Upgrading DIY JBLs?

[martin2395]

Hello Everyone,

I have recently bought a pair of big custom built JBLs, they sound fabulous, but I'm curious if there are any simple mods to make them even better?
Here's a pic of the current setup:


They have:
1x 2445J mid driver on JBL2395 slant plate horn
2x 075 tweeters
2x 2205B woofers

The are being tri-amped with two Urei 6260 power amps for low and mid section and a simple Philips FA931 amp for the highs (maybe in the future I will get the 6290 for the lows)

Greetings from the Netherlands!
Martin

[louped garouv]

swapping the 075s for 077s (or pro equalivents),
and possibly adjusting/optimizing the XO point
may help reduce beaming of the UHF...
but is that what you want?

what are your xo points being used?

[martin2395]

At this moment the lo/mid xover point is at about 800Hz, the mid/hi one is at 7000Hz. These were recommended by the previous owner and also by JBL.
The only problem i have is getting all units at even volume, it's kinda difficult with 5 volume knobs I don't know if this is a fault in the design but the 075's don't blend with the 2445J, it's somewhat like 3 different speakers in one box.

[Lee in Montreal]

Very nice system my friend. The strong point of the bullet tweeters is the ability to be crossed at 3KHz, but it's weak point is that it tops around 14KHz. I would replace them with a 2405 slot tweeter at 7Khz or 8KHz. I also suggest to raise the boxes so that the lenses are at your head level. Most likely your speakers were a club install, and were hung from the ceiling.

You have a great set-up only requiring some fine tuning. If I were you here's what I would do. Your mids could go from 500Hz to 7Khz. This is the first channel you should start playing with. Then introduce the tweeter(s). Raise or lower the volume until it sounds right. At the end, raise the bass level until it sounds balanced. Take note what your levels are. The day after, repeat the same sequence. And the day after. Until you are satisfied. Basically, in the first 15 seconds you power up your system, you'll know if it sounds right or not. After, your brains are adjusting... You may also want to time align your drivers. Basically all sources shall be aligned so that sounds start from the same point at the same time. It can be dne physically, or digitally.

My last recommendation is to remove te passive crossovers and replace them with one active unit that will give you better control.

[martin2395]

Thank you Lee!

I'm running them tri-amped with Behringer CX3400 active xover (rather crappy, I'd stay away from them for home use, they are very noisy)
however they also have JBL3105 passive filters on the back, that I don't use, I tried them in combination with a JBL M552 2-way xo but it didn't sound too well as the 2445J are very efficient and I couldn't increase the volume on the 075's.

It's a pity that the 2405's are so hard to find (and expensive as hell) here in the Netherlands. I was even thinking about buying 4 ones with broken diaphragm and use the ones from my 075's.
I will also defineatly build some nice wooden stands for them, something like Kenrick Sound's JBLs use.

So would you recommend lowering the xo point between the highs and mids? I think that I'll stay with 800Hz between lows and mids, as this is the lowest frequency recommendend by JBL for the 2395 slants. I have read that they were designed for disco's and stuff like that but for home use they sound really amazing, very spacious and extremely detailed!

[Lee in Montreal]

I have some 2395 myself, attached to some 2441. JBL specifies 800Hz if the rear baffles are not used, but 500Hz if they are. I don't think your 2205 with felt domes sound nice above 500Hz.

Without rear baffles



With rear baffles



In regard of the CX3400, I had one and it is not a bad device. It is quieter than most digital units that are not set-up properly. The CX3400 only have very limited functions but it is great as a first crossover.

[martin2395]

I haven't used the 2395 without rear baffles yet, I will give it a dry with the frequency lowered to 500-550Hz.

The CX3400 has nice features but the noise is just unbearable.

[Lee in Montreal]

In regard of the noise/hiss, I suspect it is because your amp's attenuators are fully open while your pre-amp is at a small percentage of its capacity. Raise your pre-amp o 75%. Then set the power amps' attenuator to the level you expect to use. This is a very common problem, whatever the brand of active crossover.

[martin2395]

Well, maybe i've got a faulty Behringer but i'm sure this is the reason of the noise, everything is set on 100%/normal volume, the only volume control are the volume knobs on the amps, which are mostly set on 30-40%. The old JBL M552 was really perfectly quiet so it can't be the amps.

p.s
I lowered the xover frequency to 500Hz.....spot on! Bass became much more powerful and the sound is more spacious, it just sounds better.

[yggdrasil]

You could try to cross in the 075 higher than 7K, e.g. at 9-10K.

[martin2395]

Do you think it will be a good idea to let the 2445J go so high?

Though, lowering the lo/mid xo point was really an improvement, the bass has a lot more punch now.
Do you think that replacing the 2205's with 2235H's would improve the bass even further?

[Lee in Montreal]

That's good news. Have you measured the distance betwee the 2445 diaphram, 2402 diaphragn and 2205 domes? You can calculate the delays to apply to the 2242 and 2205 to start aligning them. Your 2445 is the furthest back, so it should stay at zero. Delay the others and align them on the 2445..

[Mannermusic]

Well, maybe i've got a faulty Behringer but i'm sure this is the reason of the noise, everything is set on 100%/normal volume, the only volume control are the volume knobs on the amps, which are mostly set on 30-40%. The old JBL M552 was really perfectly quiet so it can't be the amps.

p.s
I lowered the xover frequency to 500Hz.....spot on! Bass became much more powerful and the sound is more spacious, it just sounds better.

Yes, and it would be even better if you would add a mid-bass driver right where the 075s are and then put the UHF - either 075 or 077 - on the top. Like the 4355 except with a big (!) horn/lens. I ran a 3-way tri-amp similar to yours for 25 years and never was satisfied with the musical fundamentals (200 - 1200 Hz). The mid bass fixes that. I cross at 260, 1200, 8-9,000. You can use Giskard's 3155 network for the treble and bi-amp the bass. The big 3-way is just fine for night club/PA/rock&roll but if you are interested in Hi Fi, I'd consider 4-way. Not sure what you are looking for. Many ways to "skin a cat!" Neat project. Mike

[Lee in Montreal]

The big 3-way is just fine for night club/PA/rock&roll but if you are interested in Hi Fi, I'd consider 4-way.

I second that. I think that the 200 to 800Hz is crucial for hifi. Vocals, snare drums.... Sadly no 15" woofers goes up there, and no compression driver goes that low. Therefore a front horn loaded 12" driver could work the 100Hz to 800Hz range. Leaving all the thump to the woofers. It is actually my next step. If only I could find some affordable 2206...

[more10]

I think that the 200 to 800Hz is crucial for hifi. Vocals, snare drums.... Sadly no 15" woofers goes up there, and no compression driver goes that low.

JBL 248X. Radian 950PB. JBL 244X with Radian 2445 diaphragm. BMS 4591. They all are usable from 300.