Audio Engineering Society Singapore Section

On Monday 1st June 1998 at 7.30 p.m., 10 members and 30 guests of the AES Singapore Section gathered at the Ngee Ann Polytechnic, Singapore. for a talk by Mr Stephen Lampen of Belden from the United States. Stephen is Belden's Technology Development Manager based in San Francisco and is a member with the San Francisco AES section. He was on his first trip to Singapore for the Broadcast Asia Exhibition as well as, to present a talk for the AES Singapore Section. He gave a full insight about audio cables and its future towards digital audio with his vast experience in the Broadcast Industry. 

Stephen introduced the cable through its basic parameters of resistance, capacitance, inductance, and skin effect though he said cables are often classified through its openness, sound stage, grittiness, and detail, which are subjective evaluation of a cable and cannot be measured. He touched on the material used for cables, silver at 9.9 W, copper at 10.4 W, gold at 14.7 W, aluminium at 17 W and steel at 74 W resistance with copper allowing the best resistance properties at an economical value. Gold will be used for connectors, as it will not corrode but a poor conductor. Silver resistance is very close to copper but is much more expansive than copper. Steel is not applicable to audio as it is used for high frequency greater than 50 MHz cable transmission. 

Stephen passed out samples of PVC and Polypropylene cables to identify the difference. He said that PVC cables are cheap and will be only be good for about 50 metres before high frequency loss takes effect. On the issue of percentage to velocity of light and capacitance, it results from the different dielectric constant and air spacing between cables, typically for a 22 awg twisted pair cable, PVC (PolyVinylCloride) with 50 pF/ft and 50% velocity, Polypropylene with 33 pF/ft and 60% velocity, Polyethylene with 25 pF/ft and 66% velocity and foamed (mixed air) polyethylene with 12.5 pF/ft and 78% velocity. Inductance has no effect on audio cables, as it is so tiny at about 0.2 uH/ft. Impedance is confined to three parameters in a cable, the size of the two conductors, the distance between the two conductors and the quality of plastic or dielectric of the plastic. Accordingly, skin effect is not measurable below 250 kHz, silver over copper cable are used for digital audio. 

He went on to elaborate on shielding and noise immunity. Braid shield is good from about 1 kHz to 50 MHz and foil shield is from 50 MHz and above. Only a grounded metal conduit is able to provide low frequency 50 Hz with 27 dB attenuation. He stresses that, to manufacture braid shield is very slow and expensive as compared to foil shield. 

Going on to a revolutionary cable design called Media Twist for the same length and reduce loop area with common mode or differential connection comes a new unshielded twisted pair cable for multimedia applications such as audio, video, data, broadband and telephone all at the same time. The flat four pair cable is extruded with uniform dimensions and internal spacing. Each of these four pairs carries individual signals but the noise rejection is through differential interface devices for the signal connection. To summarise, this cable has the cheapness with such wide range applications over long distances and stable impedance that he encourages us to try it over all the standard cables available. 

There were questions and answers over these UTP cable applications on microphone signals, digital audio to high bandwidth video. The talk ended at about 10.30 p.m., the longest talk so far in the AES Singapore Section. 

Singapore Section would like to thank Mr. Moses Chew of Belden International Inc. and Mr. Stephen Low of Ngee Ann Polytechnic. for their support in making this AES event a success. 

Copyright 1998 AES Singapore Section