Author
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Topic: Confused about my OHMS
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Melvin England
Jedi Master Film Handler
Posts: 707
From: Hull, East Yorkshire, UK
Registered: Feb 2016
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posted January 19, 2017 01:22 PM
Not being electronically minded, but very aware that electricity and resistance has to be respected, can someone please guide me as to which way round it is safe to plug in an external speaker with a different resistance?
If the sound output resistance is,for example 8 ohms,is it okay to plug in a 4 ohm speaker, or a 16 ohm speaker (assuming an 8 ohm ,of course, is unavailable.) A basic question,I know, but if one doesn't know.....!
-------------------- "My name is for my friends!"
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Steve Klare
Film Guy
Posts: 7016
From: Long Island, NY, USA
Registered: Jun 2003
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posted January 19, 2017 02:17 PM
Well...
When I learned it we were told to think of it in terms of water, because a lifetime of standing at the bathroom sink every morning gives you an intuitive understanding for that. Sane folk can't see electric fields and moving electrons. (Yet, some people I've worked with....)
Voltage is like pressure. When you stand there with the faucet turned off, there is no water flowing but there is still pressure. Pressure is not power, neither is voltage.
Current is like flow rate. It's how much of the good stuff (either electric charge or gallons) flows past you in a unit of time. Flow rate is not power, neither is current.
Resistance (impedance) is like the opening inside the faucet. A given opening will allow a certain flow rate at a known pressure. A certain resistance (Ohms) will allow a certain current (amps) at a known voltage. (Amps=Volts/Ohms)
-these aren't power either!
So what (...or "Watt") is power? Its the flow times the pressure, and it's the voltage times the current.
-that's how much good stuff is flowing out per second times the energy applied to each gallon or coulomb gushing forth: Energy/Second=Power
What has this got to do with projectors and speakers? An amplifier is set up to produce so and so much voltage, and when you apply a certain speaker impedance you get this much current into it and exactly as much power as everything is set up for appears: not like magic, but like mathematics!
What this means is if you have a speaker lower in impedance than it should be, more current will flow than there should be, and therefore more power will be produced than should be, things will get hotter than should be and just maybe something expensive and important will overheat and die. Taken to the extreme (Zero Ohms), this is what a short circuit actually is.
Too high in speaker impedance: too little current, not enough power. No harm done really: more of a waste of potential.
-it's like showing up at a drag race pulling a trailer! You can't ever go as fast as you want until you reduce your load.
So mind your Ohms, and for heaven's sake clean out the sink when you are done with it!
-------------------- All I ask is a wide screen and a projector to light her by...
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Steve Klare
Film Guy
Posts: 7016
From: Long Island, NY, USA
Registered: Jun 2003
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posted January 20, 2017 03:48 AM
These are strange words. They are so important to modern life that they have become conversational, even among people that really don't understand what they mean. (This is why I said "Voltage is not power", for example.)
My first electronics job was testing high voltage power supplies (I was 18 years old...). Now I was running 15,000 Volts, 20,000 volts. (It was an uneasy feeling at first!). They actually weren't dangerous, since they were capable of only about 10 watts. Getting a hit off one of these was not that much worse than scuffing across a really long carpet and grabbing a doorknob.
-yet a 13.5V car battery can electrocute you just fine under the right (or is it "wrong"?) conditions.
Once again: Voltage, Current, Resistance, Power: related, but not the same.
I've learned to avoid other people's professional lingo: I'm from a family with a lot of medical people (mostly nurses). When they want to talk about their various "-itis"es and long gibberishy abbreviations, I tend to fade into the background: I haven't a clue and I know it! (Sometimes I think they are just toying with me!)
(Never get them talking shop over dinner: you are one emergency amputation away from losing your appetite! -Sometimes I add a second stanza of Grace when they do this: "Oh, GOD!")
-------------------- All I ask is a wide screen and a projector to light her by...
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