Using a 75 ohm RCA video cable for as an analog audio cable.

[Audiofire]

But the characteristic impedance of both the cable and the connectors does not matter at audible frequencies, and a cable that is less than a few kilometers/miles long from what I understand. I can even use no connectors at all and solder the conductors in unbalanced interconnects directly to the circuit. Am I right?

"2.2 - MATCHING AND TERMINATION
A common misconception is that audio outputs and inputs must be impedance matched. Circuit theory tells us that when source and load impedances are the same, maximum power is transferred. Although useful in some passive signal processing systems, this concept does NOT apply to modern audio signal interfaces. Their goal is to transfer voltage, not power! If Zi is made to match Zo, half the signal voltage is lost and the output drives an unnecessarily heavy load.

"However, impedance matching or termination is required for video and RF cables because the signals have much shorter wavelengths! As a general rule, cables begin to exhibit “transmission line” effects when their physical length is 10% or more of a wavelength at the highest signal frequency. This occurs with video cables over a few feet long and with CATV cables over a few inches long. To avoid reflections of energy from one end of the cable to the other, the driving source and receiving load impedances at each physical end of the cable must match the cable’s characteristic impedance. Such reflections will cause visible “ghosts” or “rings” in video images. For AUDIO cables, termination is NOT necessary unless cables are over about 4,000 feet long!"

Source:
Understanding, Finding, & Eliminating Ground Loops in Audio & Video Systems by Bill Whitlock

Correct me if I'm wrong, but I believe that 4,000 feet long is the most conservative estimate. The wavelength of sound at 20 kHz is only 1.7 cm, but we are talking about the wavelength of electricity at 20 kHz. That is related to the speed of light, not the speed of sound. A conservative estimate is that electricity travels at 50% of the speed of light (in vacuum) in normal copper conductors. This is where it is a little complex as quantum mechanics comes into play if you want to understand the technical aspects of the calculations. An online calculator gave me 24,589.3 feet as the wavelength of 20 kHz at 50% of light speed. Are you gonna need an unbalanced interconnect that is 24,589.3 feet long? Nope. So terminations/connectors are NOT necessary for RCA cables/unbalanced interconnects.

 

[Audiofire]

Limit thread replies to 50 posts. After all there is very little in audio that can't be worked out via internet searches.

Horrendous idea for a website that is about learning and having fun.

 

[escksu]

"Aluminum foil is a good conductor and nonmagnetic; therefore, it can reflect almost any exposure to electric waves, thus providing protection against EMR (Ott, 1976; Pratap et al., 2014). Aluminum foil can reflect about 90% of electromagnetic waves at wavelengths of 200nm (nanometers) up to 1μm (micrometer), increasing to about 99% at wavelengths above 1μm, and may weaken more than 80dB (decibels) of EMR at frequencies over 100MHz. The magnetic field will lose about 63% of its energy with a single sheet of aluminum foil (Pratap et al., 2014)."

Source (attached, with peer review):
Rambung, E., P. Kalanjati, V. and Abdurachman, . Aluminum Foil Shield Diminishes the Electromagnetic Radiation of Mobile Phones in the Cerebellum of Adult Male Rats. In Proceedings of Surabaya International Physiology Seminar (SIPS 2017), pages 97-98.

So a single sheet of aluminum foil can attenuate 99% of everything from 0 Hz all the way up to infrared radiation, which has a wavelength of about 1 μm. Shouldn't you have known that for years if you have a PhD in electrical engineering? I think the trick here is that one should avoid placing a huge amount of power cables, or massive transformers, magnets etc. right next to audio cables...

So yeah, your message could easily be interpreted as patronizing.

I still cant comprehend why this forum has a habit of digging up old threads and commenting/replying to what others posted...

 

[Audiofire]

I still cant comprehend why this forum has a habit of digging up old threads and commenting/replying to what others posted...

That can be annoying at times, however I think replying made more sense than opening a new thread here as there were some unsolved problems.

 

[TuliaNonTroppo]

I have a F-F RCA coupler. I would like to use it to connect two 1m 75 ohm cables for SPDIF application.

Would the coupler have any negative affect on the impedance of the combined 75 ohm cables?

 

[rwortman]

It will have an effect but it isn’t likely to affect data transfer. I dislike the aesthetics and would just make a longer cable.

 

[Speedskater]

Those couplers work just fine at much higher cable TV frequencies and much longer cables.
At SPDIF, they will work just like any other 75 Ohm cable.

 

[mhardy6647]

I have a F-F RCA coupler. I would like to use it to connect two 1m 75 ohm cables for SPDIF application.

Would the coupler have any negative affect on the impedance of the combined 75 ohm cables?

wee bit of insertion loss (1 to 2 dB-ish) ... maybe even less at low frequencies?

 

[Audiofire]

I have a F-F RCA coupler. I would like to use it to connect two 1m 75 ohm cables for SPDIF application.

Would the coupler have any negative affect on the impedance of the combined 75 ohm cables?

Since characteristic impedance is not an issue (the wavelength of 3 MHz is 100 m), perhaps this thread is more to your liking:

Is SPDIF Cable Length "A Thing?"

I've read that a digital coax should be at least 1.5 meters in length. Is there any validity to the article linked below? http://www.audiopolitan.com/blog/spdif-does-coaxial-digital-cable-length-matter/

www.audiosciencereview.com