Subjective Testing Continued

[johnieo]

A year ago, Rich posted his subjective listening results for several AR-11 pair using various NPE capacitor configurations and one AR-11 with North Creek Zen polypropylene capacitors. Three different pair-- AR-4x, AR-3a, and AR-11-- have been rebuilt and enjoyed in our home over the last year. In the first level rebuild, the AR-3a’s were configured with Solen PB-MKT polypropylene capacitors; the AR-11’s with Dayton MPT woofer caps and Solen mid- and hi-range caps. One AR-4x used two 10-uF Callins leftover from the AR-11s, whereas its mate used a new 20-uF Dayton. (At the time I questioned the value of expensive caps in a 4x.)

The sound from the rebuilt -3a’s and -11’s was deemed clearer than that from each as-received pair. I restored the 4x pair from components, so there was no history. They did not make a favorable first impression; the high range was judged to “not sound very good.” This concerned me as its early reviews complemented its high range.

Next, North Creek Zen polypropylene caps were installed in the AR-11 mid- and high-range crossover sections. The Dayton woofer caps were replaced with Solen and bypassed with a small film cap. The results were startling. The sound was incredibly better than when Solen metallized-film caps were used in the mid- and high-range crossover sections. The ability to distinguish, separately, the individual instruments playing together in a large orchestra was astounding. In this aspect, it was in one listener’s view (a trained musician) the closest thing ever to a live orchestra. Based on these results, I performed identical surgery on the AR-3a and with the same results. After measuring the paralleled 10-uF Callins caps in the AR-4x and finding them to total 27 uF, 20-uF Zens were installed in both speakers. Again, the response was superior clarity. Earlier complaints disappeared.

This listener concludes that high quality polypropylene capacitors produce superior sound to NPE or low-quality polypropylene metallized film capacitors in the mid- and upper-registers of these three speakers. It was surprising to me that the AR-4x benefited from this change.

It is possible that every listener may not hear all these differences-- there may be more to it than the frequency response of our hearing; perhaps how our brain processes sound? Not everyone “sees” the same thing when looking at a painting!

With regard to subjective versus objective testing, it is likely that some of the differences we hear are not detected in the measurements made, or the crossover models generated. Most models take ESR to be a constant, which it is not. It is highly non-linear. For example, in a “good” 40 uF Callins NPE (AR-11 midrange crossover) the ESR would be 0.32 Ohms at 525 Hz, 0.24 Ohms at 1 kHz and 0.4 Ohms at 5 kHz. Also, the values of C and DF of large woofer crossover caps measured immediately after a large-signal (5-V) pulse are different than when only small signals are applied.

Lastly, polymer film quality, winding rate, and winding tension are not the same for all capacitor brands. The amount of crystallization in a polymer film depends on the film thickness and cooling rate, while it is being pulled from the liquid. During winding, stretching will induce crystallization, alter the local dielectric constant, and produce charge traps. Models do not account for these effects, but if the charge motion in and out of these traps does not follow the applied signal, it will affect what we hear.

Stretching during winding can also produce thin regions or pinholes in the polymer in which tiny arcs between the aluminum electrodes produce noise. Some Forum members have observed the resulting noise or “grain” in some brands. The use of pink noise to “form” a new film capacitor circumnavigates-- but does not address-- this real problem.

[Guest Bret]

>The sound was incredibly better than when Solen metallized-film caps were used in the mid- and high-range crossover sections.<

I concur with your observations to the letter. Last night I got my first chance to hear Solen vs Zen and there is no contest, the Zen are noticably superior in the mid and high range.

New NPEs are much better than old NPEs. New Solens are heads and shoulders better new NPEs. New Zens are at least a full head above the Solens.

The difference, for me, is with the Callins I was hearing a cymbal in a lump of high frequency information. With new NPEs I could hear the cymbal without undue sibilance. With the Solens I could tell it was a medium ride cymbal struck with something non-wooden. With the Zens I could tell the year the Sabian 18" medium ride (struck with a nylon tipped #4 stick by a man with a slight tendency to "fan" the cymbal 3/4 to the bell. . . in his mid thirties and just had a fight with the bass player - wearing Keds) was manufactured.

If it gets better than this, I'm not sure I can handle it.

Bret