Doug Schroeder Method, Double ic

For instance, a 1m Schroeder Method setup has a source seeing an impedance like a 2m cable. Obviously the longer the interconnect the more potential for an impedance problem for a source’s output.

Doug, yes, I certainly agree with the second sentence, but the first sentence isn’t quite correct.

Doubling a cable in the manner you’ve defined (i.e., two identical cables connected in parallel) will double the capacitance, while cutting inductance, resistance, and "characteristic impedance" approximately in half. In contrast, doubling the length of a single cable will double capacitance, inductance, and resistance, and leave characteristic impedance unchanged.

Regarding your wise cautions about the slight possibility of equipment damage, the one concern I would cite in particular would be in the case of speaker cables, if the particular cables have high capacitance per unit length and/or if their length is especially long. The resulting heavy capacitive load could cause some amplifiers, especially solid state amps, to oscillate. I would be very surprised, though, if oscillations were to result from the doubling of an interconnect cable connecting a preamp to an amp.

Also, I have no way to predict what might result from doubling interconnects or speaker cables which incorporate a "network box," such as MIT and Transparent cables, because I’ve never seen a technical definition of what is in those boxes.

Regarding the possibility of adverse sonic effects that might result from doubling a cable, as opposed to the possibility of damage, I would cite the following situations as being susceptible:

(1) The situation I referred to above, involving speaker cables that have high capacitance per unit length and/or are especially long. The resulting increase in capacitance might adversely affect the sonics of an amplifier while not being severe enough to cause an oscillation.

(2) All digital interconnect cables. As I stated earlier in the thread I recommend against doubling cables conducting digital signals, regardless of how pleasing the results may seem to be, because the resulting mismatch of the cable’s characteristic impedance with the impedances of the components being connected amounts to introduction of a known and explainable design flaw into the system.

(3) Line-level analog interconnect cables that are especially long and/or have high capacitance per unit length **and** are driven by a component having high output impedance. That combination of circumstances may introduce rolloff and/or undesirable phase shifts in the upper treble region. This possibility applies to the outputs of some DACs, as you stated, as well as to the outputs of some other source components and some preamps.

(4) Phono cables used with moving magnet or high output moving coil cartridges, unless the cartridge manufacturer recommends a particularly high capacitive load (for example, 400 or 500 pf) for the particular cartridge.

Regards,
-- Al

It’s very unlikely, Ozzy.

In the case of analog outputs, some designs drive XLR and RCA outputs from separate output stages (i.e., they individually buffer them), and some don’t.

If they do, obviously connecting both would not cause either of the connections to have an effect on the other. (Aside, that is, from the possibility of introducing a ground loop and its negative effects, assuming the other ends of both cables are connected to a single component).

If the two outputs are not individually buffered, the signal provided to the RCA connector is probably the same signal that is provided to one of the two signal pins on the XLR connector. Connecting them both would do nothing for the other signal on the XLR connector, while resulting in at least a slight imbalance in the impedances of the two signals on the XLR connector, thereby degrading the noise rejection that a balanced interface can provide, at least slightly. Also, depending on the output impedance of that component and on the total of the capacitances of both cables, upper treble rolloff of whichever signal is used by the destination component might occur to some degree, and sharp transients might become more sluggish.

In the case of digital outputs, coaxial S/PDIF and balanced AES/EBU outputs would certainly be individually buffered, since their output impedances have to be different. So connecting both would not accomplish the same thing as doubling a cable, which as I’ve said I don’t recommend anyway for digital cables.

Zephyr24069, thanks for your comment.

Best regards,
-- Al

Regarding the mention of digital interconnections, one thing that theory can predict with certainty is that doubling a digital cable will result in a substantial mismatch between the characteristic impedance of the cable and the 75 ohm or 110 ohm impedance (for coaxial S/PDIF or balanced AES/EBU, respectively) of the components being connected.

That in turn can be predicted with certainty to cause or increase signal reflection effects at the high frequencies that are present in digital audio signals, and consequently to degrade waveform quality to some degree, in some manner. Which can certainly be expected to result in sonic differences in many and probably most systems, in part by contributing to timing jitter at the point of D/A conversion. And while those differences might turn out to be to be preferable to some listeners with some systems and some recordings, they would constitute a reduction in how accurately the recordings are being reproduced.

An interesting excerpt from this paper by Steve Nugent of Empirical Audio:

Another interesting thing about audibility of jitter is it’s ability to mask other sibilance in a system. Sometimes, when the jitter is reduced in a system, other component sibilance is now obvious and even more objectionable than the original jitter was. Removing the jitter is the right thing to do however, and then replace the objectionable component. The end result will be much more enjoyable.

Jitter can even be euphonic in nature if it has the right frequency content. Some audiophiles like the effect of even-order harmonics in tubes, and like tubes, jitter distortion can in some systems "smooth" vocals. Again, the right thing to do is reduce the jitter and replace the objectionable components. It is fairly easy to become convinced that reducing jitter is not necessarily a positive step, however this is definitely going down the garden path and will ultimately limit your achievement of audio nirvana.

Regards,
-- Al

P.S. to my previous post: There's one more possible effect I can think of that doing this may have in some systems. If the two components that are being connected are susceptible to ground loop issues (which might take the form of high frequency noise and/or a reduction of "background blackness," as well as or instead of low frequency hum), the lowered resistance of the ground connection between the components might reduce the severity of that issue to some degree.

Regards,
-- Al 

To a close approximation doing that will double the cable capacitance that is seen by the component that is driving the cable, and it will cut the resistance and inductance in half. For a line-level interconnect conducting analog signals the most significant of those changes is almost certain to be the doubled capacitance. The resulting sonic difference, if any, will depend on the output impedance of the component driving the cable (especially its impedance at high frequencies), the length of the cable, and the characteristics of the particular cable type. And if there is a difference, it may or may not be for the better, depending on those variables, the sonics of the system as a whole, and listener preference.

IMO. Regards,
-- Al