250Ti - 4-way active experiment

[Dagfinn]

This is really useful. Very interesting to see how much the woofer is allowed to play, "star of the show" in the 240Ti.
Btw, here's the interview Erin's Audio corner did with Greg Timbers in 2022 https://youtu.be/afeTHLLp-EI?si=KUAV4dE7uNutrncw
Poor Erin, didn't know the L250... great interview nevertheless .

[Dagfinn]

So, things didn't quite go as planned, but no problem. The two mids are mounted in small boxes inside the baffle, and cables are glued. I'll cut the c.o. cables as it's the cleanest way.

I've looked at the c.o. from the Jubilee, and read a bit about the Linkwitz-Riley 24dB c.o. The dbx has Linkwitz-Riley24dB, which is ok for tweeter/hi-mid/mid, but not ideal for the woofer to low-mid. The Jubilee has a 6dB slope for the woofer, supporting the low.mid and certainly affecting sonic properties of the speaker. Trying to maintain this slope seems important. One solution is to keep the woofer-part of the passive c.o. in for now, and feed it a fullrange signal. This should work fine, it's already prepared for bi-amping. At least I hope so .

More challenging is the low/high mid c.o., but 24dB is what I have. Hard to find data on the 108H. I'll assume it is similar to the 2118H? Not much else to do. It's obvious that a more advanced c.o. would be needed to follow the slopes from the schematic. But if it sounds good, I'll have to ponder something for the woofer, perhaps just copy the passive c.o. and keep it in the circuit.

I found a JBL spec sheet for the 104H by G.T, perhaps webmaster could put it in the archives?

[grumpy]

or... https://groupdiy.com/threads/low-pas...e-level.34480/

[Dagfinn]

Thanks grumpy. Doing it line level would naturally be better and even looks within my capabilities to make... Didn't know it could be that simple.

[Dagfinn]

Got them up and running today, all drivers going via dbx crossover for now. I think this may work out really well, set up by ear is already very pleasing. The dynamic power is undeniably improved. I think 650w/channel will be sufficient. The current 200w for tweeters is a bit excessive, so I'll swap down to 125w for tweeters and 104H, while the 108H and woofer gets around 200w each. I changed my mind about the EC since it doesn't have a gain control, which I like to have.

Next I'll measure up the passive c.o., to have a proper record of it before full conversion. I may do the line-level lowpass too, I found I l aready have the needed parts for a 348Hz corner frequency. I forget, I'll need another dbx too... not too expensive, fortunately. Maybe a used shows up, no rush. So, now I look forward to fine tuning and listening to these amazing speakers. I already hear new stuff in well known music, I like that . It as if there is more space to let more instruments out....

(not sure why, emojis don't seem to work ???)

[Dagfinn]

So, I've rigged my 2-way crossover for the passive side, biamping it using the EC AW75. Biamping is a good option, perhaps enough for many. Clearly worth it to my ears ! Easier to deal with, for sure. Before starting this I thought there were more options for crossovers, but I can't find many 4-way at all. Did a measured approach, combining pink noise and sweeps, and got a result I feel is pretty good. My levels for each driver was ok by ear, but some form of EQ is needed when including the room. The two speakers don't match exactly, as expected with this crossover. Hard to tell by listening. I'm both impressed and pleased . There's a better clarity to the lower octaves, better tonal distinction. Have to make a rear cover and connector plate, 2x speakon perhaps...

[Robh3606]

Bi-amping them is nice I built a Bi-amp Jubilee clone years ago. Used a DX-1 with custom cards I built using LEAP. I have to resurrect them at some point. I have a pair of 1400 subs with blown plate amps ready to go with them so Le-14H-3's! Originally used 121A's.

Glad you are having fun!

Rob