Documenting work on a pair of Forte ll

[jbohlscheid]

I am documenting my work on a recently purchased Forte ll pair. I'm not sure how many previous owners the pair has experience. I am not highly experienced and knowledgeable in speaker building and repair, but I am rational and try to be well studied.

I gave the cabinets a light sanding and rub down with Howard’s Restor-A-finish and bees’ wax to cover a few blemishes and try to improve some burn marks (no luck here). The risers were a bit banged up so I sanded them and went over them with a few coats of Danish Oil and some black paint in the bevel.  I was enjoying the experience, however when I was working on the positioning I noticed one of the tweeters was out. Rats.

I am fairly certain that the cabinets had not been opened before. I checked the connections, switched amps, pulled out and checked the integrity of the diaphragm, continuity of the speaker connections and wires, and I swapped the tweeters between the two speakers. Ultimately I determined the fault was in the crossover. The 1.5 uF mylar capacitor before the tweeter as well as the rest of the capacitors looked intact along with the wiring, inductors and autotransformer. As the speakers are 40+ years old, it make sense to update the capacitors, and if I am going to do that I might as well replace the resistor and the tiny inductor, and I can reuse the autotransformer (T7A) and the 2.75 mH iron core inductor.

I purchased the Gold capacitor package from a well known Klipsch parts supplier, one 1.5 uF, two 2 uF,  and a combination 100 uF and 10 uF capacitors . The package was quite a savings compared with purchasing the same items individually from other suppliers. I also purchased a 0.16 mH air core Litz wire inductor from Solen to replace the original inductor (an air core not iron core as shown on a few schematics) and a metal oxide 40 ohm 10 W resistor.  Since the PC board is quite small compared to the new components, I desoldered the components and I followed the layout of the well known Klipsch parts supplier mentioned above. I had a few struggles with the leads on the new inductor, reused inductor and the autotransformer. I had trouble making the contacts due to the enamel and lacquer finishes. Solvents, heat and a little abrasion (used separately) took care of the problem (mentioned below in the trouble shooting). The hook-up wire was 18 awg oxygen free copper from a reputable US supplier.

[jbohlscheid]

In taking apart the cabinet I was a bit disappointed with the internal build quality. There were staples that were not fully driven into the bracing and internal walls, gaps between the bracing, and there were tear outs for the screws used to mount the passive radiator and horns. One would think that Klipsch would use pilot holes to maintain the quality of the wood. Note the tear out at the top of the image and the protruding staples.

[jbohlscheid]

Next to damp the baskets and horns. The various forums have many volumes of discussion on this and I chose simplicity and my somewhat common sense.  I used a product Retro Mat from Crutchfield similar to Dynamat. I didn’t feel it was necessary to cover the entire surface of the woofer and passive radiator baskets to achieve the needed effect, so I focused on the radial parts as shown in the photo and a portion of the ring section. On the horns I placed a strip down the long unreinforced sides. If tapping is an appropriate indicator, there were changes in the volume and timbre, quieter and lower.

 

Edited October 25, 2023 by jbohlscheid

[jbohlscheid]

The damping material on horns extends from reinforcement at the bottom of the image to the flare just below where the horn mates with the cabinet. This may be hard to see from the image. I also did the opposite side.

[jbohlscheid]

Before reassembling, I cleaned the dust out of the cabinets and caulked all of the seam with a silicon bathroom product that I had on hand. I also filled the hole for the magnets and gaps between the corner braces.

You can see some of the tear out around the horn openings

[jbohlscheid]

The foam gaskets were compressed but intact, so I reused them.  I used a window seal putty rope (`⅛”) similar to Mortite to create a tighter air seal. Initially I put it on the speaker or horn but then I thought better and put it between the cabinet and the foam gaskets. We’ll see how this works out. One needs to spread it out a bit and a wet finger works well. I found laying the cabinets down flat and working with gravity works best with mounting the drivers. The quick disconnects need to be attached before screwing down the horns. The woofer can be accessed through the passive radiator opening.

 

 

FYI - The male tabs on the speaker speakers are 0.205” in width, in contrast to the typical 0.250” female disconnects normally available. These were impossible to find in Boise so I had to order from Mouser for any rewiring later on (Panduit crimped fully insulated nylon tin plated brass female connector - I would have preferred copper, but not available).

 

First went in the woofer cone, and those of you that have changed a tire, I used the star method of tightening the screws down evenly to create a secure seal (repeatedly tightening a screw [not all the way] crossing to the other side repeat, cross to a different screw, repeat, and so on). I did a similar process with the squawker and tweeter.

