JBL Master Reference Monitor

[dprice]

Anyone working up cabinets with a less boxy design? More like something from the K2 series perhaps with curved sides? Suggestions?

Also any tips on how to build a curved grill would be appreciated.

[ivica]

Hi M2-lover,

Finally some more measurements from other source.

http://www.soundandrecording.musikma...or-Testbericht

may be helpful, for DIY EQ applications.

reagrads
ivica

[Flaesh]

I came here with the same link .. I think POS will also)))

[pos]

Very interesting measurements indeed! Those German magazines always have good tests with in-depth measurements.
Too bad this article can only be get on paper, as personally I would need a translation tool to read it...

I will upload the relevant images here so they are not lost (never ever, as this forum will live forever).
I will also offer my humble interpretation, to hopefully start a discussion. Comments/corrections are welcome.

Independent driver frequency response with EQ engaged:


The acoustical LR 36dB/oct crossover at 800Hz is clearly there


Independent driver frequency response without EQ and filters (only passive network I guess), and independent EQ+filters response:


That one is very interesting.
The 2216nd response clearly matches the EDS in the stopband, with similar breakup peaks at similar positions.
This was not the case with Magnus' 1501Fe

The crossover closely matches the simulation made with rephase based on the extracted parameters in my google doc:
https://goo.gl/GdfQ7N
(rephase LF and HF presets to be found page 9)

Here is an overlay of this simulation and the actual measurement:



The only difference is up high, with a steady ~1.4dB drop in the measurement. I don't know how they measure the crossover response (IIRC the crown amp has no line output, so it is tricky) and if they compensated for the actual response of the DSP/amplifier, but looking at what happens above 20kHz it is possible that the UHF response is not completely accurate. It is also possible that the IIR biquad implementation in the DSP does not interpret Qs accurately in this range (this is a classic behavior with biquads)...
This will change from one IIR unit to the other, even with the exact same settings.
I would love to see a measurement of the BSS for example...

I also did a simulation of the averaged "listening window" response of the D2/M2 waveguide combo based on the EQ settings and actual acoustical target here.
It looks like it matches the actual on-axis measurement pretty well, as can be seen in this overlay here:



It has to be considered while keeping the on-axis vs listening-window response differences as shown here:



Interestingly in the end it looks like they did not go as far as making the on-axis response rise in the UHF to get a flat listening window curve


To be continued...

[pos]

Next comes the max SPL measurement:


Some contextual info from the article would be nice to have here...
But hey, we already know that compression drivers do generate a lot of 2nd order distortion up high, especially on CD horns.
We also know that it is barely a problem

CSD:


CSDs are always difficult to interpret and compare (to much variables and parameters...), but it looks like some breakup "smear" can be seen in the upper band of the 2216nd. Of course this was to be expected, but we would have to see other 15" drivers (2235H, 1500AL, ...) measured in the exact same way and visualized using the exact same CSD parameters to quantify what we are looking at here.

Horizontal polar plot:



Vertical polar plot:



These are normalized based on the on-axis measurement, whereas the speakers are EQed based on the averaged listening window.
This makes analyzing the actual directivity behavior a bit difficult.
What can be seen for sure is that the LF/HF transition is seamless in the horizontal plan.
The crossover is of course more visible in the vertical plan, but at least the acoustical LR provides a very good symmetry.
Reducing the c-c distance (by either turning the horn 180° of cutting the leaps) should have a positive effect on the size of the frontal lobe (ie the angle of the -6dB trace).
Another notable phenomenon, also to be expected (and already shown in the spinorama) is the narrowing in the UHF.
It looks like the narrowing starts earlier on the horizontal plan than on the vertical one.

[pos]

Next come two measurements that I don't know how to interpret.
Maybe the article would give some clue on these.

IMD and THD: (not clear for me what is what here)




?? :

[dn92]

pos,

Scan the magazine M2 article pages and mail it to me. I'll try to translate as much as I can, at least parts explaining the graphics.

Regards

[pos]

Hi dn92,

Thank you!
I tried to order the paper version and then realized there actually was an option for getting a pdf version!
No sure the text can be copied though.
I should receive a download link soon, maybe tomorrow, and I will send the article over to you.

[pos]

I edited post #1085 because my interpretation of the first graph was way off.
I hope to get the article tomorrow, some contextual info will be helpful...

[Flaesh]

Some contextual info from the article would be nice to have here...

from another forum

It shows the distortion limited SPL. That means that each frequency is measured independently and volume is increased until 1% (or in this case 3% and 10%) total harmonic distortion is reached..

[ivica]

I edited post #1085 because my interpretation of the first graph was way off.
I hope to get the article tomorrow, some contextual info will be helpful...

Hi POS,

Thank You for the presentation of M2 from other sources then JBL marketing department. It confirms Your measurements for EQ VHF driver&horn combo.
For me there are just a few expectable thing:
-M2 driver would introduce about 3% THD on about 100-110 dB SPL/1m (so about 1W power)
-M2 horn loading in 500-2000kHz region is not something that would be perfect, and is expected due to fast flaring horn walls, such as hyperbolic (OSWG) horn does, 4cm short 'pipe' throat help a little,
-M2 horn horizontal dispersion is nice up to about 10kHz, for the higher frequency it become beaming to about +/- 20deg at near 20kHz
-around 10kHz, horn horizontal dispersion is about +/-30deg off-axis
-passive network VHF driver&horn combo would be very difficult do be realized if almost flat on-axis response want to be get,
-on-axis response over, say, 12kHz is not flat but almost +6dB/oct rise sloap,
-the non-EQ bass section response is fare from the old JBL bass speakers response, so I believe , one day we can hear that a kid of sub-woofer would be welcome.
-THD introduced by the bass driver in the mid-bass region is remarkable (120-130 dB/SPL/1m), so 2216ND can be suggested as very,very good mid-bass driver.
-vertical dispersion 'holes' around crossover frequency are expected due to the LF-VHF drivers displacement, and can not be compensated anyway.

regards
ivica

[pos]

from another forum

Yes, that is what I figured out afterward, I had it backward...
Still the title is not that clear, for example what is that 115dB thing, and why are they looking for the 10% mark only under 300Hz?

[pos]

-on-axis response over, say, 12kHz is not flat but almost +6dB/oct rise sloap

That is what the spinorma says, but the measurement in this article says otherwise.
So in reality what can be anticipated is that the listening window curve will drop above 10kHz...

[srm51555]

Thanks everyone for your time and efforts on this, they are appreciated.

[Valentin]

Keep the info coming POS
Thanks

hope you you can translate the article