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Lansing L Century loudspeaker, the consumer version of the studio monitor, became the largest selling loudspeaker model of any company in the Seventies and more than , pairs were sold. Due to the materials used, the L drivers are as good today as when they were produced, but the overall sound can be vastly improved by modern crossover technology. For the LE20 tweeter you need 3 additional components. Read below. Mail received 12 August from Mr.
I am not an engineer — but I did direct the L development program. L Design Engineer Ed May was a very dear and close friend. I coordinated the work of industrial design consultant, Arnold Wolf — who, with Doug Warner, was responsible for the visual design. Arnold later went on to become President of JBL and my boss. Ed May told us all that microphone wind screen foam material would make an acceptable grille material.
Arnold Wolf gave us stunning designs. The problem was that the foam industry was basically the packaging and filtering industry. Carl Davis, without degree, without assignment and working on weekends — was the first — in the entire industry — to discover that foam could be hot wire cut — and with the required precision.
The L project had lingered more than six months in limbo while we struggled with the grille design problem. We all knew an unauthorized distribution process was under way. All drivers in mint condition and the cabs with minor scratches.
Tweeter foam had gone but can easily be replaced from eBay sellers. Having recently experienced the SEAS kit , I now realise the kit was actually a better speaker at that time. Quite similar in size and power handling, the had a better midrange and a better crossover and the 33FWK bass drivers may beat the A drivers.
Take a look at how the dust cap is glued to the cone and the fine touch of paint around the edges. It takes great skills to make such fine work. However, the LE is not an easy driver as we shall see later. This first part of the my L story will not engage in a new crossover, merely try to find out what the L was in terms of driver performance and crossover construction.
Both drivers connected via an L-Pad for attenuation. Mid connected with inverted polarity. Having a 12" bass driver running full range is a bold choice and a lot of work must have gone into designing the A driver to produce a smooth roll off. The LE25 is a better tweeter than we might think, maybe not from measuring performance, but well equalised, it can deliver some excellent treble integrating well with midrange, actually better than many modern domes in my opinion.
On eBay, sellers will completely strip an L speaker and sell it bit by bit down to the pins holding the front grille. Basically the A driver has a too high Qt to be used in a vented cabinet and the result from a 44 liter volume is a dB increase in response at 70 Hz, which is confirmed by a nearfield reading of the response.
Place the classic L Century on the floor, close to a wall, and we will have an overall 7 dB response increase from 50 to Hz. Talk about a boom box! So, two options available. Much nicer. Placing the L in corners is a no-no. Smooth bass roll-off? Well, maybe not from this cabinet, but take a look below where I compare the A response from the L cab and a 60 cm wide, curved baffle. The LE is extremely sensitive. The peak at 6. The LE25 is much better than I had anticipated.
It may change the sound, but not measuring performance. File not shown. Right: Individual response of drivers from original crossover with mid and tweeter attenuation set to zero. Some serious traffic jam around kHz - three drivers all trying to make the most of it here. No wonder the original set-up fails on vocal recordings. And the tweeter might improve performance from smoothing overall impedance. Left: The SPL response of both speakers with "0" attenuation for the tweeter and -3 dB attenuation for the mid to get the terrible peak at 6.
I found this attenuation setting to produce the best overall balanced sound. Nearfield bass response is merged at Hz. Disregard difference in bass response. Probably not correct. Now, listening to some music from this setting may be close to what we heard back then.
Quite an experience to hear that JBL L sound once again. Very impressive, lots of bass, speedy midrange. The sound of acoustic guitars is very good, but vocals? The danger of knowing what is going on. But the 6. Right: Response of midrange alone with crossover and attenuation set for -3 dB. Severe dip at Hz and the 6.
This looks like a poorly managed tweeter response. A response up to 15 kHz! I mean, a single coil to the mid might at least have produced a more flat response, but then the upper treble may run into trouble from this approach.
Not that easy, but this is close. Phase tracking between bass and mid is better that we might expect, but the tweeter is very much living its own life in the upper midrange. Left: Step response showing reverse mid polarity. The strange thing about these drivers is that the red terminal on the A bass is correct. The cone moves out when applied positive voltage.
The LE cone in moving inwards when positive voltage is applied to the red terminal. Why would JBL do this? To ensure correct polarity of drivers when plus wires from crossover were connected to drivers? But the LE5 was used in other constructions Right: The A bass in L cab, blue, and from a wide curved baffle red. Now, find a 12" driver today that will perform flat up to 6 kHz and have a smooth roll-off. In the upper midrange we have some 4 dB difference in sensitivity.
Basically this is due to differences in voice coil impedance. Right: Impedance of four LE drivers. From 5 to 7 ohms. A new crossover designed for all variants of LE drivers is a challenge and fortunately it can be done due to the very high sensitivity of the middriver. This is manageable and for those who want to do some fine-tuning, the mid level may be increased or decreased by the input resistor.
Problem solved. New crossover design criteria A lot of work has gone into designing a new crossover and numerous simulations and actual crossover constructions have been tried in order to try taming the LE middriver and provide an overall balanced sound from the L What I wanted was to maintain the basic virtues of the L, i.
To maintain 1st order filtering as high up in frequency as possible, the LE had an LCR circuit to flatten the rise in impedance at Fs, allowing the high-pass section to be one single capacitor.
To cope with amplitude and phase between mid and tweeter, the mid needs a 2nd order low-pass section and the LE25 needs a 3rd order filter at 5 kHz to get amplitude and phase in place. See graphs below. Three significant things have happened here: First of all, the LE middriver no longer peaks at 6. Secondly the mid-section was constructed in such a way that the common variation in driver impedance LE only produce minor deviation from target response.
Last but not least, both the tweeter and mid now produce a smooth roll-off below points of crossover. Should you want to increase mid and tweeter levels, you may bypass R mid and increase R tweeter from 4R7 to 5R6. Both 4R7 and 5R6 are supplied with the kit for you to esperiment.
JBL 2213H Woofer
Lansing L Century loudspeaker, the consumer version of the studio monitor, became the largest selling loudspeaker model of any company in the Seventies and more than , pairs were sold. Due to the materials used, the L drivers are as good today as when they were produced, but the overall sound can be vastly improved by modern crossover technology. For the LE20 tweeter you need 3 additional components. Read below. Mail received 12 August from Mr. I am not an engineer — but I did direct the L development program. L Design Engineer Ed May was a very dear and close friend.
∎ JBL 2213H woofer pair for 4311B, 4312, 4312A. Also 123A sub for L-88, L-100.