Q&A # 160 - February 9, 2000

Staff

Q Using a sound level pressure meter with test tone I discovered that the rear left channel was much louder than the right. It is not room acoustics as it is clearly audible (or not) regardless of listening position. I am using the Sony DA80ES with its internal amps bypassed employing Acurus 100X3 for the front speakers and Acurus 100X2 for the rear speakers (JBL Control Monitor 5). Of course I compensated with the balance control but it bothers me that the balance should be so disparate.

A There are several possibilities. Your Acurus power amplifier might be misbehaving, and to check this, reverse the amplifier channels that are driving the rear speakers to see if the problem moves from the left to the right speaker. Secondly, it could be the speaker. Switch the rear speakers to check this out. It might also be the pre-out of the left vs. the right rear having more output. See if the problem still occurs when using the Sony's own power amplifiers. This all assumes you have checked the volume level menus in the Sony to make sure the channels are set to the same level in the rear.

Q I am using 5 B&W Nautilus 805s and a pair of Velodyne F-1500rs for my surround system. Should I set the speaker setting to "small" or "large"? I am using an Acurus ACT3 pre/pro. My second question is about my subwoofer. It has an adjustable low-pass filter from 40 Hz -100 Hz with a 6dB/octave roll-off. If I set it to 100 Hz when I use the "small" speaker setting in the Acurus which also has a low-pass filter of 100 Hz and 6 dB/octave roll-off, would the combined filters result in a low pass frequency of 50 Hz with a 12dB/octave roll-off?

A You would have a 100 Hz low pass with 12 dB/octave roll-off. Set the speaker size to large and use a 50 Hz low pass frequency in the Acurus. Set the subwoofer low-pass as high as it will go.

Q I purchased two turntables and a mixer about a year back, and have been plagued by a very serious audio gremlin ever since. Maybe you can help. I have B&W 601s, Mirage twin 10" subwoofer, NAD integrated amp, Rotel phono equalizer, Vestex PMC05 pro mixer, good cables, two Technics SL1200 turntables with Stanton cartridge. The problem is that the speakers and the sub flutter to the music, and the fluttering increases with more bass and increases with volume. IMPORTANT: the fluttering occurs with a record on the platter and the needle in the groove at a stand still - as long as I just touch the record. The flutter also occurs if I don't touch the turntables or the resting table but turn the volume up to low to moderate listening levels. My amp is only 60 watts, and I can't turn it up past 1/4 volume This does not occur at all when I play a CD from my Marantz CD changer.

A You are experiencing low frequency feedback. The vibrations from your turntable go to the cartridge, to the amplifier, to the speaker, and the vibrations from the speaker get back to the turntable through the air or the floor. You can reduce this problem by isolating your turntable by putting it on a pad. There are commercial ones available, but try just using some felt furniture pads underneath the turntable feet. It may take several pads under each foot to do the job.

Q I'm seeking advice on the best and reasonable cabling alternative for the following products: Sunfire 300 amp, Sunfire Classic Tube Preamp, Dunlavy SCIIIs, and Sony Es CD. Audio interest only. P.S. This site has been so valuable to me that I feel I should make a donation to your favorite cause which I would happily do.

A I would suggest Kimber PBJ interconnects and Nordost Blue Heaven speaker cables. This will be a very affordable package. As to the donation, I have started the SDI Scholarship Program to help disadvantaged high school students get a college education. Maybe more on that at a later date when it is fully underway. The first student received his scholarship in 1999. SDI stands for the corporation Scientific Design and Information, Inc., under which I publish Secrets.

Q I am in the process of building a home theater in a dedicated room in my basement. The room will be 22' x 13.5' with a ceiling of about 8'2". I will be using the Dwin 700 FPTV with the trans scanner and the Lexicon MC-1. I have narrowed my choice of speakers down to: 1. Martin Logan Requests, ML cinema center, ML scripts surrounds (two pair), or 2. Aerial Acoustics 10T, AA CC3 center, AA SR3BR surrounds (one pair to start, two pair eventually). I have listened to both at the same store. The salesperson favored the Martin Logan setup, and I must say that the surround sound effect was better with the Martin Logan setup, but I was concerned that the Aerial Acoustic setup was not ideal in that the right and left speakers seemed to drown out the center channel (he had to move the 10Ts into the room, and it seemed to be set up more for music). I am concerned some of reviews I have read about the MLs and the difficulty I would have placing them in a room of my size, although the store assures me that this would not be a problem. Which setup do you think would be preferential for a room of my size? Should I be concerned that the Aerial Acoustic setup will not give me as dynamic a home theater sound? Also what amplifier(s) would you suggest for each setup? I have been looking at Krell and Bryston.

