Single conductor, shielded audio wire?

[smallcleverrooms]

I am beginning to make contact mics and such, however I am unsure where I can find single conductor shielded audio wire. I am currently using 2-conductor wire from Radioshack, however it is 2-conductor and very inflexible. Does anyone know of a source of flexible, single-conductor audio wire?

[isaac42]

I don't understand exactly what you're looking for. A single wire can't be shielded. The shield is a second conductor surrounding the center wire. That's called coaxial, because the two conductors have the same axis. Also, you need to have a complete circuit in order for electrical stuff to work, and the shield provides the path to complete the circuit.

 

Wire can be stranded, consisting of multiple strands making up a single composite conductor, or solid, with a single wire doing the job. Stranded wires are more flexible. I don't know what you're finding at your local Radio Shack. Might be something like RG-58, which is a shielded cable intended for RF applications such as cable TV. It's pretty stiff.

 

What exactly are you trying to do? Connect your contact mic to an amplifier of some sort, I assume, without picking up interference. Where will the mic be? Will the path to the amp be fixed, or will they be moving, relative to each other?

[smallcleverrooms]

What I have right now is this cable from Radioshack. As you can see there's a red and a white wire surrounded by the stranded, however I just want one wire, not two inside of the shield.

[WRGKMC]

^^ You're using balanced mic cable there. What probably want single core shielded wire. Something like this used for guitar cables is likely too stiff. http://www.parts-express.com/talent-gi100-22-awg-guitar-and-instrument-cable-100-ft--101-301

 

A good option might be to buy some RCA type extension cables and cut the ends off. The stuff is inexpensive and flexible.

One of these 50' cables can provide 100' of wire. These are stereo cables but you can cut the ends off then split the two sets of conductors in half. You may need a razor knife to get them going but they pull apart fairly easily. The wire quality isn't super nor is their strength but for simple projects they can work. You just need a low temp iron when soldering and possibly some heat sinking so you don't melt the insulation. .

 

http://www.parts-express.com/rca-patch-cable-50-ft-gold-plated--240-046

 

These are heftier but still flexible. They come as singles and have 100% shielding.

http://www.parts-express.com/wired-home-sc25-single-rca-audio-video-cable-25-ft--181-405

 

You can probably find better stuff that's in a bulk roll. The thinner stuff is harder to find in bulk. I have a dollar store where I can buy the 50' cables for $2 so I have a pretty good stock. For anything heavier I use guitar cable.

[Mr Temporary]

Have you looked at StewMac?

 

 

[Mmmmqac]

Do not use coax. Always use balanced whenever you can. I assume you can because you are making them yourself.

 

The shielding is to stop interference from capacitively coupled electric fields, while the balance cores are to cancel interference from inductively coupled magnetic fields. If you have a single core and use the screen as the other conductor, the interference from capacitively coupled electric fields is added to your audio.

 

Look at the way a balanced microphone is wired. The two conductors carry the audio, and the shield does not.

Another tip: BALANCED refers to the impedance "seen" by the pair of conductors, it has nothing to do with the waveform on the conductors being "mirror-imaged."

 

[WRGKMC]

Do not use coax. Always use balanced whenever you can. I assume you can because you are making them yourself.

 

The shielding is to stop interference from capacitively coupled electric fields, while the balance cores are to cancel interference from inductively coupled magnetic fields. If you have a single core and use the screen as the other conductor, the interference from capacitively coupled electric fields is added to your audio.

 

Look at the way a balanced microphone is wired. The two conductors carry the audio, and the shield does not.

Another tip: BALANCED refers to the impedance "seen" by the pair of conductors, it has nothing to do with the waveform on the conductors being "mirror-imaged."

 

The source of the signal and must be considered. Unless you need a reason to convert the signal to a balanced, it makes no practical sense to do so.

 

A dynamic mic diaphragm produces an unbalanced signal. Inside the handle of the mic is a transformer that converts the signal to a low impedance balanced signal. When it gets to a mixer or preamp its converted back to an unbalanced signal in many cases.

 

Its better if you see that kind of transmission in perspective. If you look at AC transmission from the power station, the voltage goes through transformers that kick the voltage way up and the current down very low. Wire resists current and creates heat. High voltage passes over long distances relatively easy, so for long distance transmission, you convert the AC to high voltage low current. When it reaches your home, you use Transformer that convert the AC to High current, low voltage. Then you have the current needed to do the work.

 

That's basically why you convert the mics diaphragm to a high voltage, low current output so the cable resistance doesn't degrade the signal quality. Then when it gets to the other end, you can wither use a transformer and convert it back to high current, low voltage or you can use various preamplifiers like differential amps that can use the balanced signal directly to reduce noise.

