The L-100 and by many other names is a curiosity to me.
The specific models I am referring to are 3-way with a 12" woofer, a 5" mid (about) and a hard cone tweeter with a center dome.
More important is the crossover.
The entire xover is a series cap with an L-pad on both tweet and mid and nothing on the woofer.
If you measure each on axis -
The 12” goes up to about 5kHz flat. (Rather amazing really)
The mid from 400Hz to 6kHz.
The tweet from 1kHz to 15kHz
With casual inspection you have ALL THREE drivers running in the 1kHz to 5kHz region. The capacitor on the tweeter cuts it back some, but not enough to stop overlap.
Obviously the cap on the mid does nothing to its high frequency extension.
When you model the speaker with the simple xover it uses it does not take to long to figure out that if you turn off the mid driver there is still an overlap of the woofer and tweeter (though the 12” does beam sharply as it goes up in frequency).
This causes a hump in the response that no amount of twiddling on the tweeter L-pad can eliminate (without losing the highs).
So what to do?
Well we do have a mid driver. What happens IF we flip the polarity on the mid and turn it up just a bit?
Will it cancel the hump?
Yes!
It does just that nicely.
And unless all of the owners changed the wiring that is how the drivers are wired stock.
So turning the mid up causes a “hole” to counteract the hump from all the drivers working in the same region.
I have had three similar boxes come through here from local people. It had been my intention to publish a simple 3-way 2nd order xover for free on the net since there are literally thousands of these still in use. But I ran into problems.
Many of the drivers measure different. Some no doubt came from different runs at the factory since these drivers were in production for decades.
Much of it because of use. When one mid or tweet was toasted they would order just one and the years of use on the old one that still worked made it respond very differently.
Also some models have the tweet and mid in line and others the mid is off to the side.
All these changed things enough to mean I could not count on a design working for most owners.
Anyway if you want to do some DIY fun a simple 2nd order at 300hz and another at 3kHz can make these speakers shine as never before. Keeping the high frequencies from coming from more then on driver is a design goal that vastly over shadows any foam you might paste on the tweeter or anywhere else on the baffle.
With the highs coming from three different places in space I don’t see how foam can help at all with how they sound since arrival times from the three drivers scramble things beyond what foam can do. Unless you hang it in front of the woofer.
OTOH for visuals it makes it easier to eat Mac & Chesse in the same room. That somewhat rotten orange foam always made me a little queasy.
Good luck,
Too Tall
PS- I have included a measurement of the raw responses. Please note you have to add 9dB to each curve to see true 1 meter sensitivity.