How to tell the condition of diaphragms?

[martin2395]

I was wondering, how do you see when an Alu/Ti diapragm is in good condition and when it's in need of replacement?

Do they change the colour, crack or so? What do you think of these, are those Ti's or Aluminium?

http://nl.tinypic.com/r/2m4f5zm/5
http://nl.tinypic.com/r/rwl6qt/5
http://nl.tinypic.com/r/15czf9v/5

[yggdrasil]

That's Titanium. Aluminium are much brighter.

For home use these dia's are very close to indestructible.

Did I see a dent? If so you can be sure that they have got a real beating, and you will have to consider exchanging them.


Johnny

[martin2395]

There is a dent but i think it happened because someone used a magnetic screwdriver and it got pulled against the dia :D
Of course they are probably quite worn out after many years in SR in some RH cabs.

Ti, blargh! I think that I will simply buy a pair of Radian 1245-16's.

[ivica]

There is a dent but i think it happened because someone used a magnetic screwdriver and it got pulled against the dia :D
Of course they are probably quite worn out after many years in SR in some RH cabs.

Ti, blargh! I think that I will simply buy a pair of Radian 1245-16's.

I think the best would be to do some measurements using horns for which the response of the new diaphragm is known.
My experience with 4-inch diaphragm (JBL) is that used (heavily) diaphragm would produce some less level at the lower frequency (say from 1khz to 3kHz) and some more around 8Khz to 10kHz, then dropping more.

http://www.audioheritage.org/vbulletin/showthread.php?28758-JBL-2445_46-frq-response&p=339942&viewfull=1#post339942

May be THD measurements would help too. I think that used diaphragm suspension become stiffer (but I have no confirmation).

reagrds
Ivica

[martin2395]

Yes, measuring is always the best. Who knows, maybe these old Ti's are still ok :dont-know:

I haven't noticed a big difference in output between the 2441 and 2421, the 2441 are a bit more airy/detailed.
It's always a lottery with drivers used for SR, you never know how they were used. Mine look heavily used but maintained well - they have new foam pads and cleaned connectors.

[more10]

Ti 4" diaphragms starts to breakup at 4 kHz. Aluminium at 7 kHz. Be at 15 kHz?

[martin2395]

Thankfully I don't have to hear them trying to do 15KHz, they cross at 9KHz with 2405's.

Before I order a pair of Radians i'm going to find someone to measure these old Ti's, i'm wondering how good(bad?) they are now.

[ivica]

Thankfully I don't have to hear them trying to do 15KHz, they cross at 9KHz with 2405's. Before I order a pair of Radians i'm going to find someone to measure these old Ti's, i'm wondering how good(bad?) they are now.

Hi martin2395,

Just for the reference I have done some measurements with two 2441 core and two Radian 4" diaphragm model: 1245-16. JBL horn 2311 and 2308 lenses were applied

The third figures: two drivers JBL 2450J with (D16R2445 == Ti-noRIB) diaphragm with the same horn&lenses
(2311 & 2308) are shown.

Regards
ivica

[martin2395]

Hi Ivica,

The Radians in 2441 certainly look better than Ti 2450's!
But what is the difference between graph 1 and 2? The 2nd has a smoother curve but also a major drop above 10k.

[ivica]

Hi Ivica,

The Radians in 2441 certainly look better than Ti 2450's!
But what is the difference between graph 1 and 2? The 2nd has a smoother curve but also a major drop above 10k.

Hi martin2395,

I have done measurements of TWO 2441 drivers with TWO the Radian 1245-16 diaphragms. Why the measurements differed too much I have no explanation.
May be because of the diaphragms characteristics or drivers magnetic field. May be some answers can be get if the the diaphragms be exchanged between the drivers, but (now) taking them out of the boxes would be very (heavy) difficult task to be done. May one day I will do that.
May be using up to 12-13kHz would be possible.

Regards
ivica

[martin2395]

Ah, thanks for the explanation!
Indeed one of the drivers could have weaker magnetic field or the VC gap could be different (serial number, oxidation?).

I know that removing or installing those drivers is a major pain. I almost crushed my figers while installing the front panel of my 4343's with tho 2441 mounted to it.

