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Q&A - #6 -
April 3, 1997
Q In
reading your review of the Sunfire Subwoofer, I found something
that just doesn't sound right. Your power calculation. If you use
120 volts for the voltage input to the amp, this is already an
rms equivalent. The peak voltage from the AC line is approx.
169V. Also, there is no duty cycle associated with the line
voltage, it is simply 120V rms x 3.5A = 420W. If efficiency is
90% (power out/power in), then the resulting output power = 378W.
Please clarify this if I have overlooked something, it seems
straight forward.
A The effective rms value for the 120 line voltage
is not 120 V in the power supply of the Sunfire Subwoofer. Look
at a diagram [click here]
which represents the situation in the Sunfire. There is a 1/5
duty cycle at B+ and B-, so the calculation of the effective rms
value (Vrms) is 120 x 1.414 = 169.68; Vrms = Square root of
(169.68 squared/5) = 75.88 Vrms.
Q Hello:
I think I just found a wonderful web location. I need help. I am
considering purchasing Klipschorn speakers. What do you think.
They sound wonderful in the store. They were powered by a Cary
amp. I can't afford Cary. The vendor said a Carver HTR-880
Receiver would power the Klipschorns and five smaller sets of
wall speakers I have in other rooms in my house at the same time.
Is that true? As you know the Klipschorn speakers are built to
fit snugly into wall corners. The way my house is constructed one
speaker would be one inch from the wall on both sides; the other
speaker would be one inch from one wall and 2 inches from the
other wall. Will that placement significantly affect sound
quality? If the 880 Receiver is not adequate, what do you
recommend. Another person recommended a separate amplifier with
200 watts per side. I am a novice and I need help. I am not rich!
However, I did like the Klipschorns very much. I am thinking of
an amp in the range of $1,000-$1,500 (please don't laugh). Thank
you for your help.
A Even though the Klipsch are efficient, it seems
that you might be using more than one set of speakers at the same
time. This places large current demands on the amplifier.
Therefore, I would suggest that you get separates, since amps in
receivers are usually not built for heavy current requirements.
On the other hand, as long as the receiver has pre-out RCA jacks,
you can connect more powerful amplifiers to the receiver and
accomplish the same thing. You may want to add surround sound
later on, so get a receiver (or preamp/processor) that has
surround sound decoding, and just use the stereo channels for the
time being. Carver has good products. I also saw a Yamaha 2090
now on sale for $1,000, which is a bargain. It has the 5.1 set of
inputs that will keep you forward compatible (AC-3 and DTS).
Q I
have two issues that I am confused about and I was hoping that
you could help me. The first question has to do with amplifier
power. My receiver is a Pioneer VSX-503. It is not supposed to be
able to drive 4 ohm loads but in the back of the manual it gives
a dynamic power. The values are 2 ohms = 265 watts, 4 ohms = 240
watts, and 8 ohms = 170 watts. What does this mean? The receiver
is supposed to only output 110 watts into 8 ohms. Could you clear
this up for me? Also, on most new components I have noticed the
component control connections. According to the manuals these
systems help components of the same brand communicate to make
operation easier. What exactly do these features do and are any
of the different brands compatible? A few examples of these
systems are: the Pioneer control jacks or the Kenwood CCRS
system. Thanks for your help!
A Dynamic power is a term used by the mass market
component manufacturers. It means the power that an amplifier can
deliver on a short term basis (a transient peak, such as a gun
shot or snare drum crack) into the speaker load. The 110 w/ch
rating of your receiver is the rms rating, that is, continuous
power into the 8 Ohm speaker load. It will also deliver 170 w/ch
into 8 Ohms, 240 w/ch into 4 Ohms, and 265 w/ch into 2 Ohms for
the short (transient) peaks. An 8 Ohm speaker is not 8 Ohms
across its entire audio spectrum, but rather, it averages 8 Ohms.
At any one frequency, the impedance might be 5 Ohms, 8 Ohms, 11
Ohms, etc. A 4 Ohm speaker might go down to 3 Ohms and up to 10
Ohms. For any typical mass market receiver, it is best to stick
with 8 Ohm speakers.
The component control connections are a way of getting separates
to behave like an integrated system. I have seen several
different connectors on the back of various brands of components.
They are not all necessarily compatible, but are actually
designed so that you are more likely to buy the same brand of CD
player, FM Tuner, Amplifier, etc.
Q What
do you folks recommend for cleaning speaker cabinet veneers?
A Much of what looks like wood veneer is actually
vinyl. It can be cleaned with just about anything that is not
harsh. Otherwise, some of the dye can come off. However, we use
Lemon Pledge (Johnson Wax) for all speaker cabinets. Wood veneers
are usually finished with lacquer rather than the more durable
polyurethane. A good quality furniture polish works well. For
electronic components, we clean with a damp cloth rather than any
chemical or wax.
Q I
have a quick question. If I hook up a straight DTS decoder that
sends 5 full bandwidth channels, and the .1 sub to a THX speaker
system and 6 channel amp, will I get a loss of bass below 80 Hz?
In other words, do you think a THX system will sound bass
deficient as compared to standard THX/Pro Logic?