Note: There was a bit of the caulk rope that oozed out and it was easily remove with a toothpick.

 

[jbohlscheid]

A shot into the cabinet with the caulk placed between the cabinet and the foam gaskets.

 

I then replaced the foam in the cabinet. I was wondering if this was added or was OEM as my Heresy didn’t have it and I do not recall any mention of it with the Forte ll. One thing I noticed when I originally opened the cabinet was that the foam was not symmetrical in the cabin and hung lower on one side. I’m not sure if this a big issue or not. The pieces are the same size and one was routed over the tweeter and press up and into the upper corners. The other piece was pressed into the side and upper corner. When I replaced them, I overlapped them above the tweeter and pressed the foam up into the upper corners and wedged them into the sides. The ends came down about halfway to the woofer.

 

 

[jbohlscheid]

I stood the speaker up and installed the new crossover network. I pre-drilled countersunk holes in the board and used this as a template for pilot holes into the base of the cabinet. I carefully measured the #4 wood screws and depth so I only went into the cabinet wood half way. Additionally I used ⅛” nylon spacers in order to allow for the zip ties routed through the board that held on the inductors. I attached the board to be close to the binding post cup but with a little room for my hands to make connections. Measure and prototype repeatedly before securing. I stood the iron core inductor up as this is how the Crites board orients it. Zip ties and a small dab of adhesive.

 

 

Since I used a barrier strip in copying my model, I used Panduit crimped tin plated copper fork and ring terminals for the wires (what I had on hand for #6 studs). I reuse the existing internal driver wiring and added the terminals. I reused the two speaker wire connections and added fork connectors for the crossover input. On went the binding post cup (sealant, foam gasket then cup) and screwed on using the star pattern.

Edited November 16, 2023 by jbohlscheid
More clarity

[jbohlscheid]

I did a quick test at low input to see if everything was working. No, it was not. This is when I figured out that I needed to clean the coating off of the old inductor and autotransformer. Disconnect everything, out to the garage, desolder, scrape, check continuity all around the board just to make sure, resolder and then back in the cabinet.

Low input success!

I laid the cabinet down again to place the passive radiator down and align the hole in the cabinet and basket. In went the screws and tightening with the star pattern.

On went the risers, in went the speaker cables

Another low input test. This sounds nice. A quick listening comparison with the untouched speaker - there is a positive improvement.

I slowly increased the input and then….the volume dropped to a whisper out of the treated speaker. Panic! Dismay! Disbelief! What did I do!

Out comes the passive radiator. Quick review of the connections on, to and from the crossover. Check. Polarity on the woofer. Check (easily observed). Unscrew and remove Tweeter. Polarity wrong - the “-” and “+” are a bit difficult to see on the plastic. Unscrew and remove squawker. Polarity correct (there was a bit of paint near the "+" connection. Put everything back together again.

Low power input. All the drivers are firing. A little more power, still good, a little more. On up to about 40 Watts. Sounds good and really loud.

I have not had a chance to position the speakers and give them a proper comparison yet. The initial impressions are a distinct, better detailed bass response (more "there there" but not boomy). The squawker and tweeter are cleaner and clearer with a bit better separation. I have few different amps to try also and see what fleshes out.

After I give them a good listen, I have the opportunity to try out titanium tweeter diaphragms and see how this sounds.

[Dave MacKay]

Nice work!

 

Thanks for creating this thread. I enjoyed reading it. 

[capo72]

Nice job on the documentation of your work! 

[jbohlscheid]

Thanks for the comments.

 

I have had a bit more time with speakers and the sealing and new capacitors and coil are noticeable. I went through the Talking Heads catalog last night. Wow! Tina Weymouth's bass really comes out on both speakers, and particularly distinct on the treated speaker. Additionally as a bit louder volumes and heard quite a bit more detail in the more background sonics and instrumentations.  With "Psycho Killer" from Stop Making Sense (the original CD version), I heard a bit more of David Byrne's cracking and "psycho-ness" in his voice as the song progress. Also I got more of the overtones on the guitar, and I could sense how hard he was striking the string and the sustain. With the speakers together I had a real sense of playing live and the presence of the room. Very cool. Off to some symphonic music next. I have a pair of titanium tweeter diaphragms that I my try out in the future

 

I wanted to add that I installed T-nuts in the risers that will accommodate some spikes I had and will also accept Herbie's threaded gliders. As you may see, we have an older house and the floor is not entirely level. A new sideboard from Scandinavian Designs holds the Rotel RC 1572 (Mk 1), PS Audio S300, Marantz ND 8006, Rotel RT 1084 (I really enjoy HD radio - Why don't we have more?!?), and my first piece from college, Pioneer PL-518 with a Ortofon MM Blue cartridge. I have a REL T/9i in the corner. I have not tried the First Watt clones, Akitika GT-102 and Decware Zkit#1 I  built during the lockdown. The room needs some treatment after our remodel with too many reflective surfaces. I do need to get under the house and add some bracing to the floor as it is very bouncy.

