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View Full Version : Upgraded L200A - Actual Impedance of LE15B & New Network For Adding 077 Tweeter



wlk
01-31-2012, 11:26 AM
I recently aquired a set of L200As that were upgraded with N8000 networks and 077 slot tweeters

The upgraded L200A speakers include LE15B woofers, LE85 mids, H-91 horns with diffraction grates, 077 slot tweeters, LX-16A networks and N8000 networks.

My first question is what is the actual impedance of the LE15Bs?

The label on the back of the LE15Bs says 6 - 8 ohms?

Some JBL literature including the JBL Technical Manual (L200 / L200A) says that they are 8 ohms?

Other JBL literature says that they are 4 ohms (specs on 2216)?

The DC resistance of my LE15Bs are 3.5 ohms and 3.8 ohms (as specified in the JBL Technical Manual L200 / L200A).

My impedance meter says that at 1K Hz the impedance is 4 ohms?

My second question is what network should I build to improve the sound quality of the L200As and properly add the 077 slot tweeters?

I would like to have the lower crossover point a 800 HZ like the L200Bs.

If the LE15Bs are actually 8 ohms impedance would the 3107 network be suitable.

The original LX-16A and N8000 networks are old and do not sound very good.






t

hjames
01-31-2012, 01:33 PM
I have a pair of L200s that have been reworked into 3 ways ...
I added a pair of 2405 slots and rather than adding old crossovers with aged caps, I built fresh crossovers with new caps.
What I built (courtesy of plans offered by senior member 4313B)
was a pair of what amounts to updated 3133 crossovers (as used in the 4333 speakers) ...
I later swapped the LE15s for 2235s and then for 2234s (I had both and wanted the 2235s for something else) ...
Since then I've got to external wooden midhorns for the 2425s drivers, then later swapped 2441 drivers into their place.
You do most any of those things over time ... the most dramatic would be the upgraded crossover and adding the slot tweeter.

Its been written here that the LE85/2425s don't really play well down at 800hz, even tho JBL claimed they did.
The best results are when you cross them no lower than 1200hz ...
which is why the standard L300/4333 crossovers will be your best approach.

Mr 4313B's design of the 3133 Equivalent schematic is here -
http://www.audioheritage.org/vbulletin/showthread.php?166-4333-S300-L300-equivalent-bandbass-circuit&p=1042#post1042

Anyway - I'm not the only one who has tweaked L200s on the site - but this is a start ...







I recently acquired a set of L200As that were upgraded with N8000 networks and 077 slot tweeters

The upgraded L200A speakers include LE15B woofers, LE85 mids, H-91 horns with diffraction grates, 077 slot tweeters, LX-16A networks and N8000 networks.
My first question is what is the actual impedance of the LE15Bs?
The label on the back of the LE15Bs says 6 - 8 ohms?
Some JBL literature including the JBL Technical Manual (L200 / L200A) says that they are 8 ohms?

My second question is what network should I build to improve the sound quality of the L200As and properly add the 077 slot tweeters?
I would like to have the lower crossover point at 800 HZ like the L200Bs.

If the LE15Bs are actually 8 ohms impedance would the 3107 network be suitable.
The original LX-16A and N8000 networks are old and do not sound very good.

wlk
01-31-2012, 02:57 PM
HJames thank you for the qiuck reply.

I have built the network that you specified for a set of 4333s that I built from scratch.

It is a great sounding network but I am not sure that the specified network will work in the L200As.

My L200As have LE15B woofers which might actually be 4 ohm impedance woofer.

Could you make any suggestions as to how I can modified the specified network to accommodate 4 ohm woofers.

hjames
01-31-2012, 05:32 PM
HJames thank you for the qiuck reply.

I have built the network that you specified for a set of 4333s that I built from scratch.

It is a great sounding network but I am not sure that the specified network will work in the L200As.

My L200As have LE15B woofers which might actually be 4 ohm impedance woofer.

Could you make any suggestions as to how I can modified the specified network to accommodate 4 ohm woofers.
Are you sure they are really 4 ohm woofers?
I have read a number of folks say some of the driver impedance numbers are lies ...

If you already have the crossover network available, what could it hurt to try it out and see what it sounds like in this system?
- worst case you might need to pad down a driver or two ...

These days I am a web developer and not a speaker designer.
I can build a circuit, even do a little troubleshooting but design is beyond me right now.

Some of the L200 mod folks have even made a little doghouse/bumpout on the back of the cabinet
so they can run the L300/4333 (2312) Long horns instead of the shorter exponential horns like you have now.

I can dig up links for that from Toddalin and Subwoof - both of whom have done that upgrade.

wlk
01-31-2012, 07:12 PM
The actual impedance of the LE15B woofers is the big unanswered question.

There is so much conflicting information in the JBL documentation I am not sure what to believe.

Is the impedance 4, 6 or 8 ohms?

If I knew the actual impedance of the LE15B woofers I could attempt to use as is or modify the equivalent bandpass network for 4333/S300 /L300 that was posted by 4313B.

