Acoustics of BTE hearing aid 'plumbing'

["Richard H." <auditory@xxxxxxxxxxxxxx>]

Hi,

I feel that the acoustics of behind-the-ear hearing aid plumbing i.e. the 
tubing, the "horn", "filters", "dampers" and the earmould are little 
discussed.

Can anyone recommend a book or PDF which has a considered & detailed review 
of the acoustic performance (bandwidth, resonances etc) of these various 
components?

Many thanks.

Richard