Polish translation: glosniki szerokopasmowe lub pelnozakresowe
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Explanation: Absolutely the word "szerokopasmowe" (plural) is correct. It menas "wide-range" and is used in this meaning for the last 40 years or so.
"Zasięg" proposed by someone is on the other hand ABSOLUTELY NOT correct in this case, as the word means range but in terms of distance. This would be OK in case of e.g "the rifle's range is 1200 yards", or "full range of my new electric car is whole 30 miles!:)"
szerokoposmowe, pełnozakresowe głośniki samochodowe montowane na drzwiach
Explanation: I think that answer 1 is the most fruitful, my addition is just a form of expanding reply 1 into a complete phrase as requested, I pressume.
Apart from nicely clarified "szeokopasmowe" "pełnopasmowe" could do but is less frequently in use, I am afraid.