Length of microphone cable

[hellboy80]

In the instruction manual for HV20 is written: "Use commercially available condenser microphones with their own power supply and a cable no longer than 3 m.
Why "no longer than 3 meters"?

[Huy Vu]

Because the HV20 uses an unbalanced audio connector and long cable length can result in signal interferences.

[Gillvane]

In the instruction manual for HV20 is written: "Use commercially available condenser microphones with their own power supply and a cable no longer than 3 m.
Why "no longer than 3 meters"?

If you have XLR connections and cable, you can go 20 feet or more with no hum. If you don't use XLR cable and go past 10 feet or so you will get hum or buzz.

If you have to go farther than 10 feet, then you get something like this:
http://www.bhphotovideo.com/c/shop/8673/Camcorder_XLR_Adapters.html/mnp/0.0/mxp/0.0/sortDrop/Brand%3A+A+to+Z/pn/1

[bobafet1]

this post cleared some things up for me. Thanks for the info everyone

[paulears]

It's a bit more complex than that though. If a camera is fitted with an XLR, then a cable run of pretty well any length generally works fine. 100m (300ft) isn't a problem. Hum and noise is a bit different. Mic levels are very low, so passing a cable through any area that has lots of potential interference sources can still be a problem. The cable will have a screen. Cheap cable doesn't have very good screening. Better quality cable does. You can even get double screened cable too for very nasty environments. Better cable also has the internal cable twisted together during manufacture which also adds even more protection, BUT only for balanced circuits. If you have unbalanced cable, and unbalanced microphones, then any noise or interference is going to be worse. How much worse depends on cable quality and length.

Sometimes, those cameras that have warnings of only using short cable lengths on unbalanced condenser mics have a small design 'issue'. With mics of this kind, a small polarising voltage is superimposed on the audio cable to power the microphone. Electret condensers vary in their power requirements, but generally they need 5-10V to make them wor optimally. Some give a lower figure, but there could be mention that performance will be degraded. Depending on the camera battery voltage, there may not be much to spare. For example, a 6V camcorder battery can only supply up to this to the microphone. If you increase the length of thin cable, the internal resistance drops the voltage, so it can drop below what the mic needs in just a short length. Hence the doom and gloom warnings. In most cases the mics will be ok - but maybe not all of them? To avoid complaints, it's simpler to just advise people to not use them!

There's no real reason that an unbalanced mic cable has to be short. However, hum rejection will be compromised, so it could be great, or maybe not. More of a gamble. What is certain is that high impedance sound sources such as guitars, or high impedance microphones (thankfully rare now) do not like long cables. Not really to do with hum or noise, but lack of treble -which in this case means long cables = dull sound.

If you have xlr sockets, I'd not worry about cable length at all as long as you avooid rubbish cable. Medium priced stuff is always safe. If you work regularly in electrically noisy places, like I do, then interference from lighting dimmers is the main problem - but decent cable always solves it for me.

[ZetKey]

paulears (http://www.dvxuser.com/V6/member.php?u=48027), thx for the valued info!