ohms?

The resistance of an electronic circuit is measured in Ohm, named after German scientist Georg Simon Ohm (1789-1854).

Ohm's law (1821) states:

Voltage = Current x Resistance

U (Volt)= I (Ampere) x R (Ohm)

So Ohm was the first to describe this relationship.

One ohm is equal to the current of one ampere which will flow when a voltage of one volt is applied:

R = U/I

 

We don't ever make fun of ANYone, unless they ask a stupid question. Yours isn't.

PS, well explained JMX.

 

It's not a matter of sound, but of matching the cab to the amp and vice versa.

Ok, you have a combo where the speakers have an impedance of 8 Ohm (impedance is the basically the same as resistance, but for alternate current circuits, the term resistance is used for direct current circuits).

Bass amps usually can handle 'loads' down to 4 Ohm (some even down to 2 Ohm - check the manual or amp backplate for the specs).
That means you can add another 8 Ohm cab.

Running two 8 Ohm cabs in parallel means that the total load will be 4 Ohm which the amp can handle.

Adding a 4 Ohm cabinet though will give you a load of 2.67 Ohm which is too low for the amp.

You calculate it like this:

1/R(total)=1/R(cab 1) + 1/R(cab 2)

so in the first case it's:

1/R(total)=1/8 Ohm + 1/8 Ohm = 2/8 = 1/4 =>

R(total)= 4 Ohm, fits the amp perfectly


2nd case:

1/R(total)=1/8 Ohm + 1/4 Ohm= 3/8 =>

R(total)= 8/3 Ohm = 2 2/3 = 2.67 Ohm, too low for the amp


Another thing: The lower the load is, the more power the amp can deliver.

Usually it's roughly like this:

The amp gives you around 30% more power @ 4 Ohm than @ 8 Ohm.