JBL Master Reference Monitor

[pos]

Nice, thank you!
Could you please share the impulse response wav of the close mic measurement?
This is with EQ and filter settings on, right?

[Synthetic]

It won't let me because of file size restrictions. Here are dropbox links:

Impulse(wav)
Mdat file

First graph is with EQ and filter settings. Second graph is with "FIR bypass".

[srm51555]

Synthetic,

Welcome to the forum and thank you!

Thanks,
Scott

[JeffW]

Those darn horns are $350/ea now, and the adapters are up to $120/ea Somebody say "ya snooze, ya lose"?

[pos]

Here is the close mic measurement of Synthetic's original M2s with factory EQ enabled, with the same scale as those posted here :


Here is the same measurement with 3 factory EQ points around 200Hz removed (197.5Hz, 236Hz, 254Hz):


It can be seen that these EQ are much more on point here than in either Scott's or mine clones !
There still is something around 280Hz that could probably be addressed, although it is probably a bad idea to do it based on a single measurement...
This might be due to woofer-to-woofer variations... or not.
So here is an attempt at addressing it anyway, with the following EQ point instead of the 3 points listed above:
197.5Hz, Q=6.31, +1dB (was +0.9dB)
236Hz, Q=6.56, +0.6dB (was +0.4dB)
257Hz, Q=10, +3.2dB (was 254HZ +2.6dB)
282Hz, Q=7.5, -2.1dB (new EQ point)

[pos]

Comparing Synthetic's measurement of the original M2 to Scott's it appears that the phenomenon in the 200-250Hz range are similar, but lower in frequency and slightly more pronounced in Scott's version.

Here is an attempt at correcting Scott's clones, instead of the 3 EQ points listed above:
187Hz, Q=6.31, +2dB
210Hz, Q=14, +4.9dB
225Hz, Q=7.7, -2.4dB



I am not really at ease with these high gain corrections though, especially when based on a single measurement...

In my clones the phenomenon is less pronounced than in either Synthetic's original or Scott's clones, maybe because the enclosure is deeper (~50cm) and the absorption material thicker (5cm on the back wall).

[Synthetic]

Let me know if you guys need any more measurements. You've literally saved me thousands of dollars so I'm happy to help.

[ivica]

Let me know if you guys need any more measurements. You've literally saved me thousands of dollars so I'm happy to help.

Hi,

1.
I would never suggest to do any measurements as shown on:

http://www.audioheritage.org/vbullet...l=1#post392359

as a very large influence from the floor can be get. I would suggest to lay the box on the back side of the box, put mic about 1m (or more) above the center of the driver....and then see what would be get

2.
time window has to be properly defined, but if it is too short (less then 5-10ms) resolution would be not so detailed, any how reflections have to be cut out.

3.
outdoor measurements would be preferable away from the walls.


regards
ivica

[pos]

ivica, close mic measurements are not intended to be representative of the actual response of the sepaker, but can be used to analyse certain things, like here (see posts above the one you linked).

[Synthetic]

Hi,

1.
I would never suggest to do any measurements as shown on:

http://www.audioheritage.org/vbullet...l=1#post392359

as a very large influence from the floor can be get. I would suggest to lay the box on the back side of the box, put mic about 1m (or more) above the center of the driver....and then see what would be get

2.
time window has to be properly defined, but if it is too short (less then 5-10ms) resolution would be not so detailed, any how reflections have to be cut out.

3.
outdoor measurements would be preferable away from the walls.


regards
ivica

While I agree that this would be the general procedure for capturing the full range amplitude response of a speaker, what you suggested is not the best way to characterize an individual woofer.

[pos]

Let me know if you guys need any more measurements. You've literally saved me thousands of dollars so I'm happy to help.

What amps are you using?

One interesting measurement you could do, if you find the time, is the tuning frequency of the original cabinet with an impedance measurement, or by manually finding the lowest excrusion frequency...
It is supposed to be 27Hz but that was not confirmed.

[ivica]

ivica, close mic measurements are not intended to be representative of the actual response of the sepaker, but can be used to analyse certain things, like here (see posts above the one you linked).

Hi POS,

I can understand that some things can be done in that way, but when a kind of peak or notch happened, I will try to see is there any systematic error present, because here the distance from the several flat nearby surfaces can interfere with the driver response....so may be to move a box out of the corner first, and if the response is the same, then ???? ..the driver in such box has a problem...
Have You measured the vent response, is there more the one peaks....may be some resonance in the box...we have seen such thing here on the Forum

Regards
ivica

[ivica]

While I agree that this would be the general procedure for capturing the full range amplitude response of a speaker, what you suggested is not the best way to characterize an individual woofer.

Hi Synthetic,

So I can conclude:
that is OK for the box measurements, but not good for the drivers response individually ? ...interesting....

ivica

[pos]

Ivica,
A close mic woofer measurement should be immune to reflections from boundaries.
Albeit not representative its purpose here was to compare the reponse of our clones with an original M2, as a target.

Regarding port measurement, most of the resonances that I measured under ~150Hz through the woofer also appear there:

[Synthetic]

What amps are you using?

One interesting measurement you could do, if you find the time, is the tuning frequency of the original cabinet with an impedance measurement, or by manually finding the lowest excrusion frequency...
It is supposed to be 27Hz but that was not confirmed.

I'm using a Crown XLI 2500 per speaker.

I'll get an impedance measurement, but it'll be a little while. You might have to explain a little more on the second option. How would I do that?

I did a close mic of the port. Looks like 22Hz?


Also I took more close mic measurements at 3 different spots on a different m2. They all have that peak at ~282Hz.