fe167e and Alpha 15a OB arrived

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just got going a fe167e and Alpha 15a OB. Thanks MJK for your website.

sounds great so far and running them both fullrange till i get the x-over built. even with no x-over sounds very very good.

very open and airy. detailed. relaxed sound. bass is good for a passive ob.

probably go with the x-over MJK mentions if no one has anything that would work better.

maybe go with those phase plug things also.

any ideas for x-overs?

pictures to follow probably.


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The only potential problem I see with your set-up is that the FE-167E is 94 dB/W/m efficient and the Alpha 15A is 97 dB/W/m as predicted in infinite baffles. My original design targeted a 90 dB/W/m finished system efficiency with a smaller full range driver. You will need to be careful with the crossover to get them to blend and produce a flat SPL response. Maybe allow the FE-167E to run full range and only crossover the Alpha 15A so it helps offset the open baffle roll-off. Or maybe pad down the FE-167E a few dB and crossover both in the 200 Hz range similar to the original design with the FE-103E. The default set-up in my three driver OB worksheet uses the FE-167E and two Alpha 15A drivers and it is predicted to work extremely well (see the pdf on my Models page). If you can handle the level mismatch correctly, I think your system will be outstanding.
is that x-over points and padding down for 1 fe167e and 1 alpha15a per channel?

any ideas for what values of cap and inductor for the drivers?

or should i just use a notch filter on the fe1673 to reduce shout?

i want to filter the fostex for the bass.

listening right now i really do not feel that the fe167e is that more sensitive.

but padding down the fe167e might make it sound EVEN BETTER!!!
Crossovers are Linkwitz-Riley 12 dB/octave. You can use the lowpass part from MJK's design. For highpass I suggest you use my values from 'The Volks-OB' :http://www.audiocircle.com/circles/index.php?topic=46951.0 , 30 uF Obbligato capacitor and 8 mH inductor. Obbligatos are available from DIY Hi-Fi Supply and are really good and cheap: http://www.diyhifisupply.com/diyhs_ob_caps.htm. The L-pad could consist of 3.3 ohms in series and then 11.5 ohms over the Fostex, that should give an unchanged 8 ohm impedance for the crossover.

Or, there's and alternative to an L-pad: Semi-active approach.

Use two amplifiers. Run them from the separate preamp. One of the amps could be an "integrated" one, so you can adjust its volume compared to another amp. Use passive crossovers, as before.

This solution has some advantages:

You can increase the level of the amp driving Alphas, to match the level of the amp that drives Fostexes, resulting in higher overall sensitivity. You can use your tube amp just for the Fostex, and can use some high-powered SS amp for Alphas. You get better bass and also midrage may sound better since the crossovers are separated;

If you don't have the separate preamp ouputs, you can "tap" the bass amp from the output of the tube amp, before the high-pass crossover...

All you need is another SS amp...

Of course, you can use active crossovers, but that's another story...

The values are OK. But alternative L-pad values of 2.7 and 15.5 ohms will give 3.6 dB damping which may be a better solution to start with and adjust further if necessary.

If you would go for cheaper high-pass you could choose Dayton DMPC-30 30uF 250V Polypropylene Capacitor at Parts Express(which I don't know the quality of) and later upgrade to Qbbligato if you are not satisfied.

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