Whats going on here in this passive

[Jeremy009]

Crossover gurus, please help me understand whats going on in this passive cross. Its off a jbl gto 609c. The site just says 12db slope. But what frequency, is the woofer crossed? 

Woofer and tweeter are 3ohm

[Joe X]

 

 

With a phone app and a $10 multimeter it is possible to know exactly what it does.

 

Someone posts the backside of the board and then I mirror the image:

 

 

 

From this image you can see that the woofer is directly connected to the inputs so no low pass filter in this crossover. The woofer own inductance acts as a natural low pass filter.

 

The schematics of the tweeter high pass filter can be obtained from the above image.

 

Still not enough information to model the tweeter filter because:

 

1) I don't have the inductance of the coil.

 

2) Don't have the capacitance of the small disc capacitor in the center near the top edge of the board.

 

 

If you can't get those values the use the multimeter method above.

 

[Jeremy009]

15 hours ago, Joe X said:

 

 

With a phone app and a $10 multimeter it is possible to know exactly what it does.

 

Someone posts the backside of the board and then I mirror the image:

 

 

 

From this image you can see that the woofer is directly connected to the inputs so no low pass filter in this crossover. The woofer own inductance acts as a natural low pass filter.

 

The schematics of the tweeter high pass filter can be obtained from the above image.

 

Still not enough information to model the tweeter filter because:

 

1) I don't have the inductance of the coil.

 

2) Don't have the capacitance of the small disc capacitor in the center near the top edge of the board.

 

 

If you can't get those values the use the multimeter method above.

 

I got a multimeter.. whats that method?

[Joe X]

It's a 10 minute procedure is just that I describe in detail:

 

 

1 ) get a "tone generator" phone app making sure the output is a sinewave

2 ) connect the phone to your head unit and make sure you can hear the tone generated through your speakersand tha no distortion is present.

3 )  with your head unit off. connect  the crossover as normal but remove the woofer and tweeter,

4 ) Firmly connect the multimeter leads to the tweeter terminals of the crossover.

5 ) set the multimeter to AC Volts.

6 ) turn on the multimeter and then turn on your head unit.

7 )  set the frequency of the tone on the phone app to lowest possible.

8 )  your multimeter should read 0 or close to 0 volts.

9 ) increase the frequency of the tone slowly on the app.

10 ) at a certain frequency you will notice that the voltage reading starts to go up.

11 ) keep increasing the frequency until the voltage reading reaches a maximum.

12 ) take note of that voltage.

13 ) slowly start lowering the frequency on the app until the voltage is 0.71 of the maximum reading you wrote down. Stop lowering the frequency.

14 ) take note of the frequency.

 

That frequency should roughly be the crossover frequency you were looking for.

 

If you want to calculate the slope of the rollof then you need to get additional readings and convert to dB.

 

 

[Joe X]

 

 

 

 

 

L1 value is from around the net.

 

R4 turns out to be a PTC to protect the tweeter from overpowering.

 

R2 has a switch to bypass it to control the strength of the highs.

 

 

The crossover frequency seems to be around 3.8-4 Khz (-3dB)

 

The slope is as you read: 12 dB/Octave.

 

Measuring yourself as described above should get you a similar value, if not let me know.