Microphone cable differences

[kaltavilla]

There is an audible cable effect I've noticed over the years that you can hear when you tap on some guitar cables when plugged into an amp. Its got a name but I can't remember it at the moment. It's kind of like microphonic tubes only not as severe. There's an orange casing two conductor shielded Belden wire I've used that does it. If it makes a sound when you tap on it, wouldn't sound waves in the room also have a subtle effect on the wire too? Kind of like print through with recording tape. Its there, but you only notice it when the conditions are right.
I think the more insidious cable defect is inadequate shielding from old or poorly made wire because any hum harmonics that get into your system are not going to occur at the same frequencies as musical harmonics that are mathematically related to A 440. They will beat againt the music even when they are at a very low level.

It's called triboelectric noise. Basically, everything has static potential, like silk and glass are at opposite ends of the static spectrum, likewise your hair and the vinyl or latex of a balloon. So, like you did in 8th grade science class, you rub the two together and you can charge them to their max static potential and then get balloons to stick to stuff like walls or glass rods etc.. Anyways, the same crap happens inside a cable. There is a difference in static potential between the copper and the conductor insulation. If the insulation is cheap enough, the cable can be microphonic. This is fixed by extruding a thin layer of conductive plastic over the insulation and under the shielding. The conductive plastic has a static potential in between that of the copper and the cheap insulation. drastically reducing the static potential between the two elements of the cable. The effect is most dramatic when used with economy cables but high quality cables benefit from the same technique as well. Gepco, now General cable used to make a guitar cable called LN888 that used this method to great effect. Truly awesome stuff, and very flexible.

 

[kaltavilla]

I think any extreme measurable differences in capacitance between elements or shielding or insulation/filler meant to damp microphonics are unlikely to show up with high output dynamics or condensers, more likely with ribbons. Then, only at some great length, longer than I ever work in studio, but sometimes work on remote jobs….but then, ribbons aren’t being hung on extremely long lines and if they are, there’s a booster pre close to the mic driving said long line.

Star Quad is it’s own thing that will save your ass on a 200 meter run across a coliseum floor crossing dozens to hundreds of electrical cables and dimmers on the way to a remote room or truck outside.

I have a few of the fancy Grimm TPR I made for ribbons, and hear no difference other than in microphonics tests while stomping or shaking a cable resistively loaded on one end and high gain pre on the other. Better than many others. The internal molding/insulation is more elaborate than most, more like some coax. Hear it over a signal? Doubt it. Cable handling is atrocious enough to make me avoid using it.

I do have some super cheap stuff that handles like limp spaghetti and tangles constantly that I also avoid using, which measures wildly high capacitance between elements compared to everything else, but in a 25 foot run makes no audible difference. I’d never roll out 100 feet of it for multiple reasons beyond sonics.

Star quad is a relatively high capacitance mic cable. You run 200 meters of that stuff on a mic signal and the high frequencies will never make it to the end of the cable. It's dramatic. A little less noticeable on line signals but still, at those lengths it is a very effective low pass filter. I try not to use starquad any longer than 25ft, 50ft max and only if I'm on a really noisy stage.

 

[kaltavilla]

Any idea in what years this transpired? I remember hearing something like that awhile back but didn't notice it with other Gotham cables. I have many hundreds of feet of various Gotham part numbers (not GAC-7) purchased 5-10-20 years ago and it's all relatively soft-handling cable, not great for live work in terms of destroy-ability, fabulous otherwise. A chair killed one with just a quick glancing blow. I ran across some NOS GAC-3 from probably 40-50 years ago with a Temmer Gotham tag on it and I can't see a diffidence in feel or under magnification inside compared to recent GAC-3. The old brown Gotham cable is said to be different somehow.

As far as I've seen, Gotham changes the part number by adding a material-type suffix indicating a change, I wouldn't be surprised by unannounced changes though. Cables make a difference like anything else all else equal, I've been through many in many contexts over time and always come back to Gotham for unbeatable high quality at low price, pretty much a trade secret. Not sure how I was turned on to them, probably from broadcast interactions.

