Well, I tried that tiny 0.7L rear chamber today, and its even better now!

That 300-750Hz valley is now not not so deep, and also the bottom end now has a nice steep rolloff just like the top end.

I did some offaxis measurements as well, and its remarkably smooth in most off axis positions too.

Sure was a "squeeze" to get the back volume 0.7L, used quite a few blocks to take up room around the driver.

Above two show the rear chamber

Perfect fit!

Am very happy with the horn. Thanks for the nice comments and suggestions Bill and Wayne.

Adrian