Originally Posted by tuxedocivic
Very nice EV.
I notice you mentioned you had to boost the low end to hit your XO point. Does your transfer function actually go above 0db or did you attenuate the tweeter then boost, such that maybe you were still below 0db at the XO. You mentioned that it would be tricky with a passive filter. Granted active is a good way to go with a speaker of that calibre!
Good eye - you so quickly identified one of the issues to be careful with when using the miniDSP as the controller, and one of the reasons I'm going to be switching to analog-active once the later stages are complete (the other being that I like the miniDSP as a quick-prototype tool).
is what gets attenuated in order to "boost" the output, if that makes any sense. All actual tweeter
attenuation is actually done at the next stage, not within the miniDSP itself as this helped keep electronics noise floor low.
I simply played my highest voltage source with a signal direct into the miniDSP and watched the levels to see how they would approach zero - both on the input side and the output side. The miniDSP software is really cool like that. If I had identified anything getting close to the zero mark, I would have attenuated the input until I have some headroom.
I've determined that currently there's no apparent clipping even with the boost applied. Part of that is because the boost is almost cancelled out by the simultaneous high pass. It just helps shape the frequency response more than actually boost the natural response. The most gain
actually comes at ~25khz due to the treble shelf filter in the top two octaves (4khz to 16khz), and that could easily have been done differently with negative gain instead. I think one could pull off +/- 3db response passively with a big higher an XO point (maybe around 1.3khz instead) and no boost. I just don't see the point of running a 15 inch woofer up there, plus if i'm crossing that high I'd probably get the small Radian Aluminum or Be tweeter instead.
The way this system works currently is a bit unique. It's so inherently "prototype-phase" that there's no modern HT electronics there. The amp, which doubles as a volume pot, is a Marantz SR6300 (yes, you read that right). It's an old, early 2000s 6.1 channel receiver I picked up off of kijiji. I simply run the MiniDSP into its analog surround inputs and then attenuate the "surround" (tweeter) channel the correct amount. The point was just to get something working in the meantime and avoid clipping either digital or analog and I feel I've hit the objective. Once a true analog active crossover is ready, I would prefer to use some outbound fixed-gain amps and run it off the pre-outs of a modern prepro or receiver. I don't trust the miniDSP being driven by dedicated pre-outs because I've experienced it clipping first hand off of my own electronics.
Second thing was that you're gonna tint the baffle red with transtint. Careful with tint on birch. I've used transtint on maple, which has a similar staining properties as birch, and it was not pretty. I found doing a shellac coat then another tinted coat of shellac was much better to get the wet red (black for me) over wood look.
Interesting. I had a bunch of scrap birch (that I had cut out as bracing until it ended up excess) I was going to test out on anyways before getting straight to the baffle, but I'll take your advice for sure. How do I tint the second coat of shellac the right colour? I'm all ears.