Biamping JRX115, is it worth the experiment?

[LowerBeef]

Hello everyone,

I have a system in my basement used solely to amuse myself when my wife and daughter are out of the house and I want to hear some loud music. Currently it is:

dbx DriveRack PA2
Crown XLS 1502 (not currently in use)
Crown XLS 2502 (driving JRX115 full range stereo)
Crown XTi 1002 (driving MP418S bridged mono)
JBL JRX115
JBL MP418S

And it sounds okay. The subwoofer is great, but the JRXs can't keep up. I know these are JBL's economy speakers, but I've found that they use the same drivers in other more expensive speakers, for example the AC2215/95 uses the same M115-8A low frequency driver and 2412H (JRX115 is 2412H-1) compression driver on PT-F95HF-1 (338800-001) waveguide.

So, would it be worth it to modify the JRX115 by pulling out the passive crossover and rewiring it for biamping? I'd use the XLS 1502 on the highs and the XLS 2502 on the woofers.

Thanks!

[Ed Zeppeli]

Yep. I think you'll receive the same benefits as anyone who tries bi-amping. I'm fairly certain they'll be better able to 'keep up' with your sub if you do it right.

Make sure you can mimick or properly duplicate any contouring involved in the horn EQ.

Go for it!

[edgewound]

Hello everyone,

I have a system in my basement used solely to amuse myself when my wife and daughter are out of the house and I want to hear some loud music. Currently it is:

dbx DriveRack PA2
Crown XLS 1502 (not currently in use)
Crown XLS 2502 (driving JRX115 full range stereo)
Crown XTi 1002 (driving MP418S bridged mono)
JBL JRX115
JBL MP418S

And it sounds okay. The subwoofer is great, but the JRXs can't keep up. I know these are JBL's economy speakers, but I've found that they use the same drivers in other more expensive speakers, for example the AC2215/95 uses the same M115-8A low frequency driver and 2412H (JRX115 is 2412H-1) compression driver on PT-F95HF-1 (338800-001) waveguide.

So, would it be worth it to modify the JRX115 by pulling out the passive crossover and rewiring it for biamping? I'd use the XLS 1502 on the highs and the XLS 2502 on the woofers.

Thanks!

Personally....I wouldn't bother.

The JRX is an entry level collection of drivers, and the 2412H is always the weakest link. The 2412H started life as the 035ti tweeter as used in studio monitors and hi fi models, crossed over at 5khz. Once you feed that driver with it's own amp and you try to adjust the crossover lower than 5k, you're living on the edge. It's already living on the edge in with the passive crossover. Whoever thought it was a good idea to convert this little 1" voice coil tweeter into a compression driver must've had the additional vision of replacement parts sales and/or ruining JBL's reputation as a serious pro audio company. The first time I serviced one of these systems, I literally laughed at what has become of JBL that was trying to satisfy every market segment with the brand name alone. It should have been marketed as an entry level sub brand instead of compromising the legacy of JBL. Long view fail in my opinion. Someone didn't pay attention in marketing class when studying the folly of GM by rebadging a Chevy Cavalier as a Cadillac Cimarron. That said....it should be a marvelous tweeter in a three way system crossed over high enough to take advantage of it's upper reach to 20K.....namely 5khz. The M115 is basically an Eminence driver. In fact, JBL was buying drivers from Eminence before dealers touring the factory and saw stacks of Eminence boxes on the floor wondering what the hell was going on n the pro audio division. It's a "meh" performer.

The JRX box is a decent platform, especially for stationary installations because they don't hold up too well being dragged and dropped from gig to gig by bands and DJs....but hey....they're cheap and and have a revered JBL logo.

I'd fill the boxes with other drivers that can keep up the the mid-level MP418S. Don't waste your time and money on the original drivers for biamping.

Just my two cents on servicing this stuff for nearly 30 years.

[LowerBeef]

Make sure you can mimick or properly duplicate any contouring involved in the horn EQ.

Ed, would this be the horn EQ contouring?



I got it from "AC2215-95 Bi-amp with Sub for FDS-366.pdf"

[LowerBeef]

Personally....I wouldn't bother.

