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Thread: 4345 Bi-Amp Crossover Questions

  1. #1
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    4345 Bi-Amp Crossover Questions

    Good day all,

    I have a stock pair of 4345. Currently I am running an electronic JBL 5235 urei crossover with the 4345 cards. Both high-range and low-range going through it.


    Recently picked up a Minidsp SHD. It has 4 analog outputs for bi-amping and I can digitally setup the crossover points.

    How do I set up crossover?

    For low pass I found the recommended 310hz cutoff with a LR 24dB/oct filter. Going to the low range amp.

    But what about for the high-pass section? Or should I just run it full range into the 4345 high-range?

    Any help will be much appreciated. I am quite young and inexperienced, but this is so exciting falling down the JBL rabbit hole.

    After this I will be running Dirac room correction through the SHD with the minidsp measurement microphone. Any other useful softwares to conduct measurements?Name:  IMG_20200509_111017.jpg
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  2. #2
    Administrator Robh3606's Avatar
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    No you should also high pass as well. Try the same and see it you like it.

    Here is the schematic. You can see the biamp switch takes out a couple of poles in the high pass

    network http://www.jblproservice.com/pdf/Net...%20Network.pdf



    Rob
    "I could be arguing in my spare time"

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    Quote Originally Posted by Robh3606 View Post
    No you should also high pass as well. Try the same and see it you like it.

    Here is the schematic. You can see the biamp switch takes out a couple of poles in the high pass

    network http://www.jblproservice.com/pdf/Net...%20Network.pdf



    Rob
    Thank you for the response. The sound isn't dynamic or attractive when I use this minidsp to bi-amp. Tried a few combinations but not doing it.

    Next in line is the bryston 10b crossover.

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    Quote Originally Posted by Robh3606 View Post
    No you should also high pass as well. Try the same and see it you like it.

    Here is the schematic. You can see the biamp switch takes out a couple of poles in the high pass

    network http://www.jblproservice.com/pdf/Net...%20Network.pdf



    Rob
    What is the value of the choke on the 18"?

  5. #5
    On Holidays Ian Mackenzie's Avatar
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    5.4mH

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    Quote Originally Posted by Ian Mackenzie View Post
    5.4mH
    Interesting, thanks. Seems like a lot of capacitance for a 5.4 mH choke. For a 2nd order Butterworth, 5.4 mH would go with 42 mfd for a frequency of 335 Hz. I guess they wanted to increase the rolloff above that frequency.

    An 8mH/62.5 mfd is used for a second order Butterworth at 225 Hz. I have been using 8 mH/77 mfd on the 2241H.

  7. #7
    On Holidays Ian Mackenzie's Avatar
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    Hi Todd,

    This is off topic. If you want to start a new thread by all means....

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    Quote Originally Posted by Ian Mackenzie View Post
    Hi Todd,

    This is off topic. If you want to start a new thread by all means....
    Not necessary. Thanks.

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    I was doing some measurements with pink noise. Is it easy to blow up the high frequency components by doing this? I thought the crossover has some filtering to prevent this. But now my high-end sounds strange, there is sound coming out of all the drivers but more weak and compressed sounding.


    Or... did I blow my hearing

  10. #10
    Senior Member grumpy's Avatar
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    Let it rest (particularly your ears) What levels were you testing at?
    Unlikely to blow those speakers at levels where you can stay in the room (factory crossovers).
    Much more likely to pop with sustained tones.

  11. #11
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    Quote Originally Posted by jbljr View Post
    I was doing some measurements with pink noise. Is it easy to blow up the high frequency components by doing this? I thought the crossover has some filtering to prevent this. But now my high-end sounds strange, there is sound coming out of all the drivers but more weak and compressed sounding.


    Or... did I blow my hearing
    If you some how hit the tweeter with full range or almost full range pink noise at a high level it could have damage the diaphragm, same goes for the compression driver.

    If your using the word "what?" a lot in conversation lately after your testing then maybe the testing was too loud!!!

    You may want to apply a high pass filter as well on the low output channel.
    Maybe 35 hz. at least a 18db BW filter.

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