PART III - SERIES II SPEAKER CABLE
Lots of questions on the cross-over aspect of the series I to series II. Since the VP is approaching zero at DC, the two Vp traces to blend into each other the lower we go in frequency. There is a “region” where the Vp differential is small, and we can nab this off and use it to our advantage.
A chart shows where that region is. The YELLOW region is where most all speakers cross-over the woofer to to mid/tweeter (three or more way) or tweeter (two-way). My speaker is at 200 Hz as an example. I may be good at listening, but bass frequencies are full of distortion any way and a 1%-4% Vp differential is REALLY hard to hear. This allows the two cables to be “spliced” together. So we see in GRAPH form this result.
But, you’re right! That isn’t all there is to it is it. We need a “voice” that is the same, too. To get that I made sure we share INDUCTANCE at 0.08uH/foot nominal and the IMPEDANCE traces also BLEND in the same region. Looking at the impedance we see the open-short test looking pretty consistent, where the 1313A (yellow) is way out there. We’d like to avoid that difference to our cable’s “voice”.
OK, now lets look at how all those dang nab wires really are working. We have two resistances in the cable to make matters more complex. We have the 48 individual wires resistance, and we have the “total” aggregate DCR of all the wires. Both are important.
If we use a zip cord, like 1313A,we can eliminate one of the DCR factors, but lose the ability to tune the cable response. This is OK if that change is inaudible to you, but the cable is measurably and different in calculation.
We’ll do the aggregate DCR first. This is the resistance we test doing and open-short impedance sweep. It looks at ALL the small wires at the same time.
We aren’t all engineers so I will make this simple. We now have 48 individual SODA STRAWS! Take any one soda straw size and suck a milk shake, water and air through it. Not all will let you draw the stuff at the same speed as the liquids DENSITY is different. We didn’t change the soda straws ID, but the density of what we are drinking. Each “frequency” has a different density, and the Vp changes from a milk shake to pure air at RF (assuming we use an air dielectric).
We can adjust the Vp with resistance, yes? We saw the equations for all that. There is that “R” value in there and this is where making a straw bigger, or smaller, can tune the Vp, or how easy it is to draw the liquid through the straw.
Let’s compare soda straws, a big ID one and a small ID one. Let me run you around the room sucking on that single SMALL straw! UGH, you can’t breath too well. The bigger one sure helps. That would be a 28 AWG small soda straw and a 10 AWG 1313A FAT soda straw.
What if, (thanks HP) we instead of using one small 28 AWG soda straw, I stuck a bunch of 28 AWG soda straws in your mouth? Same ID, just more of them. At some point they will EQUAL a 10 AWG soda straw. Did I change the air going in and out of each of all those straws? No, each individual straw is the same as always, but now we have a bunch at the same time and that makes it easier to breath through all those soda straws. We LOWERED the resistance…this will alter the IMPEDANCE (lowers it). But, the SPEED of the air through each straw is still fixed by the one straws ID and what ever the liquid (frequency) you are trying to draw through it.
How does this work and can we calculate all those soda straws properties as we add a bunch? Yes, we can. Several ways to cross check the answer, too.
Here we go, three answers that are pretty close. Why not exact? Because we make approximations on the size of the wire in some, and use the real deal wire resistance in the measurement. Remember, all this stuff has an error range to it or standard deviation. We need to be aware of what “guesses” we make or what variables we decide are too small or too big to matter.
What is our circuit?
This is what we have. I didn’t want to draw 48 individually insulated lines so pretend that that box is that. EACH one of those soda straws has a fixed ID or resistance. The Vp, or liquids speed (frequency based) uses that resistance to arrive at it’s properties. The capacitance is shared across ALL the wires measured from the cable end, but the current LOOP path is through each individual wire. How does that work?
The above is a simple example of the amazing world of physics. There is a law that states the current through parallel resistors will SPLIT between them based on the ratio of the resistances. In the diagram, we can see the current magnitude, represented by the black lines thickness, GROWS as the resistance (1,3, 6 ohms) gets smaller.
We can calculate the circuit if we wanted it to look like ONE resistor by adding up all the currents through EACH wire, and divide that into the voltage applied. So a single soda straw would be 0.67 ohms and allow the same current as three parallel soda straws of 1,3, and 6 ohms. We know for a fact that each soda straw act “differently” than the others as the current splits into the individual resistances.
To keep the soda straws Vp at frequency SPEED the same, I used all the same wire size and plastic dielectric (sets the capacitance). Remember, the Vp equation through audio (with R and C kept in the error mitigated zone…not too high or low) uses both R and C to set the Vp.
The use of many small soda straws allows a flexibility we lose with one fat straw. We can tune the draw (Vp) speed with ID (resistance) changes and the straws total parallel capacitance. The capacitance could be viewed as the room pressure applied to the end of all the straws. More room air pressure slows the speed in conjunction with the straws ID. We can manipulate R and C, both.
All of this impact all our analog cables. Yes, we can use many different sized straws but the speed of each straw will differ and add a distortion. The AC signal will start the same but become different and deliver voltage at a different rate in time. This is called group delay. All the differences will add one voltage on top of another at the end of the wire, and it will distort the signal sent down the wire.
If we take two coaxial cables. One is 66% Vp the other 87% Vp. One is a copper covered steel signal wire, the other is pure copper signal. One is a 75-ohm cable and one is a 50-ohm cable. We can tie them in parallel, yes? Sure we can. The signal sent down both wires at the same time won’t get to the end of the wire at the same time. The Vp is different based on R and C of each individual loop path. To avoid that, I use BONDED pairs and all the same wires size.
Why use a specific DCR? Easy and hard answer, both. We lose voltage across a cable that is intended for the speaker. It is a passive loss so not really audible but not efficient, either. And yes, it does change the amplifier damping factor as the amplifier sees the cable+speaker as the bulk load. Smaller DCR means less loss on the cable, especially at low frequencies.
If we hit a test scope with a white noise signal (equal signal amplitude at all frequencies) and look at the spectral signal magnitude through a cross-over of a speaker we’ll get something like this;
60 Hz 1000 watts
100 Hz 16 watts
3K 1 watt
10K less than .003 watts.
Since the series II is used above 200Hz-2000Hz, we don’t need all that wire to reach “perfection” in the bass. Not that a 11.5 AWG 7632 CMA wire is wimpy;
for 10 feet 10 AWG = 0.0100 ohm x 2 (there and back).
for 10 feet 11.5 AWG = 0.0126 ohm x 2 (there and back).
That’s a small difference in loop DCR. Where the advantage lies, is that the SERIES I is less expensive than the series II so why charge you more and see technically less performance in the bass region? THAT cost is real. To improve the treble we can keep the cost lower in the bass region for bi-cable customers. If we design the cable right, we can smoothly splice them together as we see in the design calculations.
Thanks so much for being patient on the news and the what, HOW and WHY of it all. Hope this makes cable seem like a real component and something we would not use on a lamp…well, for most of us.
Best,
Galen Gareis
