Thanks for replying. I know nothing about nothing, so everything is a learning experience for me haha.
I was planning on upsizing the existing speaker to a four inch and then adding a second one. My concern is that will be too much of a load for the system. So I have been scouring the internet to try and understand the different components to figure out what I may have to upsize and am not having any luck. There is lots of information on how to build a tiny radio with a tiny speaker, but I am struggling to figure out what to do in order to acommodate two or three times the speaker output. Maybe the 7w PA is all I need???
As long as the speaker's impedance (this is specified in Ω and is often printed on the back of the speaker magnet) is the same or greater than the original one, it won't be a problem. The power rating of the speaker is not how much power it will draw from the amplifier, but the maximum amount of power it can take before being damaged. The amplifier will be designed to drive a minimum load impedance and going lower could result in damage or the protection circuitry activating which would distort the sound.
This is due to Ohm's law:
P = V
2/R
So if your amplifier outputs a voltage of 1V and your speaker impedance is 8Ω:
P = 1
2/8 = 1/8 = 0.125W
Reducing the speakers impedance to 4Ω, will double the power dissipation, hence why the risk of damaging the amplifier.
If you replace the speaker with a physically larger one, with the same impedance as the original, the power delivered by the amplifier will not change, but it's likely it will be louder and sound better too as the larger speaker will be more efficient than the original one.
Adding another speaker to the output will result in more power dissipation. The total impedance seen by the amplifier again can be calculated using Ohm's law, more specifically the formula for resistors in parallel:
R = (R1*R2)/(R1+R2)
Hint: if R1 = R2, then the resistance is simply halved, so if you have two 8Ω speakers, the impedance will be 4Ω.