Ok, here comes a long and thorough summary. If you don't want to read it, the important stuff is this:
* K200/400/600 sounds fantastic at a length of 2.5 m.
* Do not go shorter than 2.4 m, as your system will sound restless.
* Longer than 2.5 m is ok, but you will gradually loose performance.
This is what I did when determining the 2.48 m length:
The speaker cable was always Linn K400, often but not always cut in half (so that it becomes two pairs of "K200"). If you pick any other cable, the optimal length is likely to be different. I used both newly purchased rolls of K400 and some older runs (3-5 years?) I had lying around. They all sounded the same. The length of the cable was always measured from beginning of copper to end of copper, before any termination took place.
I mostly terminated them with Linn Knekt bananas, but on some occasions with Deltron 550. Linn Knekt sound better, but the optimal length of cable didn't seem to be affected (I say "seem to", because I am not 100% certain of this). In all of the final comparisons between 2.4 and 2.8 m, I used only Linn Knekt. They were soldered with my own 60/40 solder wire at 353°C with my Weller WSD80 soldering station and WSP80 pen. The temperature is valid only for this particular station, pen and exact soldering technique. For example, my other Weller WD1 station differs by 7°C.
Worth knowing: Linn Knekt bananas have changed, perhaps a year ago. The bend of the four aluminium "flaps" that determines the contact pressure is different. The old version had a mild bend right in the middle of the flaps. The new one has a sharper bend, closer to the end of the flaps. The reason for the change could be an attempt to make it last longer - they have been known to loose their springiness pretty quickly, and for that reason many shops don't use them.
The new version of Knekt fits considerably harder than the old! As contact pressure is an important parameter for sound quality, this change affects performance. All connectors sound best when they fit "just right", which is tight but not so tight that it becomes difficult removing it, or the materials making loud cracking noises when their surfaces move against each other. If the contact pressure is too high, the music becomes hard and distorted. If the pressure is too low, the sound becomes sloppy and uncontrolled. While Knekts appear to have very little variation in size, banana holes can vary quite a bit (and on older Linn speakers such as Kan, Sara, Isobarik etc, Knekts don't fit at all as the holes are smaller). So when you connect your Knekt, notice how hard it grips into the hole. If it feels very tight, unplug and replug it many times, until it looses some of it's resistance and fits more easily.
When evaluating, I always did at least two pairs of cables at the same time, in the exact same way, but with different lengths. It's not possible to compare cables which are of different age, unless they are all more than 4 months old and have stabilised in performance. I started at 3.9 m and went as short as 0.5 m. Pretty quickly I concluded that the optimal length was somewhere in between 2 and 3 m.
I used Linn Majik, Linn Akurate, Tundra and Tundra Mono power amps. I used Linn Majik 109, Akurate 212, 242 and Klångedang T1 loudspeakers, both single and multi-wired. On a few occasions, I also used aktiv 242's (no passive filter involved). All of these units appeared to perform best with the same length of loudspeaker cable, which leads me to believe that the length I found optimal is a property of K400 itself.
In addition to any component's "quality in itself" there is however also a degree of interaction with the environment in which it operates. This became evident with the Klångedang T1's, which have their passive filters in separate boxes outside the loudspeaker cabinets. Now, the optimal length of the single wire speaker cable required between the power amplifier and the T1 filter boxes is as short as possible - not 2.48 m. I use 0.4 m, but recommend 0.5 m as it's more practical. But between the filter boxes and the T1 loudspeakers, where a bi wire cable is required, the optimal length was 2.48 m.
Passive loudspeakers do perform better single wired than bi- or multi wired. The closer I came to the optimal speaker wire length, the more obvious this became. Almost always the tweeter + and - inputs should be used.
Why exactly 248 cm? Ok, I confess: The very last cm is my guess. I had arrived at 2.40 m versus 2.50 m. Now, just like when using a precision torque tool on a fastener somewhere in your HiFi system, I find that the closer one gets to the optimal cable length, the more pronounced the differences get. They also become easier to understand and appreciate, as if one is approaching a peak where things just seem to snap into place. Therefore I actually find it easier to compare 2.40 m with 2.50 m than to compare 1 with 4 m.
2.40 is very upfront, agile, willing to attack and almost a bit tiring to listen to. Anything shorter than 2.40 gets tiring and restless, with an emphasis on the attack of each note. Avoid! Too long is much less of a problem - what happens then is that the music gradually looses its dynamics, in particular the attack of each note, and becomes gentle and cozy. Not bad, but less precise and thrilling.
2.50 takes one half step back from 2.40, finds a good groove and pulls you in. It's less in your face and slightly more forgiving. Yes, it's better than 2.40! But perhaps a tiny bit too laid back and easy going? I made more than ten comparisons back and forth between 2.40 and 2.50 with different types of music before I decided that 2.50 sounds like it might be a little too long. Half way in between the two - 2.45 m - didn't seem right to me. I made a pair at 2.48 m and it is the best I have heard so far.
I have not yet tried 2.46, 2.47 or 2.49. The problem is that once you are on that peak of performance, small random variations begin to affect the comparisons. So I'm not even dead sure that 2.48 is better than 2.50, it could have been those particular soldered joints that turned out a tad better. To get from dm to cm in precision, we need to compare more pairs than two.
EDIT: Added Akurate 212 to the list of loudspeakers
Last edited by lejonklou
on 2013-11-08 23:13, edited 1 time in total.