Unfortunately the equivalent bandpass networks for 4333/S300 /L300 that I built are mounted inside my 4333s and it would be a significant task to remove them and try them in the L200As.

Robh3606
02-01-2012, 04:02 AM
Why don't you just measure one? You can use DCR as an indication of what 'imp' coil you have in them. Look up the 2215H and 2215A in the table and look up Re. The H is 8 ohms the A 16. Use that as a reference.


http://www.lansingheritage.org/images/jbl/reference/notes/tech1-3a/page08.jpg


Rob:)

wlk
02-01-2012, 09:32 AM
Robh3606
Thanks for the suggested method of determining the actual impedance of the LE15B and the Thiele / Small table.
As stated in my original post the DCR of the two L15Bs is 3.5 and 3.8 ohms which is as per the JBL technical manual spec sheet for the L200A / LE15B.
This same spec sheet states that the impedance of the LE15B is 8 ohms.
As per your recommendation the actual impedance of the LE15B is 4 ohms.
This was also my intial thinking when I measure the DCR but I wanted to make sure I was not missing something.
JBL must have made a mistake on the spec sheet.
Once again thanks for the help.
Now the question remains how can I alter the equivalent bandpass circuit posted by 4013b to accommodate the 4 ohm LE15B woofers?
Anybody have any suggestions?

spkrman57
02-01-2012, 09:38 AM
DCR of 3.5 ohms to 4 ohms could still be a 8 ohm driver.

Unless someone reconed the drivers and used a different voice coil I think you are safe enough to treat those drivers as 8 ohms.

Just my 2 cents worth of course!

Regards, Ron

Mr. Widget
02-01-2012, 10:14 AM
I'd either buy or borrow a WT2 and measure the damned thing or just assume it is 6 ohms. I've had LE15Bs years ago and they were labeled 4-6 ohms and definitely had a lower impedance than JBLs with an 8 ohm designation. The LE15A is one of the handful of vintage JBLs that are confusingly labeled both 8 ohms and 16 ohms even though the actual impedance is in between... the LE15B was never labeled anything but 4-6 ohms, and the pro variant, the 2216 was labeled 4 ohms.


Widget

wlk
02-01-2012, 01:13 PM
Gentlemen all the feedback is greatly appreciated.
I am about to undertake a relatively significant project restoring and upgrading the L200As and your feedback will help me do it "right" the first time.
The JBL labels on the back of my LE15Bs state that the impedance is 6 - 8 ohms.
If we assume that the LE15Bs are 6 ohms impedance (middle ground from all the feedback I have gotten) can I "get away" with using the Equivalent Bandpass Circuit posted on the forum by 4313B (an excellent sounding network that I built for my 4333s)?
Can I "get away" with adding a 2 ohm wire wound 40 watt resistor in series with the LE15B to get closer to 8 ohm impedance - I know I will waste a bit of power.
I have a relatively inexpensive impedance checker made by Raymer (model LTS-1) which measures the impedance at 1K Hz and it says that my LE15Bs are 4 ohms.
Unfortunately it would not be possible to rent a high quality impedance measuring device close to where I live.

Mr. Widget
02-01-2012, 02:21 PM
The JBL labels on the back of my LE15Bs state that the impedance is 6 - 8 ohms.That must be what mine said too then and I mistakenly remembered 4-6 ohms.



If we assume that the LE15Bs are 6 ohms impedance (middle ground from all the feedback I have gotten) can I "get away" with using the Equivalent Bandpass Circuit posted on the forum by 4313B (an excellent sounding network that I built for my 4333s)?
Can I "get away" with adding a 2 ohm wire wound 40 watt resistor in series with the LE15B to get closer to 8 ohm impedance - I know I will waste a bit of power.Since you are using an entirely different woofer, I don't think I would expect that network to perform as intended with or without the addition of a 2 ohm resistor.



I have a relatively inexpensive impedance checker made by Raymer (model LTS-1) which measures the impedance at 1K Hz and it says that my LE15Bs are 4 ohms.I bet it is 4 ohms at 1KHz and likely 50 or more at resonance...

Here is an impedance plot of a very different JBL, the 1500AL... you can plainly see that it isn't 8 ohms at every frequency. In my experience only ribbon tweeters tend to have a linear impedance at all frequencies.

Widget

wlk
02-01-2012, 04:37 PM
Well ..........., at this point I guess I have two viable options for restoring and upgrading the L200As.
The first option is to build a new network as per the schematic in the JBL Technical Manual for the L200A (LX-16A network) and add the components to accommodate the 2405 tweeter (N8000 / 3106 network).
The second option is to find a new home for the LE15Bs, use a set of 2235s and build the Equivalent Bandpass Network posted by 4313B.
I will also have to re-tune the cabinets.
I have got to give this one a bit of thought because I already have a set of upgraded 4333s and upgraded 4430s.
Once again thanks everybody for the help.