JBL 2445_46 frq.response

[withTarragon]

In my experience a notch that narrow and deep is usually due to a "bounce" somewhere. Since you get it at different distances, it is probably not a floor bounce. The obivous question (and you probably already know this) is whether there is a hard surface about 2-4 inches from the mic.

I have measured 2446's mounted on tractrix horns (Klipsch) and CD horns (Electro-voice HP series) and I have not seen that behavior.

Just an oddball possibility, is the seal between the driver and horn nice and snug (is there a gasket)?

BTW, I am a fan of the 2446. It is a great driver, but you need to stay from after-market diaphragms.

-Tom

[Earl K]

Also, inexplicable notches can be caused by a poorly fitted diaphragm .

Heres' one such example .



I've never had any success in getting a proper fit with this one Radian diaphragm .
The pic shows separate attempts on two different Altec driver bodies ( an 802 & a 902 ) .

<> cheers

[ivica]

unfortunately I have done a lot of measurements in different positions using even several measuring methods (one of them is my own based on spread spectrum techn.), but all of them including well known TrueRTA "recognized" the mentioned deep notch about 3kHz. I want to emphasize that almost the same character can be find on another 2445 driver (I have). Reading some help docs for AkAbak simulation software I realized that may be some small change in the volume of the cavity where the voice coil is accommodated can produce such deep notches. I did mine easy simulation using mentioned AkAbak (fig.3) and I can easily get such notches. That give me some "idea" that there exist some kind of cavity that interact with the diaphragm.
May be the main reason is that I have used D16R2450 (diaphragm for 2446 ) instead of D16R2445, or there is something else.



-Tom[/QUOTE]

[ivica]

unfortanety I can not attach pictures now.





-Tom[

[ivica]

Also, inexplicable notches can be caused by a poorly fitted diaphragm .

Heres' one such example .



I've never had any success in getting a proper fit with this one Radian diaphragm .
The pic shows separate attempts on two different Altec driver bodies ( an 802 & a 902 ) .

<> cheers

If mentioned notch can be neglected (#@#$%&), the response on both 2445 drivers are very similar, of course not absolute identical, so it is expectable that there would some differences but mentioned notch is my 'vital' problem.

[Earl K]

Mine 2445 original membrane had gone out, so I put new original JBL 2446/2450 (16 Ohms) Ti "ribbed" membrane.

Are you positive that those replacement diaphragms you bought are original JBL equipment and not just some counterfeit Chinese/Thai junk ?

<> cheers

[ivica]

Are you positive that those replacement diaphragms you bought are original JBL equipment and not just some counterfeit Chinese/Thai junk ?

<> cheers

I buy them from local authorized JBL dealer (mentioned on JBLPRO site as responsible for my country) . Box seem original, and concerning lot of marks on voice coil former it seems that it is from JBL, but nowadays nobody is sure, especially for JBL that is closing most of their plants and mainly keeping sales dept. in USA....but such is known story for many other not "profitable" company.

[Earl K]

I buy them from local authorized JBL dealer (mentioned on JBLPRO site as responsible for my country) . Box seem original, and concerning lot of marks on voice coil former it seems that it is from JBL, but nowadays nobody is sure, especially for JBL that is closing most of their plants and mainly keeping sales dept. in USA....but such is known story for many other not "profitable" company.

Tom,

Thanks for answering that queston . Your diaphragms certainly seem legitimate .

I'm not aware of any known ( official JBL ) restriction against putting a D16R2450 diaphragm into the 2445 body .

For now, I guess I'm out of ideas .

<> cheers

ps ; One last idea, have someone else measure a single unit of yours ( with a 2311 horn ) and see if they can confirm your findings .

[ivica]

Tom,

Thanks for answering that queston . Your diaphragms certainly seem legitimate .

I'm not aware of any known ( official JBL ) restriction against putting a D16R2450 diaphragm into the 2445 body .

For now, I guess I'm out of ideas .

<> cheers

ps ; One last idea, have someone else measure a single unit of yours ( with a 2311 horn ) and see if they can confirm your findings .

That "restriction" of putting a D16R250 into 2445 for sure would not "smash" phasing plug for sure , but really such behavior near 3kHz was not expected for me.

[grumpy]

I have examples of both the 2445 motor and 2446 diaphragm at home.
If I remember to, I'll put them together with a 2311 and independently measure
with and without the 2308 lens.

I seem to recall doing this before (different horn, no lens) and not noticing
such problems, but I can't find the files, so I might as well duplicate the
setup as closely as possible.

-grumpy

[ivica]

I have examples of both the 2445 motor and 2446 diaphragm at home.
If I remember to, I'll put them together with a 2311 and independently measure
with and without the 2308 lens.

I seem to recall doing this before (different horn, no lens) and not noticing
such problems, but I can't find the files, so I might as well duplicate the
setup as closely as possible.

-grumpy

That would be nice, so may be the mystery will be "uncovered"
Thanks in advance

I have now my figure and AkAbak script file. What is importanat that the mentioned notch at 3kHz can be simulated as
a cavity around voice coil and its path ( Ha, ds and ls in attached script file)

[grumpy]

status: 2445 and 2441 assembled. Need to fit 2446 diaphragm and test.

I would have gotten it done but my daughter had a tire blow out on her way to work
yesterday evening... she's fine. I'll still get to the testing.

[ivica]

I have examples of both the 2445 motor and 2446 diaphragm at home.
If I remember to, I'll put them together with a 2311 and independently measure
with and without the 2308 lens.

I seem to recall doing this before (different horn, no lens) and not noticing
such problems, but I can't find the files, so I might as well duplicate the
setup as closely as possible.

-grumpy

Here are some measurement done with 3133 compatible network
with 2445 body with D16R2450 Diaphragm and 2311&2308 horn-lens,
and for comparison measurements of 2421 with its 2307&2308 horn-lens

iti s added (on one measurement) Beyma CP21F UHF driver, unfortunately I have no 2405

[ivica]

status: 2445 and 2441 assembled. Need to fit 2446 diaphragm and test.

I would have gotten it done but my daughter had a tire blow out on her way to work
yesterday evening... she's fine. I'll still get to the testing.

I have seen some measurements that other member (4313B ) did with 2445 body and D16R2450
diaphragm ( as is in 2446 driver) and everythink is perfect

[grumpy]

good to have that 2421 measurement for comparison (not likely to be an inherent
measurement problem). I'm happy to do another independent measurement and
it would be good to dust off the test gear, so no problem I will not be using a
complete network though (3133 or otherwise), just a large capacitor.