JBL Master Reference Monitor

[pos]

Hi POS,
Ma be interesting study of : Maximizing Performance from Loudspeaker Ports

http://koti.mbnet.fi/jahonen/Audio/P..._PortPaper.pdf

regards
ivica

Interesting paper, thank you Ivica.

Here is the patent listed in the M2 brochure:

https://www.google.com/patents/US7890312
as a pdf: http://www.patent2pdf.com/pdf/07890312.pdf

[Valentin]

Hére aré some pics. Of the M2







The internal measurements are
28cm deep
45cm wide
116.5 tall

all bracing is 21mm mdf

the woofer is in the exact center of the enclosure

[pos]

Thank you so much Valentin!

So based on your data, the exploded view, and actual external dimensions (from Don McRitchie), it looks like the walls are probably 1"... or maybe a little more:

width: 500mm exterior (the JBL description states 508mm ?...), 450mm interior, which leaves 2*25mm for the walls (or 2*29mm if using JBL's dimensions)
height: 1220mm exterior (ignoring the 12mm "plate", and the feet), 1165mm interior, leaving 2*27.5mm for the walls. Might the interior dimension be closer to 1170mm?
depth: 350mm exterior (ignoring the waveguide/additional baffle/grille/port plate), 280mm interior, leaving... 2*35mm for the walls???

On the exploded view it looks like the rear wall in indeed thicker, but it might just be the perspective.
The front baffle already has an additional ~12mm wall (to line up with the external gasket on the 2216).
So it might be something like 25mm for the front baffle (+12mm from the additional baffle), and 45mm for the rear one?...
That seems a bit too much.

Any though?

[Valentin]

Thank you Valentin!
Is there a tubular part in the middle, or is the profile constantly changing?
Could you measure the smallest diameter inside the tube?

I think a 70mm tube with large inner and outer flares needs to be around 8" to get a 27Hz tunings in a 140L box.

There is no tubular part in the middle it is a two part port and it is symmetrical the fiscal length is 16cm the inner diameter is 60mm or so I could not get it exact
it has a constant curvature
hope this helps

[pos]

I also noted two interesting things in Valentin's photos:
- The M2 has a "M2 D2430K" sticker on it, which would support the idea of a specific (sorted?) D2430K version for the M2 (different part number, no diaphragm available, etc.)
- The small Wima cap is a 3.3uF, and the PCB is marked "rev B" whereas the value of the smallest cap in the original (rev A?) network published in the technical manual is 4.7uF.

[pos]

hope this helps

This helps a lot!

[Valentin]

Thank you so much Valentin!

So based on your data, the exploded view, and actual external dimensions (from Don McRitchie), it looks like the walls are probably 1"... or maybe a little more:

width: 500mm exterior (the JBL description states 508mm ?...), 450mm interior, which leaves 2*25mm for the walls (or 2*29mm if using JBL's dimensions)
height: 1220mm exterior (ignoring the 12mm "plate", and the feet), 1165mm interior, leaving 2*27.5mm for the walls. Might the interior dimension be closer to 1170mm?
depth: 350mm exterior (ignoring the waveguide/additional baffle/grille/port plate), 280mm interior, leaving... 2*35mm for the walls???

On the exploded view it looks like the rear wall in indeed thicker, but it might just be the perspective.
The front baffle already has an additional ~12mm wall (to line up with the external gasket on the 2216).
So it might be something like 25mm for the front baffle (+12mm from the additional baffle), and 45mm for the rear one?...
That seems a bit too much.

Any though?

Yes the walls are 1" and the front baffle has an extra 15mm in the woofer position more in the port area
yes the high may be 117cm it was difficult too measure since I had to remove de fiber too some extent and with the laser measure it was not easy

but the interior depth and wide are correct

[pos]

This is the small cap: http://www.ebay.com/itm/2pcs-WIMA-MK...item233124e482

Wima MKP 10, 3.3uF, 250 VDC / 180 VAC

[4313B]

Thank you very much Valentin!

So ~ 46" x 17-3/4" x 11 " = 5.2 cubic feet gross volume.

[macaroonie]

I'm wondering how you chaps are planning on going about making the curved front of the baffle.

Sure you can shape the add on 15mm but as we know MDF gets a bit nasty on the inside , all flaky and fibrous. This then leads to added complication with finishing if you are going for a paint finish.
Veneering , not so bad as CA can be used to stabilize the MDF core.

In my various researches I have come across a company in the US that does a natty line in curved birch plywood , even tubes.
I seem to recall them doing curves up to 96" radius.

http://www.aitwood.com/

http://www.roberts-plywood.com/

Plenty of scope for some alternative methods.

M

[cooky1257]

Yep finishing an mdf curved panel is a pain, that's why I covered mine in leather.

[Mctwins]

Nice Pictures

[Flaesh]

.. specific (sorted?) D2430K version for the M2 (different part number, no diaphragm available, etc.)..

so reconingspeakers's "JBL D2430K Tweeter for JBL M2 #5032754X" may be not "JBL D2430K Tweeter for JBL M2"?..

[Earl K]

so reconingspeakers's "JBL D2430K Tweeter for JBL M2 #5032754X" may be not "JBL D2430K Tweeter for JBL M2"?..

What pos says makes sense ( & that philisophy usually applies to any studio monitor ) .

ie ; Studio monitors generally get loaded with more tightly matched ( hand-picked ) components ( that actually live up to the design specification ) .

I doubt that the common guy can buy "the very best" D2430K drivers .

[Flaesh]

I doubt that the common guy can buy "the very best" D2430K drivers .

Will see at the end of the month when, as reconingspeakers said, they must be in stock.