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Thread: JBL 4429 biamp and dsp correction

  1. #1
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    JBL 4429 biamp and dsp correction

    I have sold my 4365:s. They were too large and expensive. I have now downgraded to 3 pieces of 4429 instead as L-C-R speakers in my living-room cinema.

    I will try this procedure, that Greg Timbers used, for the fun of it, and see where it takes me.

    Quote Originally Posted by 4313B View Post
    "I haven’t gotten back into working with the DBX or with any other speaker models. I am using an AllDSP model PLP226 Signature. It is basically 2 in and 6 out which works for my Tri-amp system I am not using the UHF at all. I actually did my design with my speakers in place in my living room. I put in a 4 th order LR crossover target (750 Theoretical) and made 4 mic measurements of each of my woofers and HF units. Averaged the 4 positions for each transducer and used those 6 curves as the transducer measurements. I then applied the necessary crossover slopes and frequencies to get the acoustic measurement to match the electrical target as closely as possible. It doesn’t matter what electronic slope and frequency is used so long as the actual acoustic response is close.

    Next I applied the necessary EQ to get the crossover slopes tuned in. Once done, I turned everything back on and made a Left (or Right) channel measurement using the same 4 mic positions averaged. The summing came out nearly perfect, as it should. I did the time delay by choosing one of the mic positions that gave the smoothest curve through crossover and inverting the polarity on the HF. I adjusted the delay for the deepest and most symmetrical notch at crossover. Flip the phase and all goes flat again. Finally, I applied some global EQ to the entire system to clean up any remaining room of summing issues. It is very simple to do, but it takes forever due to the multiple measurements and repetitive nature of things. My results were awesome.

    The DBX Driveline 260 can do the job nicely although it is a little limited in PEQ filters. You have to be pretty efficient. I am currently looking at other High End solutions which incorporate built-in Preamp functions so I can ditch my analog preamp. Among the contenders are the Ground Sound DCN28 and the DEQX HDP-4. All are pretty pricey. The DBX is cheap at about $1000."
    The equipment I will use:
    Crown CTs-1200 amplifiers
    JBL 4429 speakers
    REW measuring software
    Calibrated mic
    Focusrite 2i2 sound interface
    DBX 4820 dsp

    Comments, help and tips are welcome down the road

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    If anyone has access to 4429 unechoic measurements or spinorama diagrams, now is the time to post them!
    4313b, you had it for the 4365. Do you have it for 4429 as well?

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    To get all the measurement gear up and running, I started with some delay tryouts.
    My experience from the 4365 was that finding the perfect delay makes a big improvemement. But that it also is hard to get clear readings when measuring this from listening positions due to my room interferences.
    I tried different delay settings around the approx. 10cm physical offset between the 1200fe-8 and the 175Nd-3 drivers on the 4429.
    I measured 1m from the speaker on-axis horizontally, with the mic in the middle between center of woofer and horn vertically.
    0.375ms delay on LF gave me the smoothest and deepest cancellation around the crossover frequency when inverting phase on HF.
    1/6 smoothing. Single-position measurement.
    Speaker position in left corner, where I usually have it. I did not pull out the speaker in the middle of the room. I interpreted Greg post that he had the speakers in their normal position, and that he measured with mic in different listening positions. But this is a guess from my side.

    Subjectively, it sounds better. It sounds less like an speaker playing. The sound is more released from the speaker.
    Note, this opinion is not from blind-test, so it might very well be imagination from my side! But I can turn on and off the delay on-the-fly in the dbx, and the difference is there every time.
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    Magnus, delay can only correctly be set after the final high pass and low pass filters are in place.

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    Quote Originally Posted by pos View Post
    Magnus, delay can only correctly be set after the final high pass and low pass filters are in place.
    Yes I know. But maybe I choose only to do delay-correction, and no other EQ. I suspect that will be the end-result of this.
    This was for me to get up-and-running with the measurement gear. If I do other dsp-corrections to get the slopes right, then I will redo the delay measurements.

    I have measured 4 mic-positions now, for both speakers, both LF and HF+UHF separately. Now the analysis starts. What could possibly go wrong?!

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    Mic position 1a: Left speaker. Mic 1.5m on-axis. 85cm to floor. 155cm to roof.
    Mic position 1b: Right speaker. Mic 1.5m on-axis. 85cm to floor. 155cm to roof.

    Mic position 2a: Left speaker. Mic 5m on-axis. 85cm to floor. On back left corner of sofa. 155cm to roof.
    Mic position 2b: Right speaker. Mic 5m on-axis. 85cm to floor. On back right corner of sofa. 155cm to roof.

    Mic position 3: On middle of corner sofa seat. 85cm down to sofa seat. 1.09cm to roof.

    Mic position 4: On middle of main listening position sofa seat. 67cm down to sofa seat. 1.26cm to roof.

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    I wonder if 750Hz LR24 is the theoretical target for 4429? Looks more like 700Hz on my single-position delay test. But I know single-position measurements sucks...
    I will post the 4-positions averaged measurements for every driver soon.

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    Left and Right 4-position averages.
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    Then I guess Greg averaged the averages for L and R, and did the same settings for both speakers. Because his end-result were one set of settings.

    This is the curves I should use to generate EQ for getting a more perfect acoustical LR24 slope on, if I understod Greg's procedure right.
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    I do not see how to add a target LR24-slope into REW, and generate correcting EQ to my slopes.
    REW seems to be too limited. I can only see some kind of generic 24dB target slope, that does not look like Linkwitz-Riley.

    Can I do this step with rephase, Thomas?

    I am thinking the LF-bump at 1500Hz should be reduced. Maybe an woofer breakup?

    The big suckout at 150-250Hz is a room-node, or a speaker boundary interference, I guess. Both speakers are positioned deep into corners, angled 45 degrees into the room.

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    JBL TS of 1200fe-8 shows no such breakups at 1500Hz.
    But it might be something else causing this maybe, like a resonance in the cabinet, a backwave, or something like that?
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    port resonant freq?

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    Quote Originally Posted by grumpy View Post
    port resonant freq?
    Yeah, maybe!

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    It's cool how these useless in-room single-spot measurements togheter averages into something seemingly useful/correct.
    The lesson of the day.

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    Quote Originally Posted by bubbleboy76 View Post
    JBL TS of 1200fe-8 shows no such breakups at 1500Hz.
    But it might be something else causing this maybe, like a resonance in the cabinet, a backwave, or something like that?
    The dip around 1.2kHz and bump around 1.3kHz are visible in the anechoic measurement.
    You should probably not worry too much about them as they are some 20dB down already.

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