Ohm Undertanding; Questions
Thread Starter
0 Watt CAFz'r
Joined: May 2009
Posts: 15
Ohm Undertanding; Questions
Don't read unless you are bored or looking to kill time.
Ok as a noob to car audio i have been reading a lot lately. Lot of info out there, little overwhelming. I started reading up on voltage, ampage, ohms, watts, grounds, ect. I am having no problem finding awesome technical info. With the sites i have found (some from the sticky in General from this forum) i have pretty much all the "how's" covered.
I am having a hard time finding out the why's though. I understand that if you double the ohms you cut the power in half, and that if you cut the ohms in half you double the power. A metaphore that made it even more clear was a running tap opened half way or full way or quarter way ect. I really want to know why this is.
What is the ohm?
It restricts current, is it a physical restriction?
Seeing how 1 ohm gives the maximum amount of current possible why don't all speakers/amps run on 1 ohm?
A sub that can run at 2 or 4 ohms is the exact price as the same model sub that runs at 4 or 8 ohms. What differentiates the two? Is the manufacturing cost is the same?
What advantage would a person have running his subs at 8 ohms vs 4 ohms? I know the loss of half the power is the downside, but what is the upside and why is it only possible with the restricted current? (sound quality i assume is the upside)
If you took the time to read this and answer any of the questions thanks.
Ok as a noob to car audio i have been reading a lot lately. Lot of info out there, little overwhelming. I started reading up on voltage, ampage, ohms, watts, grounds, ect. I am having no problem finding awesome technical info. With the sites i have found (some from the sticky in General from this forum) i have pretty much all the "how's" covered.
I am having a hard time finding out the why's though. I understand that if you double the ohms you cut the power in half, and that if you cut the ohms in half you double the power. A metaphore that made it even more clear was a running tap opened half way or full way or quarter way ect. I really want to know why this is.
What is the ohm?
It restricts current, is it a physical restriction?
Seeing how 1 ohm gives the maximum amount of current possible why don't all speakers/amps run on 1 ohm?
A sub that can run at 2 or 4 ohms is the exact price as the same model sub that runs at 4 or 8 ohms. What differentiates the two? Is the manufacturing cost is the same?
What advantage would a person have running his subs at 8 ohms vs 4 ohms? I know the loss of half the power is the downside, but what is the upside and why is it only possible with the restricted current? (sound quality i assume is the upside)
If you took the time to read this and answer any of the questions thanks.
Administrator
Joined: Feb 2006
Posts: 16,860
The ohm is defined as the resistance between two points of a conductor when a constant potential of 1 volt across these points produces a current of 1 ampere.
Unfortunately, definitions usually don't mean jack.
Really, your question has to look past just the speaker and consider the amplifier. In home audio things tend to be standardized on 8ohm impedances. In car audio though things are not so standard and some car audio amplifiers perform best at 8 ohms (not so much now), some at 4ohms, some at 2, 1, 0.5, etc. Note that *perform* here means different things to different people - maximum output wattage is not always the goal many are after.
The reason for so many differing impedance choices in speakers is simply to match up with the amplifier you intend to use.
As for the differences in something like a 4ohm vs. an 8ohm woofer. It comes down to the coil and the wire used. An 8ohm coil could potentially have twice the length of wire that the 4ohm coil does. This messes up other things though like the strength of the magnetic field produced and the moving mass of the cone. The 4ohm coil could use a larger gauge of wire than the 8ohm coil which would be less resistive. Usually it is a combination of the two - the manufacturer tries to trade off the diameter of the conductors with the lengths to try to get two speakers that perform reasonably the same albeit at different impedances.
I'm not sure where you got this idea but it's incorrect. For a given voltage V, a lower resistance R (ohm) will result in a higher amperage I (current) The three are related by the formula:
V = I * R
Amplifiers produce voltage and for the same output voltage, as the resistance goes down, the current goes up, and this requires different circuit consideration within the amplifier. Consider three amps that all show 40 volts at the terminals, one when a 4 ohm load is applied, one at 2 ohms, and one at 0.5ohm:
40v = 4ohms * 10amps
40v = 2ohms * 20amps
40v = 0.5ohm * 80amps
What's the difference then? The difference is we deal in Power aka watts, and Power is defined as Voltage * Amperage so then:
40v * 10amps = 400watts
40v * 20amps = 800watts
40v * 80amps = 3200watts
Again, the design of the amplifier has to be radically different to operate at that 0.5ohm load and deal with all that current than one designed to operate at 4ohms. I'm not going to get into amplifier designs but very loosely amps designed for low impedance, high current loads generally don't sound as good as those designed for higher impedance, moderate current loads. For something like a subwoofer it may make little difference in sound so a high current amp is perfect. That and trying to replicate that 3200watts at 4ohms would result in an amp needing to produce way more voltage (113v), thus it would be WAY bigger physically and wildly expensive.
Unfortunately, definitions usually don't mean jack.
Really, your question has to look past just the speaker and consider the amplifier. In home audio things tend to be standardized on 8ohm impedances. In car audio though things are not so standard and some car audio amplifiers perform best at 8 ohms (not so much now), some at 4ohms, some at 2, 1, 0.5, etc. Note that *perform* here means different things to different people - maximum output wattage is not always the goal many are after.
The reason for so many differing impedance choices in speakers is simply to match up with the amplifier you intend to use.
As for the differences in something like a 4ohm vs. an 8ohm woofer. It comes down to the coil and the wire used. An 8ohm coil could potentially have twice the length of wire that the 4ohm coil does. This messes up other things though like the strength of the magnetic field produced and the moving mass of the cone. The 4ohm coil could use a larger gauge of wire than the 8ohm coil which would be less resistive. Usually it is a combination of the two - the manufacturer tries to trade off the diameter of the conductors with the lengths to try to get two speakers that perform reasonably the same albeit at different impedances.
Seeing how 1 ohm gives the maximum amount of current possible why don't all speakers/amps run on 1 ohm?
V = I * R
Amplifiers produce voltage and for the same output voltage, as the resistance goes down, the current goes up, and this requires different circuit consideration within the amplifier. Consider three amps that all show 40 volts at the terminals, one when a 4 ohm load is applied, one at 2 ohms, and one at 0.5ohm:
40v = 4ohms * 10amps
40v = 2ohms * 20amps
40v = 0.5ohm * 80amps
What's the difference then? The difference is we deal in Power aka watts, and Power is defined as Voltage * Amperage so then:
40v * 10amps = 400watts
40v * 20amps = 800watts
40v * 80amps = 3200watts
Again, the design of the amplifier has to be radically different to operate at that 0.5ohm load and deal with all that current than one designed to operate at 4ohms. I'm not going to get into amplifier designs but very loosely amps designed for low impedance, high current loads generally don't sound as good as those designed for higher impedance, moderate current loads. For something like a subwoofer it may make little difference in sound so a high current amp is perfect. That and trying to replicate that 3200watts at 4ohms would result in an amp needing to produce way more voltage (113v), thus it would be WAY bigger physically and wildly expensive.
Thread
Thread Starter
Forum
Replies
Last Post
