Well I cant do what I wanted to do
I hoped I could simulate the FR of the original Vifa and the Morel, on the original stock crossover so I could compare the results.
The raw FR of each driver is quite similar down to 2KHz where the Vifa rolls off steeply and the Morel much less. The Morel extends down way past the Vifa. This indicates that we may be getting more output SPL below 2KHz even with the standard RTL2 crossover in place*. So we need to tweak the crossover to pull down that sub 2Khz slope, which its not originally designed to do.
*Anyone else finding the lower treble/upper mid a bit dominant and the tweeter sounding a bit stressed sometimes with some recordings? I am.
However,
Ive been speaking to James and he tells me that the very different impeidance plots of the 2 drivers mean that the the Crossover function's quite differently between the 2 drivers. This is a phase issue as far as I understand. So simply tweaking the cap value to try and pull down that sub 2KHz slope on the Morel isnt as simple as it sounds.
Now the main thing that's stopping me from trying some simulation's is that I have no idea what value the inductor is on the high pass section of the filter. Its not labelled and I cant measure it. Otherwise I've not been able to find a nice simple beginners software for doing the simulations. Those that I have looked at are asking for driver paramaters that arent shown on the Vifa D20TD or Morel MDT30 datasheet (VAS, Qms, Qes, Qts...all missing) I presume these are only obtainable by measuring the drivers in-situ?
Theres a lot to learn when it comes to speaker and crossover design and I'll hopefully get there someday. In the meantime I have to settle this nagging question about modifed RTL2's: How much better can they sound with a crossover thats optimised for the Morel MDT30s? Im sure Im not the only one who'd like to know, right?
There is a company called
audio-components.co.uk which isnt too far from me, but not as close as I'd hoped. They offer a loudspeaker measurement and crossover design service. I've spoken to the guy there sometime last year and he charges by the hour but at a reasonable rate. So I'm going to take the plunge and get my speakers checked out, and the XO modified accordingly. I'll share the info here.
In the meantime I'm going to try some tweaks. I currently have the series resistor replaced with a wire link. My gut feeling is that a small amount of resistance is needed, something like 0.5 - 1ohm, just to reduce the tweeter output a touch. Also, to pull down that sub 2KHz output Im going to try slightly less capacitance. 5.6uF I can try initially and if it sounds better I might go a little lower. But I'd be doing this by ear with no idea of how its effecting phase or anything so I wont go spending loads on new caps just yet.
Some food for thought
