sub distortion?

I read some subs have a lot of distortion. Is this important? Because amps might have .0001 distortion, but if subs have 1%, is that bad?
How much does one have to spend to get high quality sub for music
Thanks Bob-reynolds. My bookshelfs go to 55Hz or 65Hz. I was using a sub for music fixed from 80hz and below , is that too high? It didn't sound that good.
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I think bass replacement. Sub was plugged between the poweramp and preamp. maybe room placement was a problem.

I noticed asc sells a subwoofer stand. Is this a good idea? they say it
prevents vertical nodes
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