AudioAficionado.org - JBL L220 Labor of Love-Part 2

Hello fellow AAers....

Anyone who knows me at all knows I'm a die hard JBL fan from way back. I currently own 4 pairs of JBL's, 2 large JBL subs, and some in-wall and in-ceiling JBL's in my bedroom surround system. If I had room for more, I'd have more! Many of you know that my L220A's have resided in my main system for many, many years. Purchased new in March 1982, means they've been with me 38 years. They've served me very well, and have shown up every improvement I've performed on the rest of the system with aplomb. I've maintained them to the very best of my ability over the years, and they are in nearly pristine condition, especially for their age. In 2016, I posted a thread outlining a fairly major project on them, involving the rebuilding of the crossover networks (necessary after over 30 years), and the fabricating of custom grilles with cutouts for the midrange lenses. For those of you who missed that thread, here is the link:

https://www.audioaficionado.org/showthread.php?t=37796

This thread also goes into how I started my journey with JBL, my purchase of the L220's, along with some discussion about its design.

The Question

The L220's design centers around the LE14H 14" low frequency driver, a 15" passive radiator (PR15C) a 5" cone midrange driver (LE5-9), and an elliptical ring radiator tweeter (076), commonly referred to as the "cat's eye". The midrange driver is coupled to an acoustic lens, a refracting waveguide the provides midrange disperson over a wider area, while also recessing the midrange driver the proper distance from the front baffle to attain "acoustic alignment" with the other drivers. This alignment was also said to be achieved with the 076 elliptical ring radiator, once again setting the driver (diaphragm in this case) back the precise distance needed to achieve this alignment. Aligning the acoustic centers of the drivers, according to JBL, "ensures that frequencies are heard in the same relationship to each other as they were recorded...". It's never been entirely clear to me exactly how this distance could be precisely defined, given the many different recording techniques that are used. But what I do know is that the L220's design does, as JBL claimed, produce "a loudspeaker system that is audibly superior". It did, however, strike me a bit odd, even in my early days of L220 ownership, that JBL chose to put a 5" cone midrange behind the lens, when every other JBL model that I could think of that utilized a lens had a compression driver and horn behind the lens. These included the highly revered L300, the 4344, 4345, the famous Hartstfield, and others. The list goes on. It sort of begged the question: why was the L220 apparently the only model to break suit? I never fretted over it really, in fact, the midrange clarity, dispersion and imaging were all attributes that I loved about the L220. As to why the cone driver instead of a horn loaded driver, I just wrote it off to the acoustic alignment concept touted by JBL. Or, as some prefer to call it, "time alignment". That must be the reason.

Fast forward 23 years

Sometime around 2005, I began frequenting sites like Lansing Heritage Forums. Here, all things JBL are discussed day and night. I began reading with interest how some JBL guys had modified their L220's by installing a compression driver and horn behind the L94 lens. The idea here was to emulate the midrange performance of other horn-loaded models; the one that most comes to mind is the L300, famous for its powerful, articulate midrange. That system utilizes the powerful LE85 compression driver, coupled to the H92 Horn. One fellow owned three pairs of L220's, and as I recall, he modified all of them, and said he'd never go back to the cone driver. I began to hear how the LE5-9 cone driver was the one "weak link" in the L220 design. Mind you, nobody ever said it was bad, the stock L220 was no slouch by any means. But, they said, nothing could compare to the power, clarity and resolution of the JBL compression drivers.

The problems

The first, and most obvious problem facing us with performing the horn modification is the depth of the horn/driver assembly. The L220 cabinet is 14-1/2" deep, from the front baffle to the back of the enclosure. Then there is the fact that the midrange sub-baffle is recessed behind the front baffle. Adding to the problem then is the crossover network board, which is mounted directly behind the midrange cavity. When all is said and done, you just don't have enough depth to mount a long horn and driver, and still close up the back of the cabinet. To overcome this problem, most DIY'ers have extended the back panel (which occupies the upper 13 inches of the rear of the enclosure) a few inches beyond the back of the enclosure. I never did like this idea, not only is that unsightly, destroying the nice, tapered appearance of the L220 cabinet) but I really cannot do that, because of the way my right channel speaker is placed. This problem, along with a genuine fear of messing up my beloved L220's, discouraged me from making the attempt.

