Does speaker-level input to sub by pass its electronics?

It's a question of where the crossover is. 

My current Velodyne 12" servo self powered sub: full range l/r line out to Carver Amp. Speaker wires from Carver Amp to sub speaker wires in. Sub's crossover sends low bass only to it's internal amp. Then Sub speaker wires out to front l/r. 

This method: the Carver Amp is amplifying all frequencies, no relief to it's job; however the primary l/r no longer try to make low bass, an advantage to them. Their highs/mids/upper bass are not in a cloud of self-imposed distorted low bass they had no business trying to handle.

IF you go to a crossover first, i.e. line out to self powered sub, then sub sends line out (no low bass included) to the Amp. Now the amp gets a break, it no longer has to make low bass, and it sends upper bass/mids/highs only to primary l/r. speakers also get the break of not trying to make low bass.

Reducing the low bass load from both the amp and the primary l/r is important when trying to keep amp power needs down, especially tube amps.

 To the contrary, I was concerned that speaker-level input might treat the subs as ordinary 15" speakers, but the high input impedance of subs is always stressed as the reason it doesn't stress the amp.

That would be a very odd design!

It's a lot easier on everyone if the speaker input presented even a normal 8 Ohm load as that would require large, and expensive parts, and completely different crossover components.

As Duke points out, it's usually a high impedance input with a voltage divider.  Your amp will see a parallel 1,000 Ohm load or so, and the subwoofer's electronics will see a vastly reduced voltage swing (Say from 50V to 2).

Al, I think you warned me about that once before but I forgot. Given I mostly listen to jazz and baroque in the living room, and the unaided LS50s do a nice job of the bass, I’ll satisfy my lust for pipe organ music and Mahler in the media room where the Reference 1s are supplemented by a pair of HGS-15s with SMS-1 acoustic room correction  -- I don't notice the subs until a pedal note or explosion draws my attention.

Again, thanks.
db

Um, uhh, Al is no longer with us. Though even residing in the beyond, he continues to help us mortals.
Al, you are missed.
Bob

Bob, I'm embarrassed to admit I didn't see the post was a quote and when I checked out the link I discovered the extensive coverage of using an A7e with high-level inputs.  Also I was sorry to learn that Al is no longer with us.  I have valued his advice in the past.

db