Speaker Asylum General speaker questions for audio and home theater.

---

[ Follow Ups ] Thread: [ Display  All  Email ] [ Speaker Asylum ]

---

[ Alert Moderator ]

---

Re: ?????

Posted by Kal Rubinson (R) on March 9, 2007 at 09:26:24

In Reply to: Re: ????? posted by Dave Kingsland on March 9, 2007 at 08:50:36:

One thing at a time.
"Suppose, for purpose of argument, that the speaker is a 4 ohm resistive load, with 8 ohms at the low posts and 8 ohms at the high posts, and the speaker cable resistance is 1 ohm. Using a single cable, the total impedance of the cable plus load is 5 ohms (1 + 8/2). When bi-wiring with two such cables, the total impedance is 4.5 ohms ((1 + 8)/2)."
Your math is fine but your assumptions are far from real world. An 4ohm system cannot be 8 + 8 across all frequencies (even simplifying it to resistance and not impedance) since each leg has an increasing resistance with frequencies beyond its passband, even at crossover. Also, a cable resistance of 1ohm is HUGE! Using this assumption, unreasonably magnifies all the effects you describe.

"If the crossovers were perfect brick walls and there was no overlap in frequency between the high and low networks, then bi-wiring wouldn't make a bit of difference (assuming the cable behaves linearly). But since there is overlap, in the region around the crossover frequency the cable impedance will be different in a bi-wire circuit vs. a single wire circuit. That will affect the amount of current delivered to the speaker in that frequency range, and thus the speaker's output in that frequency range."
The cable impedance does not change appreciably with frequency regardless of the crossover. It is the load represented by the speaker that changes. The amp sees that change but, since it is paralleled by a complementary change in the parallel leg, it is minimal.

"Now, what if you use the same two cables to double up a single run (connecting them together at the speaker terminals) instead of bi-wiring. In my example above, the total impedance was also be 4.5 ohms, same as bi-wiring. But there is a difference. With the double run circuit, the impedance difference compared to a single run is the same across the whole frequency range. With the bi-wire circuit, the impedance difference compared to a single run is limited to the frequency range in which currents flow to both high and low crossover networks."
So, first, the real world differences are MUCH smaller since 1ohm cables are generally not in play. Second, any impedance variation seen by the amp in one leg is compensated for in the other and has nothing to do with the fixed resistance of the cable.

In fact, one might argue that a typical crossover benefits from single-wiring since that assures the intended complementary shunting of out-of-bandwidth impedance rises of one network/driver leg by the other. Introducing real world cables, with their complex impedances, between the legs would certainly complicate that process. Of course, I would think to suggest something as radical as that. :-)

Kal

This post is made possible by the generous support of people like you and our sponsors:

Kimber Kable

---

[ Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2024, Audio Asylum, all rights reserved ]

---

[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]

---