Cable geometry investigated

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Cable geometry investigated

Max Townshend is an engineer first and foremost, he doesn’t pay much heed to the marketing and styling which is part and parcel of selling audio equipment today. His components are very much in the form follows function camp and nowhere is this more obvious than in the Isolda speaker cables. These are made up of copper ribbons placed as close to one another as possible with just a thin strip of insulation in between. This approach has been used by a few other companies over the years, Goertz made the Alphacore cable that was much the same and Electrofluidics had a variant on the theme. Today only Townshend uses this topology or geometry of conductors and not without reason, it has a very close impedance to that of the loudspeaker that the amplifier has to drive and does not suffer from the rising response seen with other more popular geometries.

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The reason why no one else makes cables with this geometry is that it’s not something you can make with a machine, at least it’s not something that’s made by the larger cable making industry. It’s a lot easier to buy a figure of eight or twisted pair cable off the reel and as few audio companies manufacture cable this is a significant factor. The second issue is that the Townshend geometry results in low inductance but high capacitance and some older amps (chrome bumper Naim being the best known example) rely on cable inductance to remain stable, the spaced pair geometry of Naim NACA5 speaker cable provides this. It’s notable that the Super Lumina speaker cable at the top of Naim’s current range has much closer spacing. Townshend incorporates a network into their speaker cables so that older Naim amps see a load that they can live which overcomes this issue.

In an attempt at explaining the advantages of sandwiched ribbon geometry Max Townshend has created a method of measuring what happens to the frequency response when a signal is sent through a selection of different cable geometries. He used a computer spectrum analyser between an amplifier and a speaker and produced a simplified chart of frequency responses for seven different cables. This is shown schematically below with the beast itself is further down the page.

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The black line at the bottom of the chart shows the sandwiched strip geometry, and in the test environment this produces a virtually flat response across the chart. The other six cables show a wide variety of tonal discrepancies which according to Townshend are due to multiple reflections caused by a mismatch between the cable’s characteristic impedance and the impedance of the load. If you are technically minded, you can read more about this in his white paper.

The graph shows that geometry is a critical factor when it comes to cable design, and the further apart the positive and negative conductors are, the further from a flat response is the measured result. These are not a subtle deviations either, in the widest spaced examples the response is extreme, not many brands go in for such wide spacing however and none have positive and negative runs totally separate as shown by the red line, but the closer spaced example shown in pink is not uncommon. There is no specific example for a twisted pair but Townshend says that the result comes out as per ‘close spaced conductors’, the amber line.

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As a long time user of Townshend cable I have to say that the sonic character does match that shown in the graph, or to put it another way most of the other cables I’ve tried are too bright for my tastes. You can see reviews of Townshend Isolda and F1 Fractal on the site where I attempt to explain the things that they do which few other speaker cables appear to match. If this were not the case and Townshend more of a marketing oriented company this sort of research would not be of great interest but the sonic results do seem to correlate and that doesn’t often happen with audio measurements.

Jason Kennedy