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Introduction 
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Analog crossover/equalizer

My friend and neighbor in Sea Ranch, Nelson Pass, was inspired to develop an analog crossover equalizer for the LXmini. The transfer functions for the LXmini woofer and tweeter equalization were derived from free-field acoustic measurements and originally implemented, together with a standard LR2 crossover, in a miniDSP 2x4 digital signal processor. 
Nelson approximated the original woofer and tweeter frequency response curves of the DSP with minimalist analog circuitry.
Above 1 kHz there are deviations, which have surprisingly small sonic consequences. But we are not yet completely settled on a final curve. As it is now, I could gladly live with what we have, and refinements would likely be very subtle only.
All active devices are unity gain, complementary JFET buffer stages. Harmonic distortion is below 0.001%. It rises to 0.01% at 7 Vrms output, which is far more voltage than needed to clip most common power amplifiers.

Note the low component count and simplicity of circuit topology. Though that comes with limitations in what frequency response curves can be realized, it fits Nelson's philosophy of Zen-like beauty in design and nicely matches my design philosophy behind the LXmini.

The circuit runs off +/-12V rails, which are derived from an inexpensive 24VDC switching supply.

 

Here is the LXmini ASP implementation, which very much follows the construction format of an earlier xo/eq product from Nelson's First Watt company.

His craftsmanship and quality of work are impeccable and  admirable.

An inexpensive, high quality blank circuit board for the LXmini ASP will become available via the DIYAUDIO STORE and all LXmini construction plan owners will have access to the DIY circuit assembly information via their support page.

 

 

 

Meanwhile, Nelson developed his ASP further: A 3-Way ASP, that can be used for LXmini, LXmini+2 and LXstudio.  XLR or RCA in-/outputs
(stuffed pcb with case or bare pcb with case and matched jfets or bare pcb) from LINKWITZ.store

 

 

August 31, 2017 update - LXmini ASP

Nelson has laid out a small circuit board for the LXmini Analog Signal Processor, has selected currently in production JFET's and matched them into pairs for the buffers, has selected a small power supply and chassis. All this should be available for DIY from the diyAudio Store and/or Madisound by the time of:

Burning Amp 2017  -  burningamp.org

Still in the works is a circuit board design for the LXmini+2 ASP. It would also serve the LXmini without dipole subwoofers. Nelson's plan is to show a working LXmini+2 analog system at Burning Amp 2017.

We both will give talks. Mine is likely to be about: 
Baffle design, diffraction, radiation pattern and stereo imaging (PDF

See, for example, a related discussion on diyAudio: 
What are some good example of baffle design to improve diffraction

Hope to see you there.

 

PS:
Be sure to read the stereophile interview with Nelson. It's just as I know him!

Nelson Pass: Circuit Topology and the End of Science

 

Watch Nelson's presentation at BURNING AMP - 2017

 

Generally, the required LXmini crossover/equalizing can be realised in the analog domain (ASP based) 
or in the digital domain (DSP based)

 

ASP based crossovers (Nov 2018) are e.g. 

 

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What you hear is not the air pressure variation in itself 
but what has drawn your attention
in the streams of superimposed air pressure variations 
at your eardrums

An acoustic event has dimensions of Time, Tone, Loudness and Space
Have they been recorded and rendered sensibly?

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Last revised: 02/15/2023   -  © 1999-2019 LINKWITZ LAB, All Rights Reserved