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Building Forte II Cabinets. Any Modification suggestions?


Mikerodrig27

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I just bought a pair of Forte II speakers. All of the drivers except for one passive radiator are in great shape. I found  a recone kit that will solve that problem. 

 

I wanted to see if anyone had suggestions on modifying the dimensions on the cabs etc. I was thinking of adding an extra 1/2" of depth so that i can add bracing to the inside and not take up too much volume. Then I thought, would adding 2" of volume make the speaker sound better? 

 

Let me know if any of you have successfully modified the specs of the cabinets. I will be reusing the front baffles but that is it. I may be able to salvage the rears but I don't think they are critical. 

 

I will likely wrap these in walnut veneer like the originals. Other thoughts are Mahogany which is cheaper and more spectacular looking. 

 

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Edited by Mikerodrig27
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Unless you know how to model your changes with software, I would never change the stuffing of a sealed enclosure, port length of a ported/vented enclosure, weights on a passive radiator or change the volume of any enclosure. This has a direct impact on frequency response and power handling. 

 

I rebuilt some KG 5.5's, completely new cabinets with new dimensions (taller and more slender for a sleeker look rather than short and fat), I added battens (braces in the corners) and 1" dowels all over, left to right, front to back, but I calculated the volume for all of those and my final cabinet volume with everything installed and assembled is within .01 ft^3 of the original enclosure. I changed the port to a nice flared port but that required its own calculation as well. 

 

Good luck!

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If a little is good more rarely is better.

 

Be careful with this bracing stuff – it can get out of hand real fast doing more harm than good. Smaller well placed braces can help a lot more than a bunch of randomly placed pieces of wood inside the cabs.

 

 

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3 hours ago, tlarwa said:

I modded a pair of Forte IIs a while ago ... great project, and the speakers sounded really good.  Link here ... might give you some ideas.  

 

 

Curios if the 3.5% volume displacement was based off the total cubic volume of an empty cab or with the volume of the installed drivers factored in?

 

 

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9 hours ago, Mikerodrig27 said:

 I was thinking of adding an extra 1/2" of depth so that i can add bracing to the inside and not take up too much volume. Then I thought, would adding 2" of volume make the speaker sound better? 

 

 

 

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the Forte III is also deeper by 3/4  of  an inch ---a full 13 inches ---so there should not be any problem -

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Thanks for the responses. I may try building one a little larger to see what it sounds like. I eventually want to get a MiniDSP mic or something similar to measure results. From what I have seen with DIY speaker kits, enlarging the cabinet, switching from ported to bass reflex doesn't require crossover changes. This is with fairly high end speakers as well. 

 

I am going to start doing some research tomorrow night (tonight I am finishing up a rebuild of a Marantz 2215b). From my brief time reading about it, the passive radiator (PR) acts as a port essentially. If I enlarge the volume in the cabinet, I need to add a little more weight to the PR in order to tune it down so that the woofer doesn't put out too much bass. I guess the only question is, will the woofer work well in a larger lower tuned cabinet. 

 

Dampening I am not concerned with. I can add and remove that easily. I will have some bracing in the new cabinets. The dampening would be to just cut down on reflections in the cabinet. There is a lot of dialogue that comes from the woofer... At least in my Forte I's (another set that I have) that I have spent some time messing with. 

 

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21 hours ago, Alexander said:

 

Curios if the 3.5% volume displacement was based off the total cubic volume of an empty cab or with the volume of the installed drivers factored in?

 

 

This goes back a ways, but I believe it was based off the internal volume of the empty cabinet, sans drivers.  

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4 hours ago, Mikerodrig27 said:

 If I enlarge the volume in the cabinet, I need to add a little more weight to the PR in order to tune it down so that the woofer doesn't put out too much bass. I guess the only question is, will the woofer work well in a larger lower tuned cabinet.

 

nope , the Forte III uses the same PR and it is already a deeper  cab , so all should be ok with the woofer -  if you sense any issues , just line the rear panel with acoustic foam of 1/2 to 3/4 inch thick -simple -

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11 hours ago, Alexander said:

 

Be careful with adding weight to passives,  tried that trick on a pair of forte IIs against the advice of @BEC a few years back. I ended up having to re-cone them after they were so badly torn up.  I believe it was ~ 2-2.5oz added IIRC.

 

I need to recone one passive radiator. It is all beat up from the Previous owner. I am leaning towards not messing around with the weight. I think the 15" driver is fragile. Messing with the broken one a little bit it seems to be a rather thin material that rips easily. 

 

10 hours ago, RandyH000 said:

nope , the Forte III uses the same PR and it is already a deeper  cab , so all should be ok with the woofer -  if you sense any issues , just line the rear panel with acoustic foam of 1/2 to 3/4 inch thick -simple -

 

Awesome. I never liked the tall skinny look of the Forte's. This will help mitigate that. Between the extra depth for the bracing that I am going to add and the 3/4" of depth it should help mitigate that. 

 

Using tlarwa's spec of the bracing taking up 3.5% of the space, that would ad a depth of roughly 1/2". That combined with the 3/4" will equal 1 1/4" of extra depth. I agree that I can just fill the space if I don't like the sound for some reason.

 

Thanks for all of the responses!

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  • 4 weeks later...

Surprisingly, my biggest obstical has been learning how to do nearfield testing with a calibrated mic that I bought (UMM-6). My latest knowledge is that you measure the woofer, the port and depending on how high in frequency your test goes, mid and tweeter. All nearfield. 

 

Once I figure out the tuning frequency, I am going to order a precision port:

 

https://www.parts-express.com/precision-port-4-flared-speaker-cabinet-port-tube-kit--268-352

 

I have a pair of Forte I's that I am comparing them to. As of right now, I can say the new cabinets, dampening produce way cleaner bass. I have hope!

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