The growing chorus

Fast forward another 14 years or so....I begin frequenting a few more JBL oriented groups (one in particular: Vintage JBL on Facebook) and I begin reading more accolades from L220 owners who have modified their L220's. The testimonials are unanimous, everyone who does it never looks back. Most seem to opt for the LE85 driver/H92 Horn combo. Some suggestions are offered to contend with the depth issue. Some managed to close the back, though with less than ideal methods, in my view at least. Some members also offered up some very interesting stories:

One fellow said he'd spoken to a previous designer at JBL who said the L220's original design called for the LE175 Compression driver and the 1217-1290 Horn (sometimes called the "potato masher" due to a screen lens of sorts the disperses the sound in a conical fashion from the horn throat). I don't know if this is true, as to the original design intent. But it is certainly interesting.

Another member tells me that he'd toured the JBL plant back in the day saw a number of L220's with open backs that had the compression driver and lens installed. He was told that this version of the L220 was available as a special order. This is also interesting, and probably not all that surprising, given the number of JBL horn fans there are out there.

I did some looking into the particular horn mentioned above (1217-1290) and found that, according to JBL, this horn was offered "for applications where the enclosure requirements do not permit a longer horn". At this point, I'm becoming seriously interested, and I start shopping.

To do or not to do: the technical aspects

How feasible is this when we look at some numbers? As to operating ranges and crossover frequencies, I see no problem: The L220 crosses over at 800hz and 5000hz. Both the LE85 and LE175, according to JBL, are for use above 500hz. Both have been used in 2-way systems, so to operate either in the range from 800 to 5000hz shouldn't be a problem.

The main difference between the LE85 and LE175 is the size of the magnetic structure, with the LE85 being larger, and heavier. From looking at the specs, I'm not sure what difference there would be sonically in my application, if any. Physically, they are the same depth, but the LE85 has a larger outer diameter.

I find a very nice pair of LE175 Drivers on eBay, with 1217-1290 Horns with a fron flange mount (that will help me with depth, though it will require a new midrange mounting plate). Having decided that these will work, I make the seller an offer, and he accepts.

But isn't the horn I've decided on "too short"?

I admit that I'm not an expert on horn applications, but I think this will work. One member over at Lansing Heritage Forums advises me that I shouldn't use this arrangement under 1200hz, and my crossover crosses to the mid at 800 hz. I counter that JBL rates this unit down to 500hz. He counters back that just because it can, doesn't mean you should, and that a longer horn goes deeper. He may be technically correct, but I'm committed at this point.

I do offer one counterargument however: the LES-9, the stock mid for the L220, according to JBL, is for use in applications over 800hz, the very frequency that the L220 crosses to the mid at. So aren't we stretching the limit here? With the LE175, I have 300hz "to spare".

What about the timing?

Here we are back to the "acoustical alignment" that JBL touted pretty proudly when they introduced the L220. Doesn't setting a driver further back from the lens destroy this aspect of the design? Or, given the examples of other JBL models with acoustic lenses and horns (ala L300) was this perhaps more marketing than anything else? Did JBL make a last minute cost-cutting decision and opt for a cone driver instead of a horn loaded compression driver? The fellows who I've communicated with who have modified their L220's have all pondered this as well, and they tell me that it has not compromised the "timing" to their ears, for whatever reason. It didn't seem to matter. At any rate, by implementing the shorter horn, I'll be doing less to negate any timing criteria than I would be using a longer horn, theoretically.

What if I make the change, and don't like it?

This is the best part.....the L220's design is such that, if we don't like the results, we can always convert it back to the original configuration. After all, we aren't cutting the front baffle, or anything like that-since everything pertaining to the midrange is sub-baffle.

What new parts will be needed?

In order to mount the new horn, a new sub-baffle will need to be designed and fabricated (we want to retain the old one anyway, in case we want to revert back). We also need a new back enclosure plate, with a new, higher access point for the L-pads, which will be relocated off of the crossover board. This is because we will stash the circuit board inside next to the horn, to clear the way for the new drivers. We'll also install new L-Pads, since JBL made the old ones very difficult to remove (the knobs are pressed on so as to be nearly impossible to remove) and also because, well, just because.

Okay, so lets look at the new components:

Here is the LE175 compression driver, mounted to the 1217-1290 Horn:

https://live.staticflickr.com/65535/...bd21a9fa_b.jpg

Here is the new Horn mounting plate, and the new back plate:

https://live.staticflickr.com/65535/...2223b4c1_b.jpg

Checking the fit: (Helicoil inserts were used for the machine mounting screws)

https://live.staticflickr.com/65535/...ed13486a_b.jpg

And the new parts painted: (also showing the new aluminum L-Pad mounting plates installed)

https://live.staticflickr.com/65535/...21f5c06_b.jpg"

https://live.staticflickr.com/65535/...7062c038_b.jpg

https://live.staticflickr.com/65535/...27cbff28_b.jpg

So, the big day arrived, and I began the installation. The first two photos show the stock LE5-9 cone drivers, mounted on the stock mounting plate, next to the replacement horn/driver.