Lake Cable USA is good, their stuff sounds fine and looks like Belden designs, heavy jackets, definitely not easy/perfect-lay, apparently they make their own copper.

"People that know want to know, people that don't won't."

Lake makes good stuff. I started their broadcast cable assembly department over 10 years ago. Yes they do draw their own wire. Another good outfit is Clark Wire and Cable. I ran that assembly department for years and a good friend of mine still manages it. They too have some great audio cable offerings and know what they are doing in terms of cable building.

 

[abbey road d enfer]

It's called triboelectric noise.

Your description of triboelectricity is correct. However, is it what happens when hitting a cable? As I wrote earlier, I maintain its piezo electricity, which is a related but different effect.

 

[abbey road d enfer]

Star quad is a relatively high capacitance mic cable. You run 200 meters of that stuff on a mic signal and the high frequencies will never make it to the end of the cable. It's dramatic. A little less noticeable on line signals but still, at those lengths it is a very effective low pass filter. I try not to use starquad any longer than 25ft, 50ft max and only if I'm on a really noisy stage.

Well, let's put some figures in action.
Typical starquad is 150pF/meter, so 200m is 30nF.
With a 200 ohms resistive source, it results in a -3dB HF point at ca. 26kHz, or -1.9dB @20kHz
It doesn't really qualify as a dramatic disparition.
Considering that 200 ohms is rather large, that the actual impedance of a dynamic mic is slightly inductive, which pushes the HF response a little, I don't see it as dramatic.
And after all, who cares about the 20 kHz response of a dynamic mic?
There are a few mics that have a higher impedance than 200 ohms, e.g. SM58@300 ohms, which one should be aware before connecting to 200m of cable, starquad or not.
Most condenser mics have an impedance of about 100 ohms, some much less (Schoeps at ca.25 ohms)
Of course, I wouldn't use 200m of starquad with a source of more than 200 ohms, but which are they in practice?
Most equpment has more or less adhered to a non-written standard of 100- ohms.

 

[JohnRoberts]

Star quad is a relatively high capacitance mic cable. You run 200 meters of that stuff on a mic signal and the high frequencies will never make it to the end of the cable. It's dramatic. A little less noticeable on line signals but still, at those lengths it is a very effective low pass filter. I try not to use starquad any longer than 25ft, 50ft max and only if I'm on a really noisy stage.

Starquad is like 150pF/meter so 200 meters with a 150 ohm microphone is down -3dB (half power) at 35Khz, more than -1 dB at 20kHz.

OK abbey beat me to it and he used a 200 ohm microphone but the 20kHz typical HF passband will make it to the end of that cable.
===
Yes mic cable capacitance matters and in the old days on movie location recordings, before wireless mics were invented, some mic runs could be a mile or more long. Their solution back then was to use 50 ohm mics. These days it's not a problem.

JR

 

[abbey road d enfer]

In the 90's live recordings saw a resurgence of activity.
The worst situation is when both an OB van and a remote recording facility graft themselves to a typical FOH/monitor combo. Then, although the antenna length is aceptable, you can have very high total capacitance.
Many hire and remore recording companies built passive splitter boxes, on the basis that transformers would "isolate" cables. They quickly found out it was not the case. These passive splitters solved the problems of hum and buzz due to differential "ground" voltages between desks, but not the capacitive loading.
I was asked by broadcast and remote recording facilities to produce active splitters.
The splitters I produced had unity-gain, so as not to disturb the existing balance, and a low output impedance (ca. 40 ohms), which allowed to drive easily 500m of mic shielded pair.
Today, it's not necessary, with the preamp/converter near the stage and distributing MADI to the various desks.

 

[Rob Flinn]

Your description of triboelectricity is correct. However, is it what happens when hitting a cable? As I wrote earlier, I maintain its piezo electricity, which is a related but different effect.

