12" Mid Horn

After a lot of touring with my old system (see photo at right), it became obvious that midrange performance was not up to scratch. It was not untill affordable measuring systems and simulating software became available that I was able to determine the exact cause and remedies.

By this stage, the old Altec horns had been replaced with JBL 2445s, and it was decided to combine HF and mids into a composite cabinet. To keep up with the power capabilities of the JBLs and the sub speaker upgrade, I selected the Eminence Kappa 12 speaker rated at 400W RMS.

Having seen some of the old Martin "Philishave" mid cabinets with their phase plugs, I decided to investigate this more.

Using David McBean's Hornresp program, it became obvious that a small throat area was needed to squeeze the top end out of the 12"s, and phase plugs would be neccessary to achieve this. Not having the time for extensive experiments meant utilising all available info to produce final box without prior prototypes.

The boxes' first gig - an outdoor show

Overall response of these is quite good, being reasonably flat from 200Hz to 1.5kHz where the JBL 2445 is crossed over. Attempts at increasing the top end of the 12 were unsuccessful, and as such the boxes exibit some harshness around 2kHz thanks to the 2" HF drivers

The phase plugs used. Made from layered MDF and shaped to the contour of the Kappa cone and dustcap. The front taper maintains proper flare rate into the horn and brings effective throat area to 75cm^2, horn length to 49cm and minimises front chamber volume.

Bare box during construction. HF driver support panel can be seen. Also just visible on the sides are integral fying points - 2 on each side with internal steel strapping so that timber is not stressed.