What's the difference between 4 ohm and 2ohm when talking about amps? Oh yeah, and what's MOSFET?

Thanks,

jshmoe

 

MOSFET = metal oxide semiconductor, field effect transistor

It's not important what that means, and it would be complicated to explain

An Ohm is a unit of resistance, and in this context they're basically telling you what kind of load the amp can deliver power into. It's easier to deliver power into a load with a lower resistance at a given voltage (p = e^2 / r), so generally you want an amp that will deliver power into a 4 ohm or 2 ohm load. Sometimes you may even wire subs up to present a 1 ohm load, but many amps are not stable and will burn up or otherwise malfunction when connected to this kind of load - you need to look for one that's rated for it if that's your intent.

Basically, for full-range speakers you don't need to worry about it - they're all pretty much 4 ohm in car applications nowadays, so look at the 4 ohm power ratings for the amp you are considering to see how much power it can deliver to your full-range (non-woofer) speakers.

For subs it can be more complicated as many are dual voice coil, and many times you'll be wiring up more than one sub. This gives you options in the load that you can present to the amp, so you need to look at the various ratings to see what it can do with various configurations.

Example:
1 sub, dual 4 ohm voice coils

You could wire the coils in series, for an 8 ohm load.
You could wire the coils in parallel, for a 2 ohm load.

In this example, it's a no brainer - wire them in parallel at 2 ohms, look at the amp specs for a 2 ohm load, and that's what you're going to get.

Ok, add another sub. Now you could choose from 16 ohm (all coils in series), 4 ohm (coils from each sub in series, subs in parallel with each other), 1 ohm (all coils in parallel), or a couple of other weird not-worth-mentioning configurations. (Or, you could power the two subs from seperate channels / amps )

So anyway, you then have to look at the specs on the amp for that particular load rating to see how much power you'll get. And you have to hope that the amp manufacturer isn't exagerating!

Matt

 

Thanks that was very informative. I am also a little lost when speaking of amp specs. Bridging is mono? What is the difference between 2ohm mono and 2ohm stereo. Is 2ohm stereo not a cleaner power? But mono thumps more correct?

 

http://www.bcae1.com/bridging.htm
http://www.bcae1.com/hcvsnohc.htm
http://www.bcae1.com/spkrmlti.htm

loads of info. give it a read, then if something is confusing you -- ask me. don't worry about all the math if you're willing to believe what his conclusions are...