Ring Radiator Production

[blackwell]

Thought you might get a kick out of this, hopefully it's new info for you.
One of the guys I work with (he shall remain nameless) working at JBL Pro for over 20 years and over the years went from the line to engineering. Anyway, he told me about the production of the ring radiators 2405 etc. The production yield was very low. Fall out because of the high standards for frequency response JBL required was killing them. Then a lady on the line figured out a way of fixing the diaphragms that did not pass. The tooling guys tried and tried to implement this fix into the die but they just couldn't get it to work as well as her method, she had the magic touch. And what was this method? She would simple run the tip of a ball point pen around the diaphragm, this added crease made the diaphragms play very smoothly and within spec. I don't know if this is true but he swears it is and says that you can see it on many of the old diaphragms if you look closely. It's a great story, especially how the tool guys couldn't duplicate the results, a personal touch.

[Steve Schell]

Hi blackwell,

Welcome to the forums.

I heard this same story from ex JBL Vice President Garry Margolis and have told it a time or two here.

It makes sense though, as the cross section of the diaphragm is a shallow V. There is really no way for it to move without distorting the diaphragm surface in some way that would most likely be harmful to the response. Adding a tiny bit of compliance at the edges would allow it to have some excursion without oilcanning the surfaces.

[scott fitlin]

I have heard that story, dont know if its really true, but since Steve says he heard it from Gary Margolis, it might be.

One thing I do know though, is that in the last several years, sales of tweeters had declined. Really the only ones that were seriously using tweeters much anymore were dance club systems, all the pro and touring rigs have CD horns that go all the way up.

If the story about them not being able to get the diaphragms to spec because of a pen poke in the right spot is true thats really kind of sad! How could a company like JBL not know how to make their product work?

[Harvey Gerst]

I certainly don't recall it ever being done during the production of the original 075.

[Ian Mackenzie]

It explains a lot. I have not seen two 2405 responses the same yet!

[scott fitlin]

I certainly don't recall it ever being done during the production of the original 075.Hey Harvey, there have been so many stories over the years.

One story I have heard many times, is that the aluminum they used to use years ago was different and better quality then the aluminum used in the last 10 to 15 years. Is there really any truth to this?

One story someone once told, is that JBL used to go to the WWII aircraft graveyard and buy scrap aluminum off the war planes and that it was better than the later aluminum.

Its another tale that has been told!

What say you?

[blackwell]

I have heard that in the "old" days JBL used a softer alloy. Then in an attempt to enhance the life span of diaphragms and increase high freq. resp. they went to a harder alloy. The older diaphragms would work harden and break like glass. But of course, I've seen AL diaphragms made in the early 80's just before Ti that broke like glass too. Who knows?

Eric

[Harvey Gerst]

Hey Harvey, there have been so many stories over the years.

One story I have heard many times, is that the aluminum they used to use years ago was different and better quality then the aluminum used in the last 10 to 15 years. Is there really any truth to this?

Possibly true; I don't know what they used in the last 10 to 15 years.

One story someone once told, is that JBL used to go to the WWII aircraft graveyard and buy scrap aluminum off the war planes and that it was better than the later aluminum.

Its another tale that has been told!

What say you?
Scrap aluminum from WWII aircraft graveyards? LOL!!! I don't think so.

[Baron030]

Gee, who needs Adam Savage or Jamie Hyneman, when we have Harvey?
This tread is starting to read like an episode of Mythbusters.

Harvey can you please tell us some more wonderful JBL myths.
Besides, the top secret military "Brown Note" research at JBL for example?:rotfl:

We all enjoy reading your posts.
Baron030

[scott fitlin]

Scrap aluminum from WWII aircraft graveyards? LOL!!! I don't think so.Well, its one of the stories that float around! I never put to much creedence in them.

What Blackwell posted about the older phragms having a different composition of alloy, that makes sense.

I know that as we got into the 90,s and the big new extremely powerful amps began coming out, power handling became a serious problem. Guys wanted to use the BIG Crown 5000,s and Crest 9001,s, and then power to HF devices began to creep upwards too. As one manufacturer explained it to me, the days of powering compression drivers with 30 watts at a big show are over, and with the older, lighter diaphragms, 75 watts and better, and they were just shattering everything. They had to make diaphragms more withstanding.

This is one of my big problems with vintage gear, and speakers. Unless you have components with the actual 1979 cones and diaphragms, they arent really vintage. If they have been rebuilt with new parts, many times the new parts do work to a degree, but are NOT 100% like the parts originally made and used.

[Harvey Gerst]

Gee, who needs Adam Savage or Jamie Hyneman, when we have Harvey?
This tread is starting to read like an episode of Mythbusters.

Harvey can you please tell us some more wonderful JBL myths.
Besides, the top secret military "Brown Note" research at JBL for example?:rotfl:

We all enjoy reading your posts.
Baron030
I don't remember any "brown note" research, but Ed May came damn close to it when we were on Casitas. Ed built a very long throw, low distortion LE15, and mounted it in a large cabinet located in the corner of the sound room, and fed a 27 Hz sine wave into it at a pretty high volume. No overtones, just pure 27 Hz.

When you walked into the room, it felt like you were underwater; you could barely breath, let alone talk. Most people couldn't last more than a few seconds in the room without coming out sick.

I still remember that experience to this day.

[Harvey Gerst]

Well, its one of the stories that float around! I never put to much credence in them.

What Blackwell posted about the older diaphragms having a different composition of alloy, that makes sense.
On further reflection, there might be some possible truth to that story, but not the scrap metal part of the story. You must remember that Bill Thomas worked at Marquart Aircraft for a number of years before JBL, and Bill was still very close to Roy Marquart.

