In the past, Synergistic Research (and other cable manufacturers) have “split” a speaker cable’s geometry in half to provide separate leads for high and low frequency terminations. On the surface, this seems the most logical choice, and was our preferred method of bi-wiring for nearly 20 years. Theoretically, this method for bi-wiring connects the amplifier to the filter halves (crossover) separately to prevent inter-modulation, generated by one driver, from influencing the other driver.

However, If you look at the damping factor that reduces the unwanted signals, you will find that they differ very little, with or without cables (with 5 or 10 meter long cables for example). When using a tube amplifier, the cables (in practice) have no influence at all when dampening the signals from one side of the filter to the other, because the damping factor is too low already in the power amp. The signal will slip through to the other driver, despite the cables. Apart from that, a well designed crossover filter will provide a certain protection against “leaking” inter-modulation, since each half of the filter (the crossover in a two-way system) will damp each half of the frequency range.

Another method of bi-wiring is to run two different cables in parallel, thus giving the amplifier the ability to choose separate cables that are especially suitable for each half of the frequency range. This has been a hallmark of Synergistic Research cable design, going back to our fist Signature speaker wire: The Signature No. 2. If you assume that the signal always takes the path of least resistance, the right path will be chosen automatically.

Disadvantages of The Traditional Bi-Wire Termination
When you bi-wire your loudspeakers, the input of the high and the low pass filters are fed with different input signals. This difference is a result of the high and low frequencies being forced to travel different paths, perhaps through different types of cables, but under all circumstances through cables that have seen different loads. A tweeter with a high pass filter has a completely different impedance response compared to a woofer with a low pass filter!

The drivers do not integrate when their filter halves (crossovers) are fed with unequal signals. The result is the generation of phase error that effects the sound and transfer of phase information to the different drivers in a speaker. This phase error occurs because there will be non-linearity in the low and high frequency paths.

What does this sound like? Well, usually, just as you would expect from physics, it appears as a change in the reproduction of space and sound staging. The impression after a week or month is that all recordings sound very much alike.

Integrated Frequency Termination (IFT) Bi-Wire
All Tesla speaker wires, from Vortex through Apex, function as a “lens” to control electromagnetic inter-modulation. Accelerator through Apex contain at least one Tricon lens geometry, to precisely control electromagnetic fluctuations, for perfect phase time transfer. IFT Bi-Wire ensures that your amplifier “sees” consistent loading, from low to high frequencies, for sound staging that is as expansive as it is precise. Low frequencies are further tuned, in series, with high frequencies, through a transmission line precisely tuned to low frequency transfer, that exactly match the speaker wire geometry.

Shotgun Bi-Wire vs. TESLA IFT Bi-Wire
One option that does not take advantage of IFT Bi-Wire is a “shotgun” termination of two parallel speaker wires, terminated to a common set of spades or bananas at the amplifier end. Obviously this option would double the cost of bi-wiring your system (when compared to IFT Bi-Wire). but would it carry higher performance? The simple answer is NO. First, by separating the high(er) frequencies from low frequencies, the amplifier sees very different loads, and transfers your music as a mismatched signal, with significant phase distortion to your speakers. It is as if you are “focusing” on the upper frequencies with a wide-angle lens, and focusing on the low frequencies with a telephoto lens. This presents high frequencies and low frequencies in different aspect ratios, for a sound stage that sounds “bigger” in the upper registers than it does in the lower registers, and this then introduces sound staging problems. A far better option would be to spend the extra money on a higher end speaker wire (with IFT Bi-Wire), thereby elevating your systems presentation in an equal and balanced way.

If the manufacturer of your speakers insists on running separate speaker wires to the high and low frequency of your speakers binding posts, we can arrange for you to audition two speaker cables in “shotgun” vs. the equivalent higher end IFT Bi-Wired speaker wire (of approximately the same value). You can make the final call as to which bi-wire option delivers higher performance.

IFT Bi-Wire vs. Jumper Cables
So how is IFT Bi-Wire termination different from standard jumper cables or binding straps? Simple: Jumper cables are rarely tuned to the frequency range that they are intended to transfer, and are often times of a much lower quality then the speaker cables they are used with. Furthermore, jumper cables introduce additional hardware, in the form of spade lugs or banana plugs, that further degrade the sound. Bi-wire binding straps are almost always worse then jumper cables, as they are little more then plated metal of a quality and build that introduces considerable distortion in the form of harsh highs or muddy lows.

For the purpose of auditioning TESLA Speaker Wire, many dealers opt for non-IFT Bi-Wired speaker wire models, and will instead provide you with IFT Bi-Wire Jumpers; identical to the “hardwired” IFT Bi-Wire speaker cables. Aside from the addition of an extra set of connector hardware (spade or banana), the performance will be similar to that of our IFT Speaker Cables.


Figure 1: From this graph you can see the damping factor, and the real damping effect, that are the result of different cable lengths and different cables, as well as different amplifiers. With a good transistor amp, the damping will be decreased about 4 dB with a 5 meter cable. With a good tube amp, the damping will lose about 2 dB (the original damping with the tube amp was about 14 dB less, however).

IFT-graph-2Figure 2: These two curves show the crosstalk from the woofer to the tweeter. Crosstalk from a bi-wire configuration is represented with the lower curve.


Figure 3: This is a simulation diagram. The two components at the far left simulate the woofer resistance and inductance. The next two components are the low pass filter for the woofer. Of the next six components, the horizontal graphic represents two cables, and the vertical graphic represents the output impedance of the amplifier. The broken line converts from bi-wire to single wire. After the conversion, the first two components represent the high pass filter to the tweeter, and the five remaining components represent the tweeter.

IFT-graph-3Figure 4: This simulation is based on the diagram in figure 3. Here you can see that a phase difference arises when bi-wiring is used. The phase difference is largest just above the crossover frequency, due to the inductance of the cable, combined with the capacitance of the high pass filter. The inductance of the low pass filter is represented in this range when a single wire is used. The most probable reason for the capricious sound of bi-wiring is that in addition to a steady state error, another, transient induced phase error between the cables will appear when playing music. This changes the dispersion pattern of the speaker output. The human ear is very sensitive to such phenomena.

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