I see specs for amps that say X amount RMS at 2 ohms. And x amount RMS at 4 ohms. What does that mean?

 

Let's say it states RMS power is 100 watts x 2 at 2 ohms.
That means it will do the power of 100 watts per channel (in this case, there are 2 channels) at 2 ohms. Each of the 2 channels can handle an impedance load of 2 ohms... it is 2 ohm STEREO stable.

If it states RMS power of 100 watts x 1 at 2 ohms, the amp is stable to 2 ohms MONO (1 channel). Most class AB amps (most 2 channel amps) are 2 ohm STEREO stable, not 2 ohm MONO stable. Most class D amps (most subwoofer amps) are 2 ohm MONO stable, or even 1 ohm MONO stable.

How does that apply to speakers? Speakers are SINGLE or DUAL voice coil speakers. Each coil measures a certain impedance load, usually 4 ohms. If you have dual voice coils of 4 ohms each, and you wire them in parallel (positive to positive, and negative to negative) you will reduce the overall impedance of the sub to half (in this case that would be 2 ohms). Now if you bought that amp that is 2 ohm MONO stable, and ran just this 1 dual 4 ohm sub(wired down to 2 ohms now) off this amp, you will get the full power of the amp, because it is working at it's recommended specs. And so on, and so on... Wiring the voice coils in series, will cause the overall impedance to double (2 4 ohm voice coils will now be wired to 1 8 ohm load when in series)

You can always double check your wiring skills with a digital multimeter, so you will know that you are doing exactly as the manufacturer rates their amps... always remember to measure the impedance without the speakers hooked to the amp... your readings will be accurate then...

Hope this helps!!

 

Look at #57 here, or simply put....

The amp will put out more power with a 2 ohm speaker attached to it than it will with a 4 ohm speaker.

 

...if it is stable down to that impedance load, yes it will... if it is not, it will shut down and go into protect...

 

yup!

 

RMS stands for root mean square and it defines the effective power that an amplifier can deliver to a load. Your home receives 120 volts alternating current, that is, your home receives a sinusoidal waveform from the power company at 60 cycles per second that starts at zero volts and rises to 170 volts, then falls through zero volts, changes polarity and rises sinusoidally to 170 volts and back down to zero. This describes one complete cycle of alternating current. Since the voltage varies with time, and the average voltage is zero, the way to tell what your house current can do is to calculate the voltage vs time over one cycle and take the square root of it (root mean square) and the number you get tells you the effective voltage and in your home, that is 120 volts. A light bulb that has a filament will operate at the same brightness when 120 volts ac powers it or when a 120 volt direct current powers it. A 120 watt light bulb would draw 1 amp at 120 volts d.c. but on a.c. the voltage and the current would vary sinusoidally but the rms value (the voltage times current area under one complete cycle of a.c. has the same area of the voltage times the current on d.c. for the same length of time, 1/60 second) of the a.c. is the same as the d.c. , or 120 v and 1 amp.