It is possible that he worked out a deal with Marquart to buy higher grade aluminum from them at a lower price, because of Marquart 's better purchasing power.

Johnny Edwards would know more about that than I would. Anyway, all this is pure speculation on my part.

[scott fitlin]

Interesting!

Harvey, your the best.

:)

[Harvey Gerst]

Interesting!

Harvey, you're the best.

:)
Nah, I'd say I was "blessed", not "best". I was just very lucky to be in a lot of right places at exactly the right times.

[scott fitlin]

Nah, I'd say I was "blessed", not "best". I was just very lucky to be in a lot of right places at exactly the right times.Well, however you want to put, you put a good ending to a story thats been floating around for a while.

And this ending actually makes sense, if a manufacturer can get something cheaper, and at the same time, better, YES, it could very well be.

Aircraft grade materials are known to be some of the best available.

:)

[hardtime]

Speaking of tweeters, I have a 2405 and some one has pushed one of the locator pins down flush. What is the fix for this?
Thank you

[SMKSoundPro]

Speaking of tweeters...


I have had VERY good luck with 2402,2404,2405 magnet assemblies(motors) that have been dropped and the top plate glue joint has let go, sending the outer ring towards the pole piece with outstanding magnetic force!

My friend, the Admiral, machined a centering jig for me with two brass locator insert pins, so that the top plate can be re-glued and centered, perfectly! It is SO simple. I have reglued four motors, so far, and all of them have come out great!

Remember my wife's motto: "No more JBL paper weights!"

I will send photos to show, soon. I did not have my camera at work that night, but can assure you that end product will be a useable tweeter motor! (I do not have a gauss meter, and can make no assurances that some flux density is not lost in the process.) But they do sound exactly as loud as an alnico or ferrite motor tweeter when A-B'ed.

If any of you have these "paper weight" tweeter motors where the top plate has shifted, please consider sending them to me, and I will re-glue and re-center them and mail them back to you.

Always trying to help when asked,

Scott.

PS> If you have a 2410, 2420, 2440, 2470 0r 2480 style of driver with a problem, please contact me also, as the Admiral and I came up with a jig to fix a problem I had with a 2470 to become a 2420.

[blackwell]

Here's another 2405 story I was told.
When 2405 production was stopped due to running out of metal phase plugs they used to just grab 077 plastic phase plugs and spray paint them black. I know it sounds sloppy but the thickness of paint is so thin that I don't think it would hurt and after all they did pass QC. It's just interesting to think that someone out there has a nice prism painted black:)

[blackwell]

Hi blackwell,

Welcome to the forums.

I heard this same story from ex JBL Vice President Garry Margolis and have told it a time or two here.

It makes sense though, as the cross section of the diaphragm is a shallow V. There is really no way for it to move without distorting the diaphragm surface in some way that would most likely be harmful to the response. Adding a tiny bit of compliance at the edges would allow it to have some excursion without oilcanning the surfaces.

I have just confirmed this story.
I opened up a 077 and pulled out the diaphragm. It was an original blue JBL diaphragm and under a microscope you can clearly see the pen mark. It goes all the way around the diaphragm outer edge where the V meets the outer blue ring. The slight groove left behind even has ink on it from the pen. Very cool. Thought you'd like to know.

[Hofmannhp]

Hey Harvey, there have been so many stories over the years.
....One story someone once told, is that JBL used to go to the WWII aircraft graveyard and buy scrap aluminum off the war planes and that it was better than the later aluminum.
.......

Hi all,

this myth can be busted......

airplanes are made from Duraluminium (short: Dural) and this material, with values like steel, can not be formed like you need to form it for a dia.
Dural is 95% aluminium, 4% copper and 1% magnesium and very brittle.

HP

[scott fitlin]

Hi all,

this myth can be busted......

airplanes are made from Duraluminium (short: Dural) and this material, with values like steel, can not be formed like you need to form it for a dia.
Dural is 95% aluminium, 4% copper and 1% magnesium and very brittle.

HPJBL has always said they make their aluminum diaphragms from Duraluminum!

What I have learned thru the years, is that the older phragms were lighter and thinner. However, when we got into the 90,s, and the power amps got more powerful, and they were shoving 75w into drivers designed for 30w, etc, they kept shattering the phragms.

The manufacturers made a heavier, thicker phragm, that could handle the workload, but, the sonics changed.

I had a long talk with one MAJOR manufacturer, who I wont name, and I alsked why cant you make both? Heavy Duty, and light weight, let the user choose what they need? The manufacturers response was its too costly to have two parts for the same driver, and the tour sound companies will never go back to what was, and if they make the older style phragms, they will just keep blowing them with high power. He also told me that reputation of consistency and reliability is an important factor for any company, so they make what works for the current trends in audio.

Now, my own personal opinion, companies are in buisiness to sell products and make money. Just as I am too. They cant make money selling parts for old, discontinued items. They need to sell NEW products, too.

It is what it is!

[Predrag Dukic]

Hi all,

this myth can be busted......

airplanes are made from Duraluminium (short: Dural) and this material, with values like steel, can not be formed like you need to form it for a dia.
Dural is 95% aluminium, 4% copper and 1% magnesium and very brittle.

HP

Duraluminum is subjected to thermal processing during manufacture:

First it is brought to some high temperature, so that copper dissolves in aluminum, creating solid solution of copper in aluminum.
Then it is "quenched" ie. cooled rapidly, so that copper does not have enough time to precipitate.

This quenched duraluminum is soft, can be forged, deep drawn etc.