A Both the Aerial Acoustics 10T and the Martin Logan (ML) are low impedance and low sensitivity speakers. The MLs, like all electrostatics, have to be carefully placed, but they are not "difficult" to place. You will simply be somewhat more restricted to where they can be placed. As long as you keep them out from the walls a few feet, you should be fine. If you liked the ML sound, then go for it. I would suggest having the same ones in the front and rear. This is best for today's digital surround sound. You will always need to use an electrostatic center channel to keep the tonality the same across the front (a dipolar ribbon might also be OK). Because of their impedance and sensitivity, get as much power as you can afford. Both the Krell and Bryston will handle them fine. Get a minimum of 200 watts per channel.

Q I recently purchased a Yamaha HTR-5150 receiver with a JBL SCS125a speaker/subwoofer set. I have the option of wiring the speakers through the subwoofer (speaker level inputs) or wiring them directly from the receiver and the subwoofer as "line level". The receiver is 85 watts and the subwoofer is powered at 75 watts. I am new to setting up surround systems. What are the advantages/disadvantages of both types of speaker connections?

A The speaker-level connections consist of running the speaker outputs of your receiver to the speaker-level inputs on your subwoofer, and the speaker-level outputs from the subwoofer back to the front left/right speakers. It is for when your front left/right speakers are very small and cannot handle low frequencies. However, because the crossover is after the speaker output, it does not really save you any amplifier power. The crossover absorbs the low frequency energy. If your speakers are small, however, you should use this configuration. Line-level connections allow all the frequencies to reach your front left/right speakers, since the speaker outputs of your receiver go directly to the speakers. I have not found any clear evidence that either type of connection is better for the subwoofer under all conditions. It seems to work fine both ways.

Q I've been given numerous conflicting opinions about the best type of speaker to use for the rear channels: Bipole, Dipole, or Direct Radiating. Could you comment on this and your opinion as to which is the most useful mode for HT using DPL, DD, and DTS? By the way, my rear speakers are the Polk Audio F/X 500 which have a bipole/dipole switch and due to space constraints, they are placed on the side walls some 8 feet behind the couch.

A Back when it was just Pro Logic, the recommendation was for dipoles or bipoles in the rear, to give a diffuse surround. Now that the rear is full range, with DD and DTS, the choice is really optional. The rear surround still tends to be for ambiance (diffuse presentation is best), but there are also some very distinct directional sound effects once in a while. My recommendation is to use the same type of speaker in the rear as in the front (dipole, bipole, or direct), if not the same exact model.

Q I�ve just purchased a new Denon AVR-3200 along with a Toshiba 3109 DVD player to go with my Kef Q-55 speakers. I am using the DVD player to play audio CDs as well. It strikes me that the sound produced when playing audio CDs is actually better via the analog connections from the DVD player than when using the digital bitstream. Can the Denon DAC really be inferior to the Toshiba? I�d hate to think I spent a fair amount of cash for the Denon product only to find the Toshiba DAC to be better! Or is it normal for this to occur (something about the bitstream, perhaps?) What I am finding is that the signal from the Denon DAC is very "thumpy" and just a bit too muddled for my liking. The analog sound from the Toshiba DAC seems brighter and more defined without as much bass thump.

A It could be a difference in the DACs, but outboard DACs have their own set of problems other than just quality. You have to use a 75 Ohm cable to connect the transport to the DAC. The jacks in the transport and DAC have to be good too. There could be timing issues between the transport and DAC that cause the differences you hear. So, it is not necessarily that the Denon DAC isn't as good as the Toshiba DAC. But, in your specific situation, since you prefer the analog connections, use them. That is the nice thing about having a choice.

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