2450SL vs 2452SL

[pos]

Both share the same 1.5" aperture, same bolt pattern, same diaphragm, same flux in the gap, but the 2452 only weigths 2kg whereas the 2450SL wigths more than 4kg.

The 2452 core looks like a lower price evolution of the 2450SL/2451 core.

2450SL:



2452SL (pictures from Zilch):


For one thing, the back cap looks smaller, and the damping pad is also much smaller.
Any idea on what was given up during this transformation?
Low freq extension? (not really useful anymore with these rapid flare deigns)
Flux "stability" ? (if that makes any sense)

It is interesting to note than JBL came back to the older bigger design as the root of the 476 core:

[subwoof]

The 2450SL magnet design first came out in 1989 so it's an old one by todays standards. Better mfg methods, magnet design / composition mean smaller mass all around.

Do you still have your 19" computer monitor from then?? a tad bit large?

And the consumers who pay that kind of money for a top-end driver want to look at it too. The rest of us hide them in cabinets and listen..

[pos]

But then why did they go back to the bigger magnet for the 476 core? Only to include the longer copper sleeved pole piece?

And what about the effect of the smaller back chamber?

[grumpy]

could be that the industrial design for the 476 cap (sort of matching in theme
with the 1500AL "Legion of Doom headquarters" look) was completed early on...
requiring a 4-hole cap mount pattern (vs the three, in the 2452 assembly)

... and one could certainly insert more effective back damping material into
a deeper cap... I'm missing a 476 to do a 3-way comparison.

all pure speculation, of course (no smiley).

[subwoof]

The 476 was specifically engineered to work with the Be diaphram. There is a recent post describing it somewhere here. My bet is that they needed a little more room inside for the mods and therefore went with the larger size structure.

And the backcap measurement fiasco was also documented here and it was determined that the extra volume did not impart any better LF response.

sub

[grumpy]

right... acoustic venting under the suspension, and the copper pole piece sleeve.

you could be right about the ability to perform further mods on the older/larger case/motor
assembly (more modular?)

I remember the back-cap discussions, measurements and that the FR's looked
essentially identical in the area of interest. That put it to bed for most, and rightly so for most uses.

I was thinking more about absorption of delayed/reflected HF energy...
more difficult to sort out at home, and more pertinent (maybe) with diaphragms
that have a smooth(er) extended response, such as the Be. I should go back and
refresh my memory re what was measured and how.

[pos]

Would you have a link to that particular thread?
I remember reading some 435Be/2435 comparisons, but nothing about 2452/2451/2450SL

[grumpy]

you might be right... I -know- there were 3" dia rear cover comparisons,
I could just be imagining such a 4" version/thread.

I don't have time to tackle this right now (or a larger rear cover).
If someone thinks it sounds better with a bigger cap or certain
pad material, I have no need or reason to argue.

[pos]

I just noticed you created a similar thread not so long ago:
http://www.audioheritage.org/vbullet...2H-SL-question

I even remember having read it now...
sorry

[grumpy]

no problem for me. I hardly remember writing it
nothing about rear caps though...

I've been using the 2450SL cores with TruExtent dias
and haven't even felt the urge to measure. I have a single
2452H that came with a dead diaphragm, so if I ever get
the urge to start up yet another measurement thread,
I'll be sure to post some comparisons (and try to remember
to include a with/without rear-cap set).

[subwoof]

The aforementioned back cap discussion was for the 3" not 4" coil but one could interpolate similar results.

And for interest: the air volume behind the sealed 2416 type diaphram is pretty tiny and they were still used to 1000hz in some of the older SR boxes...even though the motor structure is very similar to the 2426. They were rated at lower power (I think) because they just couldn't get rid of the heat. 90% of the ones that came in bad were bubbled.

Haven't had a chance to play with a 476 so all I know is what I read but it looks to be a specific design that wasn't required to "back" fit into existing applications ( like the cone were....)

[JeffW]

1audiohack has a 2452 and a bucketful of diaphragms including TruExtent that he's going to measure when time allows. Not sure what kind of horn he'll use.

[grumpy]

Cool

[cooky1257]

I now have 2452's with Truextents and can say they sound lovely.
The pad in the 2452 back cap doesn't feel like it is absorbent at all-it isn't felt or foam to these eyes anyway.

[pos]

Nice! How much of an improvement is it compared to your 2435? And how is the UHF, also compared to when you used the 045ti?

Concerning the 2452H damping pad, I can see a recurrent dip at 3khz on my measurements on different horns, and I was wondering if this could be the cause... But it sure does not appear on any other measurement by other people I have seen so far (though smoothing blurs it quickly).

Concerning the magnet assembly, looking at the curves from the 2452SL spec sheet it looks like the impedance is rising fast in the highs (x2.3 between 4khz and 20khz), whereas it is more stable on other modern 4" drivers: look at the second graph (plane wave tube measurement) of the 2451H. Is is difficult to compare because the impedance scale is in log, but you can see that it is lower at 20khz than the peak at resonance ~600Hz, contrary to the 2452.
So, lack of copper pole caps?...
Anyway, the 2452SL seems to maintain a good efficiency in the highs, similar to what you would expect from a 2450SL...
Maybe that is due to the stronger flux density in the 2452: 1.9T vs 1.875T for the 2450H, and BL 12.8 vs 12.7.


EDIT:
I just pulled the trigger and bought a pair of 2450SL.
I also have a pair of 2452H (not SL) here, so I will try to measure them on the same horns with the same diaphragms.