Help me replace the woofers in my ML SL3's, please?

So before you point out the fact this has already been discussed... let me just say this up front: all the latest known substitutes are "Out of stock".

So.. I have a pair of ML SL3's. This past weekend.. a buddy decided to hold a rock concert at my house (while I was gone) and - literally - lit the bass xover inductor of one on fire. Obviously.. the woofer is damaged.

Looking around the interwebs, I have already learned all the obvious stuff:

-> My original woofers are Vifa - no longer in production
-> ScanSpeak made an "official" replacement (according to ML service) - no longer available
-> A couple other drivers were available, but also are "out of stock" and no longer made.

I want to repair these... but would like to keep them (externally) mostly original.

Looking at all the drivers on Madisound and Parts Express.. It seems most Woofers and Subwoofers are really optimized either for SMALLER enclosures OR vented/ported. If I want to replace the woofers with a modern driver and stop worrying about trying to match the sealed cabinet space requirements - I have two options:

1) Reduce the SL3 sealed enclosure space. I think this could be done by buying some SCH40 PVC at Lowes and cutting a length w/ 2 end caps. Seal the tube up and stick it inside the enclosure. Bam! I just reduced the effective space.

2) Port the enclosure. I can find plenty of really nice ports of virtually any size needed on Parts Express. Getting into a traditional vented enclosure for the lower end kinda scares me, however. I personally have always preferred the sound of sealed or TL's.

So... first question: how feasible is option #1? If I built two sealed PCV tubes of a known volume and placed them inside the cabinet, then attached them securely to the inner bracing.. Would this effectively reduce the space acoustically to get things in line with a new drivers requirements? This seems like the easiest solution.

Second question: these newer drivers that expect smaller sealed enclosures... I get the feeling they also require more power to properly drive them cleanly - correct?

I have run a basic (should be fairly accurate) measurement of the existing SL3 enclosure. It comes to 1.3ft^3.

Most all the drivers on Parts Express are expecting a .3-.8 ft^3 space. I imagine I could build a sealed tube that reduces about .5.. I understand the speaker will further reduce the space... and I can fine-tune with the polyfill from there.

Crossover-wise.. If the exact impedance does not change, why would the bass crossover need to be tweaked? Sorry.. but my limited knowledge of crossover design tells me: you need 2 numbers (impedance of driver and desired xover freq) in order to calculate the needed inductor. If impedance does not change... the inductor should not change, either. Or does the impedance behave differently when the driver is actually mounted in the enclosure? Keep in mind: the bass xover on the SL3 is nothing more than a single inductor. There are a couple resistors that run in parallel with a switch to (seemingly) shift the xover point.. But that whole bit aside... nothing more than the inductor and woofer.

Regardless: I can order new inductors of virtually any needed value. So the whole "tweaking the xover" should not be an issue.

Part of this upgrade will involve an additional switch that "bypasses" the inductor. So when I get my dual Adcom GFA-545's, I will bi-amp with an active crossover. The bass units will then be driven directly. (Actually, I will be Tri-amping - two GFA-545's and a single GFA-555 for the dedicated subs I will build). That said, I want a solution that let's me easily switch these back to re-enable the crossover in case I sell OR move them to another room (simpler setup).

Then there is option 2... I do not like option 2 a whole bunch.. But perhaps tuning the enclosure with a port is not so bad? There are some pretty bad-a$$ed 10" drivers that perform really well in vented enclosures from what I hear.
 
Last edited:
So.. I ordered the Dayton 10" reference series. Even if they sound like crap - I can use em for something else.

1) Many report great performance of this driver to nearly 1000hz(!!), so should do very well frequency-wise.

2) x-max of over 12mm (!!!). Should be a bit of an upgrade.

I ran this sub through a couple calculators and - suprisingly - when a target Qtc of .707 is desired, the [sealed] box works out to.... 1.3ft^3!

The F3 will be around 40hz - a bit higher than original. However.. I have a dedicated [powered] sub that picks up at 60hz.. so this should not be an issue.

Worse case scenario: I need to shift/tweak the xover a tad. I can always add a .1 or .2mh inductor in series with the sub and/or tweak the shunt capacitor (again, these parts are really affordable online).

I ordered a new [original] 5.1mh inductor from ML yesterday. So that will all be back to normal - assuming the value is good with the new drivers.

Then again... this may be a good excuse to just bite the bullet and order a MiniDSP and say to hell with all the passive xover components completely.

I *did* look at the peerless 10's... honestly, the Dayton seems to get better reviews and they are both at the same price point. Given the Dayton just went on sale (PE does this every few months with random drivers).. the decision was a no-brainer.

Will report back soon once the new drivers come in.