Active net for Klipschorn

[nre]

From where I'm parked, the crossover network of the Klipschorn, or any 3-way horn-based system, is best tackled with an active network and, to keep things as simple as possible, the implementation is limited to the bass section of the horn system. 

Implementing complex elements in a passive net, for example, notch filters or band-pass elements with so-called "steep slope" low and high-pass side bands add all sorts of artifacts and distortions that are apparent when a side-by-side comparison, to an actively filtered unit, is made.   

That said, the sound quality of the Klispchorn can be significantly improved by implementing and dedicated bass horn amplifier that sends a 4th order, bandpass filtered audio signal to the horn woofer.  When compared to a stock Klipschorn using a passive AK-6 network, the difference is stark and determined to be quite improved, even for old ears.

My approach (first in 1984 and then again in 2017) was a bit complicated, I first designed a "universal" active filter that provides for a range of band-pass filter topologies and then designed the a PC board of just the right size to be "shoe-horned" into a relatively low-cost Crown stereo amp (an XLi series). The design will work for any bass horn and, I'd propose, or something like it, for every bass horn.

The amplifier with the filter installed and working across an 8 Ohm power resistor is shown below.  This is what a 4th order, band-pass looks like:



This is the amplifier at a few different output levels:



This is the acoustic response of the Klipschorn bass unit with and without the filter operating:



The filtered response makes the transition to the mid-horn much better and it's without the weird artifacts associated with a passive.






         

[nre]

This is the filter board:



And installed in a Crown XLi-1500: