question about the JBL S3100 crossover design

[vince]

Hi all,
I just got thrilled when I read all the infos that were on this forum recently, looks like there's fun over here, I also love DIY , but it is quite new to me, I always had a 2426J JBL and a 2234H pair as main DIY speaker, but it never sounded really HI-FI as the crossovers weren't done with care...and I decided to fix that, so I built a custom salad bowl horn and took some measurements in order to make decent crossovers , what I start to do well now!, but I would have a technical question concerning the S3100 , I saw that in the MK1 or Mk2 , on the LF section of the crossover, there are either 2 82 Ohm or 2 150 OHM resistors in parallel with the speaker, and was wondering what it was for, and would it be interesting to do the same on my LF section crossover (I have a crossover point at about 600hz) on the 2234H made out od a 6mh coil and 52uf caps...
any input would be cool about those resistors!
Vince

[Earl K]

Those twin conjugate ( load ) resistors ;

(i) Help flatten the impedance curve a bit.

(ii) Ever so slightly, increases the ratio of resistive to reactive load that the amps sees when driving the woofer. ( An amp would prefer a purely resistive load so anything that swings the pendalum that direction can be construed as amp friendly )

(iii) Try the twin 150 ohm setup first . Remember adding parallel resistance will lower the overall impedance load that your amp senses ( as well as what the passive components will be seeing ).

[vince]

Hi EARL,
thanks for the info, sure the 150Ohm setup looks like right, I tried the 2 82Ohm also, but then bass starts to get a bit loosy...but twin 150 helps a bit to get less boomy , so I guess it's the right setup for me!
thanks!
Vince

[vince]

Hi guys,
I have spent great deals of time looking at the s3100 crossover, cloning it, and tweaking it for the specific combo I currently use (2234hand 2426Hon salad bowl custom horn),
just thought I should share this if anyone has the same questions as I did,
concerning the twin resistors in parallel with the LF speaker, I have spoken too quickly, I made many tests with the twin 150 and twin 82 Ohm, and finally, once my HF crossover was well set and tweaked for the 2426(about +/- 1db from 1.5K to12K) then it made the audible change on the LF more easy to appreciate, and in my specific case , I noticed neither the twin 150, nor the twin 82 should be used, there is about 0.8db loss in the 82ohm combo, but this isn't the most noticeable drawback, actually it is clearly audible that the bass are feeled like uncontrolled and higher , actually loosy, but even resonnating in the local I use that is quite small it is easy to ear it...
So I guess that they really should be used with care, they surely are amp friendly, but only test can help you decide...

about the HF crossover, I cloned it, then tweaked it a bit, even adding an RLC notch (for a 1800hz +3db peak), then it runs cool, I added a 0.06mh coil with the bypass cap to boost a bit the uhf ...(was originally 6uf in the original jbl crossover, but I had to use a 1uf, so I used 0.06mh what should boost around 15khz)not really sure about that either!

I'd have a question anyway, I kept the first rlc notch from the original crossover, that is to say 30uf/0.16mh and 10Ohm, butwhat is it supposed to do exactly? any input? I read that excellent thread about this specific crossover, when one of the members simulated the crossover in Pi spice, but I still don't get it
cheers!
Vince

[Zilch]

I showed it a couple of pages later. The HF network has a huge impedance spike at that frequency. The purpose is to level that out so it's more friendly to various amplifier types. Measure and you'll see....

[vince]

Thanks for the info ZILCH, I actually have no equipment to test that unfortunately, but it surely works very fine with it...
but may I ask, what is the frequency peak of that network (if you have any info) and where is the related thread you talked about it? I read the one where you spiced the 2 crossovers s3100 and 3100MK2, with the curves , but I don't think that there was mention of that peak (but I will re read it) just in case if it isn't in that thread, could you just link me to the right one?
many thanks!
Vince

[Zilch]

http://audioheritage.org/vbulletin/s...9869#post79869

There's discussion before and after that post:

http://audioheritage.org/vbulletin/s...100#post101376

[vince]

Zilch,
I just love your place, I could live there, and even sleep there (i'm sure it happened to you) great place and great informative postes, i have to take the week to read and study them, lots of information indeed!
cool!I'll be back with some RTA picts of my trimmings and system I use
Cheers!
Vince