Smoothing

and

Flatness

Some manufactures use a 1/3 octave smoothing on their frequency response graphs.  This is not regulated by the FTC.  My wife and I have heard some quite liberal commercial applications of 1/3 octave smoothing.  My graphs do not use 1/3 octave smoothing.  What you see is what you get.  There is no "airbrushing" here.

I include all of these graphs so that you might see a glimpse of the enduring work that Dennis Murphy performed to make the 1801 absolutely perfect.

This first graph depicts a flat on axis response.  This is very nice, but not subjectively preferable by most.  The excellent overall dispersion of the tweeter tends to sound bright in most rooms.

Most prefer slightly more padding on the tweeter.  The result is this:

The off axis response is this:

That 3khz hump depicted above is certainly audible "in room".  Dennis created a dip to smooth things out.  The on axis result is this:

The off axis result is this:

Ah, perfection!