I have a Peavey Escort PA on the back it reads 75 watts into 4 ohms (17VRMS) and 50 watts into 8 ohms (20VRMS). The speaker that came with the Peavey have nothing label on them.

I have 2 extra speaker cab which each have 15"speaker, Tweeter , Horn and on the back of each it has a rating of 8 ohms.

Now to the question: Can I use the extra two speaker cab along with the one's that came with the PA making a total of 4 speaker cab?

by addind speakers your going to change your ohms. what is the pa rated at and is it adujsable ohm output?

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(80’s Hair Metal) = A snapshot in time before Grunge ruined Rock & Roll forever!!!!

The only ohm info I have was what I read off the back which I listed in the op don't see anything else other than it 150 total watts.

Should it say somewhere what the adjustable rating is?

Ohms explained…
Basics

1. An ohm is a term used in measuring impedance, a property of speakers that prevents electrical currents from flowing through. A circuit with high impedance tends to have higher voltages and lower currents. On the other hand, a low impedance circuit has a low voltage and high current. Impedance is a physical characteristic that generally does not change. The ohms are used in order to determine how much power can be derived from an amplifier towards a speaker.

Measurement

2. The ohm of a speaker is usually indicated on the labels printed by the manufacturer. For more accurate measurements, digital multimeters often have an ohmmeter function that can help you determine the impedance measurement of a speaker. Most commercially available speakers have an impedance level of 4, 8 or 16 ohms.

Ohm's Law

3. There is a relationship between voltage, current and impedance. Voltage is what moves the electrical current. Thus, an increase in voltage can increase the current as well, as long as the impedance does not change. On the other hand, lowering the voltage also lowers the current. George Simon Ohm formulated this relationship by writing down Ohm's Law. This formula states that in a circuit, the current is directly proportional to voltage and inversely proportional to impedance.

Significance

4. Knowing about speaker ohms is important because it is a safety issue. Connecting too many speakers to a device such as an amplifier can result in overloading. When this happens, there is a risk that it may blow up. Amplifiers give their maximum power to the speaker when the impedance of the speaker is similar to the output impedance of the amplifier. If the speaker impedance is lower than the amplifier's, then the amplifier has the tendency to overheat. In the opposite situation when the speaker impedance is lower, the result is a poorer quality of sound.

Connections
5. Speakers can be connected to each other in two methods: parallel and series. If the speakers are connected in a series, the impedances are added to each other. For example, two 8-ohm speakers in a series have a total impedance of 16 ohms. In cases where speakers of the same impedance are connected in a parallel, the total is the impedance of one speaker divided by how many speakers there are. For parallel connections of speakers with differing impedance levels, the total impedance is computed by multiplying the impedance of the speakers. The product is then divided by the sum of the speakers' impedance.

It sounds like the PA adjusts itself by that what your driving it through if the speakers that came with it are 8 ohm then you should have no problem…If there 4 ohms then your system will only drive 50 watts to the 8 ohm speakers and be way underpowered on the 4 ohms set resulting in a huge volume difference between the two sets of speakers ( and possible overheat on your transformer)… certainly you would never do this with a guitar amplifier because for example 2 sets of 8 ohms speakers cabs run series would change the rating to 16 ohms resulting in excess current in the wires and transformers can’t handle unless switched to 16 ohms. This can and will result in a wire over heat and transformer burn out……. Now I must say I’m not as schooled with Pa systems. My guess is it will drive both sets but if the impedance if different on both sets of cab you have you may very well damage your PA amp.

Hope this helps you out.. I would multi meter the original PA speakers to see if there 8 ohms…if they are not I would not use both sets (one or the other depending on what watt rating you want.

Cheers
Bill

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(80’s Hair Metal) = A snapshot in time before Grunge ruined Rock & Roll forever!!!!