Project M2 DIY Thread

[ivica]

Hi Ivica,

I use a 2453h-SL on a JBL 2384 waveguide and have found the need for a 1/2" spacer. Here is a before and after:

In addition, if I rotated the CD a quarter position, the response would change, in each of the 4 possible positions. I have no explanation for that, other than the spacer is not perfect and neither is the fit - some variance in mounting. The one shown in red is the best response.

Hope that is useful.
Kind regards, Mitch

HI Mitchco,

Your 2384 horn is 'pretty larger then STX825, or PHF95HF horns, but UHF response is may be almost the same behaviors.
I only wonder is it possible than no one in JBL have not ever tried to measure the mentioned 2453SL driver with the mentioned STX825 horn, especially as there has been a speaker with such driver&horn combo, bit mentioned notch has not been empathized in the speakers data information.

regards
ivica

[sebackman]

Hi Mitcho,

That was encouraging. I have never really found a way to “cure” the dip on the243X drivers. I will try to make an adapter next week and try. I have a pair of 2453 in the shop.

The older 4” / 1,5" drivers do not show such dip.

Please also bear in mind that there are several versions of the plastic waveguide. Albeit looking similar, they do not measure the same and certainly do not sound the same.

The one you should aim for is the one in VTX F12/F15 and STX825. Part no #5006815.

The others and including PT-XXXX (or PHF-XXX) are not as good IMHO. And some of them do show a much narrower coverage pattern.

Kind regards
//Rob

[Mitchco]

Hi ivica, user notnyt on the AVSForum has measures of the 2453h-SL on the STX825 waveguide: http://www.avsforum.com/forum/155-di...r-channel.html

A 1/2" spacer is required:



Quite similar to my response on the 2384 waveguide. My system is JBL 4722 (plus subs) with digital XO at the recommended 630 Hz crossover, hence why the larger waveguide. I tried crossing higher, but the image pulls higher vertically towards the waveguide. At the recommended 630 Hz, it blends perfectly between the woofer and waveguide. Notnyt crossed at 800 Hz to the STX825.

Hi Rob, re: The 4" drivers do not show such a dip. Not sure what you mean, the 2453h-SL is a 4" driver, Ti + aquaplas. In my opinion, for the dollar value, pretty smooth response and really low distortion driver.

Kind regards,

Mitch

[sebackman]

Hi,

Sorry, meant the older 2447 & 2450SL & 2451.

Post corrected

Kind regards
//Rob

[ivica]

Hi ivica, user notnyt on the AVSForum has measures of the 2453h-SL on the STX825 waveguide: http://www.avsforum.com/forum/155-di...r-channel.html

A 1/2" spacer is required:

Quite similar to my response on the 2384 waveguide. My system is JBL 4722 (plus subs) with digital XO at the recommended 630 Hz crossover, hence why the larger waveguide. I tried crossing higher, but the image pulls higher vertically towards the waveguide. At the recommended 630 Hz, it blends perfectly between the woofer and waveguide. Notnyt crossed at 800 Hz to the STX825.

Hi Rob, re: The 4" drivers do not show such a dip. Not sure what you mean, the 2453h-SL is a 4" driver, Ti + aquaplas. In my opinion, for the dollar value, pretty smooth response and really low distortion driver.

Kind regards,

Mitch

Hi Mitch,

Interestingly (for me) that added 1/2-inch 'spacer' to STX825 horn 2453 combo
http://i.imgur.com/0Cq9ux1.jpg

would reduce UHF notch round 12kHz, but I wonder how that make an influence on the horizontal and vertical ( such driver+spacer_stx horn combo), UHF dispersion, as there (in stx825 horn) there is no throat diffraction slot as would be expected. From some JBL technical notes about 'short horn application to JBL new CD 4"-diaphragm drivers' it can be concluded that JBL tendency was produce spherical (not flat) wave front at the driver mouth, so enhancing driver dispersion at the UHF frequency. But here adding 1/2", would introduce a kind of short pipe (can be seen on 2447 driver too), forcing spherical wave front to become more planar, but may that would make an influence to the driver&horn dispersion. I have seen some measurements of the 2447 driver with STX825 horn that would produce very nice UHF response without notches, very much the same as 2450SL shown here from the forum members.

regards
ivica

[ivica]

Hi,

Sorry, meant the older 2447 & 2450SL & 2451.

