0 Members and 1 Guest are viewing this topic. Read 5224 times.
Hi,I power my Supertowers with a Yamaha DSP A1 home theater amp. It has EQ for each channel, and while experimenting with the settings I noticed adding 6 dB of boost at around 1 kHz makes things sound much better. Sort of as if a blanket was removed from the towers.
When I mentioned this to Brian he told me there is a dip in the Supertower response at 1 kHz and recommended an upgrade to the 12” midbass Misco driver, a midrange capacitor change from 50 uF to 54 uF, and a woofer inductor change from 1 mH to 2.8 mH. This was to change the woofer to mid crossover from the original 650 Hz to 450 Hz and eliminate the response dip. The upgrade seems to have helped but not completely, I still need to add 3 db of boost at 1 kHz.
Checking into this further I ran some numbers on some online crossover calculators
using first order Butterworth. Using 8 ohms for the midrange driver impedance (2X four ohm drivers in series) works out to very close to 54 uF. However I am having trouble verifying the 2.8 mH inductor value for the woofers (one 8 ohm 15” and one 8 ohm 12” wired in parallel making 4 ohms).
When I use 4 ohms and 650 Hz I get 0.98 mH. When I use 4 ohms and 450 Hz I end up with 1.4 mH. The 2.8 mH value works when I use 8 ohms. Seems Brian may have calculated the new woofer inductor using 8 ohms for the woofers instead of the 4 ohms. By the way, using 4 ohms and 2.8 mH I get a crossover point of 225 Hz.Question: Please check my math. Do I have the wrong inductor in my cabinets? For a 450 Hz crossover point using one inductor with two 8 ohm woofers in parallel, what should be the value? I know it depends on the driver characteristics, but should my 2.8 mH really be 1.4 mH? Would a Supertower owner be nice enough to check what he/she currently has? Extra points if using the Misco 12” driver.Also, the woofer inductor is connected in series between the negative terminals of the drivers and ground. On the wiring schematic there is a wire from the midrange driver side of the 54uF midrange crossover capacitor to the junction of the negative woofer terminals/2.8 mH inductor. I don’t understand the purpose of this wire. Question: If any Supertower owners could check to see if this wire is present either on the schematic if you have it or in the cabinet I would appreciate it. If anyone can decipher what this wire does that would also be appreciated. I can post the schematic here if there is interest.Thank you,Ed
I have the original "ribbed" poly cone 12" mid-bass driver, so lacking this resistor might be the issue. I might throw a rheostat in there and see if that changes things. That might be the magic sauce.
I still don't understand how a single 1.0mH inductor can provide a cutoff frequency for the 15" at 200 and the 12" at 600. Does not compute.