The JRX is an entry level collection of drivers, and the 2412H is always the weakest link. The 2412H started life as the 035ti tweeter as used in studio monitors and hi fi models, crossed over at 5khz. Once you feed that driver with it's own amp and you try to adjust the crossover lower than 5k, you're living on the edge. It's already living on the edge in with the passive crossover. Whoever thought it was a good idea to convert this little 1" voice coil tweeter into a compression driver must've had the additional vision of replacement parts sales and/or ruining JBL's reputation as a serious pro audio company. The first time I serviced one of these systems, I literally laughed at what has become of JBL that was trying to satisfy every market segment with the brand name alone. It should have been marketed as an entry level sub brand instead of compromising the legacy of JBL. Long view fail in my opinion. Someone didn't pay attention in marketing class when studying the folly of GM by rebadging a Chevy Cavalier as a Cadillac Cimarron. That said....it should be a marvelous tweeter in a three way system crossed over high enough to take advantage of it's upper reach to 20K.....namely 5khz. The M115 is basically an Eminence driver. In fact, JBL was buying drivers from Eminence before dealers touring the factory and saw stacks of Eminence boxes on the floor wondering what the hell was going on n the pro audio division. It's a "meh" performer.

The JRX box is a decent platform, especially for stationary installations because they don't hold up too well being dragged and dropped from gig to gig by bands and DJs....but hey....they're cheap and and have a revered JBL logo.

I'd fill the boxes with other drivers that can keep up the the mid-level MP418S. Don't waste your time and money on the original drivers for biamping.

Just my two cents on servicing this stuff for nearly 30 years.

Edgewound,

Thanks for the info, especially the background on the heritage of the drivers. I was considering the popular Selenium D220Ti to replace the 2412H, would that make it any more worthwhile or should I skip straight ahead to my plans for a compact 2206 + something speaker?

[edgewound]

Edgewound,

Thanks for the info, especially the background on the heritage of the drivers. I was considering the popular Selenium D220Ti to replace the 2412H, would that make it any more worthwhile or should I skip straight ahead to my plans for a compact 2206 + something speaker?

You're welcome.

You're also on the right track for a much better inexpensive/value upgrade with the D220ti. It has a 1.75" voice coil which will obviously take more power, and replacement diaphragms are also very inexpensive. You won't be out much cash with this, and you might just be satisfied with results. That way skipping ahead to your 2206 project could be either delayed, or even more enticing.

If you don't mind sacrificing your 2412H, you'll probably understand what I was getting at...and have a valuable experience of not banging your head against the wall and expecting a different outcome. Like I said...the 2412H makes a great tweeter....in a suitable system for it where it won't be abused. It's like putting in a 10 year old to catch for Nolan Ryan. It's gonna break.

[LowerBeef]

I got to work on my JRX115 biamp project last night, removed the crossovers and am going to rewire the Speakon connector for biwire. I forgot to order some big film caps to protect the CD. Do I really need them? From the JBL crossover schematics I've looked at they don't use them. I have some non-polar electrolytics I can bypass with some smaller film to get me by.

And my Selenium D220Ti seem to be a new version, D220Ti TRIO? Only info I can find online is in Brazilian (Portuguese?)

http://i-jbl.a8e.net.br/static/pdf/28031090manutec.pdf

They seem to be slightly different in some of the specs from the D220Ti.

[edgewound]

I got to work on my JRX115 biamp project last night, removed the crossovers and am going to rewire the Speakon connector for biwire. I forgot to order some big film caps to protect the CD. Do I really need them? From the JBL crossover schematics I've looked at they don't use them. I have some non-polar electrolytics I can bypass with some smaller film to get me by.

And my Selenium D220Ti seem to be a new version, D220Ti TRIO? Only info I can find online is in Brazilian (Portuguese?)

http://i-jbl.a8e.net.br/static/pdf/28031090manutec.pdf

They seem to be slightly different in some of the specs from the D220Ti.

You'll want to put a protection capacitor in series with the compression driver to protect it from turn-on thumps and/or DC voltage. JBL puts them on ALL biampable systems.

10uF should be sufficient...smaller if you want to protect it from lower frequency adjustments so you don't have an "oops" moment.

Mylar caps are good for this, and they're pretty cheap. NP electrolytics will work, too.

