New MJK Baffle Article

[MJK]

Peter,

I think that an active crossover with some added boost to the Alpha 15A's is probably your best bet. If you go passive, you might come up a little light in the bass.

[seanzozo]

MJK,

I know you have used the Alpha 15 in this sort of application. With a crossover at 300hz it seams that the 10db rise at 2K is still an issue, do you use a notch?

Sean

[MJK]

Sean,

In both my OB designs the crossover for the Eminence Alpha 15A is second order at 200 Hz. At 2000 Hz, the input signal is down 40 dB according to my quick calculations. Are you worried about a 10 dB peak for a signal already down 40 dB with respect to the reference SPL? I am not too worried about it and have heard no evidence of a peak at 2000 Hz from my Lowther OB system which uses two Alpha 15A's per side.

Hope that helps,

Martin

[seanzozo]

MJK,

DOH!, I need to remember to actually check my math. Between using 300hz as the CO and missing a doubling when doing the mental estimation (meaning I really used a 600hz CO) I was off by ~16db.

Sean

[MJK]

Sean,

Glad it worked out. The Eminence Alpha 15A is really a great driver for an OB speaker. Well built and good deep bass in a "small" baffle without any need for biamping. I cannot recommend it highly enough.

Martin

[Pano]

Originally posted by renfrow
How about putting an L-Pad on the full range speaker, wouldn't that help to tailor the efficiency?

Kind of what I did. Had to pad down the big horn to match the single OB 15". The horn is so effecient that it really doesn't matter, and horns seem to like some resistance inline.

[Vix]

Originally posted by Nelson Pass
Yep. Designed with OB and FR in mind. I have a nice one
now, but it's going through a revision. If you come to RMAF
you can listen to it.

Thanks!
I'll be building an OB soon. Yesterday I played a bit with some cardboard and passive x-overs. It was a bittersweet experience. In the OB, the sound is very relaxed, but I was disappointed by the passive xo performance and efficiency mismatch between Visaton B200 and Eminence Beta 15. My main amplifier is ZEN V9 without feedback (so, a transconductance amp), and I have hoped that, even if run via passive Xo-s, it could provide some bass boost (As Dick Olsher noticed in his review of the Visaton No-box). However, it didn't work that well. I may repeat the experiment when I build the proper baffles. And I am not really willing to put an L-pad to Visaton B200.

So, my next plan would be this:Biamp. Run Visatons via ZV9, with only a PLL Xo, first order. There could be a small cap at the input, or, since ZV9 output is capacitor coupled, just reduce its output cap at a small value (50-100 uF) to obtain a first order rolloff.

Then, use active Xo/EQ and another SS amp to drive the Betas.Experiment with crossover value and slope until I find the right match. ( I have a gainclone amp just collecting dust, but I doubt that it would be powerful enough after EQ).

Hope I am not far off-track. Any suggestion is welcome.

Regards,

Vix

[Geoff H]

Quoting Vix: "So, my next plan would be this:Biamp. Run Visatons via ZV9, with only a PLL Xo, first order. There could be a small cap at the input, or, since ZV9 output is capacitor coupled, just reduce its output cap at a small value (50-100 uF) to obtain a first order rolloff. "

It's better to perform the roll-off in front of the amp. This reduces bass energy causing the amp to clip. The damping factor of the amp can still control bass resonance of the upper driver.

Geoff.

[Vix]

Originally posted by Geoff H
It's better to perform the roll-off in front of the amp. This reduces bass energy causing the amp to clip. The damping factor of the amp can still control bass resonance of the upper driver.

Geoff.

I'll do it. Thanks!

[MJK]

I'll be building an OB soon. Yesterday I played a bit with some cardboard and passive x-overs.

.
.
.

Experiment with crossover value and slope until I find the right match.

Instead of doing a trial and error set of experments, why not do the design work up front and build it once. The chances of you getting an optimum result by cut and try and playing with crossover points and slopes are not so great. Doing the design work will save time, money, your efforts, materials, and produce an advanced design right out of the gate. How do you know that the components you have selected will ever work well in an OB speaker system under any conditions?

The whole point of my article was to optimize by design, rule out the not so great ideas, and understand the significant contributors to the final SPL response. In my opinion, it will take as much effort to design an OB speaker system as it does to design any of the boxed speaker systems.