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Sorry for the long winded story. I built a pair of Statements in 2007 (or is it 2008 i cant remember that long ago). Moving to a new home every other year, I never put a nice finish on them worrying about destroying the veneer in the move. Fast forward many years to today and I went to finally finish them, but before i did, i wanted to take a few measurements because i was never honestly "wowed" by the sound, when compared to a pair of Modula MT's i made years before them. I found this surprising as so many people love them. They just had alot more bass (too much, i needed to EQ it down alot) and a bit better sound stage. I generally attributed it to the smaller untreated rooms they were in, and never gave it a second thought. I'm now in a forever home and they are in a much bigger room (about 40' by 17' by 9') and they still have the same issue. I found I could even EQ the Modula Mt's closer to flat in room response than the Statements. This got me to realize that I probably have something wrong with the build (given the perfect paint its still the painter that makes the painting!) and I should try to correct it before I finish them. This sent me down a rabbit hole. I got a UMIK1 and a DATS impedance analyzer. I checked the impedance of the system, looks to match up reasonably with Curts original plots. (see attached photos)
I have curved sides and the box volume is slightly smaller then the original deisgn, I calculated about 95 liters and the port is tuned to around 23 Hz measured from the impedance of the system (using the minimua of the first trough), I think i aimed for 25 Hz, so not great but not bad. Looks like i might have a little issue around 85 Hz, that could be addressed as well, but nothing came screaming out at me, that would be so broad band. I wondered if over the years and moving the drivers got damaged, and they all tested out well. T/S parameters were close to spec sheets. I did have some melted zip ties on the resistors, but i have checked them and they are all within 1% nominal still. I still pan on replacing them with some Zistors since i have everything torn apart. As a side note before i did al this i check the usually suspects like polarity of the drivers making sure they were phased properly.
So if the drivers test out, and the individual electrical components test out fine (i de soldered every component and tested inductance capacitance and resistance for each). It must be something else. I went to basics. I went to the 2nd order low pass LC filter and reconstructed it and only it. Wired it to the bass drivers and re ran a frequency sweep with and without the filter. I took the ratio, knowing that should show me the transfer function of the fitler. As you can see in the picture, the -3dB point doesn't hit until around 870 Hz (ignore the over 15khz thats noise). I did some math, the transfer function for this should be roughly estimated by: h=-r2./(-r1-r2-i.*l.*w-i.*c.*r1.*r2.*w+c.*l.*r2.*w.^2); where r2 is the parallel driver resistance at a given frequency, r1 is the inductor/wire resistance C is the capacitance and L is the inductance, i is the complex sqrt(-1) w is radians/sec. I plugged this in and plotted it out using the measured impedance curve for my drivers. And it looks like the -3dB point is around 107 Hz (see in the photos) with a nice roll off 40dB per decade once that cap kicks in, and that looks to correspond to Curts original plots pretty well. So I'm at a loss to explain why my speakers aren't actually measuring out that way. If the inductance was reduced to about 1mH then the modeled response would match the measured. This makes me think i have a parallel inductance somewhere that is drastically altering the inductance in the filter for these drivers...giving me way to much bass and maybe even some out of phase interference with the mids. Anyone have any thoughts or ideas of how or what could cause this? I feel like im missing something but im running out of ideas!
I have yet to move on to the midrange and tweater, i thought i would start "simple" first.
Thanks for anyone's thoughts/time to read through all that i know its alot.
I have curved sides and the box volume is slightly smaller then the original deisgn, I calculated about 95 liters and the port is tuned to around 23 Hz measured from the impedance of the system (using the minimua of the first trough), I think i aimed for 25 Hz, so not great but not bad. Looks like i might have a little issue around 85 Hz, that could be addressed as well, but nothing came screaming out at me, that would be so broad band. I wondered if over the years and moving the drivers got damaged, and they all tested out well. T/S parameters were close to spec sheets. I did have some melted zip ties on the resistors, but i have checked them and they are all within 1% nominal still. I still pan on replacing them with some Zistors since i have everything torn apart. As a side note before i did al this i check the usually suspects like polarity of the drivers making sure they were phased properly.
So if the drivers test out, and the individual electrical components test out fine (i de soldered every component and tested inductance capacitance and resistance for each). It must be something else. I went to basics. I went to the 2nd order low pass LC filter and reconstructed it and only it. Wired it to the bass drivers and re ran a frequency sweep with and without the filter. I took the ratio, knowing that should show me the transfer function of the fitler. As you can see in the picture, the -3dB point doesn't hit until around 870 Hz (ignore the over 15khz thats noise). I did some math, the transfer function for this should be roughly estimated by: h=-r2./(-r1-r2-i.*l.*w-i.*c.*r1.*r2.*w+c.*l.*r2.*w.^2); where r2 is the parallel driver resistance at a given frequency, r1 is the inductor/wire resistance C is the capacitance and L is the inductance, i is the complex sqrt(-1) w is radians/sec. I plugged this in and plotted it out using the measured impedance curve for my drivers. And it looks like the -3dB point is around 107 Hz (see in the photos) with a nice roll off 40dB per decade once that cap kicks in, and that looks to correspond to Curts original plots pretty well. So I'm at a loss to explain why my speakers aren't actually measuring out that way. If the inductance was reduced to about 1mH then the modeled response would match the measured. This makes me think i have a parallel inductance somewhere that is drastically altering the inductance in the filter for these drivers...giving me way to much bass and maybe even some out of phase interference with the mids. Anyone have any thoughts or ideas of how or what could cause this? I feel like im missing something but im running out of ideas!
I have yet to move on to the midrange and tweater, i thought i would start "simple" first.
Thanks for anyone's thoughts/time to read through all that i know its alot.