Thank you for pointing this interesting article, although I read the contrary of your summary:
"The standard Carolingian helmet appears to be most clearly portrayed in the Psalterium aureum.46 The helmet can be described as follows: the cap tapers toward a projecting neckguard, with an obvious rim encircling the entire helm. This rim appears to rise to a point at the forehead, where a button marks the intersection with a band descending from the apex. This band may form part of a crest running across the whole of the cap, which some sources depict bearing a plume as well.47
Most of these features can be observed on the helmets in the Stuttgart Psalter, although the neckguard is less pronounced, and the band displaced from the center of the forehead.48 The same helmet type is also portrayed in the Bible of San Paolo fuori le Mura,49 and in several of the decorated Bibles from the Tours scriptorium.50 Similar helmets can also be seen in the Utrecht Psalter51 and the Bern Psychomachia,52 and on ivories such as a worn tablet now in the Louvre53 and a diptych in Milan.54
Two factors suggest that the Psalterium aureum helmet represents a type which was genuinely worn by the Carolingians rather than one which originated in external pictorial tradition. "...
The spangenhelm, states the author, was probably also used.