Car blog edited the following
Q&A: What is the difference between 2 ohms and 4 ohms in terms of subwoofers for car audio. Which is louder?
The pictures have nothing to do with the content!!
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….
The following is the answer:
Answer by Nivardo F
Its not that one is louder that the other, ohms are resistence so the higher number of ohms the larger the resistence and the less amount of wattage that can pass to the speaker. Think of ohms as a pillow that fills your car, if you have 4 ohms (or pillows) you will get less sound instead of 2 ohms (pillows). Also keep in mind that a lot of amps are not 2 ohm stable, meaning that they cannot function properly at 2 ohms, they might work but in time you stress the amp and eventually blow it. For wiring options you can go to www.rockfordfosgate.com and go to the woofer wiring wizard under support. I know the pillow sounded stupid but its the best way to explain it. contact me if you need anything else.
Answer by JT
Here is some info and links to help you out, good luck!
Impedance: Measured in ohms, his value represents the “load” that the speakers present to the amplifier. In other words, the impedance is the amount of resistance to current flow from the amplifier section of your receiver or power amp. Low-impedance speakers (less than 4 ohms) or multiple speakers wired in parallel can cause problems with amplifiers which are not designed to deliver large amounts of current.
Answer by pcpy
Er uH Duh.
Sorry, I was reading stereo install guy with his pillows.
Speakers actually are not measured in resistance but impedance. Impedance is variable by frequency and is produced by the expanding and collapsing electromagnetic field in a coil.
A speaker (simple) works by having a magnet, a coil and a diaphragm (heh heh, I said diaphragm). As a CHANGING current passes through the coil it moves the magnet that is attached to the diaphragm. This, when done rapidly, causes waves in the air (sound waves). Low frequency uses more power because the diaphragm moves farther and the diaphragm and magnet is usually larger. Low frequency also passes through media more easily than high frequency. You only need a lot of power to drive big subs. That’s why you only hear these deaf people’s bass as they’re drive down the road. Just thought that I would through the speaker stuff in.
The answer to your question is to find the impedance match to your output driver (amplifier). This has to do with power output. 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.
Same thing applies with your wattage worries. Power is measured in terms of watts and the formula is easy to remember cause it’s a good dessert; P=IE. Power equals Current (I) times Voltage (E). Your car runs on a 12-volt system. Some really high zoot (or cheap junk designed for the audiophile wannabees) will have a step-up transformer that allows a higher voltage but at the expense of current. 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. That’s a ton and you will need to make sure that you have the proper cable and connectors. It’s best to have an audio place do the install (just find out where 10 year speaker installer works and STAY AWAY).
Find out what your driver output is and then purchase a properly matched speaker. You can purchase really high wattage subs but unless you can drive them then your wasting your money.
I hope this helps and I hope you enjoyed my little sidetracks.
PS
Sparky needs to go back to school! Not all speakers are made the same; I was trying to give you a good idea without confusing you, it is true that the voice coil is attached to the diaphragm in most higher end speakers but in many low cost speakers the “button” is attached to the diaphragm and gee, isn’t that a little easier to understand that trying to picture a coil vibrating back and forth. Driving a 2-ohm speaker with a 4-ohm output driver is not the same as turning the volume down anymore than trying to broadcast with an unbalance load in RF. You will not be able to pull 9 amps through the 100W setup (100/12 = 8.33, the amplifier is supplied by 12V input, not directly by the alternator) even if you have no line loss, which you will. Don’t be confused with the introduction of Root-Mean-Square (RMS), ~ .63 of peak power) it’s not an issue in this example. Like I said, I wasn’t trying to BLOW you away with numbers, just trying to give you something that is understandable. Guess old Sparky (you’ve got to be kidding) just had to share. Thanks Sparky.
I’ve run afoul of automotive guru’s before, that’s why I always do my own work.
Answer by sparky3489
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.
-or-
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.
Answer by andypilotttt
run a cord from the house ac and connect the wires to the speakers. you might not like the result, but the rest of us will be much happier.
Know better? Leave your own answer in the comments!
