New crossover?

[joetech]

I have some L-88s that I have been tweaking for about a year now. I have replaced the original 8uF cap with a new polycap and upgraded the binding posts. I have added more fiberglass to the back. Now I have gone and replaced the old LE25-1 tweeters with some 035Ti’s. I must say they sound pretty darn good. Both the old and new are suppose to cross at 3 kHz.
I found a crossover formula datasheet at www.mhsoft.nl (http://www.mhsoft.nl/) and http://ccs.exl.info/calc_cr.html#lpad both gave me a whole bunch of different values for one thing. A first order xover shows using a 13.25 mH inductor on the Woofer and a 13.25 cap on the tweeter. Does the fact that there is an inductor here change the value required for the cap?
I have also looked at some of the crossovers that JBL uses for the L1 and L20T both of which are 2 ways with different woofers instead of my 123a.
Question is, should I make a new xover? Right now the modeling program shows a x over point of5000 with an 8uF cap. Below are the T/s specs I have found on drivers.

035Ti 123a
Re 4 8
Fs ave 1900 25
Z max ave 15 ?
F1 ave 1500 ?
Qms @3 5.3
Qes @1.5 .54
Qts @ 1 .49

Somewhere on this forum someone published the specs for the Le25 and the 035Ti and 035TiA . Above are an average for the measurements he found. The 123a are the specs from unibox. I wrote down the specs for the 035 and now I can’t find the thread to write out the specs on the Le25. I’ve looked at many threads here on the L88, 035 L100 etc. and I am very confused. It seems that plugging the port is the way to go but in my situation it may not be. My main listening room is 13’ wide x 15’ The speakers are on the bookshelf (appropriate enough) about 40” off the floor to clear some heavily padded furniture and that’s the only place they fit. They are about a foot from a very short wall. Both sides open up with large archways to other rooms. A 6ft archway on the left to a 10x10 room and on the right a 9’ archway into a room 14x15 so I get almost no gain from the walls. The 035s have opened up the sound stage. Being better at dispersion than the old cone tweeters and not as beamy. I must say I like them very much the way they are but I always say if it isn’t broke tweak it.
I see lots of options but none of the thread I’ve read on this and other forums seem to match. Do I copy a later JBL crossover even if it isn’t a 123a woofer? Anything close? Do I use a 1st order xover with an inductor? Change the cap only?

[Zilch]

It's gonna cost under $10 to try the port plugs. Notwithstanding boundary reinforcement, they're boomy by design. The plugs strip off the boom and leave the rest.

Yes, when you go from 6 dB to 12 dB filters, the cap value changes.

I've got filters on the woofers, but my design isn't final. Start with a Zobel and an inductor....

[joetech]

yes I've read the long thread from a (few months ago?) about the closing of the port. I like the idea of using a plumbing test plug. But wasn't all that on a 3 way L100? Temporary and easy to remove if I don't like it. What value of inductor do you suggest I put on the woofer? Also, if I'm not mistaken, the Re of the LE25 is 8ohm and the 035 is 4ohms. I know this changes things as well. A zobel is an interesting idea but isn't a L-pad really the same function only more variable?

[Zilch]

Most of the work in that thread was done using L88, including the damping studies:

http://audioheritage.org/vbulletin/showthread.php?p=123070#post123070

L100 was merely a "Sidebar."

Zobel flattens the impedance so that the inductor works predictably.

No L-Pad in the woofer circuit.

Look to standard designs for an inductor value starting point....

[joetech]

Yes I know the Lpad is just for the tweeters. It was suggested on another forum (yes I've been seeing another forum:eek:) That a 1.1mH choke on the woofer and 8uF 2 cap on the tweeter and a 2ohm resistor be used but they didn't say if the restitor was in parallel or series. I assume one cap was in parallel and the other in series? I didn't follow up at the time for clarification.
Does this sound like a good approach. I plan to check out in more detail the xovers for the L20t and L1 that both used the 035Ti. Any thoughts would be appriciated.

[joetech]

I went to a Cleveland Orch concert today. They were to play, among other selections, Stravinsky's Symphony in 3 Movements. I have a good CD of this. So, on Saturday I listened to it very closely. Then I went to my shop and made some plugs for the port. I listened again to the Stravinsky and others and the bottom end was less boomy.
At the live concert, I must say my speakers do sound very good in comparison. Of course, a 3 hour plus time delay isn't a real comparison and nothing can compete with the live sound of a great orchestra in a very well designed venue. However, I wasn't 'suprised' to hear new sounds I hadn't heard before.

Now my next experiment will be to see if adding a cap to the existing one will make much difference. Right now tweeter has an L-pad and 8mF Cap. That's all. The original tweeter, LE25-1 was 8 ohm. The new 035Ti is 4 ohm. Doing some quick calculations that means the tweeter was coming in at 2500 Hz (literature sayes 3000) but the 035 at 4 ohms is coming in at 5000! (If my calculations are correct.)

So if I want to bring in the tweeter at 3K again, I need to increase the Cap to 13.25mF. I think I will try to do this by putting in parallel a 5mf cap. and see what happens. If I want to cross at 4000 I would have to go to 9.9 mF so I would put in a 2mF cap. Comments please.

I know Troels Gravesen is working on redesigning some L-100s I was going to wait to see what he comes up with before I do anything drastic.

Thanks Zilch for your input. The plug I made works great. I don't need plumbing supplies. I have a lathe. In fact I have 3. 1 wood and 2 engine lathes. I could go into business. Right now the plug is a temp but I think I could modify it to use an O-ring and center bolt to sqeeze the o'ring out and make it very rigid yet removable and flush to the baffle. Made of MDF instead of your silver pine plug:D

[Zilch]

Why do you believe the 035 is 4 Ohms?

Do you hear the difference in the bass response?

Mr. Widget's test for a good seal is to gently press the woofer cone in about 1/4" and it should return to neutral sluggishly.

[He said "snail's pace," actually, but slugs are kinda the same thing.... ;) ]

[joetech]

This is a 4 ohm because JBL literature says it is. I also found, a few weeks ago, where someone had measured some 035Tia and 035Ti and all were 4 ohm nominal.
Yes, I do hear some difference in the bass. Not quite as much 'punch' but a better over all sound. For example, in the Symphony in 3 movements there is a bass drum and tympany. Before the bass kind of overpowered the tympany but now they are more distinct. I just did this on 3 days ago and haven't had time to listen extensively.

Yes, the woofers do return more slowly than before.

[Zilch]

http://www.jblproservice.com/pdf/Studio%20Monitor%20Series/4410LR.pdf

DCR spec. is 3.5 - 4.2 Ohms.

That ain't the impedance.

The diaphragm kit is D8R035tiA, 8 Ohms nominal....

[boputnam]

... Of course, a 3 hour plus time delay ..Dood - that is a REALLY long room!! :rotfl:

[joetech]

OK I assume it would see 8 ohm because no matter what because I forgot about the L-pad which is 8ohm. So it looks like the tweeters still kick in about 2500. This is the same point the L60T crosses.