 

I do have a question for the Peanut Gallery - How was the foam inside the cabinets originally placed for the Forte ll? When I opened the cabinet the two pieces were routed over the tweeter and down the sides. I read in another audio blog site where the foam was between the tweeter and squawker or behind the tweeter and the back of the cabinet. Any thoughts? I saw the inside of the Forte lV has a denser, stiffer foam attached to the sides and the ceiling of the speaker cabinet.

 

 

 

 

 

[DirtyErnie]

That's a very classy set-up you have there, enjoy!

[jbohlscheid]

After many hours of enjoying the system, there is a notable "much more there" in the treated speaker. The sealing of the cabinet and new capacitors and inductors make the speaker stand out from the stock speaker, particularly with the bass response when I swap the treated speaker into the corner. Note the photo above. One can really feel a cello or a full symphony.  Next step is to build the ALK crossover described in another forum thread and listen for a difference. Obviously assessing the sound stage presentation is not possible with one speaker. Unfortunately I'm not set up to take measurements for empirical confirmation. I'm getting pretty quick now disassembling the units.

[capo72]

I think the way you are doing the mods on one speaker to compare with stock, is very smart. Measurements of any difference would be great as you stated, but at least you have listening proof and not just placebo or confirmation bias!

[Deang]

It should make sense that if you make physical changes to the loudspeaker you will hear changes to the loudspeaker. No surprise there. The problem is that without measurements, you have no idea what is going on. You have nothing to tell you why you are hearing what you are hearing. Something can curve terrible and a person will tell you how great it sounds. 

 

 

[jbohlscheid]

I agree 100% that without measurements objective improvements/changes cannot be confirmed. I do not intend to appear snarky or cheeky. As someone that is well versed in experimental design and statics (not in the audio realm), only measuring one speaker provides the slimmest portion of information to note change. If I had my way, I'd need many pairs of speakers, many sets of capacitors, potentially various sources, components, power supplies and a very stable space for measuring, such as a semi-anechoic chamber. Frankly, I would dearly love to do this. If there is anyone interested in building such a facility please let me know and send cash. We could test any piece of kit and hypothesis.

 

For me, this project allowed me to take care of a faulty tweeter circuit and, to the best of my perception and a few other casual observers, produce a small but noticeable improvement in the clarity and sound stage of the speaker system. As the rebuilt crossovers are easily removed, I could potentially isolate the physical changes to the cabinets from the new crossovers.

 

I have now (re)built ALK-style crossovers using what I believe are the same layout and components (except I had to use a Crites 3636 autotransformer rather than a 3619) and given them a quick bench test to confirm the crossover frequencies (I didn't realize at first the design maintained the original frequencies). I do have a small oscilloscope, frequency generator, and multimeter. And no, I didn't determine the crossover slopes so I won't go there.

 

I had a very curious event upon installing in the speakers and giving them a listen. In each speaker, and I individually installed the crossovers and powered up each speaker, I blew out the original phenolic tweeter diaphragms. Remember that I had tested the continuity at the beginning of this process. I slowly increased the volume in only one speaker at a time (using PS Audio Stellar S300 amplifier and Rotel RC-1572 preamp using soft non-dynamic sound). Nothing dramatic, just no sound. I pulled out the diaphragm and test the continuity. None. I pulled out the crossovers and checked the voltages and current. Nothing different. I put the other crossover in the other speaker and the same thing happened. I did have a set of titanium diaphragms on hand and put them in. No problem. I took a look at the diaphragms and could not detect any obvious physical damage in the unit and the coil wire. Very interesting. Now another set of parameters to test!!!!

 

I gave the ALK-style crossovers a few days break-in and listening. They did appear different and agreeable (non-fatiguing), but I didn't have time to dig deep.

 

I put the new-old crossovers back in and have been listening to these since.

 

Happy New Year to All