Stray capacitance?

actually that call as static electric because we also have a very little static electric on our body . sometimes after you finish watching TV , use your hand to touch the screen of TV when you off it . you will hear some sparks sound . correct me if i'm wrong ^_^

Take an ohm meter and set in at 100k ohms and hold one probe between the fingers of each hand and read the meter.

The human body including the skin is 70% salt water, which is a good conductor of electricity, so there's no reason why it shouldn't conduct electricity. Electricity will also be conducted by the neurological system.

"Electricity will also be conducted by the neurological system."

Otherwise we'd all be dead. I believe that in the cases of over ingestion of water, such as the stunt a few years back by the radio station in LA, that the level of salt is reduced to the point that signals from the brain to the rest of the body just don't get to the right place.

Speaker self powered or not?

Speaker with amplifier built-in will EASILY pick up the nearby electrical signals (60Hz/120Hz buzz from home wiring) that are capacitively coupled to your body, then conducted through touching the speaker leads.

Even with NO amplifier, there can be enough capacitive coupling to your body to make the buzzing sound in the speaker (though it should be a quiet buzz).

Conductivity of humans varies a lot and is mainly limited by skin resistance. Dry skin = lower conductivity, wet skin = higher conductivity.

It is truly amazing how pervasive that 60 Hz hum is. Not only 60 Hz but its harmonics through 5 kHz.

I'm a VLF/ULF enthusiast and, with even simple gear, I can easily hear AC hum 40 miles from the nearest AC mains.

A fellow enthusiast in Finland can accurately tell you when different parts of the US power grid have bought and sold electricity and even tell you when it is a particularly hot day on the East Coast - all from changes in the hum pattern from the US power grid which he can hear in Finland on his home-brew VLF/ULF gear.

It's no wonder, then, that you can hear it in an un-amplified, un-powered speaker.

60Hz is very ULF, I'm surprised that without a serious notch filter there at the front end your preamp isn't clipping.

I know submarines use VLF for comm but sensing 60Hz from thousands of miles away? Hard to believe given the ambient noise.

Do you run your house on DC?

Just curious.

yea i think so...

Humans do conduct electricity, as anyone that has received an electric shock will tell. These days, a residual current device is introduced into safety-critical circuits so as to disconnect the supply should the current to earth (possibly through a human) exceed, oh, typically 30mA.

Remember the analog pick-up connected to turntable amplifier on a record player (this was a device that was used before the CD player was invented, which played music recordings that had been made on those funny circular black vinyl sheets with a hole in the middle)? Disconnect one of the four pick-up leads while the amplifier is still energised, and mains hum comes out the speaker. The volume varies with a lot of things, including how well the individual that disconnected it is earthed.

Those were the days...

Nostalgia isn't what is used to be.....

"... those funny circular black vinyl sheets ..."

"Licorice pizzas" we called 'em.

As europium points out, the body is a conductor of electricity and an antenna. Since the 'antenna' is not connected to a 'receiver/tuner', all the electromagnetic signals in the area are present in the signal, and the 60hz signal from your local electric wiring is by far the strongest. So when you touch the tip of the plug to your computer speaker system, all these signals pass through your skin into the metal connector. The amplifier in the speakers amplifies this signal enough that you can hear it. If you have fluorescent lights nearby you'll pick up the 60hz from the ballast, and the buzz will be even louder.

I worked as a guitarist for way too many years, and the same thing happens when you unplug the guitar cable at the guitar while it is still connected to the amplifier. Even if you don't touch it you hear the buzz, and when you touch the tip (hot lead) the buzz gets louder. If you touch both the hot lead and the shield (the longer cylindrical part) the signal is party shorted out and buzz nearly goes away.

Yes, humans conduct electricity. And I have the marks to prove it!

ouch.

I was under the impression that human beings and other animals were conductors, though the down side to that was they might not live though high amp and voltage functions in that role.

I was also under the impression that sound equipment hums altered by touch of the hand indicated that the equipment was not very well grounded.

I am more familiar with ac power than dc power so I cannot fully explain where you got your charge to pass to the speakers. However I do know it is not a great idea to touch everything all the time, and specifically I know it is very important never to become "ground", or way to ground.

It is good to be positive.

"I am more familiar with ac power than dc power so I cannot fully explain where you got your charge to pass to the speakers."

Take the case where one side of the speaker is connected to the equipment whilst your hand is touching the speaker's other terminal. In this scenario you are not touching any other conductors, and you are wearing clean, dry sneakers which insulate you from the surface on which you are standing.

Now, draw a schematic of this setup and be sure to include yourself as one of the major circuit elements; a capacitor in this case. More specifically, include yourself as one half of a capacitor - a plate. The other half consists of all the other conductors, including current-carrying ones, grounded ones and floating ones (in the electrical sense of not being in contact with other conductors) both within the room and Beyond.

