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Purifi Millennium crossover help

Hello all,

Whilst being bored in lockdown,
It’s somewhat comforting to have a hobby that keeps me off the streets at night.

This is all driven passively with a crossover I developed. My first crossover design.

Attached are on-axis and ~45 degrees off axis response, measured at 50cm; 1/24 octave smoothed, also showing distortion components.

As the may notice the dip and peak at 2.5Khz & 4Khz is due to the tweeter position on the baffle, and sharp cabinet edges, but they largely disappear off axis. (See tweeter only measurements)

I’ll be fine tuning this in weeks to come, by experimenting with a lower crossover point to take advantage of the Millennium tweeter- it’s got an underhung voice cool and generous Xmas- I can see why the late Siegfried Linkwitz (RIP) took it all the way down to 1.5Khz (see attached). At the moment it’s about 2.2KHz (+/- 100Hz).

Newer modern tweeters are much more affordable (like SB SDAC29, which I also have on hand) but this one fit my cabinet (110m faceplate)

This cabinet is 21L tuned to 40Hz

Are they other measurements I can/should take to optimise the crossover?
Listening tests?
Test tones?
Take it outside and measure at 2-3m?
Ground plane?


  • Not sure what you are showing. If this is the finished x-o tweeter only it seems fine, but it would be good to see the whole speaker frequency response. If you are trying to generate files for x-o design then there are a more comments we can make.

     John H, thanks to JP I did get that email
  • Sorry,

    I think I attached images in wrong order-

    First image is on-axis of tweeter; measured at 50cm.
    1/24 octave smoothed.
    Room response is included.

    2nd image is at 45 degreees

    3rd image (Bottom) is the tweeter; on baffle, raw response down to 500Hz, no HPF attached.

    Woofer only response is missing is missing; let me try and add that later.

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