(N.C. Fulmer US 2787332 filed 1952 “Loud-Speaker System”) was filed about same time as Karlson's first installment of "Acoustic Transducers". Karlson used the slot in a coupled cavity cabinet and Fulmer in hopes of broadbanding a line. Fulmer said it gave a more natural sound.
this pipe looks about the size of half-horn including those by RCA-Fan
article
Pg1
http://img455.imageshack.us/img455/8639/ful11oy.jpg
Pg2
http://img455.imageshack.us/img455/2694/ful20tm.jpg
Pg3
http://img455.imageshack.us/img455/5733/ful37mu.jpg
Pg4
http://img451.imageshack.us/img451/8349/fuld3px.jpg
RCA-Fan's comment on vent size
http://db.audioasylum.com/cgi/m.mpl?forum=hug&n=104845&highlight=fulmer+freddyi&session=
this pipe looks about the size of half-horn including those by RCA-Fan
article
Pg1
http://img455.imageshack.us/img455/8639/ful11oy.jpg
Pg2
http://img455.imageshack.us/img455/2694/ful20tm.jpg
Pg3
http://img455.imageshack.us/img455/5733/ful37mu.jpg
Pg4
http://img451.imageshack.us/img451/8349/fuld3px.jpg
RCA-Fan's comment on vent size
http://db.audioasylum.com/cgi/m.mpl?forum=hug&n=104845&highlight=fulmer+freddyi&session=