2123H vs 2122H in a 4343 monitor

[GordonW]

Yep, at some point, you have to start looking at increasing the series inductor value as well. Damping is important to maintain... something I've personally learned the HARD way here and there!

Regards,
Gordon.

[Guido]

Hi Earl!

I changed that cap value in my SIMPLE Network calculation programm.

The programm shows me rising midband response with increasing the cap value.

Am I wrong with something? Or is my program too simple.

[4313B]

Hi Earl,

Can you please post impedance curves of the two 2012H's that you have for us?

Thanks

[Earl K]

Hi Giskard

Because of present show duties , I'll be unable to provide full motional impedance curves for a 2012h (minus the circuit & enclosure ) until sometime next week .

- But having said that - I do have some notes I made yesterday .

-The following values are AC circuit impedance measurements ( in box with circuit ):

With the 16 ohm Lpad "fully open"

400 hz - 4.5 ohms
800 hz - 4.9 ohms
1000 hz - 7.2 ohms

With the 16 ohm Lpad " approx" 1/2 on

400 hz - 5.2 ohms
800 hz - 4.5 ohms
1000 hz - 6.7 ohms

1.6 mh inductor - with a DCR of @ .4 ohms

As one can see from the above values this circuit is far from being optimized for a 2012h. The changing impedance ratios induced by rotating the Lpad show that. I did add a 1 ohm resistor in series with the 2012h this morning to see its' effect but ran out of time to do real measurements. A quick check with the RTA showed a bit of leveling or improvemet in the pass-band.

This is why I asked Guido how much rotational room he has left in the Lpad.

I suspect the Tpad needs reworking & perhaps a bit of series resistance after the Lpad. Hopefully someone with modelling software can figure this out. I would have to do this empirically - which I don't mind doing - but not until next week .

Guido ;

I don't know what you might be doing different without having the actual 3143 circuit on which to make AC impedance measurements. I would also need to be familiar with the software you own .

regards <. Earl K

[Guido]

Originally posted by Earl K
Guido ;

I don't know what you might be doing different without having the actual 3143 circuit on which to make AC impedance measurements. I would also need to be familiar with the software you own .

regards <. Earl K

Take your time Earl.

I'm sure you will come up with a good solution for optimizing our 2012H transducers.

Looking forward to it

[4313B]

Ok Earl, thanks.

"Hopefully someone with modelling software can figure this out."

Well, actually my electroacoustic model of the 2012H is coming up short. Hopefully a couple of free air impedance plots will clear it up.
Whenever you happen to get to it is fine

[GordonW]

Originally posted by Guido
Hi Earl!

I changed that cap value in my SIMPLE Network calculation programm.

The programm shows me rising midband response with increasing the cap value.

Am I wrong with something? Or is my program too simple.

Guido, try making the 2012's LP inductor bigger instead... might be a damping thing you're already running into. Let us know if that models any better... I'm guessing it will, because that will both (1) decrease the effective F0 of the filter (lower crossover point) and (2) decrease the Q (increased damping) of the filter, which will reduce the output at F0.

Try it, see if it works!

Regards,
Gordon.

[TimG]

I have LspCAD modelling software on my computer. If you can measure impedance, SPL and phase response for the driver in your cabinet I can develop a crossover model for you. The program cannot compute absolute SPL though so it would be good to have a reference SPL such as from the woofer or tweeter to match the levels up. If you can't measure phase I know where I can get a program that can estimate phase response. If would also be helpful to have the existing crossover schematic so that could be included in the model.

[Guido]

Originally posted by GordonW
Guido, try making the 2012's LP inductor bigger instead... might be a damping thing you're already running into. Let us know if that models any better... I'm guessing it will, because that will both (1) decrease the effective F0 of the filter (lower crossover point) and (2) decrease the Q (increased damping) of the filter, which will reduce the output at F0.

Try it, see if it works!

Regards,
Gordon.

Yep!

I increased the 1,7mH to 2,5 mH (in program).

The result is -3 dB at 1 kHz.

Q at 290Hz is 1,325
Q at 1100 Hz is 0,545

[Earl K]

Hi Giskard

-Here's the best I can do for impedance plots - for the two 2012h I had here last week.

-These values were quickly taken ( in their respective enclosures ) - before they were sent back to inventory - to be then sent out .

- I don't anticipate seeing these specific units again for some time. So , these values are going to have to suffice as a general impedance guide ( relating to all 2012s ).

-I chose 6.2 ohms as a mean target impedance to restore to. This would be the "working impedance" for the lowpass portion of that midbass section. Motional Impedance checks indicate that I've more or less gotten there by putting a 1 ohm resistor between the hipass section and the lowpass section of the midbass circuit. Won't really know how it works with that preceeding section without buying the inductor needed for the highpass portion - ( and I'm not planning on that anytime soon ).

- If I was starting with a clean sheet - I'd build up the circuit around an 8 ohm Lpad . A 16 ohm Lpad with these 2012 is just too wobbly ( the Lpads' impedance tracking is all over the place ) . ie - without some resistive compensation - it' changing the "Q" of the filter as well as gain.

regards <> Earl K

[4313B]

Ok, thanks Earl!

[GordonW]

Guido, IIRC, that crossover response curve there, looks very much like the OPPOSITE of the 2012 response curve... so, the SUM of that and the driver (as in working together) MAY come out just about dead-on flat.

I'd be really inclined to try that, and see how it sounds...

Regards,
Gordon.

[Guido]

Originally posted by Giskard
Ok Earl, thanks.

"Hopefully someone with modelling software can figure this out."

Well, actually my electroacoustic model of the 2012H is coming up short.

Giskard, any progress with your model of the 2012 and modification suggestions for the 4343 network?
I'm ready to try it on my stock pair of 3143.

Thanks

[4313B]

Originally posted by Guido
Giskard, any progress with your model of the 2012 and modification suggestions for the 4343 network?
I'm ready to try it on my stock pair of 3143.

Thanks

Actually, I haven't fiddled with it further. Sorry

In your case I don't think it would be wildly helpful anyway since you're operating in such a limited bandwidth. You pretty much have a constant impedance in the range you're using it in.

Did you try the notch filter?
Have you tried what Earl and Gordon suggested?
Try both of those suggestions and let us know?

[Variac]

Second question for the JBL TECHBOT: Do you have the part number for the ME150H recone kit? My JBL service center doesn't have it in his consumer listings ( I assume due to the overseas use only ) and unfortunately we cannot call carla at JBL anymore...

Hello, I am a new member here, but a regular at DIY Audio.
I just bought a pair of New Old Stock JBL's so I guess I am in this club too.

It was suggested that I could find out more about my NOS
JBL ME 150H woofers in this forum. They are mentioned in this thread so I'm hoping for the best! I would like to know what model speakers they were in, what years?, specs, any good? Overseas only- what countries?etc.

Thanks
Mark