The Audiophoolery Thread.

[Radio Wrangler]

Good! We're all agreed it's irrelevant.

Butterworth solved the issue of families of equations for generating maximally-flat monotonic filters. The roots were all-pole and the poles were distributed around a circle on a complex plane (s-plane) of frequency.

Tchebyshev took this a bit further and said that if you permit some ripple in the passband and don't insist on monotonicity, you can have a faster transition to the inevitable 20dB/decade per pole ultimate roll-off rate. Tchebyshev did this by distorting Butterworth's circle into an ellipse. He got constant-amplitude ripples across the passband and by choosing the elipticity, you chose the depth of the ripples.

Cauer took the next step and said that if you didn't need a roll-off rolling off towards infinite attenuation, you could have accelerate the transition band roll-off at its bottom end. "Complete Cauer" filters are modified versions of Tchebyshev with added poles on the real axis which produce notches in the stopband region and a finite asymptotic limit to the stopband attenuation. These filters are sometimes called "Elliptic Filters" because they are derived from elliptic functions... this has nothing directly to do with Tchebyshev's ellipse-shaped locus for his poles.

These filters get progressively closer to the ideal brick-wall frequency response transition, but they do so at the expense of non-linear phase and greater peaks of group delay. There are other families of filtars offering less ideal amplitude/frequency characteristics, but less problematic phase/time characteristics. They see value in FM receiver filtering, and in time-aligned crossover design amongst other places. They are very important in handling pulse and digital signals.

That's probably scared a ny audiophiles off.

David

[Sideband]

Originally Posted by Radio Wrangler

That's probably scared a ny audiophiles off.

David

No...they are probably laughing at OUR pseudo science firmly believing that their science is correct and Einstein and all the others got it wrong.....

[GrimJosef]

It wouldn't be impossible to make an 8 ohm audio 'cable' (not purely resistive of course). Two 25mm wide copper foil strips placed face-to-face and separated by 0.2mm thick Mylar would have a capacitance of 3.6 nanofarads/metre length. If the copper foil was the same thickness as the Mylar then the resistance of the pair of conductors would be 6.7 milliohms/metre and the resulting impedance would be 8 ohms at 4.65 kilohertz or so. A bit more copper and/or thinner Mylar would bring the required frequency down more comfortably into the audio range. I have seen this 'stripline' geometry proposed as a handy way to run speaker leads under carpets.

Cheers,

GJ

[G8HQP Dave]

The impedance would not be 8 ohms. The magnitude of impedance would be 8 ohms; the impedance would be about 5.7 -j5.7 - and that only at 4.65kHz.

[GrimJosef]

Or to put it another way its magnitude would be 8 ohms and its phase angle 45 degrees. 8 ohm speakers aren't purely resistive either, and their impedances vary with frequency too.

Your original assertion was that the cable impedance would be "nothing like" a speaker's impedance. Craig had only claimed that it would be comparable and I suppose I'm only claiming that it could be 8 ohm-ish .

Cheers,

GJ

[Radio Wrangler]

At 10kHz, lambda at the speed of light is 30km, let's say the velocity factor is about 0.6 so that becomes 18km. So 3 metres of speaker cable is going to be 360x3/18000 = 0.06 degrees long. Double that for the round trip so the electrical length seen for a round trip is 0.12 degrees.

Thus for 3m speaker cables at 10kHz, the speaker impedance is rotated by 0.12 degrees.
Given this, it doesn't really matter where the centre of the rotation lies, so the Zo of the cable is rather irrelevent.

I was also going to quip that OUR pseudoscience put a man on the moon... but then wasn't that all faked in Hollywood? and isn't the Earth flat anyway? and the moon merely a painting on the crystal sphere? Probably by that Leonardo bloke... he got up to that sort of thing, unless Galileo beat him to it.

David

[Restoration73]

I'm hoping my new 5" mylar cone speakers will give a "transparent" sound.

I have also learned that the makers of a proprietary brand of aerated chocolate imply
the bubbles are created by pumping music from a gramophone through it. Perhaps
they are unaware that in the last century some 78rpm discs were pressed in chocolate.

[Craig Sawyers]

Originally Posted by Radio Wrangler

At 10kHz, lambda at the speed of light is 30km, let's say the velocity factor is about 0.6 so that becomes 18km. So 3 metres of speaker cable is going to be 360x3/18000 = 0.06 degrees long. Double that for the round trip so the electrical length seen for a round trip is 0.12 degrees.

