L112/96 Network suggestions

[Nightbrace]

Don't worry about it, happy someone else thinks the L112 needs some tweaking. I am selling mine soon.

[duaneage]

I was asking WHY JBL decided to change the crossover so radically from the L36 to the L50. The only thing I can find wrong with the L36, besides its poor response under 40 Hz, is its resonance at around 240 Hz, not a reason to completely change the values for the mid and tweeter is it? Last I checked they have nothing to do with frequencies this low. They are 2 compeltely different animals and have virtually the same cabinet size porting and drivers.
Does the vertical alignment really call for this much change?

To answer the last question first, yes.
Physical distance between drivers greatly affects how they sound at the crossover frequency. Increasing the complexity of the network makes each driver perform only in it'sintended range, rather than overlapping and contributing too much, or in some cases detracting from, the sound at crossover. When two drivers produce even a little bit of the same sound there is likely to be trouble.

240 hz just so happens to be close to the resonant frequency of most Le series 5 inch midranges. A simple, single capacitor network like the N36 has would let more energy go to the midrange below crossover, and since the driver impedance rises at resonance, it would hamper the capacitor from doing it's job. if the small enclosure for the mid was lacking fiberglass, it would resonate more.

So the reason JBL radically changed the crossover seems to be to clean up the midrange performance, increase the power handling of the midrange, and make the crossover behave better. Remember, the midrange is where the music is.

[Nightbrace]

Thanks for clarifying, I understand that positioning the drivers differently will change the sound enough to warrant reworking the crossovers, but my question is why would JBL deviate so much from the final result of the L36? As I said they sound completely different. Correct me if I'm wrong, but if the crossovers allow LESS energy to the mids and tweeters, wouldn't it stand to reason that there will be less information sent to the mids and tweeters?

Yes, the newer versions of the LE25-4 tweeters (033,066 etc.) are MUCH better, and I guess you could argue that they don't need as much energy, but as you said the midrange is where the music is and the midranges are virtually the same in all three of these speakers and there is a noticable lack of detail in the midrange of the L50 and L112 as opposed to the L36. So I am confused as to why this is better. If its to reduce the resonance its not a worthy tradeoff, at least I don't think.

I can't remember if the resonance I hear in the L36's was there in the L50's. It sounds like its an issue with the the construction of the enclosures and the lack of fiberglass than the crossovers, after all these were amoungst the cheapest speakers made by JBL in the 70's/

[Nightbrace]

BTW, Free Air Resonance is 160Hz for the LE5-6, and I was estimating, I don't have any fancy equipment unfortunately to test what I am hearing

I will try adding some insulation, and see if I notice a difference.

[4313B]

Yes, the newer versions of the LE25-4's in the L36's are MUCH better (033,066 etc.)

What?

[Nightbrace]

I think you misunderstood, I mean the (033,066 etc.) are MUCH better than the LE25-4's..., but thanks for pointing that out, I changed it,. it should be a little clearer now .

[duaneage]

Like everything else , speakers work best in their intended range. Most 5 inch JBL mids I tested resonated between 220 and 275,but I have not tested them all.

One school of thought goes that a simple network is best because the phase of the crossover network is simple and unobtrusive. What can be easier than a single cap for the HF driver and leaving it at that?

But if a midrange is receiving information below and above it's best operating range then it may be damaged by bass and smear imaging for the highs. Midranges don't make good tweeters typically.

Cutting off the bass and highs abruptly is a noble goal but if done incorrectly or overdone it causes more problems. Complex networks are used to stop information right at the crossover frequency but they also change the phase of the signal as they do their job. Smart designing actually takes advantage of this to build a matching crossover circuit for the tweeter so when one driver is a little out of phase, another driver is coming into phase. These phase delays can also correct physical distance problems that cause response at an angle to be uneven. Look at the way 4411 or 4311 monitors have the
tweeters and mids mounted and you see an attempt to minimize distance.

I feel much of the success of JBL speakers has to do with the clever use of crossover networks over the years and the partnership between the driver engineers and the system designers who saw the big picture.

[Nightbrace]

Again thanks so much, I am learning, the crossovers are the heart of the speakers, this I know, but I know very little about them, just using my common sense.. And its good to know for me, that I am hearing resonance in the 230-260 Hz range as well, the spec sheet shows it at 160, but that may have been in a different enclosure.

My common sense is telling me that quick efficient shifts from one driver to the next will be best, but obviously this is not always the case.
I obviously need an education, as great as the majority of the JBL designs are, I know there is room for improvement. I'm not saying I'll be the guy to break the code so to speak, but it would be a skill I'd like to have.

Would upgrading the caps I have in the L36's keep the energy flowing while reducing the amount of resonant frequencies? I have spme experience with Coaxial drivers, but the cap values only change the crossover points and since its coming from the same voice coil, there is no worry about resonance. I am considering going back to my LN3's if not for anything, to learn about crossover design and proper driver loading, they would be great for this.

Would you recommend any resource material to get me started learning about crossover design and theory?

[duaneage]

If your really interested in how filters work you need to learn some of the math and concepts behind these three factors: impedance, reactance, and resistance. Speaker crossovers are AC devices that have active parts. capacitors and inductors react to AC voltage unlike resistors that do not change in value. I learned what I know about reactance years ago in electronic schools, reading ARRL manuals, and studying numerous books on electronic design, math, and project applications.

A good book for the money on all things speaker is the Loudspeaker Design Cookbook by Vance Dickinson. While not the end all of the science it is a damn good starting point. Vance explains more than you can imagine on how speakers work and how the drivers act in boxes. I have his 4th, 5th and 6th edition, the 7th is out I believe.

You can get a copy from Old Colony Sound Lab for about 39.95, probably money well spent. If you spend a few nights reading through it you'll know more about what we talk about and how things work.

There are other books I am sure but the LDC is a decent book well written and affordable.

[Nightbrace]

Thanks, I am an engineer and understand things pretty well, but am new to speaker design, but am learning quicky. I'll go to the library and see if they have that book, Care to explain reactance? Not a term I remember from my Physics 212 class.

[duaneage]

I doubt the library will have that one unless you go to the library of congress. This link explains it pretty well

http://www.electronics-tutorials.com.../reactance.htm

[Nightbrace]

UIUC has virtually every book every written, I am sure there is something I can find .

[Pioneer727]

You can get it at PartsExpress.



http://www.partsexpress.com/pe/pshow...=500-035&DID=7

Ron