Posted: Fri Oct 02, 2009 7:05 am Post subject: IEM microphonics problem
First some definitions, for those who might be somewhat challenged in the geekiness department of life...
IEM = In Ear Monitor (or those little earphones you use with mp3 players, etc)
Microphonics = the noise you get when your IEM cable brushes against clothing.
I have some good quality IEMs and have been using them for the best part of a couple of years (I have tried using several different IEMs and all with the same result, some go very thin on bass). A few months ago I started to notice the sound cutting out, sometimes just in one ear. Sometimes I get crackles. In general, it is an unpleasant distortion. I had been thinking that the problem was the IEMs themselves, or the connection I have to an extension lead for the IEMs coming out of my Edirol UA25 external sound box. However...
I have now found through a little preliminary Googling and Binging that this is in fact a common problem caused by the cable brushing against clothing with movement. Clearly, the movement involved in strumming a guitar or playing piano is enough to trigger this. And this phenomenon is referred to as microphonics.
Ok. So, I know we have some really excellent technical folks here on this forum. Can any of you guys give me some advice here? Thanx in advance. _________________ Real life website http://www.lewismusic.co.uk
Looks to me like you're the expert adviser rather than advisee on this one. I like to think my vocabulary is fairly good but I"ve never heard this word 'microphonics' before. _________________ Blog | Twitter | YouTube | Live Video
initial thoughts would be to make sure the cable runs over your shoulder/back to the source instead of down your chest. Probly less movement of clothing there. Also, if it's clipped on to your clothing? I hope you are flexible enough to clip the wire onto the middle back of you shirt.
Hmmm, I have a thought here. I'm sure Madelin would agree with me. But I don't think I'll mention it _________________ Joy is in the ears that hear
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Given the types of situations that will result in microphonics, it seems unlikely to me that a cable with at least minimal shielding could cause the effects you describe.
When you rehearse without the earbuds, do you get the same effect. What I'm wondering is if your audio is going out through an amplifier system when you play normally. Are you really sure you're solving the right problem??
It's also possible that it might be bad connections for the cable as cut-outs are pretty common from that type of thing.
Thanks very much for your help so far guys. I'll make an interim report now and hope to check things out at my concert today at 2 p.m. SLT
1. I have read something similar to your suggestion, Norris. I could try clipping the wire to the back of my collar with a wooden spring-clip clothes peg (glad we don't have webcams in SL - lol).
2. Silas, thanx for the link to the Wiki. I'm not sure their advice is quite as up-to-date as this current problem - which seems more specific to IEMs. Your comment on the cable is interesting. The IEM cable is so tiny in circumference, it can have only minimal shielding. So I dug out a decent pair of Sony cans that I bought some years ago. They have a better cable. So far I have checked out monitoring from my digital piano direct - and it is the thumbs up for them, my friend! I'll check the monitoring from my mixer when playing guitar tonight (well this afternoon, for SLT).
3. Ticious, you are a naughty girl
4. Ray, the idea of wireless is VERY appealing, and I may look into that seriously. I have to move around a lot in my tiny studio (guitar & mic one side of the room, then across to piano on the other side, getting up to go back to the laptop screen between songs, bla.. bla.. bla..) So that might be worth going for. But I know what you mean about batteries. I change my guitar battery more often than I need to, I'm sure (I just feel a bit neurotic that it is going to fade in the middle of a show).
I know this is a relatively recent kind of problem, and I know it isn't just me because you can find discussions on specialist forums (ok - fora). So I will post any progress I make back up onto this thread in case others run into the same problem here in SL.
IOW, I am dubious about the analysis of microphonics. Yes, noises can be induced in cables. However, it is very difficult to build up any sort of noticeable voltage across a low impedance. Output transducers - those which convert electrical energy to acoustical energy - are inherently low-impedance devices.
I'd be suspecting an outwardly intermittent connection before any sort of electrical voodoo. Of course, I've been wrong at least once before in my life...
Clean your connectors with DeOxit - this will sometimes cure a tarnished connector that causes dropouts. Bend every inch of the cable while listening - this will identify if an intra-cable short or open is the issue.
Or perhaps simple acoustical coupling is being mislabeled as microphonics. Any physical thing that is vibrating will transfer a portion of that mechanical vibration to any other physical object with which it is in contact. For example, wear any headphones, play your guitar, move back such that the headphone cord is fully dangling (not on the floor), then maneuver such that the headphone cable is touching your guitar neck. You will hear an added component to your sound - that contributed by the physical coupling of vibration from guitar neck to headphone cable to earcups to ear. An electrical engineer or (mechanical engineer, for that matter) would not refer to this phenomenon as microphonics, as it involves no transduction of mechanical (acoutsical) energy to electrical energy.
As far as examples of actual microphonics - you electric guitarists can hear some yourself. If Silas dials up one of his high-gain patches, takes in hand a one foot loop of guitar cable, and slaps said loop upon a table, he would undoubtedly hear microphonics -- manifested as a pop amplified through the speaker. This is caused by the physical deformation of the geometry between the inner signal conductor and the shield of his guitar cable. Any two conductors separated by an insulator form a capacitor. The capacitance in high quality cables is vanishingly low, yet still significant in this application. When one changes the distance between the two conductors in a capacitor, a voltage is generated. This is the exact mechanism upon which condenser (capacitor) microphones operate.
The difference between this scenario, and the IEM scenario is a matter of magnitudes.
Firstly, the impedance into which the signal is generated is vastly different. Most guitar amps have an input impedance of somewhere around 1 MegOhm, or 1,000,000 Ohms. Typical IEMs may be in the couple-dozen Ohm range. This requires a proportionally larger deformation of cable geometry in the IEM case to generate the same amount of voltage as in the guitar example.
Secondly, there is the matter of amplification. In a high-gain guitar patch, the input signal (e.g. due to microphonics) is magnified hundreds- or even thousands-fold before reaching your ear. In the IEM case, the gain factor is 1.
For those who have not given up some paragraphs ago, here's another experiment in microphonics. Turn on a tube guitar amp, allow it to warm up, turn up the volume, then tap lightly on the first preamp tube. What you are hearing is a voltage being induced by the tiny vibrations of the elements within the tube, relative to each other. Microphonics.
One last experiment. Turn on your turntable. Don't need to play a record. Tap on the surface of the turntable. Microphonics. The physical vibration it transmitted to the cartridge, where it is transduced into electrical energy.
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