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Q&A # 126 - July 18, 1999
Staff
Q Is there any discernable advantage to putting spikes at the bottom of speakers/speaker stands? One salesman said that was especially important for powered subwoofers.
A The reason for spikes is to isolate the speakers from the floor. This can be done with spikes, but it can also be done by placing the speakers on felt pads, or even just on a rug that is already there. This will work for subwoofers just as well as it will for other speakers. Keep in mind that spikes can damage floors if the speakers are really heavy. I use felt furniture pads (about 1" x 1" square) for a set of floorstanding speakers in my living room. It generally takes two sets of pads stuck together, under each corner of the speaker. I test the effectiveness of the pads by rapping on the top of the speaker before and after placing the pads. When there are no pads, I can hear the floor resonating while I rap on the top. After the pads are placed, I can't hear the resonating anymore. The pads usually compress after a few weeks, and it may be necessary to add a third pad under each corner.
Q I'm planning to install DSS and wire my house with RG6 coax cable. My question is, when it is time to upgrade to HDTV, I will probably have to upgrade the dish and the receiver, but will I have to rewire my house with a different cable?
A No, HDTV will still use RG6. You might want to run more than one cable to each room. While duplexers allow you to combine signals, its not always the cleanest method. You may have multiple antennas on your roof to pick up the various HDTV channels. You might want to look into Channel Master at http://www.channelmaster.com. They offer all you need now to receive HDTV. They also have a very good manual of how to do it. It's going to be war with home associations trying to put up roof top antennas to get HDTV because it is the best source available right now. And it will be for a long long time.
Q I have a question concerning my speaker setup with my Yamaha DSP-A1. I just upgraded my rear channels to the same model speakers as my large main front (Polk RT 16 towers). I will be moving the old rear speakers to the front effect channels available in the Yamaha DSP-A1 (for the derived 7.1 DSP mode) just as soon as they return from Polk's repair facilities. One speaker of the pair developed a rumbling/buzzing driver that became noticeable after I upgraded to DD/DTS 5.1. Not wishing to redirect bass at levels as high as 90 Hz, I had set my rear channels to LARGE (full bandwidth). Do you think the speaker malfunction is just a coincidence, or could this setup have caused my drivers to be overloaded somehow? I wouldn't think subjecting a small speaker to full range dynamics should damage the speaker. Wouldn't I just lose frequencies outside the speaker limits? By the way, the effects speakers are Polk's LS f/x bi/dipole speakers (2 x 4.5" mid driver, 2 x 1" tweeter) [with -3 dB frequency response of 50 Hz - 24 kHz].
Last Concern: A Yamaha tech told me that although the front effect amps are full bandwidth, DSP limits the frequency to 80 Hz-14 kHz - no trouble for the LS f/x's! However, I noticed something odd with my setup. As you probably know, when using all internal power supplies, the Yamaha DSP-A1 can exhibit 5.1 or 7.1 audio via speaker setup menus. Switching to 5.1 mode means the extra two front effect channels are muted, and all front information is sent to mains. Switching to 7.1 audio turns "on" the front effect speakers, and sound is mixed out and spread between the front mains and front effects. That's all well and good, but I am using an outboard Carver 2 x 100 watt amp for my front effect channels instead of the internal 2 x 35 watt amp provided by the DSP-A1. With this setup, I have noticed that the pre-outs to those front effect channels are not muted when put into 5.1 audio mode. So, I get 7 channels firing using pre-outs whether or not I use 5.1 or 7.1 settings. My feeling is, that in 7.1, I get what Yamaha intended to be as my 7.1 DSP audio. That is mixed sound spread to main towers and front effects so that front effects "see" 80 Hz - 14 kHz. However, I suspect that when in 5.1 mode, perhaps all front speakers get the exact same full range signal (something like having four equal front main speakers). If this is the case, I could be back in the same speaker damaging situation as before, if that can in fact damage a speaker. Do you think I am in danger of damaging my speakers again?
A I am glad to see you going to the same speakers for the front and rear. This will give you a nice balanced tonality when playing DD and DTS material. I would suggest using the DSP-A1's own built-in amplifiers for the front effects. The sound coming from those channels is meant to be very soft background. It is particularly useful when the front left/right main speakers are close together. I am not sure what Yamaha does with their DSP when using the front effects, but I suspect that, although the signal is derived from the front channels, it is not subtracted from those front channels. It simply adds ambience, sort of like putting the music in a larger hall with some reflections from large walls. In any case, because the sound in the front effects channels is low volume, it is unlikely you would ever damage the small speakers. I use small bookshelf speakers for those channels too, and I have never had a problem. You might be better off using the Carver amplifier to drive the rear channels, where those 100 watts/channel would be more useful. This would free up the DSP-A1's power supply to handle the front channels.
Q What is actually sent to the subwoofer pre-out in a Dolby Digital receiver? I think this question is important for the correct setting of the crossover of a subwoofer. I searched for the explanation in the manual for my Denon 2700 receiver, but I could not find a satisfying answer. Of course, Dolby Digital processing has 6 completely separate channels, and then the sub pre-out is used for the LFE. But what is sent to this output if I use the Stereo, Matrix, or any other than DD mode?