Most piezoelectric materials are crystaline in structure. I'm therefore wondering what part in a mic cable exhibits a piezo effect unless it's the copper itself. My Father researched piezoelectics for 10 years when he was a physicist for Philips research (formally Mullard research) & co wrote a text book on the subject.

EDIT - just found this

"Piezoelectric polymers can be classified by bulk polymers, voided charged polymers ("piezoelectrets"), and polymer composites. A piezo-response observed by bulk polymers is mostly due to its molecular structure. There are two types of bulk polymers: amorphous and semi-crystalline. Examples of semi-crystalline polymers are polyvinylidene fluoride (PVDF) and its copolymers, polyamides, and parylene-C. Non-crystalline polymers, such as polyimide and polyvinylidene chloride (PVDC), fall under amorphous bulk polymers. Voided charged polymers exhibit the piezoelectric effect due to charge induced by poling of a porous polymeric film. Under an electric field, charges form on the surface of the voids forming dipoles. Electric responses can be caused by any deformation of these voids. The piezoelectric effect can also be observed in polymer composites by integrating piezoelectric ceramic particles into a polymer film. A polymer does not have to be piezo-active to be an effective material for a polymer composite.[39] In this case, a material could be made up of an inert matrix with a separate piezo-active component."

 

[abbey road d enfer]

The conclusion is that most insulating materials exhibit some degree of piezo electricity.

 

[Mihobro]

Hi all, Over my years at Manhattan Center Studios, we ran through many different brands of cable, and had only time to run the following tests.
1. Connectivity tests, with the phantom power on , and a 150ohm termination on the end, wiggle the cables, especially the ends where there may. be open or intermittent connectivity usually start with the volume low, but increase the gain to see if there are not tics and pops.
2. Cable microphonics test. Only certain brands would pass this test. Solid brands include Mogami, Canare, Gotham, and Belden. Many of the cheap chinese brands would fail this test although recent samples show. improvement. Also, cables that had been crushed would sometime fail this test. Listen to the cable at as high a gain level while tapping on the cables with the termination resistor installed on the end. Compare the tapping noise level with the white noise level to get an idea of how significant the tapping is. I always suspected certain conductive plastics to be the cause, but I couldn't definitively prove that.
3. test with a 48V phantom powered microphone, usually a Neumann U47, or U87(not an AKG many of which run off 12V phnatom) headphones with mic, check for audible distortion, noise floor.
Some times these tests would reveal dirty connections as well as cold solders, but until the cable passed all three three tests they would stay in the bad cable pile.
Gotham cables always seemed to vary a lot in their stiffness even 20 years ago, they did perform well, but sometimes got "unwound" on the inside when carelessly wound. Canare and other mesh woven shield cables are the most durable, although this is not a problem unless the cables are carelessly wound.
I love to use "star quad" designed cables for their superior RF rejection characteristics Although I never could conclusively say that good single pair cables needed to be replaced, even though we were just down the street from the Empire State Building with all it's transmitters.
Once we ran a cable to an RE20 about 400' down to the street from the 7th floor, mostly gotham, but some Mogami, and it was perfectly quiet. Until somebody unplugged the microphone and every radio station in the neighborhood came blasting through the channel , which was immediately muted and deadpatched, a real testimony to the importance of terminating lines.

 

[JohnRoberts]

Once we ran a cable to an RE20 about 400' down to the street from the 7th floor, mostly gotham, but some Mogami, and it was perfectly quiet. Until somebody unplugged the microphone and every radio station in the neighborhood came blasting through the channel , which was immediately muted and deadpatched, a real testimony to the importance of terminating lines.

That was a concern when designing fixed install (background music) systems. These systems would routinely have surplus mic inputs left open when unused. System operators could not be trusted to always turn down unused inputs. The design compromise I settled on was to terminate the mic inputs somewhat lower than the nominal 10x bridging input. This could result in slightly less output from the mics in use, but a lot lower noise when left open circuit.

