Q I
have a home theater with Magnepan speakers all around with the
front L&R being the 3.5s. My amp for the L/R speakers is a
Rotel 2
channel 100W/ch amp and a bridged 6-ch amp for the center and
rears giving 90W/ch. I have a mirage BPS 150 sub. To get more
bass, I purchased another one and it has provided me with more
oomph but if I turn them up, they sound too boomy. I've set the
x-over for the subs at 80 Hz from my Lexicon DC-1 processor. I'd
like a tighter bass response with still more ooomph but short
of spending $5000 on the Proceed amp, are there any other suggestions
you may have, i.e., bi-wiring the Maggies or getting the Adcom
GFA 7500, etc.
A Boomy
bass from subwoofers is a very common problem. There are several
causes. One is that when you turn up the subwoofer volume, the
amount of harmonic distortion increases dramatically. Action movies
have lots of bass in the 40 Hz region, and the second order harmonic
is at 80 Hz, where the boominess is. A second reason is that subwoofers
generally do not have any damping material in the enclosure, and
this tends to emphasize the sound at frequencies around 80 Hz
- 120 Hz. To correct your problem, you need to set the crossover
frequency lower, if possible, say at 50 Hz - 60 Hz, and not turn
the volume up so loud.
Q I have a home cinema system that is mainly audio-based. Initially I had a Yamaha DSP-A590 Pro Logic amplifier, with Mission 73C for a centre speaker, Mission 733 for the main speakers, and Mission 73S for the paired rear surround speakers. I then exchanged the 73C for the 75C speaker as I was not happy with the 73C performance. Since then, I have bought the Yamaha DSP-A1, and a REL-Q50 subwoofer.
My questions are:
1) The 75C speaker has a nominal impedance of 6 Ohms, and the Yamaha-DSP-A1 is set for speakers of 8 Ohms. I think the other speakers are 8 Ohms in nominal impedance.
What, if anything, should I do to my DSP-A1 settings to overcome the difference in the speaker impedances?
2) My Mission 73S rear speakers are now the weak point in my system. Are there any speakers you would recommend to replace these ?
3) My Television is currently a Sony 25
inch NICAM TV (I live in London). It is a little small, and I
find a Lechtronic (or something) screen magnifier that expands
the screen to about 29 inches is much better. Unfortunately, High-definition
TV is not yet even discussed in the UK, although digital TV is
coming. Would you recommend a CRT projector that can produce massive
screen images, or a big widescreen TV that can support digital
TV, and DVD aspect ratios of 16:9 and component inputs for RGB?
A The
DSP-A1 has an impedance selector switch on the back for 8 Ohms
or 4 Ohms. Try using the 4 Ohm selection, since your center channel
speaker is 6 Ohms. That selection means that all speakers have
to be at least 4 Ohms, which they are in your system. You may
have to turn the volume of the center channel down a bit in relation
to the other channels, if they are connected to 8 Ohm speakers.
The 4 Ohm selection reduces the amount of voltage available, and
therefore, reduces the current that can flow so that the amplifier
will not go into hard clipping. However, at any one voltage, twice
as much current will flow into a 4 Ohm load as into an 8 Ohm load,
so there will still be plenty of watts at 4 Ohms.
If you like the Mission 733s in the front, then get another pair for the rear. Use the 73Ss for the front effects channels.
Digital TV has lots of different formats, and HDTV represents only a few of them, so if you get a digital television, it should be able to display HDTV signals when they begin broadcasting in the UK. I would suggest getting the digital TV (all of which are 16:9), whether it is in the form of a direct view or projector, although the first ones are all rear projection sets.
Q I
have read that placing just a capacitor (of the correct calculated
value) in the line from a preamp to a power amp can produce an
effective 6 dB/octave high pass filter. Has SHT tried this and
how well does it work? I'm also wondering if an inductor could
be put in another line to another power amp, thus forming an effective
low pass filter. Of course the inductor would have to be kept
away from any metal.
A Yes,
a capacitor in between the preamp and power amp does work, and
we have tried it (the cap is put in the path of the + conductor).
