Q&A # 37 - November 11, 1997
Staff
Q I have a Sony Pro-Logic A/V amplifier with 5.1 inputs, and there is a
Panasonic DVD player on sale with AC-3 decoder built in (of course with 5.1
outputs). My question is, can I just buy the Panasonic and hook it up
straight to my Sony? I've always wondered why outboard AC-3 decoders had
volume controls. Does this mean the outboard AC-3 decoders are pre-amps as
well? Are the 5.1 inputs in my Sony pre-ins? If they are, how compatible is
the Panasonic (w/ built in decoder but no volume controls) with my Sony?
My Sony is also rated at 100w@4 Ohms and can handle two pairs of 8 Ohm
speakers on the mains. My center channel is also rated at 100w@4 Ohms
but has only one set of binding posts. Can I parallel connect another 8 ohm
center speaker on the same binding posts? I'm sure you have explained
everything about Ohms and wattage severals times in Q&A so just tell me yes
or no (although I think it is yes).
A Yes, you can connect the 5.1 outputs from the Panasonic DVD Player to the 5.1 inputs on the Sony Receiver. That is exactly what the Panasonic is designed for. The 5.1 inputs are essentially pre-ins. They go through the volume control, tone controls, and balance, but usually do not go through the DSP circuits. Outboard AC-3 (Dolby Digital, DD) decoders have volume controls only for tweaking, rather than for controlling the overall volume like you would from the receiver. However, they do serve as a preamp of sorts. DTS decoders do have volume controls. The only problem you might have is the subwoofer output from the DVD player. It will have to go direct to the subwoofer, since most receivers do not have the subwoofer input as part of the 5.1 set of input jacks. And yes, you can connect another center channel speaker to your receiver output terminals in parallel for 4 Ohm loading. Personally, however, I would not do that on a mass market receiver, because the power supplies are generally not very big. By using a 4 Ohm load in the center, you may draw potential power away from the main channels.
Q I'm sure you've answered this question before: How close can I put non-shielded speakers to a television set (speakers have 8-inch woofers and the TV is a direct view, not a projection set)? I think I might have ruined my
current TV by placing the speakers about 12 inches from the edges of the
set (Note: I did NOT notice any picture distortion such as green edges,
etc.)
A Well, first of all, you did not ruin your TV. Each time you turn it on, the TV will "degauss", which gets rid of any residual magnetism that has built up in the picture tube. If you have not noticed any color distortion, then you don't have a problem at all. In any case, you can pick up the speaker and move it along the edges of the picture tube to see if it is causing distortion. As you bring an unshielded speaker closer to the tube, the edge of the image will turn blue, green, or purple. Then move the speaker away from the tube until the color distortion completely disappears. That is the minimum separation distance. It is not so much the size of the speaker driver as it is the size of the magnet on the back of the driver.
Q What's the difference between optical cable and coaxial cable? Is one better than the other, or is there no real difference?
A Coaxial cable carries an electrical signal, while optical cable has fiber optics in it that carry flashes of light (representing the same information as is in the electrical signal version). One of the advantages of fiber optic cables, such as Toslink, is that the two components connected by the fiber optics are electrically isolated from one another, which can reduce hum and other electrical interference. My experience is that there is little difference between the two, although many people feel that optical is not as good as coax. What I prefer at this point is balanced cable, which reduces hum and noise too.
Q Of all the speakers in a home theater system, how would you rate the center speaker in terms of importance? Should I spend big bucks on this, or a subwoofer, rears, front left & right? Please rate them inorder of importance. Also if you could provide some key specs and features to look for in buying these speakers it would
be great. Thanks.
A This is a very significant question. The center channel gets MOST of the sound, so it is amusing (well maybe not so amusing after all) that receivers had less power in the center channel until last year or so. Therefore, having a good quality center channel speaker is critical for good home theater. However, you should balance your system for the proper sound stage, which means getting equal quality for all the speakers, including the center channel. Spending a lot on the center channel speaker and very little on the others would not be a good idea any more than getting great front left/right speakers and a cheap center channel speaker. What is popular these days is having a set of L/C/R speakers (such as the M&K LCR-75), which means the speakers across the front are identical, except that the center channel speaker lays on its side. You can also use these same speakers in the rear, especially if you are into DD and DTS digital surround sound. The subwoofer is extremely important too, so that you "feel" the bass as well as hear it. I would look for a subwoofer that responds down to 20 Hz. On a strict budget, I would buy 5 identical reasonably priced ($200 each) bookshelf speakers for the front left/center/right (center channel needs to be shielded), rear left/right, and spend the rest on the subwoofer.
Q I've got a Mitsubishi 40" Front Projection TV (CS-40505) that I unfortunately have to
pump a cable signal into in order to get my local stations (which of
course my DSS doesn't provide). The problem that I am encountering is
white bars in the signal, mostly on the lower channels along with fits of
fluttering and distortion. My other TVs handle the signal very well with
the lines barely visible and no distortion. I'm guessing this is a signal
strength problem or there is a problem with both my coax inputs (Ant A &
B) on the Mitsubishi. I would have to guess too that the TV is very
demanding of a good strong signal since my DSS comes in perfectly. If it
is a signal strength problem and since the cable company won't do anything
to boost the signal that they feel is working fine, is there an external
device that I can use to boost the signal myself or does it sound like
there may actually be a problem with my TV? I've replaced the cables with
no effect so I know it isn't related to that. Any suggestions?
