30923 is M19 HF compensation standing alone, i.e., contoured EQ, way more than simple attenuation, to extend the high frequency response of the compression driver above mass breakpoint when used with controlled-directivity horns or waveguides.

Yes, there is some attenuation at the top, which may be adjusted via varying the value of C1, establishing the upper frequency from which the midband attenuation begins sloping downward toward lower frequencies.

Put it in Spice or mod yours to variable with an L-Pad's terminals 1 & 2, to see how it works....

JBL Technical Notes Volume 1 Number 11