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Jimbo
01-17-2007, 06:41 AM
I'm hoping someone can provide me with the correct measurements for the L-91 lenses. The 2308 lens measurments would work also. I need the flat dimensions. Thanks

Robh3606
01-17-2007, 03:47 PM
Look here. See if that helps you

Rob:)

http://www.lansingheritage.org/images/jbl/specs/pro-comp/horns-lens/page2.jpg

louped garouv
07-16-2007, 11:37 AM
anyone have the center curve dimensions of the 2395 slant plate handy? and what is the spacing distance between the plates?

thanks!

Hoerninger
07-16-2007, 12:18 PM
anyone have the center curve dimensions of the 2395 slant plate handy? and what is the spacing distance between the plates?

thanks!
Can't help with the 2395 center curve, i do only have a theoretical artilcle about lenses in general.

The distance has only to be small compared to the shortest wavelength *) (highest frequency), the material should be as thin as possible without loosing stability and without making any noise.

best regards
Peter


*)
Tipp: About one tenth of the wavelength.

louped garouv
07-16-2007, 12:31 PM
Thanks!


:)


it seems i have read a mention of a lens horn system that was able to go out to 15KHz...

must have been a spacing of the lenses issue...


I need to do some reading into the subject
(i already found the other thread with some design papers referenced)

louped garouv
07-16-2007, 01:31 PM
here...
http://db.audioasylum.com/cgi/m.mpl?forum=hug&n=7909&highlight=slant+plate&session=




slant plate acoustic lens
typical: 80 deg Horz. 50 deg Vert. coverage

[n] = 1/cos([ap])= 1.5 - refraction index (usual)
[ap] = 48.3 deg - plate slant angle from horizontal
[s] < [c]/(2*[fh] - plate spacing limit
[fh] - high frequency limit
[c] - velocity of sound in air
front surface: hyperbolic cylinder (symmetrical about x-axis)
formula: ([n]^2-1)*[x]^2 + 2*[f]*(n-1)*[x] - [h]^2 = 0
where:
[f] - distance between focal point (of circular arc wave front exiting lens) and hyperbolic apex of lens @ [x,h] = 0,0

Note: extensions to right and left are not functionally part of lens, the serve as "buffer regions" that smooth out the otherwise ragged frequency response.
Regards, Bill

now to figure out how to use the math

;)


and I thought that the JBL lenses had a "better" horizontal dispertion ~140 degrees

Zilch
07-16-2007, 05:33 PM
2395 IS spec'd at 140, but that's in trouble by 10 kHz.

The vertical beamwidth is only 10 at that frequency, and just 20 an octave lower.... :biting:

http://www.lansingheritage.org/images/jbl/specs/pro-comp/horns-lens/page4.jpg

Robh3606
07-16-2007, 07:40 PM
and I thought that the JBL lenses had a "better" horizontal dispertion ~140 degrees

It does at 1K. Figure the rule of thumb is the -6db point is your window. You can see the lobes and thing tightening up above that. If you want CD coverage you need to use a CD horn. At the highest frequencies the horn is going to control what's going on. It's still an exponential so flat on axis depends on an increasing directivity.


The vertical beamwidth is only 10 at that frequency, and just 20 an octave lower.... :biting:

I would like to see them measured with a more modern driver. A 2440 drops like a rock above 10K. That's going to skew the curves as they are essentially amplitude plots. Where are you getting 10 degrees from??

Rob:)

John
07-16-2007, 08:04 PM
anyone have the center curve dimensions of the 2395 slant plate handy? and what is the spacing distance between the plates?

thanks!

Send me a pm and ask me in detail what you need concerning 2395 lens dimensions and measurements??? :)

Are you thinking of cloning them? Perhaps I could trace a single plate on paper and mail it to you.:blah:

louped garouv
07-17-2007, 01:17 AM
2395 IS spec'd at 140, but that's in trouble by 10 kHz.



good thing i only want it to go up to 8 kHz


:D


Thanks for the explanations and replies!

:)

Zilch
07-17-2007, 05:43 PM
Where are you getting 10 degrees from??
Eargle, "Audio Engineering," p. 136.

louped garouv
07-17-2007, 10:27 PM
books on audio, who'd athunk it.....

I thought everyone was reading....


http://www.moonshine-still.com/

http://www.moonshine-still.com/Photo/thestill.gif