4345 Bi-Amp Crossover Questions

[jbljr]

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.:bouncy:

After this I will be running Dirac room correction through the SHD with the minidsp measurement microphone. Any other useful softwares to conduct measurements?86608

[Robh3606]

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/Network%20Schematics/3145%20Network.pdf



Rob:)

[jbljr]

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/Network%20Schematics/3145%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.

[toddalin]

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/Network%20Schematics/3145%20Network.pdf



Rob:)

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

[Ian Mackenzie]

5.4mH

[toddalin]

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.

[Ian Mackenzie]

Hi Todd,

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

[toddalin]

Hi Todd,

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

Not necessary. Thanks.

[jbljr]

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 :blink:

[grumpy]

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.

[Mike Caldwell]

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 :blink:

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.

[dn92]

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.:bouncy:

After this I will be running Dirac room correction through the SHD with the minidsp measurement microphone. Any other useful softwares to conduct measurements?86608


When using LR24 for Low and High filtering, in bi-amp mode, supposing that you have one amp for LF and one amp for HF, you have to reverse the polarity either at the output either of the HF amplifier or the LF amplifier, to keep loudspeakers in phase.
When using a 12dB crossover (easy with your 5235, just find two 12dB/oct blank cards and fill them with the values for JBL 4350) polarity shall not to be inverted. This is also the case with the original 53-5145 board for 5235, as per JBL set up, whereas you can try listening with the inverted polarity on one of the amps, as the two possibilities are working. I prefer the version with HF amp or LF amp polarity inverted.

If you used minidsp for LF and HF LR24 filters and didn't inverted the polarity of one of the two amps, the sound wont be good.
For 24dB/oct crossover you can also try JBL M552, or Rane AC22 (that has a delay that you can apply to the 18" to perfect the time alignment with mid.

[Riley Casey]

Not sure where you found a recommendation for a 24db per octave filter to emulate the original JBL 5235 analog crossover. AFAIK / remember the 5235 had second order 12 db per octave crossover filters with an option 3rd order and for a bump at a selectable frequency for LF enclosure tuning. Running the 4345s with the internal passive filters still in line ( as they would be unless jumpered out internally, the switch doesn't do that ) would give you a net 36 db per octave crossover slope, not likely to be what the system was designed for. Dial the miniDSP back down to 12db / oct 2nd order filters and see if that doesn't sound better.



...

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

86608