https://live.staticflickr.com/65535/...91d72f88_b.jpg

https://live.staticflickr.com/65535/...0a0bc845_b.jpg

In order to have everything line up properly, I did have to have a very small amount of material milled off the bottoms of the new horn mounting plates.

https://live.staticflickr.com/65535/...b6724c75_b.jpg

I re-used the original wooden spacers. The lower spacer also serves as a clamping support at the bottom of the horn mounting flange. These Horns are quite heavy!!

https://live.staticflickr.com/65535/...06be8835_b.jpg

And finally, the units are installed....

https://live.staticflickr.com/65535/...f5d46043_b.jpg

https://live.staticflickr.com/65535/...b0820ecb_b.jpg

The installations went very smoothly, and they are mounted ROCK solid. I was really surprised and relieved that the mechanical installation went as well as it did. Of particular concern was that the acoustic lens went back in properly on the new mount. If it did not, I'd have some problems, especially since I'd previously made the custom grilles with the cutouts for the lenses! But, it all went back together pretty much perfectly:

https://live.staticflickr.com/65535/...d0337d0d_b.jpg

https://live.staticflickr.com/65535/...20abe0dc_b.jpg

At this point, it was time for a test drive. It had been a pretty long day, and I still had those new L-Pads to wire in. I decided to save that task for the next day, and so I stashed the networks inside, and started playing the system.

The proof is in the listening

I knew from other users that once installed, it would be necessary to turn down the midrange L-Pads about 1/4 rotation. This is due to the very high efficiency of the LE175 compression driver. So I turned down the pads before temporarily stashing the networks inside the cabinets.

How does the modification sound? In a word, WOW! This is a big change, a huge improvement. The midrange is much more lifelike, much greater air, and supremely articulate. And, much, much smoother. One concern I had was whether any of the soundstaging aspects that I'd liked so much with the speakers in their previous state might be impacted negatively. For instance, many vocals will appear solidly placed between the speakers, as if there is a center speaker. Some recordings display this so well it's uncanny. A couple of recordings that come to mind here: the opening minute or two in Donovan's Atlantis. Another is Scott MCKensie's San Fransisco. I tested several recordings, listening for any losses in the great soundstaging that the L220 had previously. The result: nothing lost, even improved more! These units sound marvelous...it's a huge improvement. Within 20 minutes (or less), I knew I would never be re-installing the cone drivers. With each recording I played, the improvement was obvious. I was, and am, soooo pleased. The speakers simply are sounding glorious. The kind of vocal presentation that's "to die for", particularly female vocals. But not only voices have taken on a new life, there are all kinds of nuances in the 800-5000hz range that are a lot of fun, and I'm picking up on a lot of these that I really wasn't hearing before. Needless to say, I know I'll be having a lot of fun re-listening to a ton a music. But right now (or, the next day, actually, there is more work to do.

The finishing touches...

Here's a few shots of the new L-Pads wired in, the network card in its new location, and a look at the new back panel installed:

https://live.staticflickr.com/65535/...f43f3d1a_b.jpg

https://live.staticflickr.com/65535/...6e86fd3b_b.jpg

https://live.staticflickr.com/65535/...4a9d2108_b.jpg

https://live.staticflickr.com/65535/...ce5fcdc3_b.jpg

And why not a shot of the previously upgraded WBT Binding posts?

https://live.staticflickr.com/65535/...ba44b0d5_b.jpg

Some afterthoughts

This project was something I'd pondered doing for the past 15 years. Along the way, there were many moments of doubt, a number of people telling me don't mess with the original design, you'll be sorry, and so on. Now, I just think about those doubts and warnings, and I just smile. This was without a doubt worth all the time and effort.

Could I have done even better? Perhaps. Maybe a longer horn would be "better". But the idea of extending the back did not appeal to me at all. Would the LE85 driver be "better" than the LE175? Perhaps, but I don't have any data one way or the other on that.

Every design endeavor has trade-offs. I was willing to chance a slightly shorter horn in the interest of a tidy, closed up enclosure-perhaps at the expense of a slightly flatter frequency response. I did, when the horns first arrived, set them up crudely atop the enclosure and ran some pink noise tones with my Soundcraftsmen AS1000 Analyzer and took some readings with my own Sound level meter. I did not detect a deficiency in the 800-1200Hz range. This was hardly a scientific test, and not in a laboratory. In any event, I'm not sweating it. Because in the end, the proof is in the listening. And my ears are very, very happy.

If you've gotten this far, thanks for reading. I know this got pretty long....:thumbsup: :thumbsup: