Ohm Car Subwoofers
Apr/100
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What is the difference between 2 ohms and 4 ohms in terms of subwoofers for car audio. Which is louder?
I'm trying to get a better car audio system than my previous, but I can't remember whether to get 2 ohms or 4- Also, do you know what 2 or 4 ohms can handle in terms of watts from an amplifier...without starting a fire in my trunk....
So you best understand, think of this.... should I kink the garden hose 25%(4 ohms) or 75%(2 ohms). 100% would be 0 ohms or a dead short to the power source (the amp).
The above is actually inversely proportional to the outcome, but for explanation purposes, it'll have to do.
When loading an amp, the lower the ohms the harder it must work and the hotter it'll get. Likewise the higher the distortion.
The different speaker ohms just allows you to choose wiring methods to get the right ohms.
For instance, if you want to load an amp at 4 ohms with two subs, then you would get two 2 ohm and wire them in series. http://i81.photobucket.com/albums/j230/sparky3489/SERIES.jpg This adds the ohms together.
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if you want to load an amp at 2 ohms with two subs, then you would get two 4 ohm and wire them in parallel. http://i81.photobucket.com/albums/j230/sparky3489/PARALLEL.jpg This divides the ohms only if both values are the same. The formula for parallel is:
Where Z = total ohms and sub# is each sub (or coil in a multi-coiled sub):
Z = 1 / (1/sub1 + 1/sub2 + 1/sub3 + ...) as many as you have.
E-mail me if you want more detail on this
sparky3489@yahoo.com
Here is some info on enclosures, sub wiring methods and other tips: http://spkrbox1.spaces.live.com
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pcpy has a few typos:
"As a CHANGING current passes through the coil it moves the magnet that is attached to the diaphragm."
Should be
As a CHANGING current passes through the coil it moves the coil that is attached to the diaphragm by opposition to the magnet, which is stationary.
"Anyway, if you want to drive a set of 100-watt subs then you are going to be pushing a little over 8 watts of current."
Should be
Anyway, if you want to drive a set of 100-watt subs then you are going to be pushing a little over 9 amperes of current.
To calculate the current draw of an amplifier, multiply the number of channels by the RMS watts per channel. Double it to account for amplifier inefficiency (200 watts X 2 = 400 watts), then divide by the average output Voltage of an alternator, 13.8 volts (400 divided by 13.8 = 29 amps). Since the average music signal requires about 1/3rd of the average power in a test tone, divide by 3 (29 amps divided by 3 = 9.66 amps).
The result is the amplifier's approximate average current draw and can go higher depending on demand. So between 9.6 and 14.5 amps would be the answer.
This whole statement is incorrect:
"If you have an output driver that operates on 8 ohms impedance at 2000hz and purchase speakers that operate at 2 ohms impedance at 2000hz then you will under drive your speakers (they will be muffled and won't reproduce highs and lows, especially lows, very well), and eventually you'll damage your speakers. On the other hand if you have an output driver that operates at 2 ohms and you purchase 4-ohm speakers then you will be overdriving your speakers. They will rattle and be buzzy, eventually you will burn out your driver."
It should be
If you have an output driver that operates on 8 ohms impedance at 2000hz and purchase speakers that operate at 2 ohms impedance at 2000hz then you will over drive your amp and you'll damage your amp and speakers. Now if you have an output driver that operates at 2 ohms and you purchase 4-ohm speakers then you will be half-loading your amp. The speaker output will be lower than what it could be.
Some people feel that under powering a speaker will damage it. This couldn't be farther from the truth*. It's the same as if I turn my volume down. I'm actually under powering my speaker. Low volume, low power.
* Damage WILL occur on an under powered sub IF the gain control isn't set properly. What happens is most people will buy an amp that can't provide the power required for the speaker and try to compensate by adjusting the gain control. This causes clipping and clipping is what damages a speaker. The purpose of the gain control is to match thr RMS Volts of the head unit for proper power balancing.
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"isn’t that a little easier to understand that trying to picture a coil vibrating back and forth."
Ummm....no! The coil being attached to the cone and the cone moving up and down isn't hard to imagine at all. With the magnet on the cone, well now your talking moving more mass as a magnet is harder to move that fast than a coil is and the inefficiency would also increase. Haven’t you ever heard of inertia?!?!?
"but in many low cost speakers the “button” is attached to the diaphragm"
You are joking, right!! NO manufacturer would make a speaker this way. Why? Exactly what I stated above, inertia and efficiency. This is why you DON'T see lead balloons. Please, I would LOVE for you to show me a speaker with the coil stationary.
"Driving a 2-ohm speaker with a 4-ohm output driver is not the same as turning the volume down..."
Hmmm...it seems I'm talking about under powering and your talking about impedance mismatch...your confused.
"You will not be able to pull 9 amps through the 100W setup (100/12 = 8.33)"
You show me a true 12 volts when a car is running and I'll show you a defective alternator. It's 13.8 volts or higher. You ALWAYS have a voltage higher than the battery you are charging, look it up.
You even say, and I quote, " if you want to drive a set of 100-watt subs", now to me a "set" is a pair. That would be 200 watts according to you. With that, 200/12 = 16.67. Your funny.....
"Ive run afoul of automotive guru's before, that's why I always do my own work."
It's a wonder you haven’t destroyed something yourself, your own definitions don't make any sense....You need to GO to school.
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