 

In the end it all comes down to is the quality of sound your speakers produce and the cost of getting High Fidelity. If the Mic diaphragm and playback system doesn't produce a high fidelity signal, it makes zero sense in using circuits designed to preserve that high fidelity. If Fidelity is your goal, you must begin with a high fidelity source, maintain that quality through the entire chain and reproduce that fidelity at the other end. Applying it to address only one bottleneck only adds to the cost and can actually decrease fidelity if the entire chain isn't addressed.

 

In this particular application, Piezo signals are best preserved when a preamp is used early in the chain. Adding an additional balanced output so you have both options would be simple and inexpensive. Whether that balanced signal would ever be used is the question. If the plan is to run the cable long distance to a PA mixer, then running a Low Z balanced signal would preserve the signal quality. If its a short run, the signal to noise ratio of the preamplified signal is sufficiently strong enough to work very well. Any frequencies that may be lost wouldn't be reproduced by the amp and speaker anyway, so why add the expense adding those components if they aren't needed?

 

If the expense is low then having both options are good to have. If this was an electric guitar, you may not even want the fidelity. Les Paul made a Recording guitar that had built in transformers to convert the signals from the pickups to Low impedance, balanced outputs. The guitars didn't sell very well because the trend for high fidelity undistorted guitar was only important to certain types of music, mainly Jazz. Most guitarists prefer an unbalanced signal that can be overdriven by simple unbalanced circuits. If they need to convert the signal to balanced, then you simply plug into a DI box. Again its a matter of practicality and cost.

[Mmmmqac]

Smallcleverrooms

There is nothing to stop you wiring the contact mic to the two cores of twin shielded cable (so that the shield carries no audio) and using the shield for just that: shielding.

I repeat: BALANCED refers to the impedance "seen" by the pair of conductors, it has nothing to do with the waveform on the conductors being "mirror-imaged." The idea that the audio signal itself needs to be balanced is a myth. Just make sure your input buffer has the same resistances and capacitances on both input lines.

 

 

[WRGKMC]

Smallcleverrooms

There is nothing to stop you wiring the contact mic to the two cores of twin shielded cable (so that the shield carries no audio) and using the shield for just that: shielding.

I repeat: BALANCED refers to the impedance "seen" by the pair of conductors, it has nothing to do with the waveform on the conductors being "mirror-imaged." The idea that the audio signal itself needs to be balanced is a myth. Just make sure your input buffer has the same resistances and capacitances on both input lines.

 

I know what balanced is but you're ignoring the practical application in this case.

 

Most preamps do have the negative cold side of the input connected to frame ground. Running balanced cable without shielding would hum like a Banshee

 

 

Piezo are crystal elements. They produce a high impedance signal of around 10Megs. If you want to get that signal through a cable without allot of frequency loss you have to address the impedance which is much more important then having a balanced signal. You either want to preamplify it as close to the source as possible or convert it to low impedance and preamplify it at its destination. Running a balanced signal alone isn't going to maintain the signals integrity and an unshielded cable isn't going to block the hum you'd hear at the amp. The only time a balanced signal works well is if the preamp is designed to accept a balanced signal. A differential preamp uses phase cancellation to remove hum and noise, and even then it has to be high quality to do the job well. Most other preamps are all unbalanced. If you attempt to feed them with a signal that hasn't been shielded, it will hum.

 

One reason for running High impedance up to the preamp is so one side of the Piezo disk is grounded and blocks hum at the source. The shield has a dual purpose and on short runs the difference in resistance between the core and shield is practically non existent. If you preamplify the signal early in the chain, then you can choose to send the signal in either method you choose. Its surely not going to make any audible difference on short runs under 25".

 

I'd add this again. Those round Piezo elements that are mounted to the inside of an acoustic suck balls for fidelity to begin with so wasting time and money to preserve its fidelity using a balanced signal is a waste of time. The elements don't produce much over 3Khz so what is there to preserve? If it was an under saddle element then you'd have a reason to maintain signal integrity because the element may be producing some overtones up in the 12K region.

 

I reserve balanced signals, low or high for signals that require high fidelity with a full 20~20Khz. Using a balanced signal on short runs from poor quality sources have zero benefits. If you have done A/B comparisons to test the differences using a good frequency analyzer (as I've done in thousands of cases recording) Then overlay the two signals, you'd see how small if any differences there are. A frequency analyzer allows you to separate fact from fiction and you can then use reality to determine if the cost outweighs the results.