New Product Development - 2402/075 - Can You Help?

[toddalin]

Maybe not so classy as a 3D printed/injection molded stand, but this will work and carries the lines of the JBL original mounts. These will be 3/8" acrylic and I can do colors. Cost on these should be fairly reasonable.

[Doctor_Electron]

In accordance with the theory, the plates have to be less than 1/2 wavelengh spacing. I used 0.35", similar to JBL, that takes it over 19kHz..., higher than the 075 can go.

For the size, I used the HL-91 lens dimensions, but scaled them to the the diameter of the tweeter rather than the horn throat.

OK, the HL-91 or a flat-front biradial or a CD horn are the acoustic "transformers" to match, within physical constraints, (horn diameter and length) the diaphram's acoustical impedance with the air mass of the listening area.

For example, excluding the crossover network, the mid-range subsystem of the JBL 4350 Studio Monitor :

Midrange Driver: 2440 2" Compression Driver

Midrange Horn: 2311 2" Short Exponential Horn

Acoustic Lens: 2308 Slant Plate

Point being, in the midrange subsystem cited above, the 2440 compression driver "needs" the 2311 short exponential horn for impedance matching, and "needs" the 2308 slant-plate lens for impedance matching and to define the horizontal and vertical pattern characteristics.

But the 2402 and 2405 ring radiators are designed and manufactured with their acoustic impedance matching and pattern control built in, by way of their throat and phasing element geometries.

My question is, what will be the effects on the horizontal and vertical patterns due to the interaction of their intrinsic elements, and the slant plates? A lens is a lens. Something(s) will change. I know it can be worked out mathematically
and I wish I had those skills but do not.

How else could one predict the outcome? I think your RTA equipment will tell the tale. Ultimately, how will it sound ?

Regards, -D_E-

[toddalin]

Ultimately, the bean counters win out.

If the slant plates were truely "engineered" to the individual horn/driver combination, one would expect that the plates for the HL-91, 92, and 93 could all be optimized to that combination..., but they're not. Furthermore, each plate measures 10" across x 3" deep. Do you think that these values are based in "audio physics," or the ability to make them in production at some cost?

Similarly, the big oval horn came without a lens (Paragon) an BIG slant plate, like Keith Emerson used, a wavy slant plate (Hartsfield), and a midsized slant plate (maybe more?). If "one design" is superior for that horn, why bother with the others (maybe different throw for different venue?) BTW, the wavy plates were a nightmare, and I can't tell you how many were tossed out at VOX because of bends and dents.

Without the slant plate, the HL 91, 92, and 93 will have a circular dispersion pattern (like a ring radiator). I don't know how many degrees of coverage you get, and I've never seen a published number. I would expect the lens in front of a ring radiator would have a similar effect. We'll see.

[Odd]

If one wants to read up on the subject it is much and find here;

jbl acoustic lenses

and more

[toddalin]

I was able to get on the laser today to try to make some parts. Between the four programs used in this, there was some rescaling, but I'm getting it figured out.

The stand.

I need to move the holes out about half a millimeter and open them up a bit more. Also, I'll redo the top angles just a bit.



The drawing file for the feet did not convert properly. The picture was not dead on center when the draweing file was produced so this displayed additional (background) lines in the final file that also cut and the foot fell apart from the extra cuts. I'll get it next time.

Oh, and the image on the left could look nice on there. Nah, I couldn't do that.



This shows the slant plate assembly. Again, the sizes did not convert properly. The plates will actually be longer/deeper such that the portion that extends back hugs the outsides of the vertical stands. Also, the "backs" of the diagnol cutouts that hold the plates should be revised to be parallel with the back of the slant plate, rather than at 45 degrees to the back of the plates for a better fit/look.

[toddalin]

I got on the laser and made some parts today.

It took a few tries to get the flare "just right" (lower plate), but this is now very similar to the factory flare. The 1/8" plates show no sag or the need for spacers.



Here you can see it assembled on a tweeter. The uprights will be 3/8" rather than 1/8" and will fill the void space and provide more strength.

[BMWCCA]

Very nice! It's really coming together.

[toddalin]

Voila!

[BMWCCA]

Very nice!

[ivica]

...

Hi toddalin,


Nice work, my congratulations !
But I wonder, how such project would behave relative to the 2405 'slot horn' type "young brother", especially in F/R and off-axis response.

Regards
ivica

[toddalin]

We'll find out. I have some.

[toddalin]

[grumpy]

Interesting look. Why stop at just the mini version?

[audiomagnate]

So the size of the blades has no relation to the wavelengths of the frequencies the driver is emitting?

[grumpy]

If you were referring to my comment, I just meant why not laser beam out some 2308 replacements...