Installing 2441 diaphragm into 2446 driver

[Dr.db]

Hello,

I bought a new pair of JBL D16R2441 diaphragms.
I had them installed by a technician today, but some questions remained...

The D16R2441 diaphragms mounting surface looks different to the original D16R2450 diaphragm!
D16R2441:
http://reconingspeakers.com/product/...m/#prettyPhoto[product-gallery]/2/
D8R2450:
http://reconingspeakers.com/wp-conte...2450%20(3).JPG
The D16R2441 has 8 spacers on its back.
The original 2450 doesn´t have these at all.

I´ve allways read in this forum the 2441 diaphragm is a plug&play easy swap into the 2446 driver...
What has to be done to the 2441 to make it fit ?


My second questions is about centering the diaphragm in the magnet gap.
The 2441 diaphragms had a notepad included saying that these are not self centering!
Putting these diaphragms into the 2446 drivers, there actually wasn´t much space to move anyway. We tightened the srews and put a 20hz sinewave on it and simply checked if it runs free without any rubbing.
Is that allright or do they have to be aligned in a different way?

[1audiohack]

In the AlNiCo drivers the air leak path front to rear is made under the diaphragm rings via the little pads. Going forward with the 2445 the paths are machined into the top plate.

The istalled height is the same on all of them. I made some tools and checked.

All the best,
Barry.

[Dr.db]

Thanks a lot for your help!
These tools look very professional btw.

The istalled height is the same on all of them. I made some tools and checked.

All the best,
Barry.

So I don´t have to remove these pads/spacers on the 2441 diaphragm when installing them into the 2446 core, right?

[1audiohack]

Correct, do not remove the pads.

Barry.

[Dr.db]

Done!
Thanks for your help

Btw, the voicecoil should be allignent in hight just as in the original 2441 driver.
But the air leak path is bigger in the 2446 core now. Does this cause any problems e.g. different parameters like different mechanical properties?

[1audiohack]

Not that I can tell or measure. It would seem if there was a possible problem it would be putting the newer diapragms in the older motors where they would now be nearly sealed.

I have not been able to detect any difference at small signal test levels however.

Barry.

[Dr.db]

Do I have to measure the setup with an oszilloskop ?
Or is it sufficient to run the setup with a 20hz sinewave and watch if the diaphragms moves without touching or scrubing the magnet gap?

[grumpy]

200 Hz perhaps. Careful with those zeroes Eugene.

[Dr.db]

The technician put a 20hz sinewave on them and they made aprox. 1-2mm of conemovement

I was a little scared when I saw him doing that but he told me these diaphragm can handle it...

[1audiohack]

In short, you are probably done.

If you still have a 2446 with it's ribbed Ti diaphragm in it I suggest an experiment. These are surprisingly tough. You can push the diaphragm in with your finger down to the phase plug anywhere with zero chance of damage. Clearance is about 1mm.

Put an ≈1V 300Hz signal to them, and push them around by the edges with your finger and get a mental note of what contact with the phase plug sounds like.

Loosen all the screws and push the ring around and make a note of what coil to gap contact sounds like.

You might have to file or scrape some of the plastic away where it locates in the bore to move it enough but this is what you have to do to align them most often anyway. On the AlNiCo motors I run a #30 ream in the holes for the locating pins to gain several thousandths of an inch movement.

Assuming the gap is concentric, the first requirement is to get the coil free of any contact with the gap. This is done audibly at 300Hz in the small signal range. If you are not going to play them sound reinforcement loud or with a low crossover, you might be done.

If you are going to get loud or cross them low or just want to get them as good as they can be, this is my next: with the retaining screws loose enough that you can push the diaphragm around but tight enough that it doesn't rattle, turn them up just until you hear the diaphragm contact the phase plug, push the ring around and see if you can get it out of contact. If so, turn it up until it buzzes again and push it around until you can't get it any better and tighten it down. You wont need more than five Volt's to accomplish this. I use a Crown D45 for this.

Running your finger around the parameter pushing slightly will let you know right away where it is closest and which way to move to make it better.

I know that this will sound risky yo many but you really have to do something severe to a 2450 diaphragm to damage it. Short of poking it with a screwdriver or something, your just not going to hurt it.

Once you are familiar and comfortable with the process it's quick and easy. You will be able to get on dialed in in seconds. That's not enough 300Hz signal time to hurt anything.

I made the measurement bridges to mix and match tall phase plugs to deep diaphragms. And, pushing for max HF, tall phase plugs with shallow diaphragms.

We should make a video.

Barry.

[christo]

Well since this is sort of on topic...

Where does one buy a Truextent Beryllium Diaphragm for the 2446H?

I’ve only been able to find them at The Speaker Exchange.
http://reconingspeakers.com/product/...aphragm-8-ohm/

Is this the only vendor for the BeX4008 Truextent Beryllium Diaphragm?

[Flodstroem]

We should make a video.
Barry.

We are looking forward to it Barry
Btw a very interesting research you described here

[ivica]

In the AlNiCo drivers the air leak path front to rear is made under the diaphragm rings via the little pads. Going forward with the 2445 the paths are machined into the top plate.

The istalled height is the same on all of them. I made some tools and checked.

All the best,
Barry.

Hi Barry,
What a nice instruments....

ivica

[Dr.db]

Thanks a lot for your extensive description barry!

Actually the 2441 diaphragm hardly moved in the 2446 core, there was just very little space to move. Apparently it the 2446 works self-centering, is that possible?