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Q&A # 128 - July 23, 1999

Staff

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Q I recently purchased a new system and have been puzzled about whether I have hooked it up properly to enjoy the best sound. I have a Denon AVR-2700 receiver which has pre-outs for L/R/C as well as a subwoofer pre-out. I have Klipsch KSF 8.5s for the front L/R; KSC-C1 for the center; KSB 2.1 for the surrounds; and KSW 150 subwoofer. The Klipsch subwoofer has inputs for a receiver's speaker level outputs as well as a L/R line input for use with RCA phono plug. I currently have a cable connected from the receiver's subwoofer out to the subwoofer's subwoofer input. The front speaker size is set to "large" and the center and surrounds to "small" in the receiver. I've set the low-pass on the subwoofer to 80 Hz. Is this the correct setup? The Klipsch manual implies that I could also use the L/R line inputs on the subwoofer in addition to the subwoofer input. Would this improve my sound in all modes (i.e., DD, Pro Logic, direct, stereo, etc.)? If so, would I run interconnects from the receiver's L/R pre-outs to the subwoofer's L/R line inputs? What would the be correct speaker size setting? Finally, a general question about the Denon bass management....when the speaker size is set to "large", does the bass signal below 80 Hz get sent only to the front channels or does it also get sent to the subwoofer channel? Thank you for your help.

A Connecting the speaker-level outputs from your receiver along with the subwoofer pre-out from your receiver, all to the subwoofer, would not result in any improvement in the sound. These inputs are for use in different situations, where you need to have the subwoofer handle all the low frequencies, but the amplifiers from your receiver are needed for the satellite speakers. The subwoofer's crossover network filters out the low frequencies from the receiver's amplifiers, and sends the amplifier power to the satellite speakers. If you have outboard power amplifiers, then you can use the line-level pre-outs to go to the subwoofer's line-level inputs, and the sub again filters the lows, and sends line-level signals (minus the low frequencies) to the outboard power amplifiers. Both of these cases apply when you don't want to burden small front speakers with low frequencies. Setting the speakers to "Large" allows all the frequencies to go to those speakers. Setting them to "Small" results in everything below 80 Hz being removed. You can direct the bass to the subwoofer or to other speakers, depending on the sophistication of the bass management capabilities in your receiver. If you set a receiver to "None" for the subwoofer, then all the lows go to the front speakers. You just have to try several setups out to see what sounds best in your own home theater. Keep in mind that the high-pass to satellite speakers or to outboard amplifiers from the subwoofer usually is a fixed frequency. So, if you adjust the low-pass frequency to the subwoofer too far below the fixed high-pass frequency, you could end up with a "hole" in between the low-pass and high-pass. However, you also need to consider the slope of the crossover, since there is always a gradual decline in the response after the crossover frequency, rather than a straight up and down dropoff. If the high-pass is 80 Hz, it is likely the best low-pass setting would be around 60 Hz - 70 Hz. Setting the low-pass to, say, 40 Hz, would likely give you the hole.

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Q I am in the market for a sub, and one consideration is the connections and controls provided on the competing units. My goal is to seamlessly blend the sub with my mains . I believe that the best setup would send the low frequencies to the sub and the remaining to the mains. The added benefit is that my outboard amp would not have to power low frequencies into the mains, and thus they would play cleaner. Should the sub have line level connections or speaker level for such a setup? For either route (line or speaker) what is the function of the filters and crossover commonly found in good subs? Is one set of controls for line and the other for speaker? Is it better to use line level if you expect to place the sub a distance (20-25 ft) from the mains/amp/pre amp? The rest of my system is PSB 500i - mains, NAD 917 - preamp, NAD 912 - amp. Any recommendations for a sub that would meet your suggestions for above?  I am looking for tight, clean, musical and flat down to 20.

A The majority of subwoofers have both line-level inputs and speaker-level inputs. Their use depends on your needs (see the preceding question and answer). Since you have outboard amplifiers, use the line-level inputs on your subwoofer, and line-level outputs of the subwoofer to your outboard amplifiers. This will give you >80 Hz signals to your outboard amplifiers. Remember the caveat I mentioned above about the low-pass setting and high-pass fixed frequency. As to your desires for blending, I would suggest getting a subwoofer with a variable phase setting rather than one that only has the choice of 00 or 1800. Since you want clean bass to 20 Hz, this starts narrowing down the choices. Start with the Sunfire Signature Subwoofer and Velodyne HGS-18, and go from there.

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Q How do I configure a Yamaha RX-V795 receiver for using DD? What I need to know is the dB level I set for each channel. I have a sound level meter (SLM) that will help.

A The overall loudness will depend on your tastes. What I think you are actually referring to is the balance between the channels. Measure the SPL (Sound Pressure Level) with your meter in the sitting position. I like the center channel a bit louder than the front left/right, so I can understand the dialogue. The rear channels sound best when about 2 dB - 3dB softer than the front. Of course, that is just my own preferences. Also, you will need to adjust the volume of the various channels depending on how the soundtracks are mixed. I watched a movie the other night where the voices had been so poorly recorded, I had to turn the center channel up quite a bit. You might start off by setting all the channels to the same SPL with a 1 kHz test tone and then adjust them to your tastes once the movie starts.

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Q In my basement I have pre-wired for 4 in-wall speakers (my wife won't have bookshelf speakers) and am considering using in-wall speakers for surround sound. Would you recommend this? I am considering Radio Shack's in-wall speakers based on their LX-5 bookshelf model. I used these upstairs and they sound great on a 100-watt Sony receiver.

