4325 Saga Continued......

[Chas]

Hi everyone, over the holidays I have been busy! I found a pair of 2231A's and a pair of 2312's so that the only original components to be used in this project are the 4505 boxes and the 2420 drivers.

Still waiting for my 2405H's from JBL - man, are they always so slow? It has almost been a month since I ordered them.

Now then down to business, Earl K - I prototyped 4333A crossovers as planned before Xmas and for now, I am using Solen caps and coils. As you suggested, I used a resitive voltage divider in lieu of the tapped high pass coil similar to the circuit of the crossover in biamp mode, well guess what? With the 2420 connected I am getting a -3db point (electrical across the driver terminals) of about 1.4KHz! Does this seem normal to you guys?



Hey, maybe I'll donate the 2216's if there is ever a McRitchie boom box project!
Charles.

[Earl K]

Hi Chas

Still waiting for my 2405H's from JBL - man, are they always so slow?

In a word, Yes!
JBL Canada , around Christmas time essentially shuts down for a couple of weeks ( just like me ) . I can't speak for the US operation.

- Glad to see you're moving along on your project. I didn't realize you were going to retire the 2216 woofs for a pair of the fabled 2235/1 clan.

- The 1.4K ( vs 1.K ? ) error you measured isn't really very large when considering all the other things that can effect AC impedance.

Was this measurement made with the 2312 in place ? Horns affect these measurements, even changing the horn from a 2307 to a 2312 might have enough of an AC impedance effect to alter the acoustic result .

How did you determine ( measure ) this 3 db down point ? ( An electrical 3 db down point can be different than an acoustic 3 db down point ) . An acoustic measurement with pink noise may well show flatter response. Are you able to make that type of measurement ?
If - no - you might want to consider getting some RTA measurement software from someone like True Audio . You would need a measuring microphone and a preamp. The True Audio website makes a bunch of recommendations for inexpensive solutions.

If the acoustic response is 3 db down at 1.4 K and you prefer it do be 3 db down at 1K then you can likely get there by increasing the cap size a bit. This doesn't mean tossing what you have - just paralleling on a little more capacitance. Try 5 or 6uf added to the original 16.5uf .

Where did you get 16 ohm Lpads ?

regards <> Earl K

[Chas]

Hi Earl. I wasn't planning on picking up the woofs and horns, but I have had my eyes open for used stuff and they popped up! Now I have to figure out if the Thiele/Small vent tuning is appropriate for 2231A's in the event that I want to run full range. There is no 2216 T/S data published that I can find.

I might be okay since I think the original 4333 used the 4505 box, perhaps you would know?

I am using a Fluke 8050A for the decibel measurement at the terminals of the 2420. I am also monitoring the "flatness" of the input with an old solid state Heath AC voltmeter (a favorite of mine, it has a linear analog display).

I have experimented adding capacitance and got a lowering of -3 db point, but will probably wait until the whole shebang is assembled before I make any serious changes. That way I can listen and tweak and measure at the same time.

I too, thought the 12" horn with a different throat reactance could alter the driver impedance. I haven't get the 2312's yet so it will have to wait.

I have an old Technics warble tone genrator with a calibrated michrophone that may help me out.

I got 8 and 16 ohm L pads from MCM Electronics. They are made in Taiwan and look okay to me. The price was certainly right.
Charles.

[Earl K]

Hi Chas,

The 433x series of systems used variations on the 4503-(x) enclosure - according to my old JBL notes. I don't know the differences in these different boxes. The Lansing group here has lots of info/suggestions for tuning the 2231/5 speaker.

- What are the present port sizes ( diameter & depth ) in your 4503 type box ?
- What are the internal dimensions of the 4503 ?


regards <> Earl K