A DD/DTS receivers send the LFE (the 0.1 part of 5.1) channel analog signal to the subwoofer output jack on the receiver. When in other modes, such as Pro Logic, two channel stereo, or whatever, the subwoofer output jack has low frequency information contained in that signal. The high end cutoff is usually around 90 Hz, but it may be higher on some receivers (e.g., 120 Hz). In the case of DD and DTS, the subwoofer output is receiving its information from a discrete sixth channel, but for other modes, the low frequencies are extracted from both of the two channels in the stereo CD, FM radio, etc.
Q I'm in the homework phase of planning a new basement HT, and I appreciate all the informationI gleaned from reading your Q and As. I would like to pre-wire for the most flexibility in the future (5.1 -> 10.2), but I don't know where to place the speaker outlet boxes in the walls. It doesn't seem to make much sense to bury speaker cable in conduit only to find that you have to run 3'-5' of cable over the floor/walls to reach the speakers in their optimal listening position. I can't audition in the room as it is not built yet. Clearly a catch 22, and some compromises will be necessary. I thought I might be able to learn from other's experiences, and avoid some expensive and time consuming mistakes. We just finished remodeling the kitchen, so while I currently have been given a fair amount of freedom, I am cashed out. I'm hoping to be able to afford Yamaha's 2095 or like, but maybe once the second mortgage is paid down I could up-grade to a Lexicon level processor with room for bass shakers. Any advice for wall placement of speaker binding posts would be greatly appreciated.
A The way I would do this is to make a decision as to which end of the room the receiver will be placed and then put a receptacle about 12" above the floor in the center of the wall behind where the receiver will be placed. Then, run speaker cable in the wall around to the rear and to receptacles on the rear wall 12" from the floor and about 3 feet from the side wall. Leave about 6 feet of extra cable length inside the wall. If when the room gets closer to finishing, you decide the receptacles have to be moved more towards the center of the rear wall, you can move the receptacle and you will have the necessary length of cable to reach that far. For binding posts, here are a few links: http://www.daburn.com/~daburn/general.html, http://elexp.com/clp_bind.htm, http://www.lashen.com/vendors/Mueller/BananaPlugsJacksBindingPosts.htm.
Q I have Paradigm Monitor 9, CC-350, and ADP-170 , PW-2200 currently running with a Denon 3200. I want to upgrade to either a Denon 5700 or Sony TA-E9000ES with either an Adcom GFA-7500 or Outlaw 165 x 5 Amp. Which would be the best for my speakers, and would I notice a big improvement over the 3200 with either of these?
A Since you are planning to have an outboard power amplifier, both the Denon and Sony would give you good results. The Adcom and Outlaw are equivalent, although you will probably get more for your money with the Outlaw since they are factory direct on the Internet. And, you certainly would notice a big improvement. The 5700 and E9000ES are top notch products. Plus, with a nice outboard five channel power amplifier . . . wow! I'll bring the beer!
Q I recently moved into a new house that has been pre-wired for my surround speakers. The room dimensions are 16 ft X 20.5 ft. My screen is along the long dimension. This wall (the wall the screen is up against) vaults up to a height of approximately 12 feet. My surround speakers (Polk Audio RT-5s) are mounted flush with the back of the speakers against the wall, pointing straight out. The bottoms of the speakers are about 8 feet off the floor. The distance between the surround speakers is about 16 feet; wider than the distance of my front speakers (Polk Audio LS-50s). The problem I am having is the audio information from my surrounds seems to be going straight over my seating position (the couch is about 5 feet from the back wall). With Dolby Digital (which is supplied from a Yamaha laserdisc player), I should hear some pin-point detail (i.e., a car or helicopter moving from rear left to rear right). I'm not getting this. The room is filling with sound but not the detail I had from my past setup which consisted of these surround speakers being placed on stands 4 feet high, about 8 feet behind my seated position, 8 ft apart from each other. There is a definite difference with the surrounds off the wall vs. with them on. I'm at a loss. Is there any advice you can give me that will remedy this surround speaker placement issue with the room dimensions given?
A When Pro Logic was the only game in town, surround speakers on the walls worked pretty well, because the sound from the rear was diffuse anyway, and of limited frequencies. DD and DTS have changed all that. Your rear wall is acting like a sounding board and diffusing all the detail that is present in discrete stereo of the rear channels. You need to get your rear speakers off the wall and back onto the stands. However, I can understand your situation of having cables already in the wall. So, just go into the wall and move the rear speaker cable receptacles to a position near the floor (do it yourself or have a carpenter do it). Then, run the wire out of the low receptacles into your speakers. You may need to put an area carpet over the cables if the space behind your couch is a walkway. Use flat speaker cables in this case.
Q I have been told, and read about software that can help in designing subwoofer boxes. I was wondering if you have any idea where this type of software can be found and if it is free or not. I have been trying to find out what advantages there are to decreasing box site in the hope of increasing the quickness of the speaker, meaning I don't like subs that are boomy and slow.
A There are lots of software packages for DIY speaker designs out there. Some of it is shareware, and others are outright purchases. Here are some links: http://members.aol.com/speaker60e/speakerpro.html, http://www.trueaudio.com/, http://www.hi-fi.com/speaker/software.
� Copyright 1999 Secrets of Home Theater & High Fidelity
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