So... what *disadvantages* can waveguides have?

[Ro808]

Hardly any scientific research is available regarding the influence of the horn surface on the propagation of the wavefront.
Nextel is known to have favourable acoustic properties and has been used by Dynaudio, Revox, Reference 3A, Sehring, Vienna Acoustics a.o. as coating for the cabinet or just the baffle.

Avantgarde and Strauss Elektroakustik also use Nextel to coat horns.

 

[pozz]

Using the Klippel, you could probably define some very tight geometric parameters for the measurement arm and plot the wave propagation inside the horn. One question I always had was if the directivity of distortion is different from the directivity of the fundamental. The paper I found here suggests that it's not: https://www.audiosciencereview.com/forum/index.php?threads/speaker-distortion-polar-plots.14817/ But there may be something to this idea for horns.

The materials Kolbrek gathered (https://kolbrek.hornspeakersystems.info/index.php/blag/28-higher-order-modes) apparently have examples and methods to measure HOMs, but I have not had time to read through them.

 

[pozz]

Couldn't resist. From Markarski's PhD research (pp. 68-69):

Chapter 3 has a useful fundamental discussion of modes in horns.