----- HDTV Magazine Tips List -----
Marvin,
It does not look as we have many volunteers for your questions, so I will
shoot from my hip first very casually.
I have two SVC4s of the older style for audio distribution around the house.
One in, four out. These are the heavy-duty units, not the slim ones they do
now. I might not use them any more for my new house.
A couple of comments and recommendations if you allow me.
Get a unit with individual volume controls per pair, not just a switcher
functionality per pair. Different speaker sensitivity, impedance, or cable
length on each pair would mean different levels people would detect while
changing positions around the house; if you like to entertain you might not
want people noticing the various volumes among rooms.
Get selective impedance compensation "on each pair" along with its
independent volume control. Different speaker pairs of 4 to 8 ohms could
present different loads at the individual pair position on the
controller/switcher, you need to compensate for that, for an even load on
the amp, and for an even sound pressure level at each speaker pair.
Because some speaker pairs might be with long cable runs, anticipate that
you would need heavier gauge on the speaker wire going to the farther away
areas, which means that the unit has to have speaker connections in the back
to support fat wiring on some pairs; some units are not friendly to 12 to 14
gauge, and you would not want 24 gauge zip cord gauge on long runs (the
higher the number the thinner the wire).
Design into what exactly you might want when playing remote audio over the
whole house. A) The whole house with a single party background (one amp
with several distribution switchers) or B) several rooms with different
source audio (several amps with less distribution switchers handling
independent sources of audio, even when controlled from a central room, FM,
sat, CD, etc).
Think about if you actually need to also distribute surround and subs
channels of various rooms, like in my case, even to a deck, which means more
amps and speaker boxes than just for a L/R design.
Think about controlling the volume wirelessly on each room/deck/patio and
over which unit on the audio chain. At the source player? At the amp? the
switcher might be passive with manual volume controls to facilitate leveling
the sound pressure level at all rooms for its initial set up, but then what
if you need to bring down the volume on the deck but not the at the
recreation room, and what if you are on the patio talking to the guests at
that very moment?
Some rudimentary designs with repeaters (those cheap pyramids) could be
added to transport the IR commends via RF for control some source units on
your central setup, but a basic budget system could bring immediate
limitations if you want more flexibility.
Think about Ohms law and how that applies to speaker impedance. A basic
formula for parallel speaker setup is calculating the product of speaker
impedances divided by the addition of the same impedances, it could give you
the feeling of what would be the final load of an amp, and more importantly
what to avoid, if you like your amp.
In other words, two 8 ohm speakers in parallel would mean (8x8) / (8+8) = 4
ohms of resultant impedance seen by the amp.
Many amps are now very conservatively specified to handle no less than 6
ohms total load. 4 is trouble to some amps at loud volumes, they could
clip easily, that usually kills tweeters first with the distortion at loud
passages on the highs.
Imagine two pairs of 4 ohms: (4x4) / 4+4) = 2 ohms. The amp could see its
end of power very quickly if not protected enough. So switchers with
impedance compensation are a need for a system with many parallel speakers.
Installing speakers in series (the + of one going to the - of the next) add
their total impedance, such as 8+8+8 etc, not recommended.
Some budget oriented people play with the ohm rules by combining some
speakers in series with some in parallel without switches for a final load
not inferior to 4 ohms, I would not do that on my system. Some people add
also resistors in series in some speaker lines to bring the total impedance
up, I would not recommend that either. Additionally, the impedance varies
with frequencies of the sound you are playing, the signal the speaker sees
travels as an alternate signal.
Which brings us to the reason why these speaker boxes have impedance
compensation when switching pairs in the loop. The Niles SVC4 lets you
choose the compensation depending of the number of pairs you switch in the
loop to increase the impedance the amp sees.
Long wires do that by themselves, dissipating heat along the way, the
speaker receives a piece of the juice the amp puts out, the cable eats some
as well, a poorly designed or slim cable could be expected to accentuate
that loss.
The amp should never see a high demand of current created by an impedance
below 2 ohms, 4 to be safe, 6 in some amps. The closer to zero impedance,
the more current the amp is required to generate on the fly from its limited
energy supply, a weak design might kill the amp rather easily, zero is like
short circuit, no load, touching negative to positive, puff !!
I hope you get a safe distribution design that would not force you to
overspend for your purpose.
Niles is a good brand, long standing company, grew out to have a wide
variety of products over the last 20 years.
Best Regards,
Rodolfo La Maestra
-----Original Message-----
From: HDTV Magazine On Behalf Of
Marvin Munster
Sent: Thursday, October 05, 2006 5:08 PM
To: HDTV Magazine
Subject: Audio Distribution
----- HDTV Magazine Tips List -----
Hello Everyone.
This may not be the correct forum, but I do know that there is a lot
of brain power out there. If no answers, maybe you could direct me
in the best direction.
I am putting in a small surround system. The receiver is a VSX80TXV
Pioneer 7.1 channel which has 2 separate source outputs. In other
words, I can watch HDTV and still feed FM or a CD to the rest of the house.
The question is: Do I have to use a zone amplifier, like a NILS
SI-1230, which gives me 6 zones, and split one zone into 3 using a
NILS SS-4 speaker selector to give audio to 8 rooms, or Niles VCS
HUB8 8-speaker pair connecting block. These outputs run to impedance
matching volume controls. How does an 8 speaker connecting block
maintain the impedance to the amplifier, or does that matter?
Thanks in advance for any help.
Marvin.
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