RE: Audio signal distribution.

["Keith Doxey" <ukha@xxxxxxx>]

Hi Nigel,

I take it you are referring to
http://www.ittnss.co.uk/prodcat/detail.asp?catid=41&pid=582

Based on what I can see from the photo on the website, it looks like a
standard speaker switchbox except that it is in a rackmount enclosure with
RJ45 as the connectors. It gives no indication to whether the switching
provides correct impeadance matching or if the speakers are simply
connected
in parallel.

Given that most domestic speakers are 8 ohm and most Hifi amps will handle
a
minimum load impeadance of 4 ohms, switching on more than 2 pairs would
fall
below the minimum load of the amp and possibly cause the overload
protection
to operate. If the unit attempts impeadance matching by series/parallel
wiring the speakers then the amp will be OK but the volume will alter as
rooms are switched in or out.

That is not unusual, it is common to all simple speaker switchboxes.

It looks like they are sending speaker level directly over CAT5 possible
using 2 wires for each signal eg

BLUE/White & WHITE/Blue = Left -
ORANGE/White & WHITE/Orange = Left +
GREEN/White & WHITE/Green = Right -
BROWN/White & WHITE/Brown = Right +

This will rely on the assumption that the power levels will be kept fairly
low because even using 2 wires you still only have a cable rated at 0.5A.
100W delivered into and 8ohm speaker requires a current of 3.54A so the
maximum you could safely deliver to an 8 ohm speaker would be
0.5 x 0.5 x 8 = 2 WATTS !!!! (I2R) for a 4 ohm speaker it would be 1 WATT.

For BACKGROUND music that would present no problem because 1 watt is
actually quite loud. Sound is logarithmic and doubling the power only
increases the volume by 3dB which is barely noticable. To double the volume
requires a 10 fold increase in power. A 100W amplifier is only 4 times as
loud as a 1W.

Where power becomes really important is for music with a wide dynamic range
such as classical. Quite passages may be 100mW but to faithfully reproduce
the peaks without and limiting can require over 1kW.

Most people dont have that amount of power available. If you tried to run
audiophile grade equipment over it, which I dont believe any true
audiophile
would even try, then you would have severe problems. Many of the really
high
end speakers are much less efficient than cheaper speakers and require more
power to drive them.

As I said earlier, CAT5 is for Line Level signals NOT Speaker level. Use
thick cable for that. Linn-Knekt is distributed over CAT5 but that is
balanced line just like KAT5 from the source to the Room Amplifier then
proper speaker cable from the amp to the speakers.

You are welcome to try that system but personally, I wouldnt.

Keith


> -----Original Message-----
> From: Garwood [mailto:themanse@xxxxxxx]
> Sent: 26 May 2001 16:06
> To: 'ukha_d@xxxxxxx'
> Subject: RE: [ukha_d] Audio signal distribution.
>
>
> Keith
> I have seen a number of the home structured cabling systems that you
can
> get installed putting audio down CAT5. Such as the ITT canon Midilan
and
> something like IP Connect !!! Are they selling a crap systems
> then ? I have
> seen such a system installed in a local builders show home, it has an
> speaker to cat5 converter.
>
> Have a look at www.ittnss.co.uk under products midilan.
>
> Its not that I don't believe you, in fact I trust you more than these
> people.
>
>
> Nigel
>




Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/