[Mitchco]

I biamped my JBL 4722's and got benefits like: http://sound.whsites.net/bi-amp.htm

I don't know if your electronic XO can apply time delay, so you can time align the drivers, but there are benefits to that as well: http://sound.whsites.net/ptd.htm

I did both and really liked how it improved the sound quality of my JBL's. A heads up with respect to the Crown XLS amps, they add delay to the audio chain. As an example, I show that here:
http://www.avsforum.com/forum/89-spe...l#post49115305

Hope you have fun!

[LowerBeef]

I biamped my JBL 4722's and got benefits like: http://sound.whsites.net/bi-amp.htm

I don't know if your electronic XO can apply time delay, so you can time align the drivers, but there are benefits to that as well: http://sound.whsites.net/ptd.htm

I did both and really liked how it improved the sound quality of my JBL's. A heads up with respect to the Crown XLS amps, they add delay to the audio chain. As an example, I show that here:
http://www.avsforum.com/forum/89-spe...l#post49115305

Hope you have fun!

My dbx PA2 does do time alignment:



Thanks for the heads up on the XLS delay, I wonder how much delay the XTi series has?

[Mitchco]

That's great. I had a look at the user manual, there seems to be a basic method to set the delays. Should take into account any amp delays. An alternative way, if you have a calibrated measurement mic, and freeware software like REW or HOLMImpulse, can accurately measure the driver offset and amp delays.

You might try some experiments by adjusting the tweeters to be 10ms delayed relative to the woofer, just to hear what that sounds like... Or adjusting the delays by ear and then measure to see how close...

I use a protection cap on my compression drivers as well.

Have fun!

[LowerBeef]

I've removed the passive crossovers, rewired the Speakon inputs for biwire and replaced the 2412H with Selenium D220Ti. They sound much better, but I'm not sure if changing the CDs or biamping made the most difference.

Any ideas on how low I can go with the crossover of the D220Ti on the 338800-001 waveguides? From Gainphile's S15 project http://gainphile.blogspot.com/2010/1...owave-dsp.html they used 1250Hz.

Also changed the subwoofer to a 4645B and the sub amp to another XLS 2502

[Rudy Kleimann]

I've removed the passive crossovers, rewired the Speakon inputs for biwire and replaced the 2412H with Selenium D220Ti. They sound much better, but I'm not sure if changing the CDs or biamping made the most difference.

Any ideas on how low I can go with the crossover of the D220Ti on the 338800-001 waveguides? From Gainphile's S15 project http://gainphile.blogspot.com/2010/1...owave-dsp.html they used 1250Hz.

Also changed the subwoofer to a 4645B and the sub amp to another XLS 2502

I know this is an old thread, but...

I'm just beginning a HT project that based the JBL AE Series AC2212/95 that uses the same drivers and horn with a much better crossover.
I love the tiny cabinet for midbass-up, but Edgewound and others are dead-on about the M112-8 and 2412H. Almost anything is better than those two drivers!

From JBL, the following four screw-on ferrite 1.75" compression drivers will do well, but you'll have to be gentle with that heavy driver hanging off of the 338800-001 horn, or mount a piece of plywood in the cabinet with a hole cutout to support the magnet.

The 2415 and 2416 are a good poor-mans' 2425HS. They can also use 2425 diaphragms if you can find one of the add-on diaphragm cap that radian makes.
The 2417H sounds really good, with more HF extension that the previous drivers due to its' thinner lighter diaphragm. It will not work properly with a D8R2425.
The 2418H is the last-gen 1.75" driver, and may also work well. JBL used them on the AC2212/00 and AC2215/00 as well as in several larger Custom Shop systems with better woofers, most certainly because that poor little 2412H didn't stand a chance trying to produce enough output to fill up the horns' 100*x100* coverage area, much less higher-output woofers.
The 2425HS is a 2426H with out the bolt-on horn adaptor. A 2426 or 2427 will also work, but expect a battle to get the horn adapters off!
JBL uses a thread-locking compound to keep the adapters from loosening up and rattling from low frequency energy in the cabinet.

The NEO 2407H mylar diaphragm ring radiator (and it's ferrite twin 2406H) are excellent performers for a midpriced HT system, with response well beyond 25KHz(!). I've been listening to them in my living room on PT-H64HF and PT-H95HF horns with MTA-1 threaded driver throat adapters for a couple of weeks now and they are surprisingly good.
I'll try out the 2416H, 2417H, 2418H, and 2425H on this arrangement in the upcoming weeks to see how they stack up.