Development of the Wind River Speaker Cables

We sold a customer some late stage prototype, Wind River speaker cables.  He loved them, and asked us about our design approach and how we arrived at our current production cables.

So here you go … 15 months' development summarized in a few paragraphs.

Litz

I absolutely love litz wire.  In the late stages of development, I learned that it's best suited for interconnects, but this learning path was neither obvious nor linear.

If you clicked on this post, you're no doubt aware of the theory behind litz (skin effect and all that).  If not, here's a primer.

Auditioning & Prototyping

During prototyping, I demoed cables at customers' homes.  A system with subwoofers may be very different from one without any subs, and developing an uncolored cable that works across a wide range of system contexts is an extended information gathering exercise.

One constant with these later prototypes was litz's hallmark of extremely clean upper octaves with no audible ringing.  In some systems however, our 12 ga. cables were perceived as being a bit thin sounding due to their extended treble response.

In general, extending bandwidth at one end of the spectrum (i.e. treble) requires a corresponding bandwidth extension at the other end (i.e. bass).  Without balancing these frequency extension characteristics, your attention is drawn toward the more extended frequency extreme.  Extended deep bass without corresponding treble extension sounds muddy, and the reverse situation sounds thin, or "wiry".

Wire Gauge Experiments

We went into rapid prototyping mode to establish an ideal gauge, using wire from earlier experiments.  Litz is extremely labor intensive to work with and using one of our earlier prototype materials put the "rapid" in rapid prototyping.

We used wire which was tonally very similar to litz - stranded, tin-plated copper.  It was a close second in our early trials, with the main difference between the two being litz's slightly superior treble.  In other words, it was more than good enough to home in on the correct gauge as you'll see below.

These experiments led us to a sweet spot of 9 gauge - having balanced the bass and treble extension, with no trade-offs.

Termination Process

An interesting thing happened along the way.  While experimenting with the stranded, tin-plated copper wire, we made a set up with crimped connections.  All previous terminations were soldered, to maintain consistency with the litz. 

In order to strip the insulation off litz wire, a solder pot is employed and the result is solder-tinned wire. 

Once you've tinned the litz in a solder pot, a soldered termination is more or less mandatory.   For completeness however, we tried crimping the litz, and the result was as we expected - inferior sonics.

So, at the end of the day, termination requirements are dictated by the wire's attributes, with litz benefiting most from a soldered connection and stranded tin-plated copper being optimal with a mechanical connection.  Ranking the four variations (from best to worst):

1. 1. Crimped, stranded, tin-plated copper
   2. Soldered litz
   3. Soldered, stranded, tin-plated copper
   4. Crimped litz (a very distant fourth)

Getting to Production - Final Changes

We weren't done.  The stranded tin-plated copper was some surplus we obtained.  We now had to find it in production quantities (and of course, test it).  It took quite a few e-mails and we had nearly given up, but our perseverance paid off.  The samples passed the test and we were on our way.

Our production architecture was nearly set, but there were a few more things to try.

We began experimenting with sleeving and settled on unbleached cotton, as opposed to our earlier configuration with the ever popular polyester braid.  You can read about it here, including how we demonstrate the difference between the two outer jackets.

Up until this point, our spade connectors of choice were silver plated copper.  We "settled" on these because of litz wire's soldering requirement, but the field was now wide open after establishing the superiority of a mechanical connection in combination with stranded, tin-plated copper.

We sourced connectors from both ETI and Furutech.  Both were superior to our solder-able/crimp-able spade lugs. 

The ETI connectors (which we absolutely love) had a wire gauge limitation of 12 gauge, and so, the Furutechs were selected.

Wrapping it up ...

Running through every permutation can be time consuming, and if you skip a step, you may well be missing out.