pressure build-up ring

["Scott Fraser" scottbfraser]

<<The pdf for the MKH20 states that:
  "o High-frequency response can be accentuated by means of a
pressure build-up ring "
http://www.sennheiserusa.com/newsite/pdfs/mkh20.pdf
Can someone say what this is, how  it is applied, and how much hf
response enhancement can be expected?>>


Sennheiser unfortunately didn't provide a picture, so I would
speculate that they're referring to a ball, typically about an inch
to 2 inches in diameter, of a dense plastic, fitted over the end of
the mic, forming a spherical boundary at the diaphragm. Similar
devices are available for certain Schoeps & DPA mics. DPA calls it an
Acoustic Pressure Equalizer Ball, Schoeps calls it a Sphere
Attachment. The effect is to increase the directionality of the
highs, & add a bit of HF boost. Thus the pattern goes gradually from
omni to cardioid with increasing frequency.

Scott Fraser