実施要綱と手順 Protocol and Procedures

Manny LaCarrubbaはABXブラインドテストを行うことを選択しました。(まず「A」を聴き、続いて「B」を聴き、そして与えられた「X」が「A」か「B」かを選びます。)切り替えは「一般的な」持ち合わせの電源コードセットと装置間、それとNordost社のValhalla電源コードの完璧セットで行われました。コードの切り替えは繋がっている全ての装置で行われました。電源装置、トランスポーター、DAC/プリアンプ、そしてモノブロックアンプフィルターです。
Manny LaCarrubba chose to conduct an ABX blind test. (You listen to product “A”, then to product “B”, then you are presented with “X”, which is either “A” or “B” and you indicate which product you think it is.) Switching was between a set of the “generic” stock power cords routinely supplied with equipment and a complete set of Nordost Valhalla power cords. Cords were switched on all equipment in the chain: Power Generator, transport, DAC/preamp, and the two monoblock amplifiers.

We chose ten musical selections, intentionally varied in musical content. Each selection was repeated thrice, first using Power Cords A, then Power Cords B, finally Power Cords X. The cords used in the A and B listening sessions were always different. If A’s cords were all-generic, for example, then B’s were all-Nordost Valhalla, or vice versa. X was either all-generic or all-Nordost. Participants were asked to determine if X was A or B.

一般的なコードは、Parasound monoblocksに付属するグレーのコードで動かしました。これらのコードがBeldenコードがパワーアンプに供給するのと同じであるか、または良いのか、私は知りません。
For generic cords, I powered the Parasound monoblocks with the same gray cords that had come with them. Whether these cords are the same or better than the Belden cords usually supplied with power amps I do not know. Generic cords for the other equipment were randomly chosen from an assortment of stock cords that came with equipment that has passed through my system over years of purchasing and reviewing. Cords on the ExactPower and Theta Gen. VIII were 14-gauge, that on the transport 18-gauge. Each generic cable was used on the same piece of equipment throughout the trials.

In each of the ten trials, the choice of which set of cords would be “A”, “‘B”, or “X” was determined using the random function in Manny’s Microsoft Excel program. Manny printed out a random ABX sequence for each of our two listening sessions and kept it in sealed envelopes until the actual test began. None of us, including Manny, knew what sequence of ABX we would use until shortly before the first musical selection was played. By the time switchers opened the envelopes, they were entirely hidden from the participants’ view and had ceased talking to each other.

Because we wanted the actual sound of the cords to come through as clearly as possible, use of sound-compromising switching apparatus was rejected in favor of time-consuming manual switching. Though this resulted in a blind test rather than a double-blind test, the fact that cable switchers did not know which cords would be A, B, and X until envelopes were opened minutes before the test began, said switchers were completely hidden from view, and switchers did not create sonic and verbal cues during the procedure suggests that a double blind test would not have yielded different results.

We positioned one switcher between the two Parasounds, his back to the listeners. The other switcher sat to the side of the equipment rack. John and Manny switched in the first round, Manny and I in the second. Exactly how switchers sat mattered naught to participants, since switchers were entirely concealed behind a felt scrim secured between the speakers with the use of microphone stands.

Plans to play a boom-box during the switching process in order to conceal all sounds created by switching cords were abandoned after Manny pointed out that hearing additional music during switching would muddy participants’ sonic memory. Instead, we decided to plug and unplug cords even if the same cords were returned to equipment. (In other words, if in test 3, cable set A was Nordost, cable set B was generic, and set X was also generic, we unplugged all the generic cords after the B session and then reconnected them for X). Since Nordost and generic cords rested side-by-side and were equally accessible to switchers, switching time was constant.

Sound pressure level was held constant for each trial by using the digital volume control on the Theta DAC/preamp. For the most part we were able to switch all five cords and cue the CD in about 75 seconds. During the actual test, there were at least three false starts when we discovered that only one amp was on rather than two. I doubt the delays helped matters.

Taking my cue from John Atkinson, who determined that it was much easier to determine differences listening to the complex timbres of massed choral music with orchestra than simple, monochromatic percussion, I tried to choose a variety of music that displayed contrasting timbres. The selections were:

  • Rachmaninoff’s Symphonic Dances (RR) Track 1
  • Songs of the Auvergne (CBC) Track 2
  • Candido and Graciela (Chesky) Track 1
  • Christmas Regrooved (Koch) Track 8
  • The Art of Leontyne Price (BMG) Disc 1, Track 15
  • Rosa Passos & Ron Carter (Chesky) Track 3
  • Berlioz Requiem (Telarc) Track 4
  • Rokia Traore Bowmboi (Nonesuch) Track 3
  • Terry Evans Puttin’ It Down (JVC-XRCD) Track 7
  • City Folk (unpublished live folk music master recorded by Manny)

As you will read in the test results, the track on which people performed the best was from the Berlioz Requiem. This was the only selection to feature massed choral music in state-of-the-art two-channel CD sound. This confirms John Atkinson’s discovery that participants in his blind amp test scored best on massed choral music.

Manny LaCarrubba and John Johnson arrived at Casa Bellecci-Serinus on November 12 for pre-test set-up. As soon as we erected the felt barrier between the speakers, I discovered that it absorbed high frequencies and dimmed the vibrancy of treble sounds. (The felt had no effect on mid and lower range). Since one of the glories of Nordost Valhalla power cords is their natural shine and transparency on top, I sensed this would make discerning differences between cords even more difficult than expected. But since none of us had the time, energy, or funds to replace the highly absorptive felt with another material that might less affect the sound, we compromised by only making the barrier high enough to block the switchers from view. It is important to note that Manny considered the effects of the felt of far less significance than the absorptive power of the bodies and clothing of test participants. Given the felt’s position between the speakers, I disagree. (Editor’s Note: The felt barrier was not in any way directly between either of the speakers or any of the listeners, so whatever absorption occurred, did so with room reflections – similar to acoustic absorption panels – not the direct radiation of the sound.)