Cat5 cable VS RCA for car stereo use.

By Eddie Runner (NU5K)

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...


We put one of our oscilloscopes on a tool cart and pushed it into the sound room so we could sample different types of wire when we got the wire in close proximity to the neon high voltage cables...

The reason we used a neon transformer is because we had a very hard time finding ANYTHING that would induce ANY noise into ANY cable (cat5 or RCA)  Like I said before, noise induced through the air into car stereo signal cables is pretty rare, we tried the tests in several cars and couldn't find anything noisy enough....  I remembered 20 years ago when I worked on 2 way radios we had a piece of test equipment made by Motorola specifically for testing radio circuits rejection of close airborne noises, it was basically a high voltage transformer in a box, which gave me the idea of trying a neon transformer, we have several in the store running neon display pieces... And sure enough it DID induce noises we could see on the scope and hear on the systems in our stores soundroom.

Alot of folks condemn this test because it is not likely to have neon transformer noise in a car.  True, but we are only trying to show the differences between two types of wire and their noise rejection properties...  Like I said before and will likely say again, we are really unlikely to get noises because of the signal wire we use in a car no matter if it is RCA or twisted pair or simply speaker wire or rusty coathangers!

img border="0" src="techpics/ct2s.jpg" width="256" height="192"> 

Cat 5 and cheap RCA cables

 

The NEON strip in our car audio sound room we used as a source of noise.


We soldered RCA ends on the CAT5 cable and preceded with some tests
Settings on the scope were unchanged.


This is a cheap RCA cable plugged into a good quality amplifier and the RCA cables are brought into close proximity to a high voltage neon wire! You can see the NEON pulses plainly as they dance on the signal.
This is a computer CAT 5 cable with RCA connectors soldered on which is plugged into the same amplifier with the same settings as the above RCA cable and as it is brought in close proximity to the NEON wire you can plainly see the HUGE AMOUNT of neon pulses as they dance on the signal wires....

Why does RCA reject this noise better than the CAT 5 cable? 
Its the shielded layer on the outside of the RCA cable that helps keep out unwanted noises.

Now, alot of folks including Richard Clark that don't want to believe this test, but refuse to show their own tests, condemn the test because the wires are open ended...  I guess they didn't see the test below where the cables were NOT open ended and were plugged in on both ends to working gear!  The folks on CARSOUND (I call em Clarkies cause they follow what RC says no matter what) are still trying to discredit my tests because they claim I only did open ended tests..  Just in case they ever get this far, this is the notice the open ended tests are above and the closed circuit tests are below this point of this web page DONT MISS EM!

Now, this test is the RCA cable again, this time it is plugging into a head unit as well as the same amplifier and a small loop of the RCA cable is brought into close proximity of the high voltage NEON wire!   I see no movement in the scope whatsoever and hear no neon noise from the loudspeakers in our test area.
Now, with the CAT5 cable plugged into the same head unit and amplifier, when we bring a small loop of cat5 cable in close proximity to the high voltage neon wire we start to see the neon pulses again as well as start to hear the neon buzz in our speakers.. You can plainly see the tiny neon pulses in the picture of the oscilloscope...

 

Although the noises in the wire is much attenuated when it is actually wired in a real car audio system, the fact still remains the RCA cable is superior to the cat5 cable in terms of unwanted noises through the air in some instances, and the cat5 doesn't seem superior in any instance...

Now, I will admit, and have said it numerous times already, inducted and airborne cable noises are fairly rare in real in the car systems, and we had to go to alot of trouble and use a high voltage neon source to simulate this because we couldn't find a real instance of induced cable noise in about two weeks worth of our installations in our stereo shop...

But the tests ARE valid, even though you might use the CAT5 and never hear any noise, the fact remains that the CAT5 is not better than shielded wire for car audio use... 

Now, because CAT5 cables are wonderful computer network cables and have an almost magic ability to eliminate noises, alot of folks are trying to use them in car audio...  

CAT5 works well with computers BECAUSE computers have true balanced line amplifiers and receivers! in the network cards! 

Car audio on the other hand USUALLY uses unbalanced head units and unbalanced amplifiers so the BALANCED LINE cat 5 cables are pretty useless...

 

Please address any comments or corrections to Eddie Runner  eddie@installer.com 
Alot of folks have opinions on this one!

 

 

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