A You might be seeing the vertical sync signal of the picture. This could mean that your TV has its overscan set at 5% or less. Most TVs cut off too much of the picture by overscan, and it appears that you are not cutting off enough. This is
just a guess, and I see the same thing with some test patterns on Video Essentials
and not others because I have my TV's overscan at 5%. But I have never seen
the flicker on cable or other LDs.
If you are not getting this with your DSS, then I seriously doubt that it is
your TV malfunctioning. Cable quality in general is rather poor. Try going
with an antenna and see what results you get with that.
Q I have a Pioneer CLD-D504 laserdisc player and a Sony Trinitron
KV27S15
television connected via S-Video cable. On laserdiscs only, the
picture
flutters or blinks, it's wavy and not solid . . . not bad, but just
enough to
be annoying. The fluttering doesn't happen when I use my DVD in the
same
S-Video jack with the same cable, and neither the composite input from my
VCR nor the RF from cable does it. I took my LD apart and noticed that
when the disk spins, it wobbles a bit. The farther towards the outer edge
the laser goes, and the slower the disc spins, the worse the wobble gets.
I'm guessing this is abnormal.
Could the wobbling disc be causing the wavy picture? If not, then
what? If
so, what could be causing the wobble and can it be fixed without
dropping major $$$?
A The first thing you should try is the composite cable or the other
S-Video output on the Pioneer LD player. I doubt it is the problem, but it
should be checked. If you get the same results, take it back to the store
you bought it from and compare it to another CLD-D504 and see if you get the
same results. If it is determined that it is your player, send it to
Pioneer and get it fixed, as it should still be under warranty.
Q I have read a few articles that compare different DSS systems, but I
have not seen anything to compare Dish Network systems to DSS. The
Dish
Network seems to have the more attractive programming packages. Is
there
a difference in the quality of the Sound/Picture?
A I have not used the Dish Network before. I had heard at one time that
they did a better job with MPEG-2 but nothing since then. I do not
believe that they offer more channels to choose from. DSS has the East and
West Coast network channels that really make it a plus.
The Dish Network does have the deal with JVC and the D-VHS machine.
This allows you to make perfect recordings off of your dish. It is one unit
that includes both the VHS machine and the Satellite receiver in one box.
Q I just purchased the DENON AVR-3200 integrated A/V receiver. It is their
newest offering in the $1200 range, and offers a built-in AC-3 decoder and
provides 85W continous power on all 5 channels. The unit sounds pretty
clean for an integrated A/V receiver, and was one of the few components that
provided the 5.1 input jacks for easy connection of an Aux decoder, such as
DTS.
I am into electronics projects as a hobby, and successfuly added an AC-3 RF
port to the Pioneer CLD M401 LD player, and it sounds great with the DENON
AVR-3200. So I have DD compatibility and plan to focus most of my HT
viewing in the DD format, as well as use my system for general music (Rock, pop, classic) listening.
So to my upgrade question: I bought AR48 speakers (full size book
shelf style speakers) that I am using as my rear speakers back in 1982.
Not bad speakers in their day, but the drivers are worn out, and they don't
match up well to my Klipsch mains, so I want to
upgrade the rears.
Since I am into DIY projects, I have been considering purchasing a DIY
speaker kit and build my own new rears. I am looking at the Audax A652s,
which are a mid to high range frequency response speaker that I thought
would complement my rather more low, full range Kliptsch mains. First, are
you familiar with the Audax A652 kits, and do you think they would match my
Klipsch mains? Are there any speaker kits that you feel would better match
my system?
It is not paramount that I build my new rear speakers from a kit, but
rather, more important to choose the correct rear speaker upgrade to match
and compliment my system. The only "special" criterion I have for my new
rear speakers is that, if possible, I select a style that will sit on 24"
stands. So if you have any better recommendations for my rear speaker
upgrade (other brands, dipole, bipole, etc.) that you feel would better
match to the rest of my system; I would be very greatful.
A It would be best to stick to 8 Ohm high efficiency speakers for the rear since you are into DD with a receiver. The amplifiers in
receivers don't have very big power supplies. You might try some
Klipsch bookshelf speakers for the rear, or the Acoustic Research AR
208 HO, 308 HO series, which are extremely efficient (92 dB/w/m). Unless you are really familiar with the way finished kits sound, you probably should not invest in them. It is a lot of work to end up with something that you may not like.
Q In the latest (#36) Q & A you mentioned that placing an unshielded speaker on top of a projection TV could cause picture distortion.
I thought that this problem only occurred in direct view sets. Can you straighten me out?
A That was my mistake. When I wrote the answer, I was thinking of direct view TVs. It is quite safe to put unshielded speakers on top of projection TVs. Depending on how big the front left/right speaker magnets are, there might be some color distortion effects when placing unshielded speakers too close to the SIDES of a projection TV. Also, for someone placing a projection TV inside a wall enclosure, there could be a problem if a big center channel speaker were placed immediately BELOW the TV. The idea is to keep unshielded speakers away from the area where the CRT (Cathode Ray Tube - Picture Tube) portion of the TV is located.
� Copyright 1997
Secrets of Home Theater & High Fidelity
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