After some time (aging, ripening) copper atoms find their way out of the aluminum crystal lattice, and precipitate within and in between aluminum crystallites.
This process creates internal microstresses, making material stronger (increasing yield point).
The material is now brittle, and can't be drawn any more.

Aging takes days or weeks, depending on the temperature...

[1audiohack]

Hi Predrag Dukic;

Nice to see a new member with some metallurgical knowledge.

When I was a kid we were building a dog sled (long before I moved to Vegas) and bought a bag of aluminum bucking rivits from the local military surplus store and thought the date code was just the governments way of making sure they spent all the money they had. Well, those rivits could not be worked, they would split every time, this due to as I would later learn the aging process. Funny, as I age I am experiencing the same change in properties. :)

One other thing, I have measured many ring radiator diaphragms, old ones, new ones, gold ones and blue ones, even some with mixed color rings and silver ones and all that I have measured were 0.0020" +-0.0001". I don't know the unnamed manufacturer Scotty talked to but I haven't seen any evidence to support this in the OE JBL parts.

All the best,
Barry.

[ivica]

Hi Predrag Dukic;

:)

One other thing, I have measured many ring radiator diaphragms, old ones, new ones, gold ones and blue ones, even some with mixed color rings and silver ones and all that I have measured were 0.0020" +-0.0001". I don't know the unnamed manufacturer Scotty talked to but I haven't seen any evidence to support this in the OE JBL parts.

All the best,
Barry.

I have several 2405 and 077, ( with silver, blue and gold rings) but almost none of them has the same frequency response.
May be interesting to say that Beyma CP-21F has the same "behavior" ( every piece has different response).
Regards
Ivica

[Steve Schell]

Here's another story that Garry Margolis told me years ago. He used to travel to Japan during his employment with JBL. On one such trip he was visiting the offices of a hi fi magazine. A worried-looking engineer brought him a gnarly looking response curve of an 075 and asked "What we doing wrong?" Garry replied "Nothing; that looks about right."

George Augspurger mentioned in a 1950s magazine article introducing the 075 (I've published it here on the site somewhere in another thread) that JBL would not allow him to publish a response curve as part of his article.

Edit: George Augspurger's article can be found on page twelve of this thread:

http://www.audioheritage.org/vbulletin/showthread.php?6368-Ring-Radiator-Comparisons&highlight=ring+radiator+comparisons

[Predrag Dukic]

Hi Predrag Dukic;

Nice to see a new member with some metallurgical knowledge.

When I was a kid we were building a dog sled (long before I moved to Vegas) and bought a bag of aluminum bucking rivits from the local military surplus store and thought the date code was just the governments way of making sure they spent all the money they had. Well, those rivits could not be worked, they would split every time, this due to as I would later learn the aging process. Funny, as I age I am experiencing the same change in properties. :)

One other thing, I have measured many ring radiator diaphragms, old ones, new ones, gold ones and blue ones, even some with mixed color rings and silver ones and all that I have measured were 0.0020" +-0.0001". I don't know the unnamed manufacturer Scotty talked to but I haven't seen any evidence to support this in the OE JBL parts.

All the best,
Barry.


Barry, thank You for welcoming me,

I also have some knowledge in electronics and acoustics, and I'll try to give some contribution to discussions.

As a comment on variability of ring radiator frequency responses, they are result of diaphragm partial vibrations due to (many) flexural modes and resonancies.

Not only longitudinal stiffness or specific stifness is important. Also flexural stiffness plays a part, maybe even bigger.

Most producers choose titanium or aluminum as the dia. material.

They both have similar specific modulus (density / Young's modulus) so one would expect that speed of sound is both is comparable.

But....

Force exerted by the voice coil is divided in two components: one in the direction of the plane of the cone (or dome or...)

That one is trying to compress material, and travels with the speed of sound of this specific material.

The other component is acting orthogonally, out of plane and sends a transversal wave through dia.

This wave is much slower and can propagate in radial and circumferential directions.

Speed of this wave is determined not by specific modulus, but by higher powers of density/modulus ratio

(last two columns of the table in this wiki page. http://en.wikipedia.org/wiki/Specific_modulus

That is the reason why aluminum is better material for dia. Speed of transversal vibrations is higher in aluminum.

Magnesium could even be better than Al or Ti but it is excessively sensitive to corrosion, and possibly fatigue.

Since speed of flexural waves is dependant on thickness (local variations and overall)

to the second or third power (don't know exactly, but I'll check) all vibration modes (peaks and dips in the response) are highly variable.

Check the Proc IRE, 39: 1021-1026 (1951) Corrington " Amplitude and Phase measurements on Loudspeaker cones"

Do not expect that 2404 dia. moves as a rigid piston... It probably has dozens of resonances,

and exact frequency of each of them is very variable in every single unit due to local small uneveness of thickness of material...

[1audiohack]

Here's another story that Garry Margolis told me years ago. He used to travel to Japan during his employment with JBL. On one such trip he was visiting the offices of a hi fi magazine. A worried-looking engineer brought him a gnarly looking response curve of an 075 and asked "What we doing wrong?" Garry replied "Nothing; that looks about right."


The next plane wave tube I build will be 0.500" by 6.000" to be used with the inner horn of a 2403/2404 for evaluation of my ring radiators. It is no small feet to get any two of them to behave similarly and I think part of it is placement, you need only pick it up and put it back down again between sweeps to drive yourself mad. It's not so bad once one knows what to look for and what to and what not to worry about but I would like to know what's going in in there! :^). Finicky little devils they are!

[Predrag Dukic]

The next plane wave tube I build will be 0.500" by 6.000" to be used with the inner horn of a 2403/2404 for evaluation of my ring radiators. It is no small feet to get any two of them to behave similarly and I think part of it is placement, you need only pick it up and put it back down again between sweeps to drive yourself mad. It's not so bad once one knows what to look for and what to and what not to worry about but I would like to know what's going in in there! :^). Finicky little devils they are!

