No.
an 8 ohm speaker has a minimum impedance of 8 ohms just above its low frequency resonant frequency. Its impedance rises at high frequencies due to its inductance. Its resistance is about 6 ohms at DC.
this is treu in theory but it will be greatly affected if by the casing you put the speaker in to (if you put it in a enclosed housing its not a problem but if you put it in a poor designed base reflex housing you get much lower valey's in your impendance)
No and no.
PA equipment is made to be efficient (loud with low power) not to produce very low bass frequencies.
Pa systems are loud with low power :gtoet: 94 db a watt normaly
the poin't i want to make clear was that if you want to feel instead of only hearing music it takes more power than people do aspect
Powerful car amplifiers don't need extra car batteries, they use a switching power supply to boost the supply voltage.
No.
You can hear better bass in the cabin of a car due to the cabin effect that makes low frequencies louder down to the lowest frequency of the subwoofer which is about 16Hz. of course you can hear them and feel them.
Standing waves add as well as cancel at some frequencies. Most low frequencies have the same phase all over the cabin of a car so they do not cancel.