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JBL M2 crossover with the openDRC 6 years 11 months ago #22765

  • DorinD
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Right, sorry for my english. Indeed, chaining IIR and FIR on the same channel implies about 10ms time difference between them (for a 1000 taps/48kHz FIR). How do you intend to solve the issue, or it's not an issue at all?

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JBL M2 crossover with the openDRC 6 years 11 months ago #22770

  • pos
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I don't see an issue here: the FIR and IIR are simply chained (in an unknown order, but as everything is handled with float it should not make a difference), and the delay of the FIR simply adds up to the total delay. The FIR and IIR are handled in sequence, not in parallel.

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JBL M2 crossover with the openDRC 6 years 11 months ago #22776

  • DorinD
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You are right again, so we just have to add those 10ms delay to the remaining 100% IIR channels. In my case to the sub-bass (which is not so critical, by the way). Thank you for these clarifications, it is more clear to me now.

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JBL M2 crossover with the openDRC 6 years 11 months ago #22781

  • pos
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Yes but the delay implied by the FIR will not necessarily be the full length of it (eg 10ms for 1000 taps) : it all depends on the position of the peak within the FIR.
If you use rePhase to generate the FIR then you can rely on the delay indication shown just below the generation button.

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JBL M2 crossover with the openDRC 6 years 11 months ago #22808

  • dprice
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Got one of the OpenDRC-AN up and running. The HF section seems loud compared to the LF....or just weak bass. Is there any setting that needs to be adjusted in the plugin other than loading in the FIR filters into channel 1 and channel 2? The filters look right - the peaks match points on the curves in the crossover document. I assembled the passive crossover and it is in place...not much to go wrong there. The SQ issue could be elsewhere in the signal chain - MP3 --> cheap PC soundcard --> 1999 budget HTR --> Berhinger 802 mixer --> OpenDRC --> Yamaha amp --> M2 clone. The front half is for messing around in the garage and testing stuff. I'll work on getting the second passive XO finished tonight and will try stereo tomorrow. I'll eventually get around to some measurements later this week to see what is going on.

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JBL M2 crossover with the openDRC 6 years 11 months ago #22811

  • pos
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I assembled the passive crossover and it is in place...not much to go wrong there.

Well, it depends if you followed the original JBL M2 spec sheet, which contains an error :p
Correct cap values are 4.7uF // 3.3uF instead of 4.7uf // 33.3uF.
This makes quite a difference in the final acoustical crossover: www.audioheritage.org/vbulletin/showthre...iewfull=1#post383264

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JBL M2 crossover with the openDRC 6 years 11 months ago #22812

  • pos
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Did you use the same volume and tuning as the original M2 cabinet?

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JBL M2 crossover with the openDRC 6 years 11 months ago #22813

  • dprice
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Yep, the passive crossover is the 8 uF version and the cabinet and tuning should be close enough. I'll check with DATS to confirm. Might be as simple as needing to break in the woofs...and fix the big air leak I forgot about...

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JBL M2 crossover with the openDRC 6 years 11 months ago #22900

  • dprice
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I finally got them moved into the living room and up and running yesterday. Not quite finished with working out bugs with the gain structure in my system and trying to get rid of some ground hum...but I'm getting close. I find it a bit ironic that my attempt to set up a high SPL system has resulted in spending more time listening to nothing than something. It has turned into the pursuit of silence.

The OpenDRC settings seem to work just fine. I have the HF amps running 5-6 dB lower than the LF amps. Given the efficiency of the D2430K relative to the 2216Nd this should not be a surprise. I've only got an hour or two of listening so far but there is nothing to complain about when it comes to the sound of the M2 clones. Next step will be looking into running the Yamaha room correction stuff to get them to match up better with the rest of the system for 5.1 surround.

Many thanks for putting together the FIR filters in rePhase and the documentation.

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JBL M2 crossover with the openDRC 6 years 11 months ago #22901

  • pos
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I have the HF amps running 5-6 dB lower than the LF amps. Given the efficiency of the D2430K relative to the 2216Nd this should not be a surprise.

That should not happen: the sensitivity difference should have been taken care of with the 9dB lpad in the passive crossover (btw sensitivity rating is not really meaningful here as both drivers see their mid band very attenuated).
Both amp channel should have the same gain (and attenuation setting) as remaining gain difference should normally be entirely handled in the FIR presets.
I will have to recheck the original Crown preset to see if I am missing something though, like some additional amplifier gain setting hidden somewhere as an exact 6dB difference looks suspicious :pinch:

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JBL M2 crossover with the openDRC 6 years 11 months ago #22902

  • pos
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I doubled check the Crown settings and there is no hidden amplifier gain setting: all there is is the 0.6dB gain difference which is implemented into the FIR settings published in the google doc.

It is also confirmed by these measurement of the crossover output, made by a German magazine:
www.audioheritage.org/vbulletin/showthre...iewfull=1#post380146



The red and blue dashed lines are the actual crossover output.
You can see that the level of the LF section at 100Hz is identical to the level of the HF section at 1kHz, and this is also what be get with the FIR settings from the google doc.

Here are the FIR settings superimposed with the measured ones:




The difference in the UHF might be due to the measurement technique (measuring the output of an amplifier is not an easy task, especially with a class D amp that can have frequency response variation up high depending on the actual impedance...).
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JBL M2 crossover with the openDRC 6 years 10 months ago #23028

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Update - finally eliminated the ground hum and other noise issues....silence! Then I noticed the M2 sounded flat and lifeless...terrible. A quick turn of the knobs on the HF amp to bring it up to the same level as the LF amp...perfect! Good things happen when the wife leaves and I can spend quality time running test tracks and rewiring uncooperative components.

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JBL M2 crossover with the openDRC 6 years 9 months ago #23576

  • hlg95
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Could you please reupload the original preset? the link seems to be down. Thanks

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JBL M2 crossover with the openDRC 6 years 9 months ago #23577

  • pos
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Hello

I don't have them at hand anymore.
I will try to re upload the FIRs somewhere, and from that it will be very easy for anyone to rebuild the openDRC presets, as the FIRs do everything including level and delay offsets.

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JBL M2 crossover with the openDRC 6 years 9 months ago #23601

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Here are the FIRs, 6144 samples in the IEEE-754 format suitable for the openDRC :

LF : www.dropbox.com/s/e9aaai85l6nf6v0/M2_low.bin?dl=1
HF : www.dropbox.com/s/xu464vjg5rji2d4/M2_high.bin?dl=1

Don't forget the HF part assumes the passive network to be in place (and with the correct 4.7uF+3.3uF caps, not the wrong 33.3uF one mentioned in the spec sheet!)
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