Post corrected

Kind regards
//Rob

Hi Rob,

I think Your comments are well-come as mentioned drivers such as 2447 can be find in reasonable price, and putting the new 4"-SL diaphragm in it can be get very, very, very respectable driver-results.


regards
ivica

[iansr]

I owned the 4367's, then the Salon 2's and now the M2's. In my small listening room they each excelled in different areas.
I am happiest with the M2's, though I haven't heard the bass tonality that I heard on the 4367's yet. I don't have the right amplification it would seem.

Re the shoot out, it's interesting to note that one of the participants who owns M2s actually preferred the S2s on the day and because he wasn't fully satisfied with the performance of the M2s in his set up he actually went so far as to subsequently buy a pair of S2s. However, he then removed an Anthem processor from the chain and voila the M2s were back on top. I believe he subsequently sold the S2s.

[baldrick]

I got some ports today for M2 but a litle afraid that they are not «good enough». I though the vents would be larger, What do you think? The ports are 3» inside and outside are 4»

[ivica]

I got some ports today for M2 but a litle afraid that they are not «good enough». I though the vents would be larger, What do you think? The ports are 3» inside and outside are 4»

Hi baldrick,

do not worry. I think that ANY PVC or cardboard pipe 3 to 4 inch an be used, from the theoretical point of view, as can be seen on may JBL monitor speakers, and final tuning has to be made with the drivers mounted in the box.

regards
ivica

[bubbleboy76]

For those interested in running the compression driver (either D2430K or 16 ohms 2450SL/2450Be/476) directly without the lpad, there is what looks like a very nice THX headphone amp currently on massdrop that is able to put 6W into a 16 or 32 ohms load, with noise/THD specs to die for (similar to the Benchmark AHB2).

Massdrop x THX AAA 789 Linear Amplifier

...

Did anyone join the drop? I did, twice

Pos, will you add M2-settings to your document, to use without the passive network?
Edit: I found it in the document, kind of.

[pos]

Did anyone join the drop? I did, twice

#MeToo!

Pos, will you add M2-settings to your document, to use without the passive network?

Yes, I plan to, with a known protection cap value.

Edit: I found it in the document, kind of.

really??

[bubbleboy76]

The slope and -3dB frequency of the passive filter is described, so it can be added manually in dsp. That is how I interpreted it, anyways. And the LPAD-reduction.

Protection is for chickens!

[pos]

That would be an approximation, but even with the lpad the impedance is not flat enough to consider it a textbook 1kHz 1st order high pass filter.

[pos]

Can someone please confirm the thickness of the additional baffle board?
I think it is 16mm, but I also read 18mm.

[sguttag]

Hmm. My data does not match yours.

Using a Sennheiser ZP-3 Impedance meter:

No Network but the driver mounted on the wave guide:

1KHz: 33.0
4KHz: 36.6
8KHz: 31.7
16KHz: 33.0

The same measurements but now mounted in the cabinet and using a genuine JBL network:

1KHz: 43.8
4KHz: 35.6
8KHz: 34.0
16KHz: 33.4

The label on the driver clearly states 2 x 16-Ohms.

-Steve

Hi Pos,

The 2451SL's are 16 ohms and the dia's are brand new.

The D2's are 20 ohm impedance, please see post with curves above. There is a peak at 1,8kHz and one at just below 900Hz, measured with DATS sweep without horn loading.

Infact, they are almost flat impedance at 20ohms from 4k and upwards. That means that the difference between 16ohms and 20 ohms is less that 3db.

You can have the data and run in REW if you want. They are text files.

Kind regards
//Rob