I am also making a similar PWT. It has now become a small project of me, here at the University of Split. May take some time but I'll post my results here when finished...
Three photos posted are illustration of an attempt to get all the dimensions of the 2404 using GOM optical scanner.

[Predrag Dukic]

I am also making a similar PWT. It has now become a small project of me, here at the University of Split. May take some time but I'll post my results here when finished...
Three photos posted are illustration of an attempt to get all the dimensions of the 2404 using GOM optical scanner.

--------------------------------------------------------

Later...... PWT finished....
Here is an impedance plot of 2404H-1 on a 1/2" 6' PWT.
FR will follow later---

PWT is still not properly damped. The end of the tube is just plugged with a piece of cotton..
As a consequence of reflections, small variations of impedance are visible in the 0.5-3 KHz region...

Graph taken with ARTA-LIMP.

On the previous photos (Lab) the author of the ARTA software, Prof Mateljan is just one floor downstairs.

[Predrag Dukic]

--------------------------------------------------------

Later...... PWT finished....
Here is an impedance plot of 2404H-1 on a 1/2" 6' PWT.
FR will follow later---

PWT is still not properly damped. The end of the tube is just plugged with a piece of cotton..
As a consequence of reflections, small variations of impedance are visible in the 0.5-3 KHz region...

Graph taken with ARTA-LIMP.

On the previous photos (Lab) the author of the ARTA software, Prof Mateljan is just one floor downstairs.

Does anybody have a broken, dead, unusable 2404 (or any other ring radiator) motor assembly he doesn't need? I want to make a cross section (cut it in halve).

[Predrag Dukic]

FR of 2404H-1 on a 1/2" 6' PWT.

No damping, just impulse response gated at 10.5 milliseconds

three lines:

1. Open tube end, (Yel)
2. Closed tube end (Rosa)
3. Last 8in damped with a loose cotton plug (Green)

From 200 Hz onwards it is essentially the same line, so I can forget damping...
For some future project, let's say 2" PWT for 2445, I will extend the tube to 12' and gate the impulse response on 21 ms...

(Forget absolute pressure on ordinate, it is not calibrated... maybe later)

[Turner]

I have several 2405 and 077, ( with silver, blue and gold rings) but almost none of them has the same frequency response. May be interesting to say that Beyma CP-21F has the same "behavior" ( every piece has different response). Regards Ivica Have you tried shimming the diaphragms and/or phase plugs? Phase plugs might need to be deburred, also.

[grumpy]

My experience has been that in using cleaned/undamaged (whether used or new) diaphragms,
and with repeatable monitoring of frequency response while carefully snugging up the phase plug,
one can get what I would call reasonable agreement between these drivers (sufficient to not muck
up imaging or balance).

Otherwise, the phase "dog's breakfast" would apply to the comparison plots I've seen when
less care has been given to the process.

[ivica]

Have you tried shimming the diaphragms and/or phase plugs? Phase plugs might need to be deburred, also.

Some experiments, YES.
http://www.audioheritage.org/vbulletin/showthread.php?6368-Ring-Radiator-Comparisons&p=319363&viewfull=1#post319363

I can agree with grumpy's words:

".......My experience has been that in using cleaned/undamaged (whether used or new) diaphragms,
and with repeatable monitoring of frequency response while carefully snugging up the phase plug,
one can get what I would call reasonable agreement between these drivers (sufficient to not muck
up imaging or balance)..........."

for the single driver, but between different drivers, I haven't been so skilful, to get such results.

Regards
Ivica

[Turner]

Some experiments, YES.


hahaha, YES, I had a feeling that response was coming. Thanks for that link, lots of great info! We mainly used shims for aftermarket diaphragms - which should be avoided at all costs (aftermarket diaphragms) - paper, tape, foil, anything that worked, well, kinda. Ah, the good old days! :(

I just checked 2 sets of silver 2405 diaphragms. I think I see the crease mentioned in the OP, but it doesn't look like it was made with a ballpoint pen, not at 10x anyways.

Here's a set of 2405H with new D16R2405 installed last spring, tested this AM. Red might need some attention.

57744

[Predrag Dukic]

My experience has been that in using cleaned/undamaged (whether used or new) diaphragms,
and with repeatable monitoring of frequency response while carefully snugging up the phase plug,
one can get what I would call reasonable agreement between these drivers (sufficient to not muck
up imaging or balance).

Otherwise, the phase "dog's breakfast" would apply to the comparison plots I've seen when
less care has been given to the process.

Here is a plot of FRs (2404H or H-1) recorded with the same magnet structure, the same inner parts of the horn,
and the same PWT (to avoid positioning and angle problems with usual FR recording) in place of the outer horn.
Two pics, with different zoom factor.

Yel: 2405 dia, small (1.6") phase plug...
Vio: 2405 dia, big (1.71") phase plug...
Grn: 2402 dia, small (1.6") phase plug...
Gry: 2402 dia, big (1.71") phase plug...

Both dias original JBL, older, mfrd. before 1995

5788357884


the last, grey line, is essentially the same as the one I posted some time ago, and I disassembled the tweeter many times since.
Therefore I am able to get the similar results after remounting.
But to be sure, I will repeat this mounting/remounting several times more
to see the variability resulting from the mounting procedure.
I will post also all results.
PS: The vertical axis is still not calibrated, so absolute SPL shown is still not correct.

