That's because there really
isn't much info available!
http://www.acoustica.org.uk/impulse/impulse.html
I put this page set together, and other than the H5 bass driver and bass cabinet design being essentially the bass end of the H2 design - which is the bit you probably want to know about - the tweeter was a Seas 'Searola' single unit popped in to make it a 2-way. Looks like a Seas rebadge version of a Motorola piezo 'horn' thing to me. Never found any specs on it, and 3decades out of production I'd guess. Wasn't used in anything else Impulse even trialled...
Some years ago I had an interesting email conversation with Brian Taylor re: his Impulse designs; the H5 was passed over.Very , very few built.
The smaller, follow-up H6 was a very, very much more successful format for a 2-way speaker; not only more domestically acceptable but - wth a more natural /easier to manage handover from bass to treble for 2-way, part of which was handled in the cabinet width complementing the simple crossover design (i.e. a finessed acoustic design in the round) - also way more forgiving of placement and upstream kit, pure
fun, and a staggering bargain in terms of delivered sound quality. In some ways I do wish I'd kept my pair, but I ran out of space, what with the H2s, the ESL57s...*
[*then; it's the same H2s, or Quad 989s now: lesson thoroughly resisted
]