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View Full Version : Help, Need to Design a 2420 Xover



Chas
11-23-2003, 11:32 AM
Hi, I am a newbie here referred over by the HE asylum. Need some help on a cossover for 2420. Want to use 1K high pass and 8.5K low pass. The drivers are 16 ohm.
Any suggestions, or am I just better off cutting. pasting, measuring and llistening?
Thanks in advance,
Charles.

4313B
11-23-2003, 12:55 PM
You will probably want to run an impedance curve on the 2420 attached to the horn/lens you are going to be using to start things off.

Chas
11-23-2003, 05:27 PM
Hmm....sounds like a lot of work! Being the lazy, old geezer I am (without precision acoustic measurement gear, I thought maybe someone could at least, have done something similar.

I had thought about a trial and error method to achieve a second order electrical crossover, but my efforts in that vein always seem to sound lousy. I guess it is mostly due to the fact that what is really called for is an acceptable acoustic, rather than electronic rolloff slope.

As a starting point, I might try slightly modifying a 4333 xover and tinker with it using different values of L and C.

Charles.

Alex Lancaster
11-23-2003, 06:02 PM
What are You going to use for a woofer & tweeter?

Alex.

Tom Loizeaux
11-23-2003, 06:25 PM
If you want to go with JBL vintage "stock", you can use a JBL 3110, crosses at 800Hz @ 12dB for 16 ohm drivers and a JBL 3106 which crosses at 8K @ 12dB - which works between a 2420 and 2405 nicely.

Tom

Robh3606
11-23-2003, 07:00 PM
Hello Chas

You post this in the HE forum at AA. If so this might help you.

The original L200 used that woofer and crossed to the Le-85 at 1.2k. All you have to do is clone the crossover to get you the point you need. Not sure if you are using the same horn. Then just clone an N7000 or N8000 for the slot. Better off with the N8000

http://www.jblproservice.com/navigation/Network Schematics.html

That's a link to the JBL Pro Crossover library. You could also look into the 4344,4345,4344 all crossed at 1.2K to a 10" and then at 8500/10K to Slot.

Attached file is for the L200 has the schematic

Rob:)

Chas
11-23-2003, 07:50 PM
Thanks to everybody for their interest in my dilemma!

Here's the full story:

I am trying to build a full blown high effeciency system. I have some subs I put together years ago using four Altec drivers (two per channel) in large vented boxes.

I have a vintage pair of the 4325 monitors, essentially the same as original L-200's (I think).

The cabinets (4505) have been fixed up and I have added new, integral bases with wheels to get them up to a good height when situated on the floor. The wheels are to make them manageable to move around.....!

I added another hole to accomodate mirror imaging some 2405H's, these are on order from JBL.

So, what I'd like to do is have a three way system operating from 100 Hz to 20 Khz.

The woofers are 2216. I think the optimal range for these woofers is from 100 Hz to 1-1.1 khz. If they still sound crappy, I could always get them reconed. although their biggest problems exist below 100 hz, from what I have read.

I think the 2420/2307/2308 combo might be best from about 1Khz up to 8.5 Khz, then the 2405H can look after things from there on.

For years I have been fooling around with Altec/EV stuff with limited satisfaction, I am having a try at JBL, now that I can somewhat afford to.

Many years ago I heard some awsome JBL systems, the L-300 and 4350, etc. They blew me away.......
Charles.

Mr. Widget
11-23-2003, 08:24 PM
The 4325 is an extremely rare speaker. If yours are in decent condition it might be better to keep them stock for posterity or try selling them.

If you are after the L300 sound, you will probably never get there with those woofers. Even reconed as LE15As (2215s) they still won't sound like the 2231 or 2235. You will also want to change the mid horn. I don't believe the longer 2312 will fit in that cabinet.


Side note: Since Don has mentioned the disdain for the 4325/L200 on several occasions, I submit we purchase these for him as per the Don McRitchie speaker thread.:D

Earl K
11-23-2003, 10:09 PM
I'm in the middle of a job ,,,but I couldn't resist logging on and I find this;

Side note: Since Don has mentioned the disdain for the 4325/L200 on several occasions, I submit we purchase these for him as per the Don McRitchie speaker thread.

Now ,, that's great humour !!! Really, really, made my day. Thanks Mr Widget :spin:
:rockon1:

>< Earl K

Chas; Once the fog clears out my head , I'll get back to you with a few words.

I had seen your posting at H.E. _ A.A. and would add that since you mentioned that you are dedicated to using a sub below the 2216 (100hz Xover ) you should ;

(1) Consider putting the 2216 in a "right-sized" sealed enclosure . That should help "mitigate & suffocate/control" the boom problems that the 2216 is "infamous" for. It should also help enhance the speakers transient abilities. Since the Ts figures for that speaker doesn't seem to be published , that means a best guess for size. I'd run the Ts of the Le15 through "prediction software" to at least get a hint. Your statements of " increasing" the box size from its' present state - indicate to me - that you are already going in the wrong direction with the box ( whatever it is you were talking about "upsizing" ).

(2) Inspriration for a useful crossover can be found in JBLs pdf files - as the guys have pointed out. Choose something that has some Lpads in the horn and tweeter sections.
- I'll get back to you with more suggestions , if they don't first emerge from others .

(3) Do you know the somewhat standard formulas for figuring out values of caps & coils for specific crossover points ?

Tom Loizeaux
11-24-2003, 05:50 AM
You mentioned your 4325s. Look at my photo to the left. On the lower right of that grouping of cabinets is one of my "4320s" that I restored. It came with no crossovers. I set it up to be bi-amped. I repositioned the hole and added 2405 slot tweeters. I replaced the 2215s with 2231s and installed a JBL 3106 crossover. I cross over at 800Hz with the active unit and the 3106 crosses at 8K Hz between the 2420s and the 2405s. With the3106 in place, I can balance all of the drivers relative to the others. Pretty much an L300 or upgraded 4320.

Tom

Chas
11-24-2003, 07:09 AM
A little more background:

I believe my 4325's spent most of their lives in a bar - the (4505) cabinets were pretty beat up.

I have not increased the box volume at all, only added integral bases (MDF and 2X4's) and wheels to get them up to about 15" higher than stock so that the horns are better positioned relative to my ears when I am seated.

I added reforcement to the back of the enclosure by glueing and screwing on a sheet of 1/2" birch ply to the outside.

Also, I added a tweeter cutout on one baffle to allow for mirror imaging with the 2405H's.

I figure that between my LF 100 HZ (active - only 6 db/octave) crossover, plus maybe using some foam port plugs, I might be able to control the boomy bass issue.

So, what I think I end up with essentially, is kind of like a 4350 configuration where the 12" intermediate upper bass driver operates at 250 Hz to 1.1 Khz, my 2216 would do this function except start at 100 Hz.

I think a 2312 horn would fit in my boxes, although I haven't measured it. I did contemplate getting a pair there were some on e-bay but really have no need to crossover at 800 Hz. 1 Khz is just fine with me unless the experienced voices here say otherwise.Comments anyone?

I am aware that the 4320 did crossover at 800 Hz with the 2307 horn. This does seem to contadict the spec for the 2420/2307 as I interpret it.

I do have the original 3122 crossovers.

Thanks to everybody for their input so far. The carpentry is done and I still have to finish painting the boxes, then I will be ready to install the drivers. I boarded up the square opening in the rear where the old crossovers were and have three pairs of binding posts that bring each driver terminal to the rear to let me fool around with crossover designs externally.

Who knows? If all goes well I may one day triamp them and add driver delay too!
Charles.