[Predrag Dukic]

So here are results of the next experiment.
After trying several times more, I chose next combination
:2402 dia, big (1.71") phase plug, remounted it several times
and got the same FR, within 1 db from each other.

Then I repeated it 4 times more, but with some variations.

1st variation (blue and gray lines): Outer horn (and PWT, together with microphone)
is mounted rotated for 0 and 180 deg. lines are similar, except that one line falls smoothly at 20 kHz,
and the other shows a dip and a peak of cca 5 dB.
There is also a dip around 15 khz, which exists also with 2405 dia.


2nd variation (violet and green lines):
Examining inner and outer horns on 6 of 2404Hs, I found that casting of the inner aluminum horn
does not fit perfectly to the outer plastic horn. all of them had a small gap between the two parts, of cca 0.5 mm.
I deliberately made my PWT to replicate that small gap, and got it to be a bit thicker,
cca 0.7 mm- slightly worse than the worst of my 6 2404s .
All previous measurements include that gap.
Violet and green lines were recorded with a gasket filling that gap.
The dip at 15 kHz allmost dissapeared. I conclude from that that imperfection of the casting
forms an acoustic resonator or filter responsible for this dip.
I repeated with the gasket in place also rotation of the inner horn and pwt and got the same dip/peak around 20 kHz.
I conclude that this peak is result of a circumferential mode (HOM) at this frequency, but this requires more investigation.

For the moment I am satisfied with the finding that EVERY 2404 could benefit
from placing a gasket between two parts of the horn.
Gasket should be 13 mm ID, 22 mm OD, and 0.7 mm thick.

PS to my post of 18 dec: I chose to have my PWT end tightly plugged.
It does not change results of measurements,
but prevents external noise to enter the tube during measurement and give wrong results.
(Don't ask how I.....)
57891

[ivica]

So here are results of the next experiment.
After trying several times more, I chose next combination
:2402 dia, big (1.71") phase plug, remounted it several times
and got the same FR, within 1 db from each other.

Then I repeated it 4 times more, but with some variations.

1st variation (blue and gray lines): ...............

2nd variation (violet and green lines):
...........For the moment I am satisfied with the finding that EVERY 2404 could benefit
from placing a gasket between two parts of the horn.
Gasket should be 13 mm ID, 22 mm OD, and 0.7 mm thick.

PS to my post of 18 dec: I chose to have my PWT end tightly plugged.
It does not change results of measurements,
but prevents external noise to enter the tube during measurement and give wrong results.
(Don't ask how I.....)
57891

Hi Predraze,

It is nice to see on this form such systematic and informative works, with very useful suggestions. Unfortunately PWT tube is fare to be available for most of us, but I believe that such behavior of mechanical imperfection in the driver production may have an influence to the driver impedance, that is fare much easier to be measured for the many of us. This is only my expectation, unfortunately I can not prove it, but may be, You can, and may be , You can give us us some suggestion on how we can improve our drivers.

Regards Ivica

[Predrag Dukic]

Hi Predraze, It is nice to see on this form such systematic and informative works, with very useful suggestions. Unfortunately PWT tube is fare to be available for most of us, but I believe that such behavior of mechanical imperfection in the driver production may have an influence to the driver impedance, that is fare much easier to be measured for the many of us. This is only my expectation, unfortunately I can not prove it, but may be, You can, and may be , You can give us us some suggestion on how we can improve our drivers. Regards Ivica

Ivica,

It is in fact much easier to make a PWT than to do a proper measurement setup with speaker and microphone on the stand.
In a "normal" measurement You need a quiet place with some free space, You have to measure angles and distances, etc. etc..
My "setup" is lying on the floor some feet away of the PC....
Here is a photo. It took an hour or two to assemble, excluding time to go to the plumbers shop...
It is true that I work at the University, but this is my hobby project, and I didn't need any "heavy artillery" from there to start measurements...
Also ARTA program is freely downloadable, in fully operational version. Only saving measurement files does not work with unregistered version...
The key feature of ARTA is the "gated measurement".
It allows to get the FR from the mic, before the reflection of the pulse arrives from the acoustically unmatched end of the tube.
The process is easy to understand from the second pic.
The green portion of the impulse response is used to calculate FR, the rest (red) is simply cut and unused.

My next PWT is going to be 1", for my 2425s. I will also use green 40 mm PP plumbing tube, which has just about right internal diameter (1,025 in).


Cost of 1/2" PWT setup:

ARTA- free
Meas. Mic. 3 usd (Panasonic WM61a)
Green PP plumbing tube 3 usd
Black PP flange 5 usd
----------------------
Total - 11 usd, excluding cable, drop of epoxy glue, and three cable ties.

1" version is going to cost something around 20 usd.

[ivica]

Ivica,

It is in fact much easier to make a PWT than to do a proper measurement setup with speaker and microphone on the stand.
In a "normal" measurement You need a quiet place with some free space, You have to measure angles and distances, etc. etc..
My "setup" is lying on the floor some feet away of the PC....
Here is a photo. It took an hour or two to assemble, excluding time to go to the plumbers shop...
It is true that I work at the University, but this is my hobby project, and I didn't need any "heavy artillery" from there to start measurements...
Also ARTA program is freely downloadable, in fully operational version. Only saving measurement files does not work with unregistered version...
The key feature of ARTA is the "gated measurement".
It allows to get the FR from the mic, before the reflection of the pulse arrives from the acoustically unmatched end of the tube.
The process is easy to understand from the second pic.
The green portion of the impulse response is used to calculate FR, the rest (red) is simply cut and unused.

My next PWT is going to be 1", for my 2425s. I will also use green 40 mm PP plumbing tube, which has just about right internal diameter (1,025 in).