A THX is a set of standards that operates on top
of Pro Logic and other decoding formats. It is not a format in
itself. As more and more processing gets piled on top of each
other, you could end up with sending the < 80 Hz to one or
more of the other channels by mistake, but it would not get lost.
It would just be coming out of a speaker that you did not intend
it for. It would not sound bass-deficient unless you accidentally
had the .1 bass sent to small front left/right speakers. We have
had that problem here from time to time when a new processor
comes in for review. We just fiddle with the controls until
everything is coming out of the appropriate speakers and then
write down the settings. THX subwoofers require a switch that
removes volume control and crossover from the circuit.
Q In
your News Flash #5, were the Pioneer DVL-700s and DVL-90s
pre-production units, or post production units that were
purchased on the street? Was the DVD portion that awful? How was
the LD section - I have heard very positive things about the LD
and audio but questions on the DVD (software or hardware)?
A All of the units tested were "Post
Production" units. One DVL-90 and one DVL-700 were from one
store. Another DVL-700 was from a different store, and the others
were units provided by people who have purchased them. I believe
the problems were that bad. A DVD player and an LD player are two
different creatures all together, and they should not be sharing
the same parts. It appeared that the DVD was using the same high
frequency roll-off that the LD player used, and this should not
be the case. Again, the copy of Video Essentials was averaging 8
Mb per second (the average DVD movie disc will be around 4-5 Mb
per second), and was only a test pressing. Now that real software
is out I will try to take a look at the Pioneer and see if these
problems are as obvious. We did not compare the LD part of the
player, the actual transport of a CLD-79.
Q I
would like to know more about DVD . As I am doing a report on
this for my project , I would like to ask you how DVD is
encrypted (how it is protected from pirating). Secondly how are
data stored on DVD? Is it done differently from LD & CD?
A This is a very complex subject and is too much
to cover technically here. I will try to make it as simple as
possible. The protection scheme is called Macrovision. It has
been used on video tapes for many years now, most notably Disney
titles.
There is a circuit in your VCR called automatic gain control
(AGC), which is used to compensate for changes in video levels.
This helps your VCR make the best possible recording. TVs also
have AGC, but it works differently than your VCR. What
Macrovision does is trick the AGC circuit into thinking the video
level has changed drastically, and the AGC then amplifies or
attenuates the brightness to compensate for the change. This
results in an incredibly dark or bright picture that is
unwatchable. It is done on the luminance (Y) part of the signal.
DVD mastering is done with modified CD pressing plants. Unlike
CD, DVD is stored in a compressed format called MPEG 2. MPEG 2 is
a variable bit rate, with the minimum rate being 3.5 Mb per
second and the maximum rate 10.08 Mb per second. This rate
includes both the audio and video material. The more audio sound
tracks and subtitles you have, the less space you have for the
actual picture!
Q Has
your organization ever thought of having a face off between the
Yamaha 3090, Dennon 5600 and Onkyo 939? All of these represent
flagship AV Receivers and cost a significant amount of money. I
do not believe a magazine like Home Theater (which usually has
product face-offs) would do such a thing because it could lose
potential advertising dollars based on declaring a winner? I
think other magazines would also shy away from determining a
"Best" AV receiver of the three. Your web magazine
seems to tell it like it is. For example, the News Flash on
Pioneer Combi player's poor DVD performance (both Audio and Home
Theater explained they were pretty good units but did not really
compare DVD performance against others.) I appreciate the candor.
This said, since many people do not have the opportunity to
listen to these units side by side, could we get a "This is
how it really is" review? These units are hard to get
(availability) and represent a large chunk of change - this type
of review would be extremely valuable and help many of us with
our decision process.
Also, any other comments on the Pioneer Combi Players? I was
going to purchase one until I saw your news flash. Now I am going
to buy a Pioneer LD and wait and see on DVDs.
A The problem with faceoffs is that they take a
lot more time to do. By the time the manuscript would be ready
for publication, the manufacturers have changed the models!
Insofar as the top end receivers go, we have found that many of
them have AC-3 built-in, but no set of 5.1 discrete inputs. DTS
is a wonderful addition to the home theater possibilities, and we
cannot, in good conscience, recommend any receiver that is not
forward compatible with new surround formats (without a set of
5.1 inputs, an outboard DTS decoder cannot be connected). So, we
recommend shopping for a receiver that has the 5.1 inputs,
regardless of whether AC-3 is built-in or not. There are a couple
of receivers that have AC-3 AND DTS built-in. Those I might be
comfortable with, but they are few and far between at present.
Our first DTS decoder review is coming shortly, and we think just
about everyone with a home theater will want to have it.
Q I've
only just desovered your fantastic page! Well done! It is the
best publication I've seen. All issues are on-line! Nice to be
able to instantly refer to older editions for reviews, etc. I
like the DIY section. I'll keep my eye on this section since I'm
not loaded with a few thousand to spend on entertainment
equipment (sure would like to). I can't justify my expenditure as
it is on this stuff! The quality of the information in general is
excellent. This is the main factor for me.
A Thanks! *******************************
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Secrets of Home Theater & High Fidelity
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