Old compact tower speakers = New compact bass speakers...?

[Count Dacula]

Trying again to find the right forum.

Any advice on repurposing my beloved 2x8" sealed 3-way KEF C75s into 2x8" mini subs for my various minisystems?

These guys owe me nothing, but it would be cool to STILL use them after 35 years. However, this would be a tricky rebuild, or barely worthwhile, to replace one side mid-hi with a junkyard part for $100, only to yield two old obsolete units that still need new ferrofluid, et al. I have plenty of other newer speakers, all with varying sentimental value.

So, since I already have 2 good 8" KEF woofers, can I just brew up a unit with a small bass amp? like...

Fosi Audio M03 200 Watt TPA3255​

Right? Just enough power for 2x8" drivers in parallel. I'll just attach the thing like a wart, lol. The low/fat tower cabinets are such a nice form factor too. It's ideal, imo.

My question is about the #2 unit. Since I already have two brand new Parts Express 8" woofers, already here (somewhere) from another failed project, exactly how should I use them?

Ohms are unknown, I suppose the KEF B200s are 8 ohms each. So, should I make two different cabinet loads, one KEF and one with the new Parts, or Homebrew it with one of each, and let the amp figure it out? I don't plan on using them together, at once. It's possible, but not an objective. Ill see if one unit is better than the other too...

I think it's a good question, and hopefully meets the criteria for a post.

If those Parts Express are 4ohm, I better not put them together. I think they are "home" 8 ohm though.

Same thing for the Sealed cabinets. I assume the KEF drivers are ideal for Sealed, but will the new ones be ok if they are "for" Bass Reflex? How can I tell from volumetric specs??? Does it really matter if I put B-R in a Sealed cabinet? Should I mix them up, one and one, for any of these reasons?

 

[CDMC]

Read this, then you will have your answers.

Loudspeaker Design Cookbook, 8th Edition Vol.1 Review

The best book about designing loudspeakers just got better! Audio enthusiasts and audio engineers are in luck with the release of the 8th edition of Vance Dickason’s “Loudspeaker Design Cookbook".

www.audioholics.com

 

[Count Dacula]

Imma wing it. Just if someone saw any glaring issues, or had a preference with wiring or load. I could just ask AI to read the book on my behalf...

 

[technodanvan]

That's a lot of questions in one post! While the book might help it's really not going to give a terribly straightforward answer.

If you REALLY like the look and form factor of these cabinets then...yeah, MAYBE worth repurposing them if you plan ahead and know your way around a multimeter and a couple of power tools. But honestly for the couple hundred bucks you'd spend doing it you'd probably get more out of just making a smallish subwoofer that is purpose built. This GRS comes to mind.

https://www.parts-express.com/GRS-12PR-4-12-Paper-Cone-Rubber-Surround-Subwoofer-4-Ohm-292-820?quantity=1

What 8" woofers do you have?

 

[Count Dacula]

I understand, and am familiar with those reference books.

As it is, it'll be really easy, literally to slap in one woofer from the other speaker, chunk out the wiring and it's ready....,to test.

I ordered the TPA 3255 sub amp, which I think might attach on the back top, with just the knobs extending (?)

While it arrives from China, I have a Fosi V3 here, and a micro sub controller, that I could "test" it in stereo mode.

With the current cabinet config being 2x8, I feel like homebrew has a decent chance, without a ton of calculations or fiddling. Considering the first two drives are the actual KEF woofers. I considered buying two more, which is realistic, price and effort wise...but maybe unnecessary. I do need to dig out those Parts Express drivers and check the specs, for sure.

The thing with the reference manual is, I'm not gonna change a bunch of parameters anyway, I already have the equipment, it's just a matter of doing the best install possible with what I have, with the placement and wiring.

I figured this project deserved a thread, to get tips, then show the results. Im definitely doing it, ordered the Fosi sub amp last night, and can get the prototype started today. The cost is gonna be awesome for what amounts to a nice unique unit, in the right system. I have a bunch of C grade bookshelf systems so they wont' go to waste.

Thanks for the feedback.