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Q What are the advantages and disadvantages of three-way speakers compared to two-way speakers?
A First,
let's have some definitions: two-way speakers divide the
incoming signal into two sections (using a crossover network),
one consisting of the high frequencies, and the other consisting
of low frequencies. Three-way speakers divide the spectrum into
three sections, one for the highs, one for the mids, and one for
the lows. With a two-way speaker, usually, there is one tweeter
and one woofer, but there may be more than one driver for the
lows, and sometimes, even the highs (such as with a bi-polar speaker).
So, it is not the number of drivers, but the division of frequencies
that defines the two-way, three-way, four-way, or whatever-way
speaker. Three and four-way speakers are very difficult to design,
because the overlap between the response of the various drivers
is more complex than the overlap between just a tweeter and woofer.
When properly designed, though, a three-way or four-way speaker
can really be superb because each driver is just the right size
to handle its frequency band. For example, the upper-mids might
be assigned to a 4 1/2" driver, and the cone in that driver
can easily move back and forth in its frequency band without producing
much harmonic distortion (remember our discussion of mass and
velocity in speaker drivers, in last week's Q&A). Also, a
four-way speaker can move a lot of air, so it can be played loud
with less distortion than a two-way speaker with only two drivers.
Of course, four-way speakers are often very expensive. One way
around this is to get a good two-way speaker that uses somewhere
around a 6 1/2" driver for the lows and mids, and add a subwoofer
to handle the lowest octave (20 Hz - 40 Hz).
Q I
am currently putting together a new home theater system. I would
appreciate your advice with my following concerns. My future preamp
will be the forthcoming Sony TAE9000ES, and my DVD player will
be the forthcoming Sony DVP 7700. My current speakers are the
Infinity Prelude FR for the left and right front mains. The surround
sound rears are the Infinity Overture Ones. My subwoofer is a
Definitive Technology Powerfield-15TL. My conundrum has to do
with the center channel. Fortunately, I have the option of either
utililizing the Prelude center channel speaker (PCC), or using
two Overture One speakers (the preamp has two center channel line
outs) for the center channel. I am leaning towards utililizing
the Overture Ones due to their lower frequency response (35 Hz
vs. 80 Hz for the PCC speaker). However, if I go this route, I
will need a six channel amplifier. All of these speakers are very
efficient (93-96 dBL). Amplifiers I am considering are the ATI
1506, the ADA PTM-6150, the B & K AV6000 Series II, the Classe
Audio CAV-75, the Parasound HCA-1206, the Marantz MA-500 x 6,
and due to your information, LLano Monoblocks. Please advise me
as to what your suggestions are concerning the center channel
dilema, and your suggestions concerning the choice of an amplifier.
A You
don't need to use two center channel speakers just because there
are two center channel preamp output jacks. The two outputs are
for those consumers who want to use two speakers in the center,
one above the TV and one below the TV. This helps to give a center
channel sound that is more in line with the speakers on the side
of the TV. All of the amplifiers you mentioned will do the job
for six channels if you wish to have the two center channel speakers
though. However, you could also use five channels of amplification
and wire the two center channel speakers in series with one amplifier
channel. This would be less stressful on the amplifier than wiring
them in parallel. One other amplifier possibility is the AudioSource
Amp 3. Three of these would give you six channels (150 watts/ch
rms into 8 Ohms), a rather large total power supply capability
(weight of all three amplifiers together is 84 pounds), and at
about $1,100 from discount Internet sellers (I saw them for $359
each at J&R Music World, thanks to one of our readers notifying
me - http://www.jandr.com).
Q I
just bought a Yamaha R-V1103 Receiver and Bose Acoustimass-10
speakers. Would it overpower the bass of the Acoustimass module
if I added another subwoofer?
A No,
you would be fine because the Bose does not go that low. However,
you need to make sure the subwoofer will deliver the goods down
to 20 Hz, and then set the crossover of the subwoofer to about
40 Hz.
Q I
have a processor with a subwoofer line-out that automatically
filters out frequencies above 80 Hz. The processor also contains
a high pass filter that removes frequencies below 80 Hz from the
main speakers. The sub I am using, however, does not have a defeatable
crossover. I am currently using both crossovers in the processor
and have the crossover in the sub set to the maximum frequency
- 150 Hz. The sound is just not quite right, and I have read that
using multiple filters in the same signal path can cause interference
resulting in distortion. Is this true even when the filters are
operating in frequencies an octave apart? Is there a better way
to integrate the sub?
A It
could be a phase shift issue or overlap of the frequencies being
delivered by the high pass of the main channels and the low pass
of the subwoofer output jack. Try adjusting the crossover of the
subwoofer to a lower frequency and/or using the phase switch if
your subwoofer has one. Depending on the slope of the crossover
in the processor vs. the crossover in the subwoofer, it may sound
better with the subwoofer crossover set somewhere around 80 Hz
or even a little below 80 Hz.