Cost of 1/2" PWT setup:

ARTA- free
Meas. Mic. 3 usd (Panasonic WM61a)
Green PP plumbing tube 3 usd
Black PP flange 5 usd
----------------------
Total - 11 usd, excluding cable, drop of epoxy glue, and three cable ties.

1" version is going to cost something around 20 usd.

Hi Predraze,

Many thanks for the explanation of your measurements 'setup'. Such equipment is good if the decision is to measure smaller amount of different drivers, but me , as hobbyist, sometime different models are of interest. I know that ARAT is valuable software tools, where one of the possible solution getting F/R response is calculated based on the "truncation of the impulse response".

Been aware that the reflections can produce errors in the F/R measurements (in ordinary environments that is for hobby-user applicable) I have made my "own" procedure based on the 'Using Complementary binary sequences' in order to get impulse response of the driver, and then applying 'time domain windowing, or truncation', in order to calculate F/R. Usually I have done my measurements in my living room, with the driver positioned about 75cm from the floor ('looking at the ceiling') and microphone about 100cm (3.3 ft) apart, hanged from the ceiling. While the nice outside weather, sometime, I did my measurements outside the house. All in all, the measurements, can be repeated with 'repeatable accuracy. from the measurements to the measurements, and from day to day' . With such, the influence of the driver's horn can be get too, and try to "predict" what would the listener can expect to get.

Owing to use the two complementary (Golay

http://www.isg.rhul.ac.uk/~kp/golaysurvey.pdf ,

http://ompldr.org/vOHkxNw/fulltext.pdf

http://jenshee.dk/signalprocessing/mls.pdf -"Impulse response measurements using MLS"

http://cnx.org/content/m15947/latest/

)

sequences of about 256kbits (2^18) length each, I can get quite good resolution, which then can be "averaged" in standard 1/N octave presentation.

I can agree with You that for the scientific research your procedure is much more applicable, but I would stay in belief that such great variation in F/R You have presented us (around 15kHz), has to make some kind of the "reflection" to the impedance characteristics.

Regards

Ivics

[Predrag Dukic]

Ivica,

Yes, my project started as a hobby effort, but now I am getting more and more involved.
Solving the problem of HOM in tweeters is indeed worth a scientific project,
and it wouldn't be the first one to be undertaken. People at JBL certainly know more about it,
but the nature of their work requires to keep hardly acquired knowledge to themselves.

As for the other remarks, I wanted to separate sources of problems, and PWT is a way to do it.
I will get back to horn issues later.

I am not familiar with the algorithm used in ARTA to generate noise signal,
but I suspected it is some kind of pseudo random sequence.

I might ask the author of ARTA personally some day.
It is easy to me because we visit the same coffee shop at FESB faculty almost every day.
In fact, I am not really interested.... One can not know everything...
I will limit myself to speaker construction and "hardware". I leave software development to others...
Thanks for the links anyway.
As for the impedance changes due to the dip at 15 kHz....
Hmmmm..... let's suppose that the measuring microphone is mounted farther from the throat, not in the first 1 inch or so...
And let's suppose also that You have a nice, loosely packed plug of a long hair wool somewhere in between.

This plug might attenuate the sound wave ...let's say 6 dB, or to say, it could "eat" 75% of the driver's efficiency.
We might expect that the real impedance of this driver with Re of 6ohm falls from let's say 8 ohms to 6.5--
a corresponding 75% drop in Rt . But, the impedance will in reality remain 8 ohms (25% efficiency),
and the effect of a well matched acoustic damping or attenuation will pass unnoticed.
Microphone is going to read 75% decrease of the SPL, but impedance measurement will stay the same.
That is because the energy is not REFLECTED back to the driver, but simply DISSIPATED in the form of heat.
Therefore not every dip in FR is visible in the impedance plot,
but I will do a thorough check of this question one of the next days,

and I will keep You informed on the results and the progress.

[1audiohack]

This is very nice work Predrag Dukic. The throat leak is a real find. Thank you for sharing your work!

All the best,
Barry.

[ivica]

Ivica,

......
As for the impedance changes due to the dip at 15 kHz....
Hmmmm..... let's suppose that the measuring microphone is mounted farther from the throat, not in the first 1 inch or so...
And let's suppose also that You have a nice, loosely packed plug of a long hair wool somewhere in between.

This plug might attenuate the sound wave ...let's say 6 dB, or to say, it could "eat" 75% of the driver's efficiency.
We might expect that the real impedance of this driver with Re of 6ohm falls from let's say 8 ohms to 6.5--
a corresponding 75% drop in Rt . But, the impedance will in reality remain 8 ohms (25% efficiency),
and the effect of a well matched acoustic damping or attenuation will pass unnoticed.
Microphone is going to read 75% decrease of the SPL, but impedance measurement will stay the same.
That is because the energy is not REFLECTED back to the driver, but simply DISSIPATED in the form of heat.
Therefore not every dip in FR is visible in the impedance plot,
but I will do a thorough check of this question one of the next days,

and I will keep You informed on the results and the progress.

Hi Predraze,

I agree with You that if there is some kind of acoustic absorber out of the driver's horn (or any other kind of the obstacle) , that can make an interference with the sound propagation ( all of us are aware of the baffle edges interferences, not to mention any other nearby surfaces or objects), and all of that would make great variations in F/R response ( that is "present" at the microphone point in space).
But here I want to emphasize that I would expect that the driver's and its horn's construction and their imperfection could produce some kind of "signature" in the impedance characteristic that can be compared with expectable (correct) one. My expectation is based on MY belief that any kind of "large imperfections" ( the meaning "LARGE", here is disputable), would produce a different amount of reflection energy (compared to the "good" part), and that would, MAY BE, produce some kind of visible behavior in the impedance curves. All that is just my expectation, but may be You can find the answer.

