JBL 2446 and JBL 2450 throat size

[David Ketley]

JBL 2446 and JBL 2450 throat size?

I'm a bit perplexed the stated throat size of these drivers is 2" but they only measure 1" and 7/8" whats going on?

Of course this means that matching them to a horn gives 1/16" all round on something that is supposed to be quite critical!

Dave

[1audiohack]

I have always measured them about 1.900-1.950". In any event, thats about where they have always been. At least since the 2440-2441 (tel:2440-2441) days.

Barry.

[David Ketley]

JBL 2446 and JBL 2450 throat size?

I'm a bit perplexed the stated throat size of these drivers is 2" but they only measure 1" and 7/8" whats going on?

Of course this means that matching them to a horn gives 1/16" all round on something that is supposed to be quite critical!

Dave
Are the JBL horns a fit for these drivers or do they also measure 2"? Is this critical, is it worth trying to add material to get a better match?

Dave

[more10]

The exact throat size is 49 mm, or 1.92913386 inches. http://www.fullcompass.com/common/files/7948-2446.pdf. I have no idea how come the throat of all JBL large format drivers and horns is not exactly 2 inches.

[David Ketley]

The exact throat size is 49 mm, or 1.92913386 inches. http://www.fullcompass.com/common/files/7948-2446.pdf. I have no idea how come the throat of all JBL large format drivers and horns is not exactly 2 inches.

2" = 50.8mm so its about 1 mm out all round most peculiar. I've added some material to my adapter to bring it into alignment but I doubt if I can hear any difference.

Dave

[more10]

If you want a machined adapter there is a a drawing in my thread at diyaudio: http://www.diyaudio.com/forums/software-tools/267850-python-script-generating-exponential-throat-adaptor.html

[more10]

JBL horns should have a perfect fit.

[fpitas]

My guess is the driver opening is purposely sized slightly smaller than the horn opening to avoid a "step" sticking up into the path, in case the driver opening is slightly misaligned with the horn opening.

[remusr]

The 2440 spec sheet lists horn throat dia at 2 inches (5.1cm). From 2441 the dia is 49mm (2 in). So the 49mm = 1.929in is rounded to 2 in. The reason as noted above is likely to avoid a step up if not exactly aligned. Acoustics are like aerodynamics where a relatively small panel step up initiates significant interference waves, whereas a similar step down is almost inconsequential.
I checked 1" CD spec sheets from 2410 to 2426 and all show 25mm (1in) as horn throat. 1in is 25.4mm.

[more10]

2380a specification ( http://www.jblpro.com/pub/components/2380a.pdf)


49 mm (2 in) throat entry

If the fit is not perfect it must be JBL tooling not beeing accurate

[more10]

http://www.audioheritage.org/html/history/lansing/to_1981.htm


The Western Electric 594 driver, long absent from professional sound, was effectively "re-invented" using Alnico V as the model 375

The exit size is probably the same as WE 594

[more10]

The 2440 spec sheet lists horn throat dia at 2 inches (5.1cm)

I believe the 2440 spec sheet is wrong.

[1audiohack]

I think they just used the American pipe schedule for measurement. For instance, there is no dimension on a piece of "half inch" pipe that measures 0.500". Even the threads are tapered so where does one measure that?

The only thing close to measuring 15" on a JBL 15" woofer is the outside diameter of the front gasket and the surround OD major, not the basket OD, not the mounting hole circle and certainly not the cone diameter.

In the end, does it matter? Does a step in diameter of 0.050" total or 0.025" per side mean anything in something with no mean flow where the wave length/partical motion is less than 0.650"? I don't know. I suspect Earl Geddes would emphatically shout yes at the same time shouting from the rooftops that no one can hear harmonic distortion in a compression driver.

Often there is a support bracket sandwhiched in between large format drivers and horns, this is an interruption in cross sectional area, is it an issue? What about squezzing it all through a 50ish micron screen? How much of an area reduction is this? Or is this calculated?

I realize that this is not an answer, in any universe but I don't worry about stuff like this, I just don't.

Ignorance is bliss and life is good!

All the best,
Barry.