Quite possibly my last speakers

[IslandPink]

Steve, i didn't explain myself too well, but my thrust was that you can't avoid the speaker interacting with the panel to some extent ( and with the sound waves that come off the front). The driving energy is broadband so it's not just about getting it rigid at low frequencies. My concern was over Simon's suggestion of thin skins with spacing of some kind, then builder's foam. I have a feeling that this sort of structure could have a spectrum of resonances & intermodulation in the upper mids & low treble that would add a grey mush of sound to the upper vocal harmonics etc. I was just trying to imagine what this sort of baffle would sound like when rapped by knuckles - which is not a bad way of predicting what it adds to the sound.
For a single material I still rate perspex very highly, because it is pretty rigid , and well damped in the high frequencies.
However your suggestion of wood bonded to metal, with a compliant glue, does sound very promising. I think that both materials need to be fairly dense and void-free in themselves.

[Scottmoose]

For whatever it's worth, I find belting a panel with knuckles of very little use in determining its behaviour in actual operating conditions; the energy applied isn't really analogous to how a speaker operates. That's why CRS and aluminium can make excellent enclosures -they ring like the proverbial bell if you hit them, but as they say when people have a vaccine, belt the injection site with their hand and comment 'it hurts when I do that' -don't do that then.

Thing about drive units is that we're in inverse square law territory as Chris pointed out -as frequency rises so there is less mechanical excursion to excite panel modes, and >500Hz actual music power falls off the proverbial cliff (just look at energy per frequency distribution of a typical orchestra). As panel rigidity and Fs increases, so its Q goes up, making it even harder to excite, as the BW is narrower and you need to put a significant amount of energy into that point to significantly excite it -the remains are usually easy to address with fairly minimal amounts of damping.

Having a solid platform for both the driver mechanical motion to react against & the expanding wavefront to radiate from is largely why Avalon, Magico & others go with extremely rigid, high mass front panels, as it ensures good stability.

[vinylnvalves]

The other material if you can get off cuts cheap is corian, or any synthetic worktop material, it’s resin loaded with stone chips.
Don’t ask me to machine it though…. goes through tungsten cutters like nobodies business.

[Scottmoose]

Now that definitely can make a good baffle. Or box, if you've got the money / patience / gym-membership.

[pre65]

The other material if you can get off cuts cheap is corian, or any synthetic worktop material, it’s resin loaded with stone chips.
Don’t ask me to machine it though…. goes through tungsten cutters like nobodies business.

Water jet cutting ?

[izzy wizzy]

Now that definitely can make a good baffle. Or box, if you've got the money / patience / gym-membership.

I'm in the kitchen game and bench top suppliers/installers have a lot of waste material they need to get rid of. Many like to give it away as rubbish is expensive to get rid of. Well that's what happens here. Might be different there. Worth an ask.

[rowuk]

I am happy that we got such a response on the “constrained layer” principle. Moving the resonance of the box material up makes it easier to damp but, increasing mass can increase stored energy, so like most things in life, you just have to strike a balance. In my case, the curved sides probably also contribute to the dispersion/“reduction” of energy reaching the outer walls. The curve itself is part of that but also bending chipboard raises tension too. These are the first speakers that I have built with no foam/polyester batting or fibreglass insulation… I am interested to see where this goes.

[rowuk]

Here are the first measurements after a couple of days of tweeking. Biamped. No EQ, crossover at 500 Hz, room response from listening seat (3.5m). I just love this horn! 12dB/8va smoothing, no spliced in nearfield LF. I am happy at this early stage. Today I am working on cabinet damping.
Sticking my head in the box and singing shows an internal resonance at around 80(160/320) Hz. That will be my first target.

[brig001]

Very nice

That 60Hz is going to be fun to fill in
Do you know where it is coming from?
I have similar on my left speaker as there’s a bay window at that side - the other side is open to the dining room, so I don’t have it on the right speaker
You have it on both speakers even though your room isn’t symmetrical either
Almost makes a case for a single note sub which only plays 60Hz, but I don’t know how practical or desirable that is…

Brian

[rowuk]

Very nice

That 60Hz is going to be fun to fill in
Do you know where it is coming from?
I have similar on my left speaker as there’s a bay window at that side - the other side is open to the dining room, so I don’t have it on the right speaker
You have it on both speakers even though your room isn’t symmetrical either
Almost makes a case for a single note sub which only plays 60Hz, but I don’t know how practical or desirable that is…

Brian

60Hz will be no problem as soon as I get the subwoofer built and not for just 60 Hz. 60 Hz is the ugliest room node, but everything >80 Hz sounds best with the speakers where they are, so I will figure out something early next year when the sub is built. More important is getting the Karlson Tube tweeter done.

[brig001]

Sounds like a good plan
Looking forward to the tweeter - not seen one like that before

[rowuk]

Sounds like a good plan
Looking forward to the tweeter - not seen one like that before

Examples can be found online with the search of Karlson Tube. DIYAudio and other forums have dealt with this in depth. My interest is getting physical phase alignment, low distortion and more of a "point source" above 500Hz. If this works without other "disadvantages", I have a winner.

vonLange Karlson.jpeg (58.38 KiB) Viewed 5264 times

[rowuk]

Scheme to physically time align the woofers and horn. I adjust the 3 bolts on the front and back of the mounting plate to get the right spacing.

Hornmount1.jpg (80.98 KiB) Viewed 5131 times

Hornmount2.jpg (82.68 KiB) Viewed 5131 times

Hornmount2.jpg (82.68 KiB) Viewed 5131 times

[rowuk]

And now the tweeters
Thanks to John Carlson and his Karlson Couplers

Robin Tweeter.jpg (85.83 KiB) Viewed 4246 times

Beyma CD-1ND drivers