The ksn1188 piezo does go down to 700hz and is remarkably smooth with a 5x15 parts express horn but the efficiency is no match for a delta15. It's about 93db and a delta15 is more like 100db so it just won't keep up. But there are other 15" woofers that would work very well with this horn. But no match for a theater 4pi. Good luck. Mike H.