Regards
Ivica

[Predrag Dukic]

This is very nice work Predrag Dukic. The throat leak is a real find. Thank you for sharing your work! All the best, Barry.

Thanks... Just my two cents. A cheap way to get an audible difference. I know that some people give an arm and a leg for much smaller improvement.

The "leak" is not a really a leak through... The aluminum part has a circular ridge of cca 1" diameter around throat.
The plastic part, outer horn has a groove of the same diameter.
They should fit one into another, but the ridge is a bit higher than the groove depth, and a slightly different diameter.
That misfit leaves a small space, in a form of a thin circular chamber around throat.
It is possible to see the interface between the two from the outside, looking through horn to the phase plug.
And with a good illumination it is possible to see this thin gap.
Thickness of this gap varies, depending on Your luck, from 0.1 mm (one sheet of paper) to 0.5 mm,
which is the thickiest that I saw in my small statistical sample of 6 tweeters.

[Predrag Dukic]

Hi Predraze,

I agree with You that if there is some kind of acoustic absorber out of the driver's horn (or any other kind of the obstacle) , that can make an interference with the sound propagation ( all of us are aware of the baffle edges interferences, not to mention any other nearby surfaces or objects), and all of that would make great variations in F/R response ( that is "present" at the microphone point in space).
But here I want to emphasize that I would expect that the driver's and its horn's construction and their imperfection could produce some kind of "signature" in the impedance characteristic that can be compared with expectable (correct) one. My expectation is based on MY belief that any kind of "large imperfections" ( the meaning "LARGE", here is disputable), would produce a different amount of reflection energy (compared to the "good" part), and that would, MAY BE, produce some kind of visible behavior in the impedance curves. All that is just my expectation, but may be You can find the answer.

Regards
Ivica


Ivica, I agree, just ..... I do not accept any generalizations withouth checking...

But this dip really dees reflect to the impedance curve....
Look up my first post with impedance graph...:)

[Predrag Dukic]

Hi Predraze,


I agree with You that if there is some kind of acoustic absorber out of the driver's horn (or any other kind of the obstacle) , that can make an interference with the sound propagation ( all of us are aware of the baffle edges interferences, not to mention any other nearby surfaces or objects), and all of that would make great variations in F/R response ( that is "present" at the microphone point in space).
But here I want to emphasize that I would expect that the driver's and its horn's construction and their imperfection could produce some kind of "signature" in the impedance characteristic that can be compared with expectable (correct) one. My expectation is based on MY belief that any kind of "large imperfections" ( the meaning "LARGE", here is disputable), would produce a different amount of reflection energy (compared to the "good" part), and that would, MAY BE, produce some kind of visible behavior in the impedance curves. All that is just my expectation, but may be You can find the answer.

Regards
Ivica

Ivica, (and others ) ;

Now I have a new 1 " PWT, attached to the 2425H driver. In fact two drivers....
Drivers are with close serials, with two original JBL dias.
Two FRs are so close that I think that everything is exactly as it should be- no damage of any kind,
and also magnet flux is probably unaffected by age. ..

The problem is that it does not look like the one published in JBL documentation...

( http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=5&cad=rja&ved=0CE8QFjAE&url=http%3A%2F%2Fcyrille.pinton.free.fr%2Felectroa c%2Flectures_utiles%2Ftech_haut-parleurs%2FJBL_high-frequency-compression-drivers.pdf&ei=dY31UPm4KaOE4gTTjoHACA&usg=AFQjCNEAy-3FQ7XvkqFZFDCbZr2WTPepxw&bvm=bv.41018144,d.bGE , Figure Nr. 6)

Response is falling down 6 db/oct from 700 Hz onwards, as if the dia. mass breakpoint is around 500 Hz instead around 3500 Hz...
Has anyone ever seen independently published (not by JBL) PWT graph for 2425H driver?

1. Line (Yel) 2425H #1, 1" PWT
2. Line (Gry) 2425H #2, 1" PWT
3. Line (Magenta) 2404H-1, 1/2" PWT

Third line includes 6 dB correction for difference in PWT diameter ( 1/2" vs. 1" )
Absolute SPL is not calibrated, but relative differences are correct.

[1audiohack]

Here is one of mine, a completely brand new JBL 2425 HS on my 2" PWT with a JBL 2327 1" to 2" adapter. Using a calibrated Earthworks M30 mic. Oops, that's not true, I used a TEF TE04 calibrated mic.

[ivica]

Ivica, (and others ) ;

Now I have a new 1 " PWT, attached to the 2425H driver. ..............................

The problem is that it does not look like the one published in JBL documentation...


Response is falling down 6 db/oct from 700 Hz onwards, as if the dia. mass breakpoint is around 500 Hz instead around 3500 Hz...
Has anyone ever seen independently published (not by JBL) PWT graph for 2425H driver?

1. Line (Yel) 2425H #1, 1" PWT
2. Line (Gry) 2425H #2, 1" PWT
3. Line (Magenta) 2404H-1, 1/2" PWT

Third line includes 6 dB correction for difference in PWT diameter ( 1/2" vs. 1" )
.

Hi Predraze,

It is nice to be seen that You have setup an other measurement test place for 1" drivers.
May be some suggestions from 1audiohack would help.
http://www.audioheritage.org/vbulletin/showthread.php?31262-Plane-Wave-Tube-Construction&p=315250&viewfull=1#post315250

As I have remembered, the position of the microphone can influence the measurements results , and sound absorber applied in the PWT too.



