Cable Designer Roundtable

Equipment report
Loudspeaker cables,
Digital cables
Cable Designer Roundtable

What are the core beliefs that guide you in product development?

When measuring correctly using impedance analyzers, one understands that audio cables suffer from at least two resonances. As an example, an eight-to- ten-foot speaker cable will typically possess a series resonance somewhere below 1kHz as well as a parallel resonance somewhere between 150kHz to 250kHz.

Using a form of piecewise network analysis I optimize the cable’s resonances using additional networks, hence the network box found on all MIT cables. Our best cables possess networks that optimize the cable to function without the series resonance down to a fractional hertz, or just above DC. Looking at the high frequencies in the time domain, our best speaker cables yield a useful transient response of 2.8 microseconds, or ~357kHz.

When measuring using our test and measurement criteria, I have never come across any other cable that has a higher useful transient response than that.

The so-called speed or transient of the cable then has nothing to do with the velocity of propagation as others claim. It doesn’t matter how fast the audio signal is transported through the cable. What matters is if there is a difference in delay between some high frequency of interest, and some low frequency of interest.

We also apply proper dampening around the high-frequency parallel resonance so that reflected energy is not sent back down the cable to contaminate the incoming signal. Therefore the cable/network is only dependent on the input signal being applied presently, and not some stimulus from the past. I can’t emphasize how important all of the above is, particularly pertaining to timbre and textures, as well as maintaining pinpoint imaging and accurate soundstage size and proportions.

Next we measure and quantify the articulation of our cables. Articulation tells us how the cable will respond at various frequencies under dynamic conditions. Articulation in an audio- signal-carrying cable is simply a matter of how much energy a cable stores at any given frequency versus how fast the cable releases that energy. If the cable articulates to the same criteria at all frequencies of interest, then the music’s timbre and textures will not be changed. The settling out of the cable is extremely important regarding imaging and soundstaging properties, as well as left-to-right channel delays.

Now that the cable industry has about 35 years of experience under its belt, has cable design approached its pinnacle where further improvements are likely to be marginal? Or will the improvements we’ve seen in, say, the past ten years follow the same trajectory?

I believe we still have further to go. Some future gains will come via the development of systems where each component’s input and output impedances are held to certain values allowing the cable/interface to be optimized to those values. And some will come from independent research from companies such as MIT.

Today, unfortunately, it is sometimes done sort of “willy-nilly” in the field. Some amplifier manufacturers use 10k Ohm input impedances while some use 100–250k Ohm input impedances. Then a “random” selection of a preamplifier is inserted into the system, in the field, whereby the output impedance is never given any consideration. Then some cable with erroneous specs yielding 1000 nines of purity and bandwidth purportedly extending from DC to light is used to interface those components into something that is expected to function as a linear system.

 We manufacturers must begin to work together to build linear systems. Another word for linear is “predictable.” The random system described above might not articulate the same across the entire audio spectrum, and might also excite every impedance pole within the system. Timbre and textures, as well left-to-right channel delays, might all be affected negatively.

Regarding ongoing work here at MIT, several years back I became aware that very small delays between the left and right ear can be detected by humans. Over the past couple of years I have built five prototype cables dealing with minimizing delays between the left and right channels. In each case, we found when we tighten up the delays between left and right channels we have gained image and soundstage quality, particularly image specificity. Also, as expected, we reduced the background noise of the system by a noticeable amount. But unexpectedly, we also gained desirable timbre and texture improvements. No, I don’t think we are through yet!

In a field that is overcrowded with competing designs and technical hype, what advice would you give consumers when choosing cables for their systems?

First, listen to as much live music as you can, and remember it. Secondly, read about music, tuning, temperaments, timbre, textures, pitch, etc. Third, don’t let someone tell you it sounds good if it sounds bad to you.

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