The formula for calculating the proper value for the capacitor
is C = 1.59 / R f, where C is in Farads, R is in Ohms (input impedance
of the power amplifier), and f is the crossover frequency, in
Hertz, that you wish. So, if the input impedance of your power
amp is 100,000 Ohms and you wanted the crossover frequency (high
pass) to be 50 Hz, it would be C = 1.59/100,000 x 50, and this
calculates to be C = 0.000000318 Farads, or 0.318 µF. The
rolloff would be 6 dB per octave below 50 Hz. For the low pass,
the formula is L = R/6.28 f, where L is the inductance in Henries.
You can see from the formula that the necessary inductor would
have a very high value, and is not practical. For about $30 a
pair, you can get Filter Modules ("F-Mods") from Harrison
Labs (http://www.hlabs.com).
They are small tubular modules with an RCA jack on one end and
an RCA plug on the other. These items are used quite a bit in
the automobile sound industry, but they can also be used in home
theater. You put them in between the preamp and power amp, and
they can be plugged into the power amp input jack, with the interconnect
from the preamp plugged into the other end. The F-Mods are 12
dB/octave slope. The modules have buffers so that the impedance
of the amplifiers is not a factor. These modules might be very
handy in limiting frequencies sent to small speakers. Remember
that you will have phase shift at the rate of 900 per
order at the crossover frequency, decreasing in amount as you
move away from the crossover frequency, so a first order filter
(6 dB/octave) results in 900 shift, and a second order
filter (12 dB/octave) will result in 1800 shift. Also,
you need to remember that if you get the low pass modules and
high pass modules at exactly the same frequency, the fact that
there is a rolloff rather than a straight down drop, will create
overlap, and therefore, a hump. So, you should plan on the low
pass at one frequency, and the high pass to be somewhat above
that frequency.
Q What is the best way to mount rear speakers? I have B&W 601s for rears and I am wonder if mounting them on the wall will have negative effects on the sound. I have pre-wiring in the back walls about 8 feet high already.
Also I have a Velodyne FSR-12 subwoofer.
I heard it is better to have subwoofers in the front. Will having
them in the back of the room be terrible?
A The
601 is designed for mounting on speaker stands, or on shelves,
but you can purchase wall brackets from other manufacturers to
mount them if you wish. Since they are front ported, you probably
would not have any problems. They could be mounted behind the
listening position and above it, angled down towards the listening
position. Having a subwoofer in the rear would not sound terrible,
but you will get deeper bass if it is in the front, farther from
the listening postion. Place it near one corner, about 1 foot
from one wall and 2 feet from the other, to start with.
Q A
DVD player is my next purchase. I read "things" about
the audio laser vs. the video laser. What should I look for Two
separate lasers, one for music CDs and one for DVDs or is there
any such "animal" as a combined laser? When DVD Audio
becomes a fact will the DVD laser be adequate for DVD-Audio? I
am confused! I want "good" music so should I keep my
Onkyo DX-C606 for music or will the next generation DVD player
take care of movies and music? Do you have a DVD player in mind?
Please, please, please suggest one.
A Take
a look at this week's review of the Yamaha DVD-S700. As you will
see, it does not perform very well with audio on CDs, but no mass
market DVD player does. The reason is the laser is designed to
read the narrow track of DVDs and not the wider track of CDs.
Since the transport and laser are there, the manufacturers put
CD capability in. I would suggest keeping your CD player for CDs
and using a DVD player for movies and Digital Audio Discs (DADs),
which have music in the narrow DVD tracks (so the laser reads
them just fine). The Yamaha DVD-S700 is an excellent player and
would be a good choice. It performs beautifully with video and
5.1 audio.
