The J-Box has some big problems, according to the reviewer its not suitable for chassis evaluation due to high noise, which means you need more external devices like a separate AMP or Microphone.
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Joined 2003
We have it so good in the modern era, sometimes we forget how things used to be.
In 1991 measuring speakers costed US$4500 = $10,000 in 2025
“when I compare it to my system from 1991. The PC alone cost me $1500 and the MLSSA card and software added another $3000 to that”
Reference:
https://www.linkwitzlab.com/frontiers_6.htm#Y -
In 1991 measuring speakers costed US$4500 = $10,000 in 2025
“when I compare it to my system from 1991. The PC alone cost me $1500 and the MLSSA card and software added another $3000 to that”
Reference:
https://www.linkwitzlab.com/frontiers_6.htm#Y -
Member
Joined 2003
I just ran some basic measurements, the intent of the review was mostly to show that the device is well functioning, not a scam or junk hardware, so there is less risk for anyone interested in purchasing and using it. Certainly a country mile better than some junk Behringer UCA202/222 that some have attempted to use for measurement purpose. Mentioned in my review, "I tested a high end speaker at 315mm, using the 4.9V output. Calibrated the mic SPL level, and adjusted the gain of both the M4 and Jbox to have 120dB of headroom. Actual SPL at the mic for this test is in the 96-97dB range."
I've not encountered any issue with linearity on any of the usb interfaces I've used (Scarlett 2i2, Steinberg UR22mkii, Motu M4), condenser mics are quite sensitive, I use a similar gain setting for either line or mic input. Mic input is often a higher impedance input than line level, perhaps is part of the issue you've encountered.
Give me a little time, I can compare noise floor level and gain setting linearity with mic input.
I've not encountered any issue with linearity on any of the usb interfaces I've used (Scarlett 2i2, Steinberg UR22mkii, Motu M4), condenser mics are quite sensitive, I use a similar gain setting for either line or mic input. Mic input is often a higher impedance input than line level, perhaps is part of the issue you've encountered.
Give me a little time, I can compare noise floor level and gain setting linearity with mic input.
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Joined 2003
Here is a bit more detailed evaluation of noise floor capabilities of a mic measurement. 3 Measurements are compared
For this comparison,
Result shown is SPL accurate noise floor under these conditions. You can see that Motu M4 provides a 10dB improvement, but it is a more expensive device with higher end components, so this should be expected. Result with JBox allows for noise floor around 0dB under these conditions. This is certainly "good enough" for measurement of loudspeaker magnitude. Noise level below 300Hz is dominated by mic self-noise and/or actual background noise.
- Pink is JBox-III with the mic it comes with
- Cyan is JBox-III with Line Audio Om1 mic connected
- Blue is Motu M4 with Line Audio OM1 mic connected
For this comparison,
- I calibrated the mic SPL such that there is 120dB of headroom, ie max input before clipping is 120dBSPL
- For JBox-III with its own mic, gain setting is around 11 o'clock position
- For JBox-III with OM1 mic, gain setting is around 10 o'clock position
- For M4 with OM1 mic, gain setting is around 12 o'clock position
- I packed some foam around the mics to try to reduce background noise to a minimum. It's not a perfect situation, but I think it should suffice for this comparison.
- REW was configured for 48kHz measurement, 256k length, 4 repetitions. No audio output was used, since noise floor was the measurement intent
Result shown is SPL accurate noise floor under these conditions. You can see that Motu M4 provides a 10dB improvement, but it is a more expensive device with higher end components, so this should be expected. Result with JBox allows for noise floor around 0dB under these conditions. This is certainly "good enough" for measurement of loudspeaker magnitude. Noise level below 300Hz is dominated by mic self-noise and/or actual background noise.
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Joined 2003
Limiting factor in distortion analysis for the J-box appears to be a relatively high level of cross-talk between the audio output and mic input.
Below image shows a comparison of noise floor and fundamental measurement in REW, with no speaker connected, so the mic is simply measuring background noise during the measurement. The only difference between the "fundamental" and "noise floor" below is that the Jbox is playing back a sine sweep during the fundamental portion. If there is no cross-talk, these traces should overlay with no difference between them, however we see a significant increase in signal level in the fundamental measurement. This will be a limiting factor for low level measurements, ie distortion. For SPL measurement, this is not of any concern (hopefully everyone measures at a level >50dBSPL).
Below image shows a comparison of noise floor and fundamental measurement in REW, with no speaker connected, so the mic is simply measuring background noise during the measurement. The only difference between the "fundamental" and "noise floor" below is that the Jbox is playing back a sine sweep during the fundamental portion. If there is no cross-talk, these traces should overlay with no difference between them, however we see a significant increase in signal level in the fundamental measurement. This will be a limiting factor for low level measurements, ie distortion. For SPL measurement, this is not of any concern (hopefully everyone measures at a level >50dBSPL).
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Joined 2003
Electricity. Output and input located in the same box, without shielding. Usually required more PCB layers to address, 4 layer PCB can incorporate better shielding of PCB traces. Improvements may be possibly with 2 layer PCB with changes to trace routing to ensure input and output traces are well separated and not running parallel to each other, with ground trace in between.
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Joined 2003
Comparison of various gain settings on the J-Box, using XLR input with Line Audio OM1 mic. Gain settings are adjusted between min and max on the dial, fairly "willy nilly" to get a good sample of various gain positions. Measurement simply repeated with same output level, nothing else changed but input gain.
Aligned SPL at 1kHz. It doesn't matter where you set the gain, response will be the same.
Same test, with the included J-Box mic on RCA input. Same result.
I assume this is what you wanted to see @markbakk ?
Aligned SPL at 1kHz. It doesn't matter where you set the gain, response will be the same.
Same test, with the included J-Box mic on RCA input. Same result.
I assume this is what you wanted to see @markbakk ?
As I said earlier
Naturally, if someone has test equipment budget of $500, they can put together a rig which exceeds the performance of the j-box. But I see nothing in @DcibeL 's measurements that indicate a flaw, just simply a performance limitation that is expected at this price level.
The performance is very similar to my first test rig; A Dayton EMM-6 mic and a Behringer UMC202HD audio interface. I designed several nice speakers with that rig. If I would have had the option of the j-box, I likely would have bought it.
I think the j-box offers a very nice option for beginners who have a modest budget.
j.
Naturally, if someone has test equipment budget of $500, they can put together a rig which exceeds the performance of the j-box. But I see nothing in @DcibeL 's measurements that indicate a flaw, just simply a performance limitation that is expected at this price level.
The performance is very similar to my first test rig; A Dayton EMM-6 mic and a Behringer UMC202HD audio interface. I designed several nice speakers with that rig. If I would have had the option of the j-box, I likely would have bought it.
I think the j-box offers a very nice option for beginners who have a modest budget.
j.
Yup. It performs OK. The crosstalk between in- and output appeared in another test too (although I’m not sure it was the v3 on test there).
I take it the difference between both microphones is about whether correction files were applied or not or maybe measurement setup. All in all it’s giving other cheap options stiff competition.
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Joined 2003
Difference between measurements in post #30 is because mics were not situated exactly the same. Comparison was not intended to compare the mics, but to check gain linearity on both the RCA and XLR inputs.