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this week's OB experiments and conclusions

Posted by nl (A) on February 11, 2007 at 14:21:10

Since there has been some interest in FR drivers on OB with OB bass these days, these are some conclusions from playing around with such a setup this weekend.

The speakers are 4x4 plywood with 2x15" bass drivers per side and a Fertin EX20, plus a supertweeter. I've mentioned them before. This basic arrangement is quite nice. The room is about 20x25 with a cathedral ceiling.

I have been feeling like the FR drivers are dynamics-limited and somewhat unsatisfying with "big" music, so I dragged out an Altec 288B on a JBL 400hz exponential horn to play around with. Using the electronic crossover, I hooked this up with a 800hz 24db crossover to the 2x15" woofs. The woofers are really midbass drivers not subs, so they are intended for use up to 1000hz or so. Not bad--the crossover added considerable gunk compared to the FR, but the dynamics and headroom were enticing and the overall effect was good with loud rock. It sounded like a basic prosound setup, which is what it was, and since most rock is listened to on prosound setups, it was a familiar and satisfying effect. I listened to this for a while and appreciated the advantages to the FR setup.

Switching to the FR setup on the same music, the sound was much more coherent and satisfying, but there was the dynamic limitation and tendency to break up. I tried crossing at 100hz using the active XO, which helped a bit but not enough. I then went to 200hz, and this allowed a much cleaner sound with less compression and breakup. Also, the midbass (100hz-200hz) was better for rock via the woofers than the FR. While the FR drivers would eventually run into their limitations again at higher levels, in this relatively large room at relatively high levels (for home use), it worked well and the FR option was clearly better than the horn/bass combo. Virtually all the natural attractions of the FR drivers were retained with a 200hz XO.

So, should you run out and buy an active XO? They're great for experimentation and for bass integration (you can twiddle endlessly), but the longer term solution, in my opinion, is an optional passive XO of about 12db/octave. I say optional because I think you'd want to use a 100hz or no XO for smaller scale music, where you want to preserve the FR's full coherency and aren't worried too much about power handling. It would be nice to be able to choose different XO points depending on music.

Prosound active XOs -- at least mine -- do quite a lot of damage to the midrange, although they are delightful to work with. I think I've mentioned comparisons with the Altec horns before, but this week the conclusions were more clear.

Hope this helps.

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