My Forte II Upgrade Project

[tlarwa]

Bought a pair of Forte II's last weekend, with the intent of making them as good as I can (within my budget). I've been consulting with Moray James about his efforts to improve his Forte II's, and am following a similar path. The order of improvements:

• Brace and seal (with white glue) the cabinets. I also sealed the backs of the grille magnets.
• Build new risers to get them up to ear level (~10" high - and the stock risers were pretty beat up anyway)
• Refinish the exteriors with Howard's (just aesthetics, but it sure did clean them up!)
• Reseal all drivers with foam tape when re-installing
• Re-terminate the internal speaker connections. I used automotive spades, crimped and soldered.
• Recap crossover with Crites rebuild kit.
• Replace tweeter diaphragms with Crites Ti.
• Replace Midrange diaphragms with Crites version.
• Replace binding posts with Pomona 3770 (beefier than stock)
• Add 3 oz. of weight to the passive
• Dampen driver magnets, horn backs and woofer spiders with Dynamat.

The biggest decision was what to do with the crossovers. I seriously considered the ALK version, but just didn't have $350 to spend on them right now (and Al doesn't offer the DIY version anymore). Since the new Crites crossovers are essentially a better version of stock (from what I can tell), I didn't want to spend $250 on them. So I opted to just replace the caps for now. My plan is to replace all of the inductors with Solen air cores as soon as I can round up the funds. For now, at least I'll have the original crossovers back up to spec.

The bracing wasn't too hard. I used hardwood, and was able to brace side-to-side in three places; between the floor and the bottom of the woofer opening, between the midrange and tweeter openings, and between the tweeter opening and the top. Front-to-back I was able to brace in two locations; between the floor and the woofer opening and between the top and the tweeter opening. because of the size and postion of the passive opening, I couldnt find a good way to brace from front-to-back in the center of the cabinet. I've attached some half-*** pics to try to show the bracing.

I made my own risers after seeing that the stock ones were not worth fixing (plus, they were a little too short). I used stair treads for the tops and bottoms (they have a nice rounded front, which looks good to me) and a 1"x8" for the "H" between them. Total cost ... about $15. Time to build ... about 90 minutes. Their height is about 9 inches, which puts the mid-range dead center to my ear in my listening postion (32"). The pics show them, but they aren't finished yet. I'm planning to paint them black. I think I'll leave the bottoms smooth for now so I can push them around on the carpet as I fine-tune the placement, and once I get that nailed down I'll add spikes to the bottoms. My floor is carpet/pad over concrete, and I like the spiked connection to the subfloor. I thought about screwing them to the cabinet bottoms, but I think I'll attach them with Blue-Tack instead.

I'll take some more pics as I get them buttoned up and once they are in my listening room. Should be ready by the weekend!

Tom

[tlarwa]

Side view

[tlarwa]

Bracing at bottom

[tlarwa]

Bracing at top

[tlarwa]

Bracing in center

[mustang guy]

Wow, you have given this a great deal of thought! Great project and pics! If you can, it would be nice to see a graph of response once you are done. The two things that jump out are that you are changing the mass of the passive and you are reducing the volume of the cabinet with a good deal of bracing. My intuition tells me that the bass curve will be smoother, but I don't have any experience at all with weighting a passive radiator.

[tlarwa]

I'm following Moray's lead on the passive mod. He claims it'll give about a 3dB boost to the bottom end. I figure it's worth a try. The passives are so easy to remove that I can always take the weight off if I don't like the results.

[pzannucci]

I'm following Moray's lead on the passive mod. He claims it'll give about a 3dB boost to the bottom end. I figure it's worth a try. The passives are so easy to remove that I can always take the weight off if I don't like the results.

Be careful with what you want to accomplish. You will get more extension though it will come at the cost of some efficiency higher up in the low bass. That trade off may be acceptable based on the positioning of your speakers.

[BEC]

Also, according to the engineer I spoke to at Eminence, passive radiators are built for a certain specific amount of added mass. If you exceed that mass, there is a good chance of just ripping the cone out of the passive radiator during large excursions. 3 ounces is a lot of added mass. I don't know the maximum mass for that passive, but I seriously doubt it is made to take that much added mass.

[tlarwa]

Good input on the passive mod. Maybe I'll wait to do it until I get them buttoned up and in position to see how I like them as designed. I guess it would be easier to add them later if I wanted than to take them off. Thanks.

[Frzninvt]

By adding all that additional bracing you are altering the internal cabinet volume which is NOT a good thing. It will change the bass frequency response for the worse. There is a reason that speakers are engineered the way they are and tested in an proper chamber with sophisticated measuing equipment by engineers.

The Ti diaphrams, new caps, better wiring, terminations and new inputs are good ideas the others not so much. Raising there height also will affect the bass performance as it is no longer coupled to the floor.

[tlarwa]

We'll see how the bracing affects the bass. The volume of the bracing is only .095 cu.ft., which is only 3.5% of the total interior volume of the cabinet. It looks worse in the pictures ... kind of like the saying in golf that trees are "90% air". They sure don't look like it. I think the small reduction in volume will be made up for in tranferring energy to moving air instead of moving cabinet walls. As for the stands, they are essentially the same thing as the stock risers, just taller. And if I screw them to the bottoms of the cabinets they will be no less coupled than the original risers were. In all of my positioning experiments with various speakers, I've preferred having the mids at ear level in my listening room. The Forte II's have plenty of bass for my room size (12'x19') so I'm not worried about losing bass. I just want to get it more "punchy" and not bloated.

Like anything DIY, I'm sure I'll learn some things. Some will be good, others not so good.

[jason str]

Bob mentioned overextension of the passive cone and this is something that happened to me with an older set of my Chorus II's. No extra weight was added to the passive either.

Luckily the glue gave way instead of the cone and just a re glue was needed.

Just be careful with the volume knob and keep an eye on you drivers excursion.

[Daddy Dee]

Tom,

very nice work.

if/when you get around to adding air core and such to upgrade your crossovers, hope you will do them one at a time. would like to hear your assessment of comparison of one upgraded crossover from your reference which you now have.

looking forward to hearing your take on the sound of these sweethearts.

[tlarwa]

I just got pricing from North Creek on 10AWG and 12AWG inductors, and it looks like I can get them all for somewhere around $200. I'm getting ready to pull the trigger on it. I just need to learn how to mount them on a separate board, and whether I can wire them into the stock crossover boards, since I'm still using them (mounted to the terminal cups). I've never done this type of work, so I like to have it all lined out before I pull the trigger. I can definitely do one at a time once I get the project started. I'd like to hear the difference as well (although the real difference is supposed to be in the width/depth of the soundstage, so I'm not sure how that will translate if it's only done to one side at a time).

[tlarwa]

http://www.audiokarma.org/forums/showthread.php?t=544764

[Ski Bum]

I think you misunderstood "coupling" as it was used upthread. I'm pretty sure it was referring to acoustic coupling r/t distance from the woof to the floor, not physical coupling. But don't sweat it, it shouldn't matter too much. I have very similar room dimensions (which, lucky for us, are about perfect for these speakers), forte II (crites networks and ti tweets) on 10" stands, and any loss of bass from being off the floor is made up by their proximity to corners anyway. They sound great, and yours will too.