When I first mounted the horn, I was using the Altec 1201 XO so I will have a control of the mid/top end amplitude adjustment to blend with the woofer, it sounds nice. I then tried the 500 Hz Altec second order XO, nice too but a little too much on the midbass(prominent). I then tried a simple XO at 850 Hz(23.4 uF for the HF PIO with Fostex L pad and 1.5 mH for the woofer straight, Foil type) as I read more about it based on Dr. Bruce Edgar's post plus my mentors suggestion (Joseph E. of JE Labs)and indeed, after further evaluation, was much better sounding in my application. Aligned the drivers for the HF and LH magnet or VC plane and becomes much better still. That is why I am going to try a bigger (350 Hz, on order) horn as I am curious if it will give some more improvement to what I am hearing.
Hi,

Seems like we are both going down the same road.

It is after reading Joe's JE labs website that led me to try a simple first order crossover(around 900 Hz using Russian KBG pio capacitors and air core inductor) with my Altec 515B's and Altec 288-16G drivers(attenuated using Mills resistors by about 12 dB).

The horns are Stereolab Tactrix horns,and the bass cabinets are Bill Woods half horn design.

I use a JBL 075 Tweeter to fill in the highs.All drivers voice coils are aligned.The speakers sound superb driven by my SET 45 amp

Soon, I will be experimenting with BMS/Altec 288/PAD/Radian once I can afford them and see if it is a worthwhile improvement compared to the 800 series Altec drivers I have.
I have compared the Altec 800 series with the 288 series and the 288's are far better.They have an ease of reproduction that the 800 drivers can't match plus they sound better in the mids.A Tweeter needs to be used to add that last bit of air when the 288's are used.

Regards
Rajiv