JR

 

[MediaWorksOKC]

It's called triboelectric noise. Basically, everything has static potential, like silk and glass are at opposite ends of the static spectrum, likewise your hair and the vinyl or latex of a balloon. So, like you did in 8th grade science class, you rub the two together and you can charge them to their max static potential and then get balloons to stick to stuff like walls or glass rods etc.. Anyways, the same crap happens inside a cable. There is a difference in static potential between the copper and the conductor insulation. If the insulation is cheap enough, the cable can be microphonic. This is fixed by extruding a thin layer of conductive plastic over the insulation and under the shielding. The conductive plastic has a static potential in between that of the copper and the cheap insulation. drastically reducing the static potential between the two elements of the cable. The effect is most dramatic when used with economy cables but high quality cables benefit from the same technique as well. Gepco, now General cable used to make a guitar cable called LN888 that used this method to great effect. Truly awesome stuff, and very flexible.

Gotham has a version of GAC-1 aimed at minimizing these microphonic effects:

https://www.gothamcable.com/en/gothamcables/unbalancedcable/10012gac1ultrapro

 

[MidiMania]

Many hire and remore recording companies built passive splitter boxes, on the basis that transformers would "isolate" cables. They quickly found out it was not the case. These passive splitters solved the problems of hum and buzz due to differential "ground" voltages between desks, but not the capacitive loading.

I have been deep into that business since early 1980s and I have designed several transformer based splitters. They were on tour with Gabriel, Robbie Williams and many others. Good transformer based passive splitters are even today the most common solution in live sound for distributing mic signals to 2-5 digital mixing engines because they effectively reduce any noise to a minimum. It is not only the galvanic isolation, its the much more linear balanced drive than any electronic balancing circuit. In combination with good mic preamps its a very 'quiet' solution, even if the capacitance takes more effect than with electronic low impedance cable drivers. But the LPF effect can easily be equalised at the receiving end while noise cannot.

I have mainly been using German Haufe splitting transformers, the Swedish Lundahls work also very well. Key is that the mic preamps shall have a higher than usual input impedance. 2k is not ideal for such a situation because the input impedances will add together on the microphone feeding the primary transformer winding. This is why most digital live mixing consoles have 5-10k input impedance on mic inputs. Most dynamic microphones sound much more open and detailed with that higher load impedance anyway.

What is not being discussed here is cable inductivity. I have seen various effects from it, especially when a lot of EMI is in the air. High frequency noise from lighting gear, networks etc. can easily cause artefacts by interferences. When cables have a high inductivity they have a high impedance for that noise which means the mic itself has to deal with it. This also counts for shields resp. the efficiency of the grounding at high frequencies by the shield.
I tend to believe that many 'audible effects' from using different cables are merely depending on the situation with HF noise and mechanical influences on the cable, esp. vibration. One would have to take all these parameters into respect before making a statement about the 'sound of a cable'.

 

[emrr]

I'd add what I have seen is transformer splitters using whatever Whirlwind/etc supply that don't have sufficient internal screening and correct ground path isolation to help significantly with large differentials between distant ground paths.

 

[vintageampfixer]

E Guitar and Bass world often doesn't want / appreciate high fidelity

Yup! IMHO guitarists are addicted to "tone" first, "volume" second and "fidelity" coming in at the 'who cares' position ... with the holy grail being something they think sounds "right" ... I've spent hours on this topic with many friends who play and learned a lot from them ... meanwhile, I'm definitely not a guitarist musician

PS, this isn't meant as any sort of jibe, I've immense respect for the people I've indirectly talked about

 

[Cqwet Dbdfte]

Yup! IMHO guitarists are addicted to "tone" first, "volume" second and "fidelity" coming in at the 'who cares' position ... with the holy grail being something they think sounds "right" ... I've spent hours on this topic with many friends who play and learned a lot from them ... meanwhile, I'm definitely not a guitarist musician

PS, this isn't meant as any sort of jibe, I've immense respect for the people I've indirectly talked about

An electric musical instruments amplifier doesn't need "fidelity" as it is a Producer, not a RE-producer. Whatever comes out is "original".

 

[abbey road d enfer]

Good transformer based passive splitters are even today the most common solution in live sound

AFAIK it's not the case here on this side of the Rhine.
There are a few legacy passive splitters that don't get much use, It is most common to use the stage boxes with a digital multichannel connection or active analog splitters for occasional operations.

It is not only the galvanic isolation, its the much more linear balanced drive than any electronic balancing circuit.

AFAIK, most analog active splitters have 2 or more xfmr-balanced outputs.

In combination with good mic preamps its a very 'quiet' solution, even if the capacitance takes more effect than with electronic low impedance cable drivers. But the LPF effect can easily be equalised at the receiving end while noise cannot.

If the tour starts with the complete system it's OK, but in most cases, the need for splitters will be only a few dates, so the addition of splitters should not result in having to re-EQ everything.

I have mainly been using German Haufe splitting transformers, the Swedish Lundahls work also very well. Key is that the mic preamps shall have a higher than usual input impedance. 2k is not ideal for such a situation because the input impedances will add together on the microphone feeding the primary transformer winding. This is why most digital live mixing consoles have 5-10k input impedance on mic inputs. Most dynamic microphones sound much more open and detailed with that higher load impedance anyway.

+1

What is not being discussed here is cable inductivity.

I'm not sure it's inductivity. The inductance of a wire is pretty much constant over the usual gauges used in audio. Linear inductance varies from 1.5nH/m to 1.75nH/m for AWG16 to AWG28.
What is more significant is the capacitance, which can vary in a ratio of 1:2, and the shield coverage, which usually sits between 91 and 98% for braided or helical shield. Only Al foil gives 100% shielding but it's rarely used in mobile applications because of its stiffness. The difference in terms of radiated interference is in a ratio of 2:9.

I have seen various effects from it, especially when a lot of EMI is in the air. High frequency noise from lighting gear, networks etc. can easily cause artefacts by interferences. When cables have a high inductivity they have a high impedance for that noise which means the mic itself has to deal with it. This also counts for shields resp. the efficiency of the grounding at high frequencies by the shield.
I tend to believe that many 'audible effects' from using different cables are merely depending on the situation with HF noise and mechanical influences on the cable, esp. vibration. One would have to take all these parameters into respect before making a statement about the 'sound of a cable'.

I fully agree with the assumption that subjective evaluation of cables results from RFI/EMI effects. It should be borne that, within limits, the equipment to which the cable is connected is what produces the audible differences. Excluding very poor cables, extreme lengths, dubious sources...

 

[GJB17]

Blind. Just checked, I still have the files from the test I did. Looks like google drive took them down because I used commercial tracks, but if anyone is interested PM me and I’ll send them to you.

I would be interested in the cable tests please. Graham

 

[GJB17]

Interesting side light to this... I have heard that Brian May prefers to use a long curly-cable guitar cord... allegedly it sounds "better"... maybe different would be a "better" word. Getting back to a more technical explanation... and as others have already noted... a guitar has a high source impedance so the (higher) capacitance of the cable is going to have a noticeable effect... probably both attenuation and perhaps resonance(s). On the other hand... if you are coming from a (normal) low impedance source (100 ohms or so) ... e.g. a dynamic mic or a mixer line out... the effect would be much less noticeable quite possibly unnoticeable... or Zero!

 

[Newmarket]

Interesting side light to this... I have heard that Brian May prefers to use a long curly-cable guitar cord... allegedly it sounds "better"... maybe different would be a "better" word. Getting back to a more technical explanation... and as others have already noted... a guitar has a high source impedance so the (higher) capacitance of the cable is going to have a noticeable effect... probably both attenuation and perhaps resonance(s). On the other hand... if you are coming from a (normal) low impedance source (100 ohms or so) ... e.g. a dynamic mic or a mixer line out... the effect would be much less noticeable quite possibly unnoticeable... or Zero!

And throw in that a typical passive electric guitar pickup also sees a variable impedance due to a tone control circuit.