Thus for 3m speaker cables at 10kHz, the speaker impedance is rotated by 0.12 degrees.
Given this, it doesn't really matter where the centre of the rotation lies, so the Zo of the cable is rather irrelevent.

David

The only time that audio impedance matching was necessary was in long distance telephone lines - for voice and telegraphy. It was that which gave rise to the 600 ohm standard. There is a half way decent history of impedances in audio on Canford's (Canford is a professional audio supplier) site here https://www.canford.co.uk/Technical/Article/CableImpedance

Craig

PS Canford is where I buy XLR connectors and similar (Cheaper than Farnell) and balanced cable (at a quid or two per metre). And they sell by the metre, unlike Farnell and RS who want you to buy a 100 metre reel. The other thing, just the other day are the coloured tabs that go under chassis XLR's for cable ident. Farnell wanted to sell in packs of 10, whereas Canford sells by single units.

[Radio Wrangler]

The impedance of normal overhead phone lines wasn't ideal for the impedances of normal telephones, so for long connections they either had to change Zo of the lines, or redesign all the phones. They chose to change the lines by adding series inductance, adding 88mH lumped inductors every so many miles.

When PCM digital telephony took off, they could stuff either 24 (USA) or 30 (europe) phone calls on each twisted pair, so they removed all the loading coils and scrapped them. Radio amateurs liked them because they were a) free and b) could be used to make audio filters to improve reception of Morse signals.

Impedance matching turned into a terrible balls-up with the first transatlantic telegraph cables. Reflections and group delay variation garbled even telegraphy! The authorities of the day favoured going to higher and higher voltage in an attempt to fix it. A young William Thompson (as he was called then) suspected the real cause, but he wasn't a big wig then, and the line was damaged. An interesting event to research and the beginning of Lord Kelvin.

David

[Kevin Hoyland]

Hello.

Last week on Ebay a Hunts Capacitor Analyzer CRB3 went for £173.89 and 1 hour later a Hunts CLR 3221 Analyzer went for £126.00. I have the 2 same sets in my workshop and I paid £10.00 for the CRB 3 and £8.00 for the CLR 3221 but that was years ago.
Do you think this is related to Audiofoolery??
I know the CRB3 has a EM34 in the tester but both were listed as not working in this particular case.
Kevin

[Craig Sawyers]

Don't think is anything to do with audio. Looks more like a collector with deep pockets.

I have a Lafayette unit that does the same thing, that cost next to nothing. To be honest I mainly use it for (a) Reforming old electrolytics (b) Seeing if they have a reasonable leakage current once reformed (and if it passes both of those I use an ESR meter, and measure its capacitance) and (c) for testing regulator valves (an AVO valve tester can't do those).

Craig

[Hartley118]

The author of that Canford account https://www.canford.co.uk/Technical/...CableImpedance knows their stuff: it's a good summary of the challenges of transmitting audio, in both its analogue and digital forms.

In the early days of digital audio studios, back around 1980, we were faced with the task of the serial transmission of up to 24-bit digital audio over distances of several hundred metres. With a signal frequency spectrum extending to the tens of MHz, this posed a few challenges to those of us previously living in an audio environment, introducing concepts of cable characteristic impedance, termination, reflections etc for the first time.

However, unusually, the technical spirits were with us on this occasion and it turned out that normal studio grade twin twisted screened audio cable worked well, sometimes with a touch of equalisation. Its characteristic impedance turned out to be around 110 ohms, which is now the standard for digital audio transmission to the AES/EBU standard, known as AES3.

We faced another hurdle when it came to selecting a standard connector, but, having tested a number of exotic high speed digital network connectors, there was also another happy coincidence when it turned out that the familiar XLR audio connector did as good a job as most others and therefore became the AES3 standard for digital audio.

Martin

[Radio Wrangler]

Well, sometimes you do get lucky.

And the screen prevents RF hash being spewed all over the place. And XLRs are moderately band-proof.

David

[G8HQP Dave]

The impedance of normal overhead phone lines wasn't ideal for the impedances of normal telephones, so for long connections they either had to change Zo of the lines, or redesign all the phones. They chose to change the lines by adding series inductance, adding 88mH lumped inductors every so many miles.

I thought dispersion was the problem: the impedance (and speed) of the line varied with frequency. A 'wrong' impedance could simply have been corrected with a transfomer. The added inductance overcame the line resistance, so the line then had a resistive impedance throughout the (telephone) audio band: Z=sqrt(L/C) became true again.

