What does Nominal Impedance mean?

@ozzy Wrote:

Wonder why companies just don’t make speakers that are 8+ ohm and with high sensitivity? But it seems to be just the opposite, that is; many of the big-name speaker manufacturers produce speakers that are 4-ohm and low sensitivity.

Wonder why that is?

ozzy

Maybe Hofmann's iron law is one of the reason. Article

Mike

ditusa,

Probably, but many large speaker cabinet types still have low impedance and sensitivity requiring monster amps to drive them.

ozzy

Thank you @dweller!

I know this is a complicated subject & not as simple as this but the primary way to get decent, extended, deep bass that can play relatively loudly from smaller woofers ( less than 8” or so) is to have 2 or more of them usually wired in parallel which lowers the effective impedance ( the reciprocal of the sum of the reciprocals). 
 

The taller, narrow baffle designs popular now for the sake of theoretically better imaging lends itself to smaller woofers if the cabinet cost is to remain reasonable & not “sculpted” in some way. many new speakers today have pretty low impedance & thus their actual effective sensitivity is lower than stated. 

@ozzy it is rare that a large cabinet speaker is also not sensitive. The reason for the large cabinet is to increase its efficiency and thereby sensitivity. Small speakers are typically more difficult to drive and require greater power to overcome their lack of sensitivity and low impedance curves. Ohm’s law explains these electrical properties but I suspect it will be a little over your head unless you intend to do a deep dive into the subject.