A Well, I would recommend it considering that your spouse prefers it. However, having the same speakers in-wall that you have in the bookshelf form upstairs does not guarantee that they will sound the same. There can be a tremendous variation in tonality with the same drivers due to the enclosure and the fact that the drivers are now pretty much flush with the wall surface. The bass and low-mids will probably sound different, but the highs will be somewhat similar. I would suggest doing some auditioning of in-wall speakers at showrooms before you buy. If you can listen to the Radio Shack in-wall speakers at one of their stores, that will help your decision.

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Q I have just recently bought a $100 surge protector /line conditioner, but I am thinking about returning the unit and buying the Panamax 1000+instead. The specs seem to be the same between the two products, except for the $350 price difference. I don't mind paying the extra bucks if it really does perform and protect my equipment better. Also at the moment I am using a receiver as my preamp/processor, but I am thinking about changing it to something like a Acurus ACT3 or the Sony TA90000ES. My question is will I hear a big improvement in quality and performance, or do I have to move up to the Proceed, Classe, or Lexicon level to really hear the difference. My system consist of HK AVR80 Receiver, HK ADP303 Processor, ATI 1505 AMP, Mirage OM10 Fronts, Mirage MC2 center, Mirage MBS2 surrounds, Sony S3000 DVD, and HK 8550 CD player.

A The benefit of AC line conditioners is another one of those things that you either believe in or you don't. The effects are subtle, and if you are not tuned into them, you won't hear the difference. They attempt to filter out RF from the line as it is coming into the amplifier. The reason for this is that Intermodulation (IM) distortion can easily be in the audible band. IM is produced when two different frequencies interact to produce another frequency that is the sum of the two original ones, and also another frequency that is the difference between the two. So, if two RF signals are close together, the difference between the two is IM in the audible band. That is why it's important to get it out of the AC coming into the amplifier. I measured a 40% reduction in spurious noise at the speaker terminal outputs of an amplifier with a good AC line conditioner in the circuit, compared to when the amplifier was just plugged into the wall.

The ACT3 and TA90000ES are fine products, but receivers are so good these days, it is a tossup as to whether or not you would hear a difference. Let's just say it is possible, and probable, but not definite. The Lexicon is spectacular, but it is a $4,000 item. Meridian is also fantastic, at $10,000+. I have never heard anything better than the Meridian, and it is upgradeable from the Internet.

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Q I was wondering if you folks know of any way to attach two systems to the same set of speakers. I am considering purchasing a home theater receiver such as the Yamaha RX-V995. I don't want to give up good stereo listening. I want to connect my stereo preamp and 995 to the same set of speakers. Is their a way to do this without damage to equipment and sound quality? The reason I'm considering this is because most receivers these days convert the analog signal from a CD player to digital then back to analog before going to the power amps. Are their any receivers/preamps that have an analog bypass for stereo listening that are reasonably priced ($1000 - $1500)? I see that AudioSource has a forthcoming product that that say will have an analog bypass. But it doesn't support DTS.

A Assuming you have a stereo power amplifier to go with your stereo preamplifier, the solution is to use Y connectors between your CD player analog outputs and the inputs on your stereo preamplifier and the 995. Then, you use a speaker selector that lets you switch between the outputs of the stereo amplifier and the outputs of the 995 to go to the front left/right speakers. This bypasses the receiver entirely for use of the stereo setup.

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Q I'll be moving into my new house soon. My equipment is as follows: Yamaha DSP-A1 (110watts), Monitor Audio PMC703s for front, PMC702 for rear, and CC900 for center, all capable of handling 200 watts, a 46" rear projection TV, and Pioneer DV717 DVD player. The room I'm going to use as a home theater is 13' wide, 14' long, and 8' high. (1) Is my room big enough for my equipment? 2) I'm planning to get a good power amp for my two front speakers only, and for music only. What power amp (stereo or mono) would you recommend as outboard to my Yamaha receiver? (I thought of Proceed Amp2 or Musical Fidelity X-A200.) 3) In a room this size, can I get a projector instead of my rear projector TV (46 inches)? If yes, what would you recommend, thinking forward to DTV? 4) The room has a tile/marble floor, one side wall is 1/4 open to the hallway, the walls in the room will be 1cm wood veneer, and the external walls are brick. Should I build an extension and a door to cover the open side wall? What else can I do to improve the acoustics in this room?

A Both the Proceed and Musical Fidelity would be fine, and they would take the load off of the Yamaha for surround sound (it would be a shame for you not to use them when playing DD or DTS music and/or movies). The only thing that might suffer from the size of your room is the deep bass, so get a good subwoofer that can output plenty of SPL at low frequencies. The marble floor will be a problem though. You should consider some area carpets, and also some carpet wall hangings (or else some egg carton mattress pads which are ugly but effective). As to the TV, consider one of the new desktop LCD XGA front projectors. They will handle everything up to around 720p. Prices vary from around $3,000 up to $12,000 depending on how bright the image is, and other features.

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Q I am refurbishing a loft and will be completing my entertainment center soon. The entertainment center is built into the wall which is raised up on a fabricated steel/wood platform. Once I got all of the components into the cabinet, the vibrations from the bass forces causes my CD player to skip even at moderate levels. Do I move the sub, or the CD player? The player is old and I plan to get a new component but most likely will have to move something. Equipment: 2 Carver 250/W/channel main amps feeding infinity Kappas, and the rears are Mirage. I have one Carver amplifier for the center channel and a Pinnacle 250 watt sub.

A Your entertainment center is acting like a big speaker enclosure and resonating. It is not likely that moving the subwoofer would help, although you can try that. My guess is that the vibration is worse with the cabinet doors all closed, or even with one of them open, so you can try leaving one or more of the doors open at different angles. Putting the CD player on dampers (e.g., felt pads) might also help to reduce transmission of shelf vibration to the player. You could also try moving the player to a different shelf.


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