everything
Just use it like an 8 ohm speaker or else connect two 16 ohm speakers in parallel to form an 8 ohm load. Parallel is positive to positive and negative to negative.
This depends on your amplifier's specifications. i would recommend looking in the amplifier's service manual to avoid disapointment or damage to your amplifier or speakers.
in parallel No. Two 8 ohm 'speakers in parallel present a 4 ohm load.
You can, but the available power will only be about half of rated, and the frequency response will be slightly different. Better would be to connect two 8 ohm speakers in parallel, making an equivalent 4 ohm speaker.
Parallel
If you connect two 8 ohm speakers to the average car amp, then yes, probably. Most car amps can handle a 4 ohm load, which is what it would be.
No. Two 16 ohm speakers connected together are either 32 ohms, if wired in series, or 8 ohms, if wired in parallel. You can, however, connect four 16 ohm speakers in series-parallel to get 16 ohms, with four times the power handling capacity of just one.
Don't know how you have subs wired but should be 4 ohm load is what your amp will see.
Yes, you can safely use a 4 ohm amp with one 8 ohm speaker, but you will not achieve full power. The 4 ohm amp is designed to supply a certain voltage into a 4 ohm speaker. Supplying that same voltage to an 8 ohm speaker will result in half the power, or -3dB. For maximum power, use a 4 ohm speaker, or two 8 ohm speakers in parallel.
You can't. Two 4 ohm speakers in parallel equal 2 ohms, and two in series equal 8 ohms. It is possible to wire four 4 ohm speakers so that the load is 4 ohms though. Put two in series (8 ohms). put the other two in series (8 ohms). Then put the two sets in parallel (two 8 ohm sets in parallel equal 4 ohms).
I depends on "how" you are connecting them. If you connected the 4 ohm speakers in series (positive terminal of one to the negative terminal of the other). This will leave a negative terminal of one unconnected and a positive terminal of the other unconnected. then connect them in parallel (the unconnected positive terminal of the 4 ohm speakers to the positive terminal of the 8 ohm speaker and the unconnected negative terminal of the other 4 ohm speaker to the negative terminal of the 8 ohm speaker. This will produce an overall 4 ohm load for 1 channel (assuming you are connecting to a stereo) Or if you are connecting to a stereo with two 8 ohm outputs. Connect the 8 ohm to one channel then connect the above mentioned series connected 4 ohm speakers to the other channel for a total load of 8 ohms on both channels. Parallel connections will equal less than the individual speaker load. The formula for this is: R X R/R + R where R is ohms for each speaker ie. Two 8 ohm speakers in parallel would be 8 x 8 (64)/ 8 + 8 (16) which is 4 ohms. Series connections you just add them together ie. Two 8 ohm speakers in series would be 8 + 8 or 16 ohms. FYI. If you measure the speakers with an ohmmeter it will be less than what it says on the speakers. Speakers are measured in "impedance" which takes into account "reactance". The resistance of the speaker coil will change slightly with different frequencies applied so an 8 ohm speaker may read as 5-7 ohms (more or less) with an ohmmeter. A 4 ohm may read as low as 2.5 ohms on the same meter. Some output transformers can handle half the ohms but it is always safer, as a general rule, to go "up" in speaker impedance without any damage. It's not wise to vary any with a system with solid state (transistor or IC) output coupling. Hope I didn't get too technical. There is lots of good info on the internet about speaker configurations.
If you connect four four-ohm speakers in parallel, the impedance will be equal to 1 ohm, and will allow the speakers to run at the advertised watt RMS. The equation is 1/(total impedance) = 1/(impedance 1) + 1/(impedance 2) and so on. Parallel is like this: Power source: + Speaker+: + + + + Speaker-: - - - - Power source: - However, usually if you hook up a 4 ohm speaker to a 1 ohm amplifier, it would still function it would simply not provide nearly as much wattage as it would have otherwise. Also, if your speakers are dual voice coil (like many subwoofers) you could use 2 4 ohm speakers, connecting the two voice coils on each speaker in parallel and then connecting the speakers themselves in parallel.