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
Hi Bob trying to think what I can add and my mind goes blank wish I where a technical writer but saddly am not just a loudspeaker designer;)But I will try. Bass horns do have some problems size, cost and if not done right you can pick up much sound from cabinet vibrations. But when design is right bass doesnt get any better. The pressures amazing. I was working on one new bass horn design was running test tones. I had a new front door installed in my studio. I was running test tones arround 20hz I noticed day light arround my new doors magnetic seal. I though darn just bought it so was checking out this space with my fingers the tone switched to next one, the door was bowed out due too bass pressures and once tone was off, door sprang back smashing 3 of my finger nails;) This even pressure and detail to bass notes is the bass horns advantage. You can stand by room bounderys and bass SPL doesnt increase, in corners, near wall bass SPL is even. A sub will cause a peak or null to form. One can set up a sub to give decent bass to a few seating areas but if your close to a wall or corner bass level will increase if in a null it will be reduced using more than 1 sub can help even this loading out. With a bass horn pretty much anywhere you set it in room it will produce null near horn but even pressure through room. Bass horns also have very low distortion due to limited excursion driver doesnt need to travil as far so can reproduce notes lost to violent movements of most subwoofer designs.
Post removed 
Post removed 
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.