Although thereís no plans readily available for the various renderings of the Bertha bass horn, there are some interesting horn sites available:
My bass horn of choice is the modern design BASSMAXX cabinets.
Single 18, unloaded driver design, response down to 25Hz with an efficiency of 110 DB with distortion below 1%. The recently designed and unveiled NEOMAXX18 woofer
has been tested at prolonged time periods at over 3,000 watts program. I witnessed the first test in Houston and Iíll venture to say two B-ZERO cabs have the output of three to four professional level front loaded dual 18 subs. Compared to older horn designs like Bertha, Emerald, Cerwin-Vega, etc... BASSMAXX sounds better, cleaner, deeper and louder. The older horn designs typically roll off around 50Hz unless you start putting them in groups and the distortion is pretty high. Funny how most people think 115 DB room average with distortion is louder than 125DB room average at low distortion. At Webster Hall, four of the new B-ZERO cabinets recently replaced eight quad 18 EV boxes with excellent results. More about them at: http://www.bassmaxx.com/
For a build-it-yourself bass cabinet, take a look at the LAB sub horn. Almost on par with the BASSMAXX and plans are readily available at: http://www.prosoundweb.com/lsp/