218 kick horn

If that measurement holds water then you should consider renaming it to 218 Sub Horn :whistle:

How close were the mic to the horn mouth in this test?

2V @ 50hz, 2 meters, mic on ground.

played around with some expanding foam.....

Interesting. Any noticeable difference?

Another thing you could try were to cover the foam with some thin bendable ply or similar to minimize its absorbing property, unless thats is what you are interested in studying the effect of of-course.

I spackled the foam flat, sanded it smooth, and then coated it with fiberglass resin. Came out quite nice. I am loading the drivers back in today, and will try it out.

Nice.
Thought of that but could remember if you were using fiber glass.

Dref wrote: Interesting. Any noticeable difference?

I really am happy with the way it sounds. The top driver is also facing up (reverse polarity), so the drivers cones are very close at the beginning of the horn. Unfortunately I didn't take measurements before and after . It is REALLY loud, and I was playing all types of music through it all day 90hz down, and was very pleased. Even the lower notes were very audible. When I turned the xover up to 150Hz, the higher notes were noticeably louder, which is fine cause I built it to go on top of the BT7's anyway. I hope to get around to doing some more rta tests one day.

Nice so you have them in push-pull arrangement?
But you posted a measurement some time ago, had you already done all of the modifications at that point?

If that measurement holds any water, it will go at least as low as the servo-drives?
I would imagine a group of these to be flat to below 30 Hz.