[Radio Wrangler]

That's why they chose to modify the lines. Initial discussions had considered both the lines and the phones, until it was shown that it could not be done with the phones alone.

Some people were still feeling their way around.

David

[Hartley118]

Originally Posted by Radio Wrangler

..........

Impedance matching turned into a terrible balls-up with the first transatlantic telegraph cables. Reflections and group delay variation garbled even telegraphy! The authorities of the day favoured going to higher and higher voltage in an attempt to fix it. A young William Thompson (as he was called then) suspected the real cause, but he wasn't a big wig then, and the line was damaged. An interesting event to research and the beginning of Lord Kelvin.

David

I guess that William Thomson spent long enough outside Scotland not to worry about an English error in his surname spelling, but I'd watch out for complaints from your fellow Fife residents David .

It's really quite remarkable that those early transatlantic telegraph cables worked at all. It's also remarkable that, despite in-depth knowledge of Leyden jars etc, those telegraph experts hadn't anticipated that the line would essentially look like a giant capacitor.

William Thomson demonstrated an early understanding of the importance of gain structure in an electrical or electronic system. Whilst telegraph engineers were trying ever higher drive levels to try and get a few volts output at the cable far end, Thomson worked out that a receiving instrument more sensitive than the traditional telegraph sounder would enable more sensible (and safer) cable drive voltages to be used. The result was Thomson's invention of the mirror galvanometer, responsive to just a few millivolts.

Here are some pictures of an example of Lord Kelvin's mirror galvanometer - one item from my collection which is actually allowed in our living room. This one is a moving coil model (still working) dating, I think, from 1892, though earlier examples used a fixed coil with a compass needle attached to the mirror. When I saw it at an antiques fair a few years ago, I was intrigued by its description as a 'Marine Galvanometer' made by Lord Kelvin's company and just couldn't resist it.

It's interesting how a discussion on speaker cables can lead us to wander back into communications history.

Martin

[fetteler]

Not much 'phoolery recently... This thread has become a discussion of mundane technical details

Come on Mods - let's get it back on topic!!! I want to read about the importance of Feng Shui on cable placement and if it really makes the blacks blacker

Steve.

[kalee20]

Originally Posted by Radio Wrangler

It is good practice to include an RF diplexer on the output of a power amplifier, so that by the sort of frequency that the amp would oscillate at if capacitively loaded, it doesn't see the applied load at all, instead it is made to see a nice resistor as a dummy load.

To do this a small inductance (small in Henries, but thick in wire for low loss at audio) is fitted between the amplifier proper and its output terminals. This would naturally resonate with the cable capacitance and cause worse trouble. Planting a low-ish value resistor across this inductor kills the Q of the resonance. Its value is a compromise.

Yes, been there done that! I was designing an amplifier to drive a coil, DC to 5kHz. The load was specified as a series L-R network, but knowing that it could be driven over a long cable I added a bit of capacitance to my dummy load. Just as well I tried - it took off! So it got a parallel L//R in series with the output. As it didn't need to have distortion measured in tens of PPM, I used a powder core.

Originally Posted by fetteler

Not much 'phoolery recently... This thread has become a discussion of mundane technical details

Come on Mods - let's get it back on topic!!! I want to read about the importance of Feng Shui on cable placement and if it really makes the blacks blacker

Yes I was thinking that - I was hoping to learn more about what beeswax to use to impregnate my wax capacitors - what flowers should the bees be allowed access to, and what breed of bees would get me the most subtle highs and most presenceful lows... as it's too much to expect that these would coincide, I'm thinking of having a mercury-wetted selector switch on my next amplifier to select between different capacitor types to suit my mood and the music...

[Radio Wrangler]

And a switch to switch in different numbers of strands in your speaker cables?

Why have switches, though, with nano-technology robots, you could have little minions re configuring things and soldering as needed. But this sounds too techno and not olde worlde esoteric. Never catch on!

David

[DonaldStott]

Originally Posted by kalee20

Yes I was thinking that - I was hoping to learn more about what beeswax to use to impregnate my wax capacitors - what flowers should the bees be allowed access to, and what breed of bees would get me the most subtle highs and most presenceful lows... as it's too much to expect that these would coincide, I'm thinking of having a mercury-wetted selector switch on my next amplifier to select between different capacitor types to suit my mood and the music...

Agreed - don't know if this has been Posted already but this is one of my Audiophoolery favourites: -

http://www.machinadynamica.com/machina31.htm