Twisted pair or Coax,which might be better?

[Mark7]

<font color='#000000'>Is there any benifit to a twisted pair cable over a coaxial cable for audio interconnects? Does the twisted pair have better noise rejection,even in an unbalanced design,over coaxial cable. If you have any training in electrical engineering I would most like to hear your view point.That said, I will love to hear from any and all who are willing to respond to this thread. Thanks <img src="http://www.audioholics.com/iB_html/non-cgi/emoticons/smile.gif" border="0" valign="absmiddle" alt=':)'></font>

[Steve Eddy]

<font color='#000000'>Theoretically an ideal coax has an effective loop area of zero and therefore would be immune to magnetic field coupling.

What you might ultimately prefer from a subjective point of view is something only you can answer however.

se</font>

[Mark7]

<font color='#000000'>What is an ideal coax? If the ideal coax does not exist then which might be better:Twisted or coax?</font>

[Steve Eddy]

<font color='#000000'><table border="0" align="center" width="95%" cellpadding="0" cellspacing="0"><tr><td>Quote </td></tr><tr><td id="QUOTE">What is an ideal coax? If the ideal coax does not exist then which might be better:Twisted or coax?</td></tr></table>

Do you have Acrobat installed? If so, give this a read. It's a very good concise piece on grounding and shielding and covers coaxial versus twisted pair.

Grounding &amp; Shielding (http://www.q-audio.com/grounding.pdf)

se</font>

[Mark7]

<font color='#000000'>Not having the proper background made understanding the article you posted difficult to understand. In a book called audio reality the author stated something to the effect of &quot;A twisted pair is inherently better at getting a signal from here to there without picking up noise&quot;. He was refering to a twisted pair compaired to coax. Would you say this is a true or false statement? Thanks</font>

[Steve Eddy]

<font color='#000000'><table border="0" align="center" width="95%" cellpadding="0" cellspacing="0"><tr><td>Quote </td></tr><tr><td id="QUOTE">Not having the proper background made understanding the article you posted difficult to understand. In a book called audio reality the author stated something to the effect of &quot;A twisted pair is inherently better at getting a signal from here to there without picking up noise&quot;. He was refering to a twisted pair compaired to coax. Would you say this is a true or false statement? Thanks</td></tr></table>

Technically it would be false as stated previously, a coaxial line has a loop area of zero. Also, a twisted pair alone while having a small loop area which helps in terms of magnetic field interference (inducitve coupling), has no electrostatic shielding which would help in terms of electric field interference (capacitive coupling).

se</font>

[Mark7]

<font color='#000000'>So in theory, a coax might generally be better or is this also false?</font>

[Steve Eddy]

<font color='#000000'><table border="0" align="center" width="95%" cellpadding="0" cellspacing="0"><tr><td>Quote </td></tr><tr><td id="QUOTE">So in theory, a coax might generally be better or is this also false?</td></tr></table>

In theory, yes.

se</font>

[Mark7]

<font color='#000000'><table border="0" align="center" width="95%" cellpadding="0" cellspacing="0"><tr><td>Steve Eddy : <table border="0" align="center" width="95%" cellpadding="0" cellspacing="0"><tr><td>Quote </td></tr><tr><td id="QUOTE">So in theory, a coax might generally be better or is this also false?

In theory, yes.

se</td></tr></table>
Now the question becomes: In real world situations which might be better? My own guess is that neither are inherently better? &nbsp;If this is the case,I would probably go with coax simply because is appears to be the traditional audio interconnect design.</font>

<font color='#000000'>Hi Mark 7;
* *According to Henry Ott, for low frequency application, the twisted pair with a ground shield is slightly better at low frequency than coax. Microphone cable which has a twisted pair and ground shield will work well here. If you have a moment Mark 7 I have an article on this web site called Bulletproofing your System from Interference. You might find some useful tips.
BTW; a good double shielded coax will work well also.</font>

[Mark7]

<font color='#000000'>In a twisted pair cable (microphone cable for example) two specs are give for the capacitance one is the capacitance between conductors and the other is the capacitance between the conductors and sheild. which number is the one that you look at in an unbalanced situation. I've asked several people this question and everyone has a different and answer. Some say the capacitance between conductors. Other say the capacitance between conductors and shield. Some even say that you add the two number for the total capacitance. Which number really applies to an unbalanced configuration.</font>

[Mark7]

<table border="0" align="center" width="95%" cellpadding="0" cellspacing="0"><tr><td>Mark7 : <font color='#000000'>In a twisted pair cable (microphone cable for example) two specs are give for the capacitance one is the capacitance between conductors and the other is the capacitance between the conductors and sheild. which number is the one that you look at in an unbalanced situation. I've asked several people this question and everyone has a different and answer. Some say the capacitance between conductors. Other say the capacitance between conductors and shield. Some even say that you add the two number for the total capacitance. Which number really applies to an unbalanced configuration.</font>
<font color='#000000'>I don't know why this question can't be answered. Even the experts have given one of three possible answers. No one is in agreement. How is this possible?</font>