Q I
have a Proceed PAV/DSD surround processor, and the amplifier is
a Parasound HCA1206. I like to have sheer dynamic impact of the
cinema in my home. So I'm interested in the Bose PA system. They're
Bose 802 series II, and the sound is absolutely as I want, but
the Bose dealer recommends that I buy PA amps for their speakers,
which I'm not very sure is really necessary since the Parasound
can be bridged to have 300Watt x 2. The Proceed dealer is against
using PA speakers with their product. They said I'm already on
the audiophile side, so I should buy audiophile speakers. I believe
that no home speakers could ever produce the sound the same way
as PA speakers do. What should I do ? My room is 7.5 meters x
10.5 meters, and no matter what the main speakers are, the subwoofer
will be the Velodyne FSR-18.
A As
long as you have listened to the products you intend to buy, you
should go with what you like.
Q Like many other readers of your e-magazine, I am intrigued by the Yamaha DSP-A1. I'm just starting to piece together a home theater that will also be used extensively for good old audio CD listening, and thought I would definitely go with separates, until I read your DSP A-1 rave. I'm starting with Magnepan 10.1s, which are not huge but still 4 Ohm, and I like their power, plus a PSB Subsonic2i subwoofer.
Will the DSP-A1 be able to cleanly drive
the maggies? I'm considering the maggie surround and center channel
speakers as well, and a Panasonic 310 DVD player. Eventually,
I want to add a separate front amp for the maggies, but not for
a while ($$$$). Will I be OK for the time being, and what are
your thoughts on these pieces as a system?
A It
looks like you are on your way to a fine system. The DSP-A1 will
be able to drive the Magnepans, but not very loud. They are not
only 4 Ohms, but low sensitivity too (85 dB/w/m). You should set
the impedance switch on the back of the DSP-A1 to 4 Ohms, and
use the volume control judiciously. Later on, definitely go for
a good outboard five-channel power amplifier that will handle
4 Ohm loads.
Q I
saw a question in #72 about tubes vs. transistors, and as always,
you gave good advice about letting our ears being the ultimate
judge. Tubes are definitely better sounding to my tastes but are
incredibly expensive. Before I plunk down $4,000-$6,000 on a 100
watt per side amp, and another $2,000 - $4,000 on a preamp, can
you give me some specifics on upkeep, care, and handling? I know
that in general tubes last 2,000 - 3,000 hours, but how expensive
is it to replace dying tubes? I have auditioned Sonic Frontiers,
Audio Research, and Cary, and like the sound from the ARs best,
but the SF amp is very close. What key factors should influence
which brand I go with (they are similarly priced through the dealers
I have talked to, and have similar prices on the used market)?
Is it really important to use a tube preamp with a tube amp? Most
importantly why does a tube amp which is rated at 25 watts per
side drive speakers sounding like a 100 watt per side transistor
amp?
A Probably
the main thing with tubes is heat dissipation. You have to be
very careful to place the amplifiers in a spot that is well ventilated.
Although the power amplifier will produce the most heat, the preamp
gets pretty hot too. I carefully dust the tubes every couple of
weeks, since dust can get in the way of efficient heat transfer.
Tubes can actully last a lot longer than 3,000 hours, and except
for the output tubes, are relatively inexpensive. Write down the
tube types the next time you are in for an audition, and then
check on the prices from websites such as http://www.vacuumtubes.com/.
With tube amplifiers, there is probably more variation in sound
quality than with solid state because tubes come as triodes, tetrodes,
and pentodes, with triodes and pentodes the most common. Also,
they come as single-ended designs, push-pull, and also OTL (output
transformer-less). Single-ended triodes (they are always run in
Class A) are generally regarded as the most pleasant sounding,
but they don't have a lot of power (they work fine as preamps
though). Push-pull pentode designs are very popular. The reason
25 watt tube amps sound so much more powerful is that the power
supply for tube amplifiers has to be massive. Also, tubes tend
to distort with even-ordered harmonics, so you can turn up the
volume well into clipping and it doesn't bother your ears. The
output impedance of tube amplifiers tends to be high, so the characteristics
of the speaker will greatly affect the sound. Be sure to listen
to the exact combination of tube amplifier and speakers you want
to buy, before you actually make the purchase. Pairing a tube
preamplifier and solid state power amplifier can be wonderful.
You should not have any problem mixing the two.