RST28F and DC130A Foamcore Homage to LS3/5A

[prairieboy]

You wished to use beech? There's nothing magical about it; I suspect the BBC used it because it's a common (plantation) hardwood in Europe and would have been readily available (and cheap).
FYI, in terms of density and hardness (gleaned from the wood database): where SG is specific gravity and JH is Janka Hardness.
EU beech: SG - .71 JH - 1,450
Am. beech: SG - .72 JH - 1,300
White oak: SG - .75 JH - 1,350
Red oak: SG - .70 JH - 1,220
Hrd maple: SG - .71 JH - 1,450

 

[xrk971]

Looks like hard maple is a dead ringer. Thanks for that Prarieboy. I am going to get two sets made, one in hard maple and one in white oak, and see if we can hear or measure any differences. My cabinet builder said he was fine with either and I couuld build two identica sets and he will take the one I reject

I sort of think the BBC made too big a fuss of this "beech" battens thing. Their publication shows some data but how much of that is variations in how it is glued or the type of glue etc.?

 

[prairieboy]

I suspect that it came down to accounting and the cost of the wood. I've used beech, and it's a nice wood, but as stated, not magical.
I had a pair of DIY faux LS3/5a speakers at one time: KEF b110 and t27 with Falcon crossovers designed to mimic the BBC version. There was a synergy about them where they sounded better than the sum of the parts. Ridiculously inefficient of course, but enjoyable non the less..
I suspect your design will be every bit as good, or better. Interesting build.

 

[xrk971]

I’m going to go with 5/8in square battens - a little more room for the screws to have better purchase. Will still be doing the white oak vs hard maple experiment though. It would seem of damping was wanted, a more pliable glue like latex caulking might be better than Titebond between the battens and panels. But then it may not have enough toughness to handle rough handling or a small drop.

A little experiment today, moved them to my work computer desk (actually a big dining table sprawled out for COVID19 telework videocons) and they sound very very nice as near field monitors. Great application for this speaker. About 3.5 ft away and elevated 4in above the desktop. The bass is all there and the center phantom is perfect.

 

[Kokanee]

Hi X,

I have some 2" sheets of XPS left over from house construction. Any problem using this as long as ID's are adhered to. May look a bit bulky though. Should be strong enough though, without a lot of bracing. Thoughts?

 

[xrk971]

Hi Kokanee, if you want to use the same crossover, you need to keep the baffle width the same at 7.5in external dim. 2in will make it 9in wide box sounds afraid that’s too wide. Maybe you can use the 2in XPS for other walls except thin ply or 5mm foamcore for the sides? Or just make it all out of the wall foamcore like me?

 

[AllenB]

I'd try the wider panels and round the edges to ease diffraction.

 

[xrk971]

Good idea AllenB. Maybe 6in flat front and 1.5in radius on each side. It would smooth the response for sure but the XO might still take some tweaking.

 

[xrk971]

So the production process has started for 6 speakers. Wood is being ordered or obtained. Drivers, crossovers, binding posts, foam, and butyl liner have been ordered. CAD plans finalized. And we should have some cute little boxes singing in short order.

Debating on the type of adhesive to use between the battens and the panels. I am leaning towards white latex caulking at the moment. Keep it pliable for damping. It sticks better than silicone caulking. Going with 5/8in battens two cabinets will use hard maple for battens. Other will be experiment with harder white oak.

If anyone is interested, I can post the complete Parts Express parts numbers for the BOM which ended up at about $180/pair.

 

[AllenB]

Good idea AllenB. Maybe 6in flat front and 1.5in radius on each side. It would smooth the response for sure but the XO might still take some tweaking.

A guess, but not a bad start I'd think . Regarding the crossover, considering the tradeoff I know which compromise I'd rather risk.

 

[Kokanee]

AllenB, X,

I think I am going to do a little experimenting over the winter. I am going to use some of this 2 inch XPS, and maybe try to model up the RS tweeter and a slightly larger mid-woofer, like the ND140. I will use round over techniques or possibly cut some facets for the diffraction tendencies.

I also have some sealed mid/tweeter units and 7" woofers taken from 2 Paradigm ADP 490 surround speakers. I also have the x-overs. I was thinking of trying to model a small 3 way with these. Once I finish my speaker building tutorials/courses, I will be in better shape and have some of the modelling hardware/software that is needed.

This are projects to get to, as the first projects are building the FH9HVX and the VSQA amps / PS's. Just waiting on parts to arrive.

Thanks for all the guidance for us newbies. No Mexico for me this winter, due to C19.

MM

 

[xrk971]

Looks like a lot of DIY fun to keep you busy!
Good luck Kokanee!

 

[oon_the_kid]

Hi X,

I have some 2" sheets of XPS left over from house construction. Any problem using this as long as ID's are adhered to. May look a bit bulky though. Should be strong enough though, without a lot of bracing. Thoughts?

Hi X,

Wondering what your thoughts are on XPS foam versus foam core board. Especially considering the price of XPS foam to be quite reasonable and one could get really thick pieces.

Oon

 

[Vunce]

I built the prototype FAST TL’s with a combination 3/4” & 1” XPS foam board. They sound fantastic!! So good that I’ve procrastinated for 9 months to start the real wood cabinets

(Pink boxes in the living room are starting to get old though.)

 

[xrk971]

XPS covered with a thin 1/4in or veneer with a pliable adhesive like latex caulking might make a great CLD wall and provide better sound than wood or XPS alone. Plus, the speaker would be more durable than XPS, and very light compared to wood. The best of both worlds. I did this on the baffle of my 10F/RS225 FAST and it worked for years until I finally had a wooden version made. The wooden one did not sound or measure any better!

Here is wooden faced XPS:

 

[wilbur-x]

Is there any disadvantage by sectioning a TL - duct by XPS sheets ?

 

[xrk971]

You mean internal passages in a TL using XPS? No, in fact, it may provide benefits of vibration damping between the sidewalls and also absorbs the high frequencies we want to be fitered out of the TL.

 

[burgunder]

Shouldn't this be called a Foamage to LS3/5A?

 

[wilbur-x]

You mean internal passages in a TL using XPS? No, in fact, it may provide benefits of vibration damping between the sidewalls and also absorbs the high frequencies we want to be fitered out of the TL.

Wonderful, now we hear many saw (un)enthusiasts breathe a sigh of relief.

 

[xrk971]

I like that “foamage” to the LS3/5A. Not to be confused with the dairy-based fromage.