ribbed vs plain diaphragm in 2445 and 2447

[mini]

Hello,

Some weeks ago I launched a query on whether it would be possible to interchange the 2445 diaphragm with the 2447 one. You told me, it would at least not smash the phase plug. Well, it didn't.

The result is stunning. I measured both dias mounted to a 2447 driver attached to 2352 horn. In the range from 5kHz up the ribbed 2447 dia is more efficient than the plain 2445. The motivation to interchange the dias was a suck out with the original 2447 at 10kHz. Using the 2445 dia solves the problem in that frequencies around 10k are attenuated. The suck out shows to be a lift that unfortunately ommits the 10kHz area. O/k, plus some extra dB or two.

What would have come next was a try with the 2445 driver equiped with the 2447 dia. I can't do so. It was of no use to investigate a raw driver on the kitchen table. And I'm told not to mention my EV HP940 ever again. In spite of I could remount my 2360, but that's a huge issue.

regards

[mini]

What would have come next was a try with the 2445 driver equiped with the 2447 dia. I can't do so.


The 2445 with the ribbed dia is a 2446, isn't it? I checked it out yet and it works slightly better on the <no/no>-horn as before. Some remember this earlier one as being to good to be mentioned in this !JBL-forum.

As to summarize it was a win - win - thing. The 2445 evolved to a more modern 2446. The 2352 is way better than before now too.

Thank You for encouraging me to do the swap.

[subwoof]

The 2446 has an improved phase plug ( so does the 2447,50,50SL,51 ) over the older 2445 ( and 40,41 ) as mentioned before so it isn't a fair compare pierre...:)

Next you should try a coated diaphram in the same setup to see the difference in the HF response.

sub

[mini]

The 2446 has an improved phase plug ( so does the 2447,50,50SL,51 ) over the older 2445 ( and 40,41 ) as mentioned before so it isn't a fair compare pierre...:)

Next you should try a coated diaphram in the same setup to see the difference in the HF response.

sub

Yes, that is the next trial my 2447s have to face. But the all so new plug in the 2446 misses to be "patented" as the so called "coherent" one in 2447. This should bother You, as it makes a two fold difference from 2445 - 2446 - 2447 regarding being "new" and "mathematically" something.
The Italian company 18sound discussed the plug theme cause of an own innovation regarding that. From their perspective any radial (Altec tangerine) and anular design has to be considered as old fashioned. Not to forget BMS Germany with 1"-2" ring radiators being innovative in that field too.

The effect of the ribs on the dia is what makes the difference. Strange but for sure the 2445 on <no/no> horn raises quality from that ribs and the 2447 the other way round gains even more on 2352 horn with the plain one.

mini

[mini]

Yes, ...

Hi,

The swapped diaphragms kept their signature in harmonic distortion. Measured with ARTA the ribbed 2447 dia shows a very fine peak in 2nd HD at exactly 8kHz. The plain 2445 dia shows a similar peak but at 10kHz.

All 4 dias have been thoroughly mounted and centered far beyond the common 2.83V sweep test. From the swapping I can tell that it is neither an effect of the plug/centering nor does it depend on the horn.

Before speculations from where these very fine lines in the HD spectrum come from I would highly appreciate any comment on similar experiences. It does not happen with other driver/horns from different suppliers. It's genuine JBL so far!

Thank You

[Robh3606]

The swapped diaphragms kept their signature in harmonic distortion. Measured with ARTA the ribbed 2447 dia shows a very fine peak in 2nd HD at exactly 8kHz. The plain 2445 dia shows a similar peak but at 10kHz.

Why don't you post the plots?? May be related to the compliance resonaces.

Rob:)

[mini]

Why don't you post the plots?? May be related to the compliance resonaces.

Rob:)

Hi,

as to avoid speculations. You did some: compliance, and that is what I thought in the first place. The ribbed one may resonate more in a whole while the plain one spreads the resonance by break up modes. The peak is wider with the latter. The freq. lower with the first.

But what about Your own experiences with JBL 4" dias?

Level out of scale! May be it was 110dB with a very rough CD eq. by the amps treble control. The 2445 in that famous patented 90x40 <no/no> horn had to be attenuated by ~ 6dB due to its higher efficiency. Same level acoustically though.

Distortion levels have to be read as -20dB ~ 10% -30dB ~ 3% -40dB ~ 1%
K2 is prominent while K3/4 are stuck below noise leves @~-70dB.

Nasty peaks @8k, 10k resp., aren't they? It may earn to have a look at the distortion levels regarding that special phase plug within the 2447. The <no/no> horn loads pretty low down to 350Hz or so.

1 up here! ) Driver 2445 (2") with ribbed dia from 2447 in that glossy grey horn with fins in the throat.

2 down below!) Driver 2447 (1.5") with 2445 dia on JBL 2352 horn.