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ecl86
06-25-2007, 11:51 PM
Following this thread is crossover for JBL L166: http://www.audioheritage.org/vbulletin/showthread.php?t=16993&highlight=l166

Can someone please help me understand what is the .7MH after 8.uf for? What is it function. Also, after the LPAD, there are a couple resistors that seem to me like another attenuation circuit, why is it there when there is already a Lpad in the circuit already.

Also for the tweeter, what does the .3mH choke do to the sound for the HF.

I am used to the simple 1st order crossover with just 1 choke and 1 cap. I know that the choke is used to block out the high going to the woofer and the cap is supplying mid/high to the tweeter. But dont quite understand the purpose of the above mentions. Please help me understand this. Thanks.

Allanvh5150
06-26-2007, 01:12 AM
Following this thread is crossover for JBL L166: http://www.audioheritage.org/vbulletin/showthread.php?t=16993&highlight=l166

Can someone please help me understand what is the .7MH after 8.uf for? What is it function. Also, after the LPAD, there are a couple resistors that seem to me like another attenuation circuit, why is it there when there is already a Lpad in the circuit already.

Also for the tweeter, what does the .3mH choke do to the sound for the HF.

I am used to the simple 1st order crossover with just 1 choke and 1 cap. I know that the choke is used to block out the high going to the woofer and the cap is supplying mid/high to the tweeter. But dont quite understand the purpose of the above mentions. Please help me understand this. Thanks.


Hi, Let me try to feild a correct answer or two. In the mid circuit, we have a capacitor in series with an inductor forming a "bandpass" filter. The cap filters out the lows and the inductor filters out the highs at 6db per octave. The .3mH in the high circuit is a high pass filter which when combined with the cap, it forms a 12db per octave filter, i.e. second order. And finally, the L-pad resistor setup after the mid pad is to make the mid response the same as the high responce, i.e. similar loudness. The variable L-pad on JBL systems was usually only for fine adjustment so when set in the middle, the mid high balance would be the same. Anyone else feel free to jump in. Have a look here as well, http://www.ibiblio.org/obp/electricCircuits/AC/AC_8.html Hope this helps.

Allan.:)

ecl86
06-26-2007, 02:47 AM
Thanks Allan for your explanation. I now have a much better understanding how these things work. This is way cool.

DavidF
06-26-2007, 09:05 PM
"...Can someone please help me understand ..."

I can add some confusion for sure. OK, you get that the coil (choke) limits voltage passing through as frequency increases. Another way to say this is that the coil in line with the driver is a low pass filter. It passes lower frequencies but starts to fade out the signal going to the speaker as frequency rises. The capacitor has the inverse effect so it is sometimes called a high pass filter. The cap and coil in the mid range circuit form a bandpass circuit. It allows a certain band of frequencies to pass limited on the low end by the cap and the high end by the coil. With a bandpass the cap and coil are working independently of each other (very simplistic since they actually do have an effect on each other in the circuit). The coil in parallel in the tweeter has the effect of shorting the voltage going to the tweeter. At decreasing frequency more and more voltage is bled off from the tweeter. If tuned to work with the cap in series, it will increase the effective slope of the circuit filter (as mentioned above it can change from 6dB to 12dB per octave, or so).

Same with the explanation above on the Lpads but note that the mid range is more sensitive than the tweeter in the 166 so a fixed Lpad is used to bring down the output to where the designer wants it to be for a “0” or “flat” position on the variable Lpad.

DavidF

ecl86
06-30-2007, 08:47 PM
Way cool - Thanks David for your help....

bigredplane
09-07-2007, 04:42 PM
Hi, Let me try to feild a correct answer or two. In the mid circuit, we have a capacitor in series with an inductor forming a "bandpass" filter. The cap filters out the lows and the inductor filters out the highs at 6db per octave. The .3mH in the high circuit is a high pass filter which when combined with the cap, it forms a 12db per octave filter, i.e. second order. And finally, the L-pad resistor setup after the mid pad is to make the mid response the same as the high responce, i.e. similar loudness. The variable L-pad on JBL systems was usually only for fine adjustment so when set in the middle, the mid high balance would be the same. Anyone else feel free to jump in. Have a look here as well, http://www.ibiblio.org/obp/electricCircuits/AC/AC_8.html Hope this helps.

Allan.:)

If the mid and tweeter are on a 12db per octave and the woofer is on a 6db per octave, isn't the woofer 90deg. out of phase?
Could a person add a cap to low pass to put the woofer in phase?

Thanks