Thanks Wayne. That is great information. I'll see if I can figure out how to use Hornresp tomorrow. I'll be sure to let you know what I come up with. Most people that get into SPL competitions use simple ported enclosures. I've had great results with horns for normal listening and I have a feeling that done right, a horn might be able to out-perform a ported enclosure in the SPL department as well. I've just never seen it done before. I chose 51 hz because that is the resonant freq of my vehicle.