Why do i have such a problem understanding ohms?

[aphex]

I know ohms = resistance; however, i dont understand how this works in car audio...

Lower ohms = better; because more power when there is lower resistance?

 

[Kalvin00]

I was having the same trouble understanding how ohms figured into car audio..

I've kind of figured it out, but i'll let someone else explain it better than I can..

 

[bondboy]

V = IR, when resistance is lower, current goes up. (voltage constant)

P = IV, voltage constant, higher current equals more power

 

[aphex]

Originally posted by: bondboy
V = IR, when resistance is lower, current goes up. (voltage constant)

P = IV, voltage constant, higher current equals more power

english motherfvker, do you speak it?
Pretend like your explaining it to a three year old (which is how i feel when it comes to this stuff)

 

[bondboy]

I thought that was pretty clear

 

[Viper GTS]

Originally posted by: bondboy
I thought that was pretty clear

It was perfectly clear, you were speaking to an idiot.



Viper GTS

 

[Hayabusa Rider]

Lower resistance allows more current to flow.

WARNING! DANGER!

You need to make sure the speakers match the amp, because if they are mismatched then you are screwed.

 

[neonerd]

Resistance is futile if < 1 ohm

 

[thirdlegstump]

Originally posted by: WinstonSmith
Lower resistance allows more current to flow.

WARNING! DANGER!

You need to make sure the speakers match the amp, because if they are mismatched then you are screwed.

Not necessarily. You just won't be running them as efficient as they could however, running higher ohm output into lower ohm speakers will put more load on the speakers so becareful there.

 

[damonpip]

Alright, so speakers come in many different impedances, 2, 4, and 8 ohms are common. Voltage = Current * Resistance, which can also be written: Current = Voltage / Resistance. The max voltage that an amplifier can provide is fixed, let's just take 100 volts as an example. When the speaker impedance is 8 ohms, Current = 10 / 8 = 1.25. When the impedance is 2 ohms, Current = 10 / 2 = 5. Power (in watts) = Volts * Amps. So for the 8 ohm speakers, the power is 1.25 * 10 = 12.5 watts. For the 2 ohm speaker, the power is 5 * 10 = 50 watts.

Since the voltage supplied to a home stereo is 120 volts, it is easy to make a home amp that supplies a high voltage. Therefore, 8 ohm speakers are fine for use in a home stereo. However, the supply voltage for a car amp is only ~ 12 volts, meaning it is for difficult to make an amp that supplies a high voltage. Therefore, car stereos gerneally use low impedance speakers, such as 2 or 4 ohm speakers.

 

[RaynorWolfcastle]

I'm not positive because I haven't worked with speakers directly, but I'm pretty sure it has to do with the way speakers work. Speakers use an electromagnet to move a mechanical membrane back and forth; these electromagnets are current-based devices that make use of the fact that a varying current induces a magnetic field. Anyhow, getting back to the resistance, this resistance is mostly just a parasitic that emerges from the fact that these electromagnets (solenoids) are tightly wound wires.

This isn't the end of the story however because you need an amplifier to drive this speaker. A basic tenet of electrical engineering is that optimal power transfer occurs when the load impedance is the complex conjugate of the source impedance. Without boring you with the details, in most systems this means that you calibrate your devices to be matched to a certain resistance, usually by adding some sort of matching network. For speakers, which are current-based devices it is preferable to have low impedance (for reasons that I will explain now).

Your amplifier is a device that will... well, amplify your signal. In any case, the amount of power it can provide is limited and follows the for P = RI^2 where P is the power (watts), R is the resistance (in ohms), and I is the current (in amps). As I said previously the speaker you are driving is essentially a current-based device, which means that more current means a louder speaker. So assuming you can supply some amount of power P and want to maximize the current I in your speaker, it comes to stand that you want to minimize the amount of resistance. As I stated above, this ignores loading effects between the speaker and the amp, to get optimal power transfer you want the speaker input impedance and and the amp's output impedance to be matched, hence standards are created so that manufacturers can make sure that they design their device to have the correct port impedance.

This is why you always see speakers with specific input impedances (I think 4 Ohm and 8 Ohm are most common, but I'm not positive). Like I said, the reason that there are some higher values that exist is that its easier to design an ampt that has to feed a load with a high resistance rather than a small one.

I hope this clears things up a little, post any questions you have and I'll answer them as best I can. As I stated at the beginning though my I'm only an EE student, and my specialization is more on RF electronics than low frequencies.

 

[sharkeeper]

Ohm Sweet Ohm

 

[iwantanewcomputer]

Originally posted by: aphex

Originally posted by: bondboy
V = IR, when resistance is lower, current goes up. (voltage constant)

P = IV, voltage constant, higher current equals more power

english motherfvker, do you speak it?
Pretend like your explaining it to a three year old (which is how i feel when it comes to this stuff)

if you don't understand this you need help

 

[bondboy]

Ok, let's try an analogy:

Let's say you have a fixed size pipe. Water is flowing through that pipe (current). If the pipe has something blocking it (more resistance), there will be less water coming out (less current) and the water will come out slower (less power). No blockage (less resistance) = more water come out (more current) and water comes out faster (more power).

Hope that helps.

 

[Colt45]

P = [V^2]/R

With a constant voltage onto the load, a smaller resistor will provide a larger power..
as long as the amp can keep up, and keep the voltage at the same level.