Suggested Modifications to The IMF TLS80

This page is an edited & updated version of an email I sent to a TLS80 owner in England. These are suggestions only -- YMMV. If you try any of these please let me know your results. Or if you have some other tweaks you have found useful.

Many of these tweaks have a more general application than just for TLS80s.

Question: Have you come across anyone with tips on how to develop the TLS80 - certainly by replacing the drivers as they grow old, maybe in other ways. They have a wonderful sense of largeness and bass depth, but I confess the mid range does not now compare with the best of modern speakers.

Besides doing all the "standard/simple" tweaks, the biggest weakness of the TLS80, which is common to most speakers of that era, is the XO. The next big weakness would be too many tweeters. Then i'd think about replacing the B110.

Fortunately the enclosure for the B110 is in about the right place unlike the Atkinson TL -- which uses a B110/B139 and even more tweeters -- and it's mid enclosure is too close to the floor.

So in order of execution this is the approach I would take.

  1. "Standard/Simple" tweaks (these are intended as general directions to go as opposed to specific directions as what to do).

    • Better wire.

    • Make sure the cabinet is "tight". This might mean extra bracing (extra bracing has to be done such that it doesn't use up too much space), caulking, etc. Attention to the baffle might be particularily effective (ie a 1" x 1/2" strip vertically on the back of the baffle between the B139 and the rest of the drivers)

      In the TLS 80 particular attention should be paid to the mid enclosure. The mid enclosure is a cardboard tube. Impregnate this inside & out with a liquid stiffening material. One could use something like West System epoxy but probably most convienient and way less toxic (ie you could do it in the living room) would be a
      puzzle-coat like substance. I am using a brand called MOD PODGE which I find in craft stores. It looks & smells like runny white wood glue. You apply 3 or 4 coats with an appropriate sized paint brush. (reports back from England confirm that this makes a substantial difference)

    • Duct Seal*. This is the putty-like stuff pipefitters use to plug holes with. It remains "plastic" forever (I am recycling stuff I first applied 20 years ago). A layer of this should get applied to the baskets of the B139 & the B110 to damp out parasitic resonances. Apply some to the ouside of the mid enclusure as well.

      *(or plasticine or any of many other damping compounds).

    <the above are useful on any speaker>

  2. Play with the mid-range enclosure damping. Things like layering from the back a gradation of damping material to make the mid box more like a TL. dense foam, less dense foam, wool/dacron mix or fiberglass or miraflex (getting less dense as you get closer to the B110). A more drastic move would be to extend the entire mid cabinet out the back of the speaker and leave it open making it into a real TL.

  3. play with ways of minimizing the grill cloth holder diffractions. Ideally both the grills and the aluminum inserts to hold them would go away. If this doesn't meet with SAF then a new grill with minimal structure offset from the surface of the baffle.

    All the above fall into the doesn't cost much, just some elbow grease & ingenuity required. I have yet to run across a speaker where these tweaks didn't make less than subtle (usually dramatic) improvements.

    The following are in the class of throw money at the problem, and can make even more dramatic improvements:

  4. Tweak the passive crossover.

  5. Multi-amp. This system should be bi-amped at a minimum. And with a fast XO. The B139 has some nasty resonances that with the 12 dB/octave XO @ 400 Hz decidedly color the mids. When we were building speakers using the B139/B110 in the late 70s a 200 Hz 18 dB/octave XO made a huge difference. Nowdays I would use a LinkWitz-Riley 24 dB/octave XO and tune it to the baffle-step frequency (or a little lower), which in the case of the TLS 80 should be about 225 -250 Hz (baffle width of 18 inches).

  6. Replace the 2 Coles with a single tweeter. Today there are alot of way better tweeters available than were available when the TLS 80 was built. ScanSpeak, Vifa, Focal, Raven, on and on. Take a visit to Bob's LDGS and go shopping. Now the hard part about this is the XO. If you decide to tri-amp then no problem, it is easier to integrate the tweeter with the B110. If not then you would have to design an appropriate XO. That is a much bigger challenge. A more appropriate approach might be to do 6 and 7 together at the same time and use someone elses already well worked out passive XO.

  7. Replace the B110*. If all active XO then just pick a good one. I just signed up to get some Seas MP14RCs (Tim Garvey that a BASSList member is trying to get enuff people together for a caselot. There are lots of other good mids. If you decide to passively XO the mid & top then you should look for an already designed 2-way minimonitor with a 5" mid/bass and use those for mid/tweeter/XO. The Vifas in the TLb are a good example (and there is no simpler XO) -- cost of drivers and XO for both your TLS80s about 125 USD.

* and you could mail those to me ;^).

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