Well this has been interesting. In spite of all the excellent physics in these answers I would submit that the reason signal pairs are still twisted in a shielded twisted pair cable is primarily for manufacturing reasons with some side benefits for SI which we get for free!! Best Regards Charles Grasso -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Kevin G. Rhoads Sent: Friday, May 14, 2010 6:21 AM To: Neo Cc: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: Why shielded twisted-pair is still twisted? >Is this statement applicable to twin-ax cable? For twin-ax case, the outer >shield >thickness is also just a few mils. Can I say twin-ax also suffer AC power >interference? Simple answer: YES. But the difference is the ratios between interference frequencies and frequencies of interest. Audio band INCLUDES 50 and 60 Hz, much of what is run over Twin-ax is primarily or completely at much higher frequencies. So separating signal from interference by frequency is UNdoable for audio and typically trivial for Twin-ax signals. Of course, if you want to send unmodulated baseband audio over cable, STP will work better than Twin-ax. It is a bit like asking if a 240Z is better than a Kenilworth. What are you trying to do? Haul heavy loads: Kenilworth. Drag racing: 240Z. Comparisons not only involve the things being compared, they also ALWAYS involve a metric of goodness or worth or value. So far your metric has been unstated and implicit, so people have been answering in manners designed to allow you to use your (unstated) metric to compare. There are cases where hum pickup is a total "don't care" and for those any proper metric will assign a zero or negligible weighting to measures of hum pickup. HTH Kevin ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu