had used bass management to rout all < 80 Hz to the subwoofer instead of the mains, then, yes you would have the hole. However, lack of a hole assumes you are using a Y splitter at the main pre-outs, with one leg going to the power amplifier and the other to the subwoofer. If you daisy chain the subwoofer so that the signal goes from the main pre-outs to the sub, and from the sub line-level output to the power amplifier, you would have a hole in between the variable low-pass setting of the subwoofer (45 Hz) and the fixed high-pass that the subwoofer has (it might be as high as 120 Hz, but probably somewhere around 80 Hz). So, use the Y splitter method.

Q Upcoming DVD-Audio and SACD specifications claim superiority in audio performance over conventional CD. It is said to be achieved mainly through high sampling rates (up to 192 kHz), good definition of sound (24 bits) and higher bandwidth (10 Hz - 100 kHz). The first generation of players, however, do not  have digital outputs (copyright issues), so external decoders cannot be used. The player has to be connected to the receiver (amplifier) via 2 or 5.1 analog inputs. Question: What are the consequences for today's mass market receiver (amplifier) in respect to very high incoming frequencies? Can the receiver (amplifier) be damaged if not designed for such high bandwidth? First reviews of DVD-Audio / SACD players say that players are equipped with a "normal"/"high" bandwidth output switch, in order to protect the amplifier, but also point out that quality of sound can be degraded by this. For today's purchases, does it make the difference if one buys a receiver with "normal" frequency response (20 Hz - 20 kHz up to 10 Hz - 50 kHz), or from now on we should stick to high-bandwidth amplifiers in order to be well prepared for analog DVD-Audio input?

A Depending on the amplifier design, the bandwidth may be restricted to prevent high frequencies (say, above 50 kHz) from getting through at significant levels. For 96 kHz audio, there will be filters in the player to eliminate everything above 48 kHz and above 96 kHz for 192 kHz audio with the PCM type of DVD-Audio. For SACD, they don't use the filters. That is one supposed advantage of SACD. Some amplifiers might become unstable at high frequencies, say 100 kHz, if connected to speakers or cables that have significant capacitance, with the amplifier seeing a short circuit at those frequencies. However, this is primarily an issue with high frequency noise in the system rather than an audio signal. Music that I have analyzed shows most of the energy at 60 Hz to 6 kHz. Very little is there at 20 kHz, let alone 50 kHz. The harmonics for musical instruments fall off considerably as we go up the audible range. Also, microphones don't have much response at 30 kHz, 40 kHz, 50 kHz and so on. The marketing people tout the high frequency extension of the new formats, but what we will notice is the improved reproduction in the bands that we can really hear, such as below 10 kHz, not anything in the 25 kHz region. So, don't worry about it. Our current receivers and processors should do just fine, even without using that high frequency filter switch on the DVD-A players.

Q In regards to subwoofers being "in phase", do you mean the sub and the bass drivers of the main speakers are moving the same direction at the same time? How do you determine that your subwoofer is in or out of phase? How do you know if the phase setting you have selected is the best possible?
A Yes, in phase means all the drivers are moving the same direction (out of the enclosure) at the same time. However, this does not mean that they reach your ears in phase, because the subwoofer and main speakers might be a different distance to your listening position. That is one reason the phase adjustments exist on subwoofers. But, as I mentioned before, because of crossover networks causing phase shift above and below their setting, you will only have one frequency in phase between the mains and the subwoofer. You just have to try out the various settings, in combination with positions of the speakers in the room, to get the best results. Only your ears can tell what that is.

Q Do I need a Dolby Digital receiver if I have a DVD player with a Dolby Digital decoder built in? I have a Denon AVR2500, Denon DVD3000, Klipsch KSB2.1 up front, and Klipsch quintets for surround. I have read elsewhere that because the DVD player has a built in Dolby digital decoder, I do not need a Dolby Digital receiver.

A As long as your receiver has a set of 5.1 analog input jacks, no, you would not need a DD receiver to get DD with a DVD player that has 5.1 output jacks. Remember though, if you have the DVD player with the 5.1 outputs and a receiver with 5.1 inputs AND DD decoding built-into the receiver, you will be better off using the digital output from your player into the digital input on your receiver, because that is usually the only way you can activate many of the features of the receiver, such as DSP modes.

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