Wiring my original AM radio to rear speakers

[cataclysm80]

If you only want to connect the two new speakers, here's your options.

I think I am going to do the two rear speakers only now. So the top wiring diagram with the 8 ohms should be good right?

Yes, that's the one to use.

Enjoy your tunes.

[cataclysm80]

How would you wire it using the 8 ohm dash speaker and a 4 ohm rear speaker

For an 8 ohm dash speaker and a single 4 ohm rear, you'd want to wire them in series to have 12 ohms.
In series means that the wiring goes into one speaker, comes out of that speaker, and goes to the next speaker, look at the series diagrams above.

If you wire them in parallel, you'll have 2.6 ohms and will burn up the original radio.
In parallel means that the + on all speakers is connected to one wire, and the - on all speakers is connected to the other wire.


Ohms is resistance, so the more resistance you have, the quieter your speakers will be.  With more resistance, you'll have to crank the volume knob more to get the same sound level, and you'll have a lower max volume.  Lower max volume only matters if you're actually listening to the radio at max volume, otherwise you can just turn the volume knob up a little more and be fine.

With less resistance, you get louder speakers flowing more current, which can overheat things if you go too far.
radios / amplifiers are rated by what ohms they're stable at, and the old original radios were 8 ohms, modern or aftermarket are typically 4 ohms, higher end amplifiers can be 2 ohm stable.  It just means that the quality of the materials used to build the amplifier can take the heat without failing.

[cataclysm80]

What would happen. If they are all 8 ohms? Would it just cook the radio? No one really uses the radio in these cars anyways

If you don't turn the radio on, then it won't matter which way you wire it.   


What happens if all the speakers are 8 ohms depends on how many speakers it is.

1 8 ohm = 8 ohms

2 8 ohms in series = 16 ohms

2 8 ohms in parallel = 4 ohms

3 8 ohms in series = 24 ohms

3 8 ohms in parallel = 2.6 ohms

Once you hit 3 or more speakers though, you can start doing creative stuff like wiring some in parallel to lower the ohms and some in series to bring it back up.

2 8 ohms in parallel = 4 ohms + 1 8 ohm in series = 12 ohms

2 8 ohms in series = 16 ohms + 1 8 ohm in parallel = 5.3 ohms


4 8 ohms in series = 32 ohms

4 8 ohms in parallel = 2 ohms

3 8 ohms in parallel = 2.6 ohms + 1 8 ohm in series = 10.6 ohms

3 8 ohms in series = 24 ohms + 1 8 ohm in parallel = 6 ohms

2 8 ohms in parallel = 4 ohms + 2 8 ohm in series = 20 ohms

2 8 ohms in parallel = 4 ohms, wired in series with 2 other 8 ohms in parallel = 8 ohms  (this is the same as wiring two 4 ohm speakers in series)

2 8 ohms in series = 16 ohms, wired in parallel with 2 other 8 ohms in series = 8 ohms (this is the same as wiring two 16 ohm speakers in parallel)



You want to choose the option that is the lowest ohms without going under whatever your radio is stable for.



Keep in mind that this info is for our old single channel radios with one pair of speaker wires.
The R11 option AM Musicmaster radio only put out 2 watts, so it isn't going to power a whole bunch of speakers.  You might not get much volume.


Typical aftermarket radios are about 13 watts, have 4 channels (four pairs of speaker wires), and each is 4 ohm stable.
That's a better way to run four speakers that are 4 ohms each, plus you get the ability to balance left to right, fade front to rear, and have more volume.

[njsteve]

I just found this thread and have a question.

My 70 Cuda AM radio with factory single front speaker (replacing it with the D-412 Retrosound dual voice coil speaker with jump wires to make it 8 ohms).

The car has a factory rear speaker fader switch.

I have two vintage Kraco 4 ohm rear speakers.

What would the routing diagram look like for this setup? (I'm electrically challenged and need visual diagramatic aids)