Measure the source diameter, then divide speed of sound 344 m/s with that diameter for a -6 dB /90 degree dispersion and you’ll be in the ball park for when the driver starts to beam.
On my TD12 M from AE it is 242 mm = 0,242 m cone diameter inside the surround. For a -6 dB / 90 degree dispersion: 344 / 0,242 gives about 1421 Hz for when beaming starts.
As the Beyma TPL 150H should have an 80 degree horizontal dispersion for – 6dB, I will try with a cross over around 1550 Hz together with the TD12M. I don't know the actual cone diameter on TD15 M, I measured 303 mm on my SPB 15 from AE. If it is the same on TD 15 M, somewhere around 1240 Hz could be suitable cross over frequency to the TPL 150H for 80 degrees. A bit low probably for the TPL 150H ? A 10" or 12" driver could have been a better pairing with the TPL 150H cross over wise but if you alredy have the TD15 M, I wouldn't exchange it.
Last edited by Adhoc1; 05-21-2017 at 06:35 AM.