From TalkBass Wiki
greenboy: This was a collaboration of sorts. Knowing the Alpha6 and the 6ND410 were very similar in their high-end rolloff points and slopes, I contacted Duke and described my idea of how to address either mid driver with the same crossover - and why there would be negligible compromises in off-axis performance. Duke agreed to do measurements and design to my idea if I would ship him the little JBL waveguide. I'm very pleased how this turned out! Duke RULES!
Duke LeJeune: For those of you interested in adding a reasonably-priced high performance tweeter to your fEarful cabs, I've designed a high-pass filter for use with the Eminence ASD-1001 mounted to the 90° by 90° 6" x 6" JBL PT-B99HF-1 waveguide.
A high-pass filter is essentially half a crossover. The idea is to let the midrange driver (either the Alpha 6A or the 6ND410) roll off naturally, which both of them do smoothly in the 6 kHz ballpark. The tweeter then just fills in the top of the spectrum. Rarely do the audio gods smile on us little folk, but in this case they have: The response curves of the Alpha 6A and the 6ND410 are similar enough that a tweeter section which works well with one is going to work well with the other, assuming the difference in efficiency can be accounted for. That is done by using a variable L-pad.
The JBL waveguide is a constant-directivity device, which means it doesn't beam the high frequencies like some horns do. The tonal balance stays fairly uniform across at least a 90 degree frontal arc, so that nice, wide sweet spot characteristic of the fEarfuls can be extended up to the top of the spectrum. Also the design of the waveguide itself contributes to smoother sound as compared to many horns.
The ASD-1001 is a PA-style compression driver so it's quite a bit more capable than what's commonly found in bass cabs. And with a 6.5 kHz third-order (18 dB per octave) high pass filter, it's not being pushed hard at all in this application.
Total cost for the waveguide, driver, crossover components and L-pad (not counting shipping) is around $60 using good but not exotic parts. You can shave off about $10 by making your own fixed L-pad out of resistors; I'll describe how later on.
¤ Hi-pass parts:
0.10mH Erse Perfect Lay 18AWG .121Ω 300w Air Core Inductor - $2.51
1.0μF Erse PulseX 250v Metallized Polypropylene Film Capacitor - $1.01
0.12mH Erse Perfect Lay 18AWG .151Ω 300w Air Core Inductor - $2.71
1.2μF Erse PulseX 250v Metallized Polypropylene Film Capacitor - $1.35
Erse 8Ω 100w L-Pad - $9.86
$17.44 before shipping
back to Fearfulâ„¢ 12/6 & 15/6
