css fr125 OB

[cakeman]

I built H-frame baffles for eminence alpha 15's a while ago and paired them with my css fr125's, this setup sounds better than anything I've built before. The OB's for the fr125's at the moment are ugly and roughly 12x18 inches, made out of some leftover hardwood and they were built just to test how the OB sounds without any calculations, just for the sake of trying out OB's in general, since I've never owned a pair of OB's speakers.

Now the question is what size OB's I should build for the fr125's and where should I place the driver itself? I was thinking about placing the OB's on top of the H-frame woofers. Placing the OB's on top of the H-frames obviously limits the size of the OB' a bit, but I think I could fit 15x30 inch boards, but is that big enough to get down to like 150 hz before the open baffle roll-off starts to kick in? Or is there some other reason why design like that would be much worse than simple floor standing OB's for the fr125's?

Cheers,
cakeman

[SAC]

Originally Posted by cakeman

Placing the OB's on top of the H-frames obviously limits the size of the OB' a bit, but I think I could fit 15x30 inch boards, but is that big enough to get down to like 150 hz before the open baffle roll-off starts to kick in?

Is not the contrary true? The FR125s flat baffle will join the H-baffle at its lower edge, effectively one even larger baffle.

I.e. Flat baffle+H-baffle is effectively same/bigger than a flat baffle standing separately from the H-baffle.

Unless I misunderstood your question.

[dayvo]

I also use the CSS FR125's on an open baffle. Mine are 15" wide by about 32" tall and use Peerless SLS 12 woofers for the low end. Instead of an H-frame, mine just have wings on the side that taper from 6" at the base to 2" wide near the top of the woofers. The crossover is active, line-level using a miniDSP and the crossover frequency is steep (4th order) at 200 Hz. By 200 Hz the level of the FR125's is rolling off pretty quickly just because of the baffle, but that is probably exagerated by my choice to place the FR125's so near the top edge of the baffles. Try modeling your baffle size and driver placement in "The Edge" -- a free baffle simulation application. With my configuration, I wouldn't want to go below 200 Hz for the crossover. Also, the speaker test of the FR125 that John K. at zaphaudio.com did showed the the distortion level of the FR125 increases below about 200 Hz (if I remember correctly).

I'm extremely happy with the sound from my speakers and hope you have as much enjoyment with yours as I'm having with mine.

[cakeman]

Thanks for the input guys.

I have to admit that I'm really newbie with these open baffle things. Either way I was messing around with The Edge and correct me if I'm completely lost, but 12x24 inch baffles and placing the driver approx. 1 inch of the horizontal center line and 4 inches off the vertical center line, if that makes any sense at all.

I'm currently running these speakers with yamaha av-receiver and some left over subwoofer amp from old project and using the built in crossover in the yamaha. I know this is far from ideal situation, but amps are the next thing I'm going to invest some money.

-cakeman

[dayvo]

Keep in mind that there is going to be some mid-range emphasis associated with the dipole baffle peak. By using the miniDSP, I flatten the mid-range with a broad filter from 300 Hz to 3000 Hz that reduces the line level signal by up to 9 db (at 525 to 950 Hz). This improves the sound substantially (in my opinion).

Also, for the woofer, if you are limited to using the subwoofer amp low-pass filter, try setting it quite a bit below your intended crossover frequency. You need to counteract the rising response of the baffle with increasing frequency. If, for example, you are trying for a 200 Hz crossover, try settings on the subwoofer from 50 to 150 Hz and see what you think. With the miniDSP, I use a shelf filter that starts reducing the signal at about 45 Hz and has it down 12 db by 115 Hz. Then the 4th order crossover centered at 200 Hz takes over.

Here is what I ended up with for the in-room frequency response at the listening position -- about 2 meters from the speakers. The SPL level is not calibrated to a specific power output -- just a relative measurement.