Can you replace a 16 ohm tweeter with a 4 ohm tweeter in a car?

I don't think you'd want to go with a 4 ohm tweeter.

The amp is designed to power a 16 ohm load -- let's say at 10w.

It does this by producing a certain amt of voltage.

Ohm's law says voltage (e) = sqrt(power(p) * resistance(r)

So E = sqrt(10 * 16), E = 12.6v, and requires 0.8A to produce that 10w also from ohm's law:

I = sqrt(p/r), I=sqrt(10/16) = 0.8A

If you drop the resistance to 4 ohms the current required from the amp's power supply would increase substantially.

I = sqrt (10/4) = 1.6A, double the apparent design current. I wouldn't expect the amp to survive that sort of abuse for long.

Looking at it from the voltage angle --

We know the power supply can produce 12.6v, but if it tries to do it at 4 ohms

P=E^2/r or 12.6*12.6/4 = ~40w

A 10w amp trying to produce 40 isn't going to end well.

The actual power doesn't matter. The point is it will try do draw 2x its intended current and produce 4x the intended power.

I wouldn't do it.

For the best answers, search on this site https://shorturl.im/axTTa

You could just tag (paralell wiring)) them to to the speakers, but the main concern is that now the headunit (radio) would see a 2 ohm load and could run the headunit (radio) hot and in turn damage the headunit. May consider wiring them in series with the 3 way or use a amp that is 2 ohms stable in stereo. Check the link, 2nd wiring options diagram (4 Ohm/Series) and substitute the subs with a tweeter and 3 way speaker, hope this helps. Good Luck!

Unless you are willing to go back to your dealer and get OEM replacements, you are probably going to have to do some modifying to get anything to fit, regardless of the impedance.

A really good set of 4 ohm aftermarket tweeters, with a high RMS power rating and an inline passive crossover should probably be OK.

These Polk Audio tweeters can handle up to 60 watts RMS.

http://www.sonicelectronix.com/item_9329_Polk+Audi...

Or these Rockford-Fosgate's. With these, you have connection options for -2dB (a little less than 1/2 power), and -4dB (a little more that 1/2 power). This would have the same effect as a higher impedance. These can also handle 60 watts RMS.

http://www.sonicelectronix.com/item_18209_Rockford...

As for subs, you should be able to find DVC 4 ohm subs in practically all sizes. With the voice coils in series, they present an 8 ohm load.

sounds like you should redo the entire system.