Q I
am soon buying a sub for my home theatre system. What do you look
for in a powered sub and how big do you go for a normal sized
living room?
A This
depends on what your specific needs are, which includes how much
you and your spouse care about the appearance of components in
the living room. A couple of years ago, I put a large subwoofer
in the living room, and my wife told me to "get that out
of here". So, I replaced it with a Sunfire subwoofer (10")
which fits behind the couch. In the home theater room I use several
large subwoofers (Velodyne, Mirage, M&K), and my wife does
not care about the appearance. The living room is a sanctuary
for most wives, so cluttering it up with big speakers is not acceptable.
However, in any case, get something that has a reasonably flat
response down to 20 Hz, meaning no more than 3 dB down at 20 Hz
from what it is at 31.5 Hz (anechoic). The more amplifier power,
the better, because it takes a lot of energy to move sufficient
air at 20 Hz.
Q The
other night a storm cut my power. My concern is with surge protection
devices. Do they need power in order to protect your stuff, or
is the protection a passive design? I could see how the protector
would work if the power is on and a surge gets sent through the
line, but does it work the same way if the power has been out
for a while and then a surge runs through the line?
A The
surge protection is passive. They use solid state devices that
react in very small fractions of a second to cut the power. It's
a fuse of sorts, but it is much faster than a circuit breaker
in your main house power system. The surge protectors need to
be plugged into a grounded socket because they use ground to send
high current surges to (such as a lightning strike), but they
don't need to be turned on. In fact, when the protector is turned
off, the hot conductor is disconnected, so the neutral and ground
leads are the only concerns. During an electrical storm, I just
turn my AC line conditioner (which is also a surge protector)
off, but I don't unplug it. Obviously, unplugging the surge protector
from the AC socket is the best protection against a lightning
strike during a storm, but that is a little impractical sometimes,
say if you were away from home.
Q Sometimes,
when I play movies on my DVD player, I get vertical lines (white)
streaking across the TV screen. There's usually about two or three
that go across, then a couple of seconds later, they streak across
again. It doesn't happen all the time, but when it does, it's
VERY distracting. Is it possible for my VCR heads (it sits on
top of my VCR right now) or another piece of equipment that could
be affecting the DVD player? When it happens, and I switch from
S-Video to composite video, it really makes the problem a lot
worse. It happened the other night when I was watching "Sphere",
then I tried it again last night, and the lines were gone. The
only thing I did was to prop up the DVD player with a big cardboard
box to separate it from the VCR. However, when it happened once,
I propped it up with the same box, and the lines were still there.
If the VCR is affecting the video (I guess it's possible), would
it take a while for the DVD player to "de-magnetize"
and that's why the lines were still there when I tried to move
it away during playback?
A This
is a problem I have not seen with DVD yet. Some time ago, I took
a laserdisc and scratched it with a nail from the center to the
outside edge in a straight line to see what sort of artifact it
produced (this was back in the days when we assumed scratches
and dust are no problem for CDs and laserdiscs). The result was
a horizontal white line that stayed in the same place on the screen.
However, laserdisc video is an analog signal, while DVD is pure
digital. When a speck of crud is on a DVD, I have found that the
image becomes pixelated and will often skip or stutter. I don't
think it is associated with the proximity of your VCR though.
If any readers have seen this problem and figured out what it
is, send us an e-mail.
Q Thank
you for your one-of-a-kind useful and informative website! I want
to connect 4-6 separate pairs of speakers, in different rooms
of my house, to my A/V receiver, and I've been trying to compare
three different selector boxes in my price range: Niles
SPS-6, Russound R100SS6C (both about $130), and Rotel RSS900 (about
$200). Even on your superb website, I have been unable to find
any general information about speaker selector boxes nor information
regarding specific models. Is there anything I should know about
speaker selectors beyond the fact that they manage the resistance
an amplifier "sees?" Are there any pitfalls in choosing
a selector box, in terms of introducing noise, how the impedence
they create may be flat or uneven across different frequencies
or how well they protect an amplifier? Should I assume that the
Rotel has significant advantages, in terms of materials quality
or superior sound performance, that would justify paying more
for it?
A Speaker
selector boxes are basically switches that connect input pair
"A" to output pair "B", or "C",
or "D", etc. The impedance management consists of making
sure that only one pair of speakers is connected to the amplifier
at any one time, so that you don't suddenly go from an 8 Ohm load
to a 4 Ohm load (such as would be the case if two pairs of speakers
were put into the circuit in parallel). The more expensive ones
will have better quality contacts in the switches, such as gold,
which does not oxidize, and better quality connectors for the
speaker cables. The most important thing they will have to do
is "break before make", which means that they should
break the contact between the input and whatever output is currently
connected, before connecting to another output. Rather than make
your decision based on cost, you should take a look at the models
before purchasing and feel how solid the switches seem to be,
as well as check the connectors for their quality (heft).