Throwback Thursday

Although the high electrical resistance of 24-gauge wire makes it inadvisable for runs of more than a few feet, its low price and small diameter make it appealing to decorators, who use it unashamedly. It seemed the ideal “worst case” cable—if any cable would sound different, 24-gauge should be the one. The 16- and 24-gauge wires were cut to the same 30-foot lengths as the Monster Cable, and all the cables were terminated with Monster’s X-Terminators for consistency in the connections.

Lab, Tests
For the first part of our tests, Julian Hirsch measured the three selected cables’ resistance and interconductor capacitance. The results are easily summarized: in 30-foot lengths, the 16-gauge zip cord had a resistance of 0.24 ohms, the Monster Cable 0.09 ohms, and the 24- gauge “loudspeaker cable” 1.8 ohms; their interconductor capacitances were 420, 600, and 400 picofarads, respectively.

The cables were then connected between a high-quality power amplifier (a Perreaux PMF 21508) and two pairs of high-quality speakers (Spendor BC-1s and KEF 105.2s). A 1,000-Hz square wave was fed to the speakers through the cables, and the cables’ effects on the signal were monitored by subtracting the waveform at the speaker terminals from the waveform at the amplifier output. Photographs were made of the oscilloscope displays. There were no observable differences between any of the cables driving either speaker system. All the measurements were then set aside and not shared with the listening panel until after the listening tests.

Open Listening
In the initial open (non-blind) phase of the listening tests, the listeners individually evaluated the sound of seven different music selections played with each of the three different cables while knowing which cable was in use at each moment. They were asked to fill out an elaborate, eight-page questionnaire. In addition to ten questions about the sound of the different cables, the form asked about the panelist’s age, occupation, degree and kind of involvement with audio, and any prior attitudes toward the specific cables being tested. The procedure was designed to collect information on the panelists’ various biases and to suggest how those biases might change in a group-listening situation. For example, a listener’s preference might be influenced by knowledge of a friend’s preference or by the reputation that a particular brand or type of cable has acquired through reviews in the “underground” hi-fi magazines.

Controlled Listening
The heart of our whole project was the set of controlled listening tests. These differed from the initial open tests in that the listening procedure was designed to maximize psychoacoustical fairness. That is, in order to keep the listeners’ biases about the weight, appearance, cost, or brand of the cables from influencing their sonic preferences, the tests in this part were double blind—neither the listeners nor the test administrator knew which cable was being listened to. Switching between the different cables was practically instantaneous (less than 50 milliseconds) in order to make subtle sonic differences as apparent as possible (human beings have notoriously poor long-term memories for sounds).

To make possible such a double-blind, instantaneous-switching test, we used a laboratory-grade audio comparator developed and sold by the ABX Company. It consists of control circuits and relays that can rapidly switch between different inputs. The listener compares sounds and decides whether a particular source, designated X, is sonically the same or different from each of two other sources, designated A or B (hence ABX). The trick is that source X is actually either A or B; each connection is made at random by the ABX comparator and is not identified for either the listener or the tester. The listener writes his response on a test form. Digital memory circuits store the sequence of connections for retrieval and analysis at the end of the test.

Level matching between cables to compensate for their differing electrical-loss characteristics was not performed for every comparison in this part. The basic premise of these tests was that measurable differences among cables would become audible if they were large enough. Matching all measurable parameters—including signal loss—would make the hypothesis untestable. For one comparison, however, of Monster Cable with the 24-gauge speaker wire, we did compensate for level differences by switching in a precision attenuator between the preamplifier and the power amplifier whenever the lower-resistance Monster Cable was selected by the ABX system. The purpose of this was to determine if there were any audible dif- ferences between the two cables other than those resulting from a volume-level change.

Some audiophiles refuse to accept the validity of this kind of controlled listening test. They argue that either the test procedure or the switching systems will mask important sonic differences. The whole procedure and test setups are designed to increase listeners’ sensitivity to small differences and to bypass some of the limitations of the human hearing system so that the results will be applicable to all listeners, not just those participating in the tests. Let’s review three of the main features of this phase of our tests: (1) The ability to switch almost instantaneously from one cable to another with a precision set of low-resistance relays makes perceived sonic differences as vivid as they can be given our limited sonic memories. (2) The double-blind listening setup relieves the tester and the listeners from having to compensate for preconceptions about the different cables. (3) The use of numerous listeners making a large number of comparisons produces sufficient data for meaningful statistical analysis and generalization.

The procedure for the controlled listening tests can be quickly summarized: six cable comparisons were carried out using the ABX comparator and either pink noise or a choral music selection. Monster Cable was compared with 24-gauge wire, gain matched and unmatched; next, Monster Cable was compared with 16-gauge zip cord; then the 16-gauge and 24-gauge cables were compared with each other. Each comparison consisted of a series of fifteen tests; in each test, as explained previously, the listener was asked to identify which of two constant sources, A and B, was the same as the switched source X. The choice and order of cables being compared and program sources being used were determined by a table of random numbers, with switching randomly controlled by the ABX comparator.

Results were examined only after each listener completed the series of comparisons, and results were held confidential so that each panel member knew only his own score—after all, the egos of these “golden ears” were on the line. Moreover, in our account of the results we will consider mainly the performance of the group as a whole; individual panelists will be identified by code letter—to protect the guilty! Further details of the test setup can be found in the box labeled “Test Methods and Equipment.”

The listeners were all males with an average age of about thirty-nine years (ranging from thirteen to sixty). Although two were high-school students, most of the remaining nine were middle-aged professionals with a serious involvement with audio. Six panelists owned expensive esoteric twin-lead speaker cables, two owned interwoven audiophile cables, and one even used 14-gauge zip cord. Seven thought that controlled, double-blind tests like those we used were valid, but the others thought such tests missed the boat.

Half the panelists thought that sonic differences between speaker cables could not be explained by measurable differences in the cables’ electrical characteristics. Before the listening tests even began, ten out of the eleven listeners expected the “better” cables to show improved bass, “punchiness,” and frequency response.

The left-hand portion of Table I summarizes the pre-test attitudes of the listeners. In terms of attitudes, Monster Cable scored sig- nificantly higher on appearance and reputation than either 16- or 24-gauge cable. Although 16-gauge scored highest on frequency of use and cost-effectiveness, the preference was not statistically significant in these categories. Generally, the panel seemed to prefer Monster Cable from the start, suggesting that it would come out on top in the non-blind open listening tests, which is just what happened.

The Open Tests
When the listeners knew which cable they were listening to, Monster Cable scored significantly higher, as the data in the right side of Table I show. It was preferred to 24-gauge in seven out of ten categories. Monster Cable also scored significantly higher than 16-gauge in three categories. In the pink-noise portions of the test, 16-gauge scored higher than 24-gauge.