toddalin
11-23-2018, 08:10 PM
When I designed the crossovers for my L200s with AlNiCo 2235s, 2420s, and 2405s I adapted the L200B crossover with some modifications adding the N7000/8000 circuit.
If one looks at JBLs later offerings, you see that they placed a 20 ohm resistor in parallel with the 2420 and the 2405. This smooths out the impedience response.
I did this this to my crossovers for the same reason. But I've never been happy with the way they turned out. They were sent to Zilch Labs and received blessings and model perfectly, but to my ear, there was always a gap between the woofer and mid, and mid and highs. This imparted a "dark cloud" to Joni Mitchells voice.
While I was modifiying the crossovers for my "home brews" and looking at the spectra of both these and the L200/300, it hit me! http://www.audiokarma.org/forums/styles/default/xenforo/clear.png
When I added the 20 ohm resistor across 2420 and 2405, it changed their impedience. The 20 ohm resistor is tied to the L-pad, and these were not sent with the crossovers to Zilch labs.
So, what is the effect of this resistor?
The lower end of the horn was supposed to be at 800 Hz with a 16 ohm load. The 20 ohm resistor lowers the effective impedience to 8.9 ohms. The 800 Hz lower frequency is raised to ~1,440 Hz leaving the gap between that and the woofer that crosses at 800 Hz.
Similarly, the top end of the horns was supposed to be at ~7,300 Hz based on 16 ohms. But at 8.9 ohms, this is reduced to 4,060 Hz leaving the gap to the 2405.
The 2405 also received the 20 ohm treatment. This reduced its impedience to 5.7 ohms. The supposedly 7,300 Hz crossover point becomes 10,200 Hz extending this gap.
The remedy was to cut the 20 ohm resistor off of the 2420 L-pad. For the 2405, I added a 2.37 ohm, 20 watt resistor between the L-pad and the 2405 in parallel with the 20 ohm resistor so the load stays at ~8 ohms.
They sing so much nicer now!!!
If one looks at JBLs later offerings, you see that they placed a 20 ohm resistor in parallel with the 2420 and the 2405. This smooths out the impedience response.
I did this this to my crossovers for the same reason. But I've never been happy with the way they turned out. They were sent to Zilch Labs and received blessings and model perfectly, but to my ear, there was always a gap between the woofer and mid, and mid and highs. This imparted a "dark cloud" to Joni Mitchells voice.
While I was modifiying the crossovers for my "home brews" and looking at the spectra of both these and the L200/300, it hit me! http://www.audiokarma.org/forums/styles/default/xenforo/clear.png
When I added the 20 ohm resistor across 2420 and 2405, it changed their impedience. The 20 ohm resistor is tied to the L-pad, and these were not sent with the crossovers to Zilch labs.
So, what is the effect of this resistor?
The lower end of the horn was supposed to be at 800 Hz with a 16 ohm load. The 20 ohm resistor lowers the effective impedience to 8.9 ohms. The 800 Hz lower frequency is raised to ~1,440 Hz leaving the gap between that and the woofer that crosses at 800 Hz.
Similarly, the top end of the horns was supposed to be at ~7,300 Hz based on 16 ohms. But at 8.9 ohms, this is reduced to 4,060 Hz leaving the gap to the 2405.
The 2405 also received the 20 ohm treatment. This reduced its impedience to 5.7 ohms. The supposedly 7,300 Hz crossover point becomes 10,200 Hz extending this gap.
The remedy was to cut the 20 ohm resistor off of the 2420 L-pad. For the 2405, I added a 2.37 ohm, 20 watt resistor between the L-pad and the 2405 in parallel with the 20 ohm resistor so the load stays at ~8 ohms.
They sing so much nicer now!!!