rms?

Then there's the debate about the difference between resistance and impedance. You'll notice that an 8 ohm sub can have an impedance to 25 ohms for example at a particular frequency. If this happens to be the tuned frequency of the enclosure then your amp sees 25 ohms.....not 8!

Find out the box tuning then the primary frequency of your listening music and you'd probably see that your sub might actually be protecting itself and you have nothing to worry about.

A true idea of the impedance your amp is seeing is to use an impedance meter.  Another way would be to punch the TS parems into an enclosure design software and plot the impedance given the box volume and port if it has one.

Simple huh!?

RMS is root mean square. it is an ac value or the efficient value. it is the value that comes out from your multimeter IF it is at AC mode NOT dc. AC signal is a sine wave. hence, it has a peak value. peak value and rms is different. peak value is the peak of the curve.

a good amplifier outputs a purely AC signal. If a DC signal joins the AC signal, the output might be clipped off due to the dc signal. Clipped off signal results to a distorted audio signal. and if the DC value is too huge that goes to  your speaker, it might burn up;moreover, if the amplifier do not use a speaker protection, you can hear hums due to dc signal.

About the Ohm or load, the 4 Ohm is the maximum value (with respect to the current that will flow) that the amplifier can handle. from ohm's law, current is equal to VOLTAGE divided by RESISTANCE, thus, if your resistance is too low(meaning less than 4 Ohm), the current that will flow to the load will increase. for example, try to use a 2 Ohm load, the output current will increase and so output power will increase because power is directly proportional to voltage and current, but the components used might burn up due to exceeding the rated value which is 4 ohm. If you use an 8 Ohm load, the output power will decrease due to high resistance of the load. Ohm is a unit of resistance, while, resistance is the capacity of a component to control a current. always remeber, current is lazy. it hates to pass a high resistance component. every component has its own resistance. resistance can be measured using an ohmeter. remove all sources and isolate the component before measuring its resistance.and it has no polarity.

yes of course it can, by using a bypass capacitor.

WHAT??

bypass capacitor is used in amplifiers that uses transistors. it is a capacitor(mylar or ceramic). the reason they use it, so that no dc signal will go out. capacitors acts like an open circuit when you apply a dc signal to them. it acts like a short circuit when you apply an ac signal.