Regards
Ivica

[Predrag Dukic]

Here is one of mine, a completely brand new JBL 2425 HS on my 2" PWT with a JBL 2327 1" to 2" adapter. Using a calibrated Earthworks M30 mic. Oops, that's not true, I used a TEF TE04 calibrated mic.

It is usually said that the experiment which shows exactly what is expected, is useless. You can't learn anything from it.

If however, results differ from expectations, it can mean only two things:

1. You did something wrong. After correcting the error, You learned something.

2. If You didn't make any error, then You found something new. So again, You learned something...


My 2425H FR graph was unexpected. Not only that it had this prominent resonance, but also looked rougher than Your graph...


And then I remembered...

When I first received the drivers, I dismantled everything, checked the dia,
and also found that the rear chamber damping has disintegrated.
Well, nothing unexpected. PU foam can't last so long... even more than 25 years in this case.

So I removed it, with intention to find a suitable replacement later.

But then I forgot about it.... Yesterdays graphs were recorded without any damping...

When I realized it, of course I tried to find a replacement, which is not easy, so first I tried without a back cap...

The idea was that absence of the cap is kind of an "ideal case".
Any sound coming from the rear side of the dia is effectively dispersed and so....

But then... I wasn't sure about it... So I made another experiment,
with material that was first at hand: a common medical cotton.
Still I wasn't satisfied, because I didn't get expected results and also it is not the original damping material.

So I invested a great effort, visiting various shops and all other places that came to my mind, and finally found
something similar to the original foam. Of course, the original is probably not possible to obtain,
but this looked really close.
And it seems that rear damping material is not a trivial thing...
I still can't explain fully this strong resonance at 750 Hz, and deviation from Your,
and JBL published response, but I got some improvement.

Here are the results:

Yel : Open cap , "ideal damping?"

Gry : with cap, no damping

Orange: long fibre cotton

Cyan : Foam damping


With foam, not only that resonance is 4-5 db lower than the alternatives,
but also there is an improvement in the upper region ( from cca 2-3 kHz to almost the end of the range).
Not much, maybe only 0.5 dB in this band, but there is a measurable difference.
Also those initial smal resonancies at 3 and 6 kHz ( gray line) can be attributed to air space resonance
of the rear chamber. All other cases do not have those small peaks.

I also kept that 2404H-1 magenta line in the graph.

[Earl K]

Hi Predag


http://i1-win.softpedia-static.com/screenshots/MWSnap_1.png (http://www.softpedia.com/get/Multimedia/Graphic/Graphic-Capture/MWSnap.shtml)


- Predrag, ( as an aside & only because I thoroughly enjoy following your research efforts so much ) would you please consider using a "better" screen-capture utility( like the one posted above ) so that we can see ARTA in it's best resolution . Stay away from .jpg when resizing ( & marking-up pics ) when in Paint . It's best to go into & out of Paint using a .png file format ( if that is the finale format type ) .

- Here's the type of quality ( .png files ) that you could be posting ( instead of the current, washed-out / hard-to-follow, pics ) .

http://www.audioheritage.org/photopost/data//500/802_2_35480Fram_Sammi_Horn_a_Burst_CSD.PNG

http://www.audioheritage.org/photopost/data//500/802_35480_Diaphragm_1_Sammi_Horn_Raw_EQed.PNG


- Mind you, one also needs to link into these pics from another location ( since loading them as attachments puts them through another file conversion back to jpg & another visible down-grade in quality )

Thanks ! :)

[more10]

one also needs to link into these pics from another location

Dropbox is very good and very simple, use my invite (http://db.tt/vE290Acf) to get an extra 500 megs.

[Predrag Dukic]

@ 4313B Thanks for the photo. When I received the drivers I forgot to measure and note the dimensions of the foam inserts.
The type in this case was the one on the left; simple round piece. Could You measure its dimensions, and post results?

I doubt that the right foam alone will solve the problem. 10 or more decibels must have some other reason.

Maybe the properties of the diaphragm are also changed... Cold working of the metal in the suspension rim...
Or resin used to dampen resonancies of the diamond pattern changed its stiffness ( outer halve of the suspension is covered with some
yellowish transparent stuff- a resin or a vernice of some kind)

Who knows... I want to find the reason in principle; I want to know....

@ Ivica The damping of the PWT is irrelevant in this case. I tried open, closed end and damping in various lengths and densities.

As long as I use gating, there is no difference.

Position of the microphone is on the wall of the tube, just a 1/4 in from the throat, because I wanted later
to rotate the PWT on the driver, and check any influence or existence of the circumferential modes
( ie. whether the wave is really planar etc..)

[Predrag Dukic]

Earl,

Thank You for Your comments. I am aware that I need to change the way to present my graphs. I am new to this forum, so....

I will try to solve that problem in the following days. Maybe not immediately, because I have some obligations at the uni these days.
So there will be a couple of days of silence . After that I will try to repeat all the photos, and implement Your advices...

Till now I was using PrintKey screen capture, and gif picture format.

[Predrag Dukic]

Dropbox is very good and very simple, use my invite (http://db.tt/vE290Acf) to get an extra 500 megs.

More10,

Sorry, I can't use Your invite. Currently I am using Dropbox for a commercial project ( unrelated to my work at uni) ,

and last time I tried to connect to somebodies other Dropbox, I had some problems.

I can't afford a loss of time trying to figure what was wrong, or whether that was a Dropbox bug...
I must find some other way...

[4313B]

@ 4313B Thanks for the photo. When I received the drivers I forgot to measure and note the dimensions of the foam inserts.
The type in this case was the one on the left; simple round piece. Could You measure its dimensions, and post results?5-inch diameter
1/2-inch thick