A big, happy distributed capacitor with its own reactance, working voltage, tempco and ESR. You are so good at being a capacitor, in fact, that DigiKey has even offered $$$ to feature your handsome specs on the front cover of their forthcoming 2009-2010 Winter catalog.

Now, while your agent is hammering out the details of your highly lucrative contract, you are busily coupled, by means of alternating electric fields, to the Other Plate which, in turn, eventually connects back to the equipment that is connected to the other terminal of that speaker which you are still holding.

Voila! A completed AC circuit! One carrying enough current, in fact, that it is making that crummy computer speaker hum like a regular Pedernales Cooperative Electric Substation. Or an LCRA one, take your pick, but Pedernales' rates are lower and their receptionist is a white-hot bombshell. I pay my bill as often as possible.

Customer: "Transcendians come in polarized versions, too, don't they?"

Sales: "Only during elections."

As Founder, I am not subject to elections.

So far, all others are volunteers.

As far as my internal electrical operations, I thought I functioned on direct current circuits, and not ac.

I am hopeful that we will see the schematic in a wonderful drawing for our edification and entertainment.

In this area of electricity and electronics, I always read here and discover something I didn't know, or had forgot.

As far as my function as a capacitor, I only understand that as one of the plates, and remember a great DC shock I got from a Learjet tip tank. (They have a certain shape that makes the hand of a man reach out.) -I got a hell of a shock. No wonder we grounded planes prior to fueling.

I do not grasp how we might function naturally on AC.

Of course some charge is created naturally within by internal friction and dystolic, systolic blood flow as a circuit corrilary, if not DC generator, but I don't capture the AC rider.

I was under the impression that we were more semi-conductor 'ish

In my digital electronics class many many years ago I inserted myself into a number of the circuits we built in class and found that, among other things, I made an effective and/nand gate... this is probably exemplary of why I didn't make it very far down the electronics career path...

The body is a capacitor and you touching an electronic component can transmit 60Hz. Also several thousand volts on a dry windy day or static electricity when you touch something that conducts to ground you feel the shock or discharged. When you touch high voltage or 120VAC you can get electrocuted. This is because skin resistance is less than 1 meg ohm and inside you your blood is a little like salt water which is conductive. If your feet are grounded this completes the circuit.

Basically, aren't all things conductive? Not in the practical sense, but if you put enough potential across something won't it conduct?

As far as the human body being conductive....one of the ways to measure body fat hooking you up and running electricity through you.

It's true our bodies are good capacitors, conductors and antennas. No wonder some folks can hear radio through their teeth! You can plug that disconnected speaker connection from the computer into a crystal radio, and play it through the computer. Then touch the radio antenna to bring in stations better, showing how the body acts as an antenna. For a bizarre electronic adventure showing the human body as electrical conductor between a crystal radio and a computer screen, see my movie, "Human Conductor Plays Beta Blocker Radio" http://www.youtube.com/watch?v=J1o4lbVjAg8

You shameless self-promoter.

I love it!

Hey, as soon as I'm discharged from this hospital I'll upload my vid where you watch me get that exact same sound from ninety thousand really pissed-off killer bees.

My vid's much more exciting by far, I must admit, but I expect you pay a lot less for insurance.

Answer to title: Please watch the movie Down Periscope.

thx guys! i haven't done alot of physics so i wasnt exactly sure what was going on..

Many years ago, a friend had a dead channel on his stereo. It was one he had built from a kit so he had complete schematics and board layout. I had him open it up, and with a paper clip I touched the base of each transistor starting from the output and working towards the front. When I reached a transistor which did NOT give me hum in the speaker when I touched it, I knew I was close. I then touched up solder joints in the area and he was back in business. WARNING!! This was all transistorized, so there were no lethal voltages on the board. If this had been tube (valve) based, I would not have done this.

Another time, we were teaching a ham radio class and I brought in my scope and a function generator. Someone wanted to do Lisajous figures, and we had only one signal generator. We got a student to hold the tip of one scope probe which gave us 60 Hz out of the air for one signal, and we used the function generator for the second signal. It worked quite well.

Bill

Since there is an amplifier in the computer speaker system, even a small signal can be detected.So that's the reason why it sounds.

As a Biomedical Electronics Tech, I see the results of the body conducting electricity as well as generating electricity daily. If you have ever had an EKG or been connected to a patient monitor then you would see that the human body is full of electricity, abeit very low levels. When connected to an EKG or patient monitor, the electrical signals are normally obtained from the surface of the skin through an electrode coupled to your skin with a conductive gel. The electrical signal is then amplified from its mV level and A-D & D-A converted to display it on the screen or printed on the paper.

Another example would be a defibrillator or external pacemaker. Both of these devices rely on the conductivity of the body in order to function to restart the heart into normal rythym or to maintain normal rhythm.