Ohms on a Speaker VS Ohms on an Amp?

I am looking fixing up my cars stereo and I am not sure about how to pair a sub with an amp.  I am using crutchfield.com.  I found some speaker I subs I would like to get, they are 12" kickers and there is an 8 ohm version and a 4 ohm version.  They are rated for 50 - 150 watts.  Now my guess was to buy a 2 channel amp (I wan't two subs) and use it.  The one I am looking at is 125 watts @ 4 ohms X 2 speakers.  I read that you may want to buy an over-rated amp so you don't blow it by trying to drive excessive speakers.  Is this an acceptable combination. 

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gmoon5 years ago
You've sorta got that backwards--so long as you're using the correct speaker impedance for the amp (4 ohms), then you're in danger of blowing the speakers, not the amplifier. That's IF you are using speakers that have a lower wattage rating than the amp. If the speaker rating is greater than the amp's output, everything is cool...

The only way that a speaker could be "excessive" is if you're not matching the speaker impedance correctly to the amplifier...(like using a 2 ohm speaker for an amp that's expecting a 16 ohm load).

(NOTE--frying the speakers could lead to wrecking the amplifier, too. Doubtful but possible. A speaker coil could short and if the amp doesn't have any overload protection, PZzzzAP! Most modern amps have some sort of protection circuitry, tho,)

(NOTE 2--with guitar amps it's usual to use speakers that are rated for double the amplifier's wattage, because "peak" power is higher than the average RMS wattage. Car stereo speakers might be rated differently, I don't know.)

It's very common to use multiple speakers for the correct "load". Two 8 ohm speakers in parallel equals a 4 ohm load.

I'm sure with your amplifier it's 125 watts per channel. The number of speakers isn't important, so long as their combined impedance is correct (4 ohms for your amp) for each channel.
jj.inc (author)  gmoon5 years ago
Now what load is more 16 ohms or 1 ohm. And if your amp is made to handle more ohms than the speaker is, will it be hard on the speaker or amp.
gmoon jj.inc5 years ago
Re-design is correct--the lower resistance (1 ohm) allows more current to flow, so the amplifier works harder.

Whether you refer to that as a smaller or a larger load is a matter of semantics--I always refer to a smaller resistance as a larger load, 'cause it's passing more current (doing more "work").

Again, so long as the speaker (or speakers) is matched to the amplifier (in your case 4 ohms) then you only have to worry about the wattage rating of the speakers, not the amp.
The 1 ohm load allows more electricity from the amp to flow thru the speakers. If the volume is turned up high enough then enough then the amp will try to supply more power to the speakers and something in the amp will give out.
DexterM62 years ago
If the amp is rated for a pair of 4 Ohm speakers then get the 4 Ohm speakers.
jj.inc (author)  mpilchfamily5 years ago
But what if the amp is rated for one 4 ohm speaker, or 2 2 ohms, can you still use 2 4 ohms
If it s rated for a single 4 ohm then you can only use a single 4 ohm speaker or a pair of 2 ohm speakers.
iceng5 years ago
You do understand the dual 2 ohm speakers are meant to be in series.

There is a concept that states

For the most greatest Power transfer
the load impedance
should match the source impedance

A mismatch between an amp and speaker can cause injury to either
element.
Speakers are usually damaged by being overpowered.
Amplifiers can be damaged more ways depending on type and design.

A