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I am still concerned about the frequency response imbalance between the two sets of drivers. Unless I am being particularly dense I cannot find a way to programme separate BFD filters for each channel feeding each set of drivers. The old drivers are quite flat but roll off earlier than the new drivers. While the new drivers are stronger low down but then roll off much more quickly at higher frequencies. While they compliment each other perfectly I wonder whether I am really maximising their combined potential. I am presently limited to a single filter set applied to both channels simultaneously. Would a second DSP1124 BFD (or FBQ2496) produce a better frequency match between the two sets to ensure all drivers are working equally hard at all frequencies? Should I opt for another, cheaper BFD? Or lash out a little extra for the FBQ to have a new toy to play with? Is either likely to provide an improvement to the IB's SQ?
By sheer coincidence a question arose on an IB Cult build thread regarding the twin channels of the BFD. They say that fools rush in where angels fear to tread. I dived straight in head first without a lifesaver. Or even arm bands. Fortunately the famed and ever-patient ThomasW of the IB Cult has finally dented by unshakable belief that both BFD engine lights should be lit simultaneously. Now, of course, it seems so obvious. Whichever channel light is lit is merely a coincidence due to the last filter being set on that particular channel. (or engines as Behringer chooses to call the channels)
When both lights are lit, by pressing both buttons together, both BFD channels are compounded. Both channels receive exactly the same filtration. This is where my error of logic lay. I could not accept that a commercial product would leave a single light on one channel when both channels were active. The idea seemed so ludicrous that I could not bring myself to even consider the idea. So I had repeatedly applied separate filters to each set of drivers to satisfy my REW testing. Then had instantly undone all my careful work by compounding the channels. The idea that a channel was active despite its light not being lit never occurred to me. So I never bothered to check whether the unlit channel was active. I had searched online for hours but could find no reference to setting independent filtration of channels on the humble BFD.
Having, very publicly, discovered the error of my ways I have begun all over again to try and match the frequency responses of the two sets of drivers. Even this was fraught with difficulty because the CX called one set of drivers Right channel and the BFD called them Left. So there was some swapping of XLR plugs before I could get the boxes to agree which channel was which. By the time this was sorted out I had little time to start building new filter sets before being dragged screaming and kicking to the car to fulfill chauffeur duties for the rest of the day on a 50 mile distant, shopping trip. A small price to pay for my wife's infinite tolerance of my crazy audio activities.
It may be that simply trying to match the individual responses of each set of drivers will not match the driver's acoustic loads exactly. I may be approaching the problem entirely from the wrong angle. We shall see.
Now I have discovered a European distributor for Fi drivers (Blade ICE of the UK) I am increasingly tempted to dump my eight AEIB15s onto the European forums small ads and start from scratch with four Fi IB318s. The problem is convincing myself (and my wife) that I can break fairly close to even on the change of drivers and that it would be a certain SQ upgrade. I would gain only slightly on total displacement and lose out on total cone area. Though the manifold/box would be considerably lower but deeper and the total Vas multiplier improved. I can still remember a Fane 18" PA driver in a shop window when I was still in my teens. The sheer size of that dustbin lid of a driver has left a lasting impression to this day and is still fresh all these many, long decades later. Now there is talk of even larger drivers for IB use! Where will it all end?
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