[Dan Banquer]

<font color='#000000'>Hi Mark 7;
When you use a twisted pair with a shield and you connect the shield at both ends to ground you predominatly have only one capacitance spec which is between the two wires. I think I got that right.
* * * * * * * d.b.</font>

[Mark7]

<font color='#000000'><table border="0" align="center" width="95%" cellpadding="0" cellspacing="0"><tr><td>Dan Banquer : Hi Mark 7;
When you use a twisted pair with a shield and you connect the shield at both ends to ground you predominatly have only one capacitance spec which is between the two wires. I think I got that right.
* * * * * * * d.b.
I've seen cables made by makertek and haveinc where the two twisted pairs are attached to the center pin and the shield only is used as ground. *It is kind of like you would have in a coax cable. If you look at capacitance for any coax you will see that it is listed for conductor and shield. Would that hold true here?</font>

[Dan Banquer]

<font color='#000000'>Just out of curiosity, have you checked with the manufacturer for their spec's on the cable? They should have the information you are looking for.
* * * * * * * * * * * *d.b.</font>

[Mark7]

<font color='#000000'>Yes,haveinc lists the conductor to conductor capacitance spec. They Only list conductor to shield if the cable is coax.</font>

[Mark7]

<font color='#000000'><img src="http://www.audioholics.com/iB_html/non-cgi/emoticons/smile.gif" border="0" valign="absmiddle" alt=':)'> Happy Thanksgiving</font>

<table border="0" align="center" width="95%" cellpadding="0" cellspacing="0"><tr><td>Steve Eddy : <font color='#000000'>Theoretically an ideal coax has an effective loop area of zero and therefore would be immune to magnetic field coupling.

What you might ultimately prefer from a subjective point of view is something only you can answer however.

se</font>
<font color='#000000'>Using old style theory, yes indeedy...

I can envision a magnetic field that is capable if inducing a signal within a coax..so I would recommend a twisted pair myself.. &nbsp;And, no, it doesn't involve the 5 to 10 tesla fields we use here.

And, no, I haven't used twisted pair in any of my mobile audio field apps. &nbsp;Tain't never had a need to.

A little verbage: &nbsp;if the field that crosses the coax is relatively uniform from one side to the other, yes, the loop is zero. &nbsp;But, if there is a field gradient across the width of the coax, there will be a net difference between the shield and the center.

Cheers, John</font>

[Mark7]

<font color='#000000'>It might be that both types of cable have their benifits and drawbacks. Any input on this steve?</font>

<font color='#000000'>A twisted shielded pair is designed for use in a balanced line with either a transformer or differential amplifier input.
Its advantage is with low level signals in a high noise environment: &nbsp;the differential input cancels common mode signals. But, you cannot just change cable types and gain anything. The design of a balanced line over single ended circuitry is more exotic and costly.

Example : computer networking uses balanced lines as they link &nbsp;systems connected to different power lines and usually have AC common mode voltage variations or even high level noise transients on &nbsp;them. The balanced lines cancel this..........
<img src="http://www.audioholics.com/iB_html/non-cgi/emoticons/smile.gif" border="0" valign="absmiddle" alt=':)'></font>

[Mark7]

<font color='#000000'><table border="0" align="center" width="95%" cellpadding="0" cellspacing="0"><tr><td>Guest : A twisted shielded pair is designed for use in a balanced line with either a transformer or differential amplifier input.
Its advantage is with low level signals in a high noise environment: *the differential input cancels common mode signals. But, you cannot just change cable types and gain anything. The design of a balanced line over single ended circuitry is more exotic and costly.

Example : computer networking uses balanced lines as they link *systems connected to different power lines and usually have AC common mode voltage variations or even high level noise transients on *them. The balanced lines cancel this..........
<img src="http://www.audioholics.com/iB_html/non-cgi/emoticons/smile.gif" border="0" valign="absmiddle" alt=':)'>
So with single ended circuitry there is absolutely no benifit between a coax and a twisted pair?</font>

<font color='#000000'><table border="0" align="center" width="95%" cellpadding="0" cellspacing="0"><tr><td>Quote </td></tr><tr><td id="QUOTE">So with single ended circuitry there is absolutely no benifit between a coax and a twisted pair?</td></tr></table>



Analog audio inputs normally have a high impedance and outputs very low - so they are not matched in the first place... Thus, If you are just working in the analog audio range, you can use a twisted pair - in fact, some audio cable does this to reduce cable capacitance. The 20KHz *and below is not as susceptible to impedance mismatch - large capacitance in long cable runs can be a significant cause of freq loss in this case. But,Having the center conductor less shielded by the grounded outer may cause hum *or noise pickup......


But, if you are working at video frequencies or with digital signals, you'd be better off staying with the norm to prevent reflections at the impedance discontinuities. In this case, inputs and outputs of the components are designed to have a 75 ohm Z.

Best. * <img src="http://www.audioholics.com/iB_html/non-cgi/emoticons/cool.gif" border="0" valign="absmiddle" alt=':cool:'></font>