|
Recently an installer wqas bragging about how great UTP cable was in car audio use.
I asked "what the heck is UTP?"
I was told it was UNSHIELDED TWISTED PAIR, and it was the greatest thing to replace our old cruddy RCA cables with.
Duh! Yeah, I knew that but use in car audio was pretty rare as far as I
knew
Then on the CARSOUND forum I heard
several folks talk about how they make the UTP RCA cables from computer CAT5
cables.
Well, knowing that inducted noises in
car audio (noise radiated right into the cables) was fairly rare I figured
not having a shield probably wouldn't be noticed so if these guys wanted
to use the cheap CAT5 cables and solder their own RCA connectors on the
ends then that's fine by me...
Well not long after that I heard some
one (again on CARSOUND) say that UTP was better than shielded RCA cables
because of better rejection of induced noises...
That's NOT true.
It is true however that CAT5 cables used in a computer network system
are renowned for their ability to
reject unwanted airborn noises!
So why are these cables so good on computers and not so good on Car
Stereo systems?
Good question, but a question that many on the CARSOUND forum apparently
don't want to see.
Computer networks use TRUE BALANCED
LINE systems, that means that the two wires that carry each signal are exactly
the same, same length, same construction, same thickness, same
impedance, same capacitance! But so are the senders and receivers
of the signal in the wire... So not just the two conductors in the wire
are the same but the amplifier that sends the signal out has the same
characteristics in both of its terminals, and the receiver at the other
end of this wire also has identical characteristics in both of the
terminals... Each of the two equal wires also carry an equal
signal (although electrically inverted) when in use, there is actually
an amplifier for EACH of the pair and a receiver for each wire in the
pair
A true balanced system is THE SAME in
both wires, so they call it balanced (equal)...
In a car stereo system we call the RCA
part of it UNBALANCED.... Its UNBALANCED because the two conductors in
each channel of the RCA cable are not the same, one is a thin signal
conductor while the other is a thick braided or wrapped copper or
aluminum shield. They are not the same length (since the shield
wraps around and around and around), and they are not the same
construction, and not the same thickness and not the same impedance or
capacitance... And not only are these two conductors different
from each other but the headunit and the amplifier terminals are very
different also... At the headunit the RCA connectors are made up
of an inside with a signal and the outside which is ground (no signal)
and at the amplifier the RCA connector is made up of the center (signal)
and the outside which is ground (no signal).. There is only one
sender and one receiver i this unbalanced pair. (notice the
balanced pair have two senders and two receivers per pair)...
Well, in the true balanced systems if
any noise signal is ever picked up or induced from stray magnetic fields
in the air then hopefully each of the two wires will have an equal
amount of noise, if so the true balanced differential receivers will
cancel that noise when the signal is received... That's
neato!
Well this cancellation thing is REAL,
and it is taught in your computer networking classes so there is a good
chance that allot of car audio and techy guys have heard of this
before...
But when I talked to the computer
experts that were familiar with this noise cancellation phenomenon, I
realized not many except the real gurus realized the cancellation occurred
in the balanced line receiver and NOT the cable itself!
Again, its NOT the twisted pair cable that gets
rid of noise, its the balanced recievers! IN FACT, the balanced line
twisted pair wires are NOT shielded so that BOTH wires get equal noise, so the
noise (if equal) will be cancelled out!
Well I think this slight misunderstanding
along with some folks in the car audio industry that want to make a few
bucks are trying to push this inferior cable technology into main stream
car stereo...
Cat5 cables are not even designed to
avoid airborn noises, since these noises are simply canceled when
the noise gets to the receiver.
BUT, since unbalanced car stereo
amplifiers don't have this magical noise canceling ability, since they
are not balanced and they simply do not treat the RCA signal and ground
shield the same at all, using the CAT5 cable (or probably any UTP cable)
may NOT be the best idea!
I explained this on the CARSOUND forum
and was having a pretty good conversation with some pretty smart
folks... Then all of the sudden the moderator there RICHARD CLARK
comes into the conversation and tells me I am wrong. ???
I didnt know at the time Richard Clark was marketing some of these
cables and he was just trying to shut me up.
I reply with many facts
like I have laid them out above and suddenly the thread is CLOSED and I
am temporarily banned from posting on the CARSOUND forum!
I talked to Rob that runs the whole
Forum on the phone and he said I was arguing too much with Richard Clark
(the hired moderator). Rob didn't want to keep me off the forum but
wanted me to try to avoid Richard Clarks big ego. I told him I would
try.
Several weeks later, I end up in
another conversation with some very nice folks about UTP again, Richard
makes an appearance in the thread and makes some of his usual comments
about how stupid everyone is and how he is always correct.
The guy keeps attacking me! (well it is his forum I guess)
This time though I whip out the cables and
oscilloscope and do some tests for myself. I use a NEON transformer as a
noise source and measure the actual pickup of the noise into the
CAT5 as well as a cheap pair of RCA cables...
Richard Clark seems furious, and apparently
calls his buddy and also a moderator on the CARSOUND forum David Navone
to tell me to shut up... Now I have worked with David before and I
thought we had a pretty good professional relationship.. But David for
some reason is a real jerk about it... He tells me my tests are all
wrong, and insults me several times! He refuses to answer any questions
though about balanced vs unbalanced systems even though I relentlessly
asked the same questions over and over at least 5 or 6 times....
Suddenly that thread was closed (censored if you will) !!!
Well come to find out, Richard Clark
and David Navone are being paid to put their famous names on a UTP
product being marketed by some big money hungry car stereo wire
company....
Makes sense to me now...
ha ha ha Money talks and science goes out the window... ha ha
ha
PS. Richard Clark is the same dummy that claims
to have invented the stiffening cap! Claims he was the first one to ever use
added caps in a competition car.. He got mad at me when I pointed out that Wayne
Harris and several other guys used stiffinging caps in competitions 8 years
before Richard ever even started competing! ha ha ha...
So, ignoring the CARSOUND folks, here
are some actual tests...
|
