MAB
Major Contributor
I have been interested in the Project M2 DIY Thread for some time. I helped a friend install a fabulous home theater with 708i, but I have been fascinated by the M2. Recent reviews of the 708i were interesting, especially given my positive impressions of the speaker. Erin's review of the M2 is also interesting. The M2 and 708 series edit: share the same use different compression tweeter (and lens) and in both reviews the there was an odd increase in distortion, with a resonance peak just below 2kHz and rising distortion above 5kHz or so:
Erin's review of the M2 shows almost identical distortion. I've tried to listen for the rising distortion on the 708i, but either can't or we got too terrified with the sheer volume. I do think distortion is sometimes overblown, even if interesting.
So I just got a pair or D2430K drivers and the M2 Lens. Perhaps I can spend some idle time doing distortion measurements!
The drivers are large and dangerously magnetic:
I've had a smaller CRT TV set.
I got it propped up on my turntable, which is barely adequate:
First, I measured the tweeter in the lens with and without the crossover filters:
I was hesitant to crank the tweeter without the crossover filters, even with a protection capacitor. But you can see some of the features of the driver with and without the crossover filters.
With the crossover but no DSP, at moderate volume, I don't see strong evidence of the 2nd harmonic at just below 2kHz, and no evidence of the rising distortion at higher frequency. The distortion is dBr in this case... But even the absolute distortion is not showing the same characteristic as in the reviews.
Since the speaker isn't useful without PEQ, I applied similar settings to the the JBL M2 Crossover doc, using a MiniDSP Flex Eight. This can be done with a variety of DSP solutions.
A great starting point is the very detailed JBL M2 Crossover doc produced by @pos
You can see how JBL solved the response curve:
Using this as a starting point, I was able to get the following response in a few tries (Erin's measurements adjusted to scale on top, my measurement is the dotted line):
I did this with the following DSP. Since I am not integrating the woofer yet, I ditched some of the filters. I noticed that the 7.1kHz shelf derived from JBL's DSP is low enough and wide enough to create some overshoot in the midrange, which has another filter to compensate. So I made some changes, and perhaps compensated for my driver's characteristics... Starting from POS' guide and the measured response I got, the EQ was easy and straightforward.
The settings I got on the MiniDSP are as follows:
In any case, the result seems very useable. So I turned the volume up and gave it a go, here is with the mic about 2 meters away:
That was loud! I can see a hint of the peak at distortion at 1.6kHz, but not nearly the magnitude in the reviews. Perhaps my measurement gear is not adequate to resolve. Perhaps there is something in the full integration of the speaker. Again, none of this distortion seems to be a problem, just curious.
Lastly I did a horizontal spin:
I can't wait to get woofers!
Erin's review of the M2 shows almost identical distortion. I've tried to listen for the rising distortion on the 708i, but either can't or we got too terrified with the sheer volume. I do think distortion is sometimes overblown, even if interesting.
So I just got a pair or D2430K drivers and the M2 Lens. Perhaps I can spend some idle time doing distortion measurements!
The drivers are large and dangerously magnetic
:I've had a smaller CRT TV set.
I got it propped up on my turntable, which is barely adequate:
First, I measured the tweeter in the lens with and without the crossover filters:
I was hesitant to crank the tweeter without the crossover filters, even with a protection capacitor. But you can see some of the features of the driver with and without the crossover filters.
With the crossover but no DSP, at moderate volume, I don't see strong evidence of the 2nd harmonic at just below 2kHz, and no evidence of the rising distortion at higher frequency. The distortion is dBr in this case... But even the absolute distortion is not showing the same characteristic as in the reviews.
Since the speaker isn't useful without PEQ, I applied similar settings to the the JBL M2 Crossover doc, using a MiniDSP Flex Eight. This can be done with a variety of DSP solutions.
A great starting point is the very detailed JBL M2 Crossover doc produced by @pos
You can see how JBL solved the response curve:
Using this as a starting point, I was able to get the following response in a few tries (Erin's measurements adjusted to scale on top, my measurement is the dotted line):
I did this with the following DSP. Since I am not integrating the woofer yet, I ditched some of the filters. I noticed that the 7.1kHz shelf derived from JBL's DSP is low enough and wide enough to create some overshoot in the midrange, which has another filter to compensate. So I made some changes, and perhaps compensated for my driver's characteristics... Starting from POS' guide and the measured response I got, the EQ was easy and straightforward.
The settings I got on the MiniDSP are as follows:
In any case, the result seems very useable. So I turned the volume up and gave it a go, here is with the mic about 2 meters away:
That was loud!
I can see a hint of the peak at distortion at 1.6kHz, but not nearly the magnitude in the reviews. Perhaps my measurement gear is not adequate to resolve. Perhaps there is something in the full integration of the speaker. Again, none of this distortion seems to be a problem, just curious.Lastly I did a horizontal spin:
I can't wait to get woofers!
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