View Full Version : JBL crossover / impedance interaction

Tom Loizeaux
04-05-2004, 11:57 AM
In looking at the JBL 3110 and 3120 passive crossovers, I have noticed that the 3110 (800 hz) is listed as being set up for a 12-16 ohm woofer while the 3120 (1200 Hz) is listed as being for 8-12 ohm woofers. Those numbers vary a little from one JBL publication to the next, but it seems to indicate that the 3110 was designed for 16 ohm woofers and the 3120 was designed for 8 ohm woofers.

My question is: How will the crossover curve be affecteed if you were put an 8 ohm woofer (and the correct 16 ohm HF) on the 3110 crossover?
...I suspect that the woofer might extend a little higher, passing a little more high frequency and I suppose creating a slight rise in the overall response around 1K. ?

Any explanation on all this and what I will get using this 3110 w/ an 8 ohm woofer?



04-05-2004, 02:13 PM
The inductance value needed to attenuate the woofer at 16 ohms would reduce by one-half for a woofer of 8 ohms. Thus, an 8 ohm woofer needs less inductor by one-half at the same crossover frequency. Keeping the inductance fixed, the attenuation effect would increase if the woofer Re is reduced. Other factors will come into play making the textbook example different that the actual result, but we should expect a depressed response from the 8 ohm woofer at the same crossover frequency than over the 16 ohm woofer.

David F

Alex Lancaster
04-05-2004, 02:35 PM

In my 1982 catalog, the 3110 says 8-16 ohm LF, 16 ohm HF, and I have used them with 8 ohm LFs many, many times.

The other day, I tried 2416Hs (8 ohm), and I thought I busted the coils, next day I set the HF control to "min"; they worked great.

You should be OK.

04-05-2004, 03:18 PM

Take a look at the resistors in the conjugate/zobel networks on the LF drivers. In the 3110 it is 10 ohms and in the 3120 it is a whopping 15 ohms. The 3120 is going to be more sensitive to LF impedance than the 3110 will be. For example, an "8 ohm" 2242H has already reached 10 ohms by ~ 500 Hz.

Tom Loizeaux
04-05-2004, 06:00 PM
So, would there be any alteration of the cure with this combination(3110 & 8 ohm LF)?
If so, would you expect a hump or a dip around the crossover frequency?


04-05-2004, 06:43 PM
Probably not. I think most of the fifteens are close enough to 10 ohms at the crossover frequency so as not to matter too much. The 3110 low pass LC filter is basically looking for a 10 ohm load. Maybe I should run some impedance curves with and without the 3110 conjugate on a 2235H so you can see what I mean. If you want me to, let me know and then give me a few days.

04-09-2004, 01:33 PM
Here's an example of the 3110/3110A conjugate on an "8 ohm" JBL 2235H transducer:

Tom Loizeaux
04-11-2004, 06:46 PM
Thanks for working up this graph.
In practical terms, what does this mean? Is there no curve variation when using the 3110 crossover with an 8 ohm woofer compared to using a 16 ohm woofer?
After a brief hook-up, I noticed that I had to turn down the HF to help match the level of the 8 ohm woofer. Wouldn't a 16 ohm woofer have even less output in this circuit? I just want to know if I need to compensate for using an 8 ohm woofer with the 3110 crossover.



11-19-2005, 06:31 PM
may you send quotations for all the types of speakers you have.I would like to buy.
Borris Mukisha

11-20-2005, 06:07 AM
And could you be more specific on what you are wanting to buy!


11-20-2005, 09:35 AM

Bring cash and a LARGE truck to Spkrman57's place.... :p

11-20-2005, 01:24 PM
I had a pair of 3110's and I sold them because as far as I am concerned, the combination between driver and crossover should be a very close match. Generical JBL crossovers might achieve 80% of what you'd want, but 100% would be just a lucky shot.

thinking about if it should / would show up a peak with incorrect impedance matching is nice, but I think the generic JBL crossovers do not match any driver 100% correct like a dedicated crossover from a studio monitor [like the 4430 for instance] does

So, if the 3110 sounds good, then keep it, otherwise try something else, like building your own

regards, Frank

11-21-2005, 11:35 AM
To who or which name and details can i send the cash to?


Bring cash and a LARGE truck to Spkrman57's place.... :p