[ivica]

Ah, thanks for the explanation!
Indeed one of the drivers could have weaker magnetic field or the VC gap could be different (serial number, oxidation?).

I know that removing or installing those drivers is a major pain. I almost crushed my figers while installing the front panel of my 4343's with tho 2441 mounted to it.

Hi martin2395,

I am preparing to "convert" my 4333 (DIY) in to "small 4343"(DIY) using 2235H+E110(K110?)+2441+2405
While doing that I will do some experiments with 2441s.

Regards
ivica

[frank23]

Martin and I have to meet up sometimes, it turned out we live just 30km apart!

I just posted something related in this thread:
http://www.audioheritage.org/vbulletin/showthread.php?34847-Upgrading-from-2421B-to-2425J&p=357736&viewfull=1#post357736

[martin2395]

Ivica, it looks more like 4340/4341 than 4343 ;D


frank23,
I'm always open for a meeting but transportation is a problem since I haven't got a car and my dad doesn't give much about hi-fi stuff ;)
I was even thinking about some kind of meeting for JBL fans this summer.

[ivica]

Ivica, it looks more like 4340/4341 than 4343 ;D
.....

Yes, You are right, 4340/41, but small size ( box 4333 size)

Ivica

[martin2395]

I ordered a pair of Radians today, hope to receive them on monday/tuesday. I will also give the 2441's a good cleanup.

Btw, is it normal to hear a slight scratching while inserting a dia?

[frank23]

When placing the diaphragm for the first time you can slightly scrape the gap side of course, the clearances are smaller than the accuraty of your hand is. It shouldn't scrape when mounted.

[frank23]

I inserted the new Radians in my 2420 just now. I needed to widen the pin holes of the Radians to fit them. I have read that this can be the case with the Radians. They now fit snugly around the guiding pins without needing to force them in, which is never a good thing.

I tested my old JBL's with pink noise before removing them, and then tested the freshly mounted Radians in exactly the same setup, without moving a knob or a thing. The old JBL stayed within 5dB from 2000-15000Hz (crossover was set at 1000Hz, so below 2000Hz might also be at the right level, but was attenuated by the active crossover). The response of the Radian is worse. They sound ok, not harsh or so, but they have a dip around 5Khz and greater fallof above 10kHz. Maybe it is due to that they are fresh out of the box, so I'll test them again later and report back.

Btw, I have my M553 active crossover setup for CD compensation, I think in the 2380 position, so that is why the pink noise output on the 2344 was relatively flat. For the pink noise measurements the M553 was set to cross over to the 2420 at 1000Hz.

[more10]

You can improve your system by replacing the M553. In order to get CD compensation you will have to go digital though.

[martin2395]

Probably you have to give them some time to break in?

[more10]

a dip around 5Khz

Wavelengt of 5 kHz is 6,9 cm. Half a wavelength is 3,4 cm. I would try to find this distance within the driver.

[frank23]

I just replaced the original JBL alu half roll surround diaphragm with the Radian alu mylar surround diaphragm. I think the dip is due to the difference in diaphragm build. The JBL is raised slightly to let the air from under the surround in and out to the sides. The Radian has small holes in its mylar surround to let the air from under the surround in and out. The measurement position is also exactly the same.

Btw, I know one can do better than an M553, but I have not found a suitable analogue 4th order LR active crossover alternative. I have modded the M553 so it has lost all its coupling capacitors except for the first and last, and that improved the sound greatly.

[yggdrasil]

It could be due to alignment.

You can widen the guide holes slightly. Then push the diaphragm in a direction, e.g. up and measure. Repeat for down, left, right.

Small adjustments will have large impact on response and often it is worth the effort finding the absolute best position of the diaphragm.

[martin2395]

Received the Radian 1245-16's today, they are a snug fit in the 2441's - no drilling needed.
However the 2441 themselves were quite bad - after removing the Ti dia's I noticed lots of particles (rust etc) in the VC gap. Had to remove all that stuff and polish the surface.

I will start working on the 2nd 2441 today - it took me like 5 hours to clean the driver and install the diaphragm.

[martin2395]

Second one also fits nicely, tried to polish away as much oxidation as possible.

61327

61328

[Kalle]

Hii!

Any listening impressions yet?:)

/Karl