One of my significant other's cats likes to hear me play guitar, especially when it's tuned low. He also likes Gordon Lightfoot recordings, so I think the low registers please him. When I was in fifth grade and practicing the french horn our dog, Prince, would start to howl. My first cat, Hendrix, did not like the tin whistle or concertina, or bowed psaltery (I know, you can say, "who does?"). So I think higher register instruments can hurt their ears. The sig-o's cat certainly likes to hear tunes on guitar in CGCGCD tuning.