Here are curves of the famous Vitavox S2 on the vitavox radial horn.

Jonathan graciously allowed me to measure it. Despite its popularity, no one has posted a clear curve

Here they are.............

Radial horns always have the smoothest curve ( but not the best sounding)
Shown compared to the RCA 9584 driver on a 350Hz tractrix for comparison.
It is a very nice driver, but needs a HF horn.

Here are some muticell tests of an RCA 4 x 5 with RCA 1428b (two) Altec 2 x 5 110 deg with Altec 288 driver.

A single cell of the RCA 4x5 at 0 deg an 10 degree
For comparison a JBL 90 degree - deg.

The muticells all measure almost exactly the same off axis.
The JBL horn is down 5dB 45 deg off axis.

Here is PDF of JBL 2553 horn. Note horn is eq'd flat to show off axis curves.

Best, Bill