How to make a loudspeaker sandwich cone

A good book in german on loudspeakers is Götz Schwamkrug "Lautsprecher - Dichtung und Wahrheit", its from 1986.

PDF download here

Concerning sandwich loudspeakers here some information, page 92 in the book, showing impulse responses in comparison:

small paper cone 4,5 cm, 20cm navi paper cone and 7 cm sandwich cone.
The 7cm sandwich cone has a better impulse response than the smaller 4.5 cm paper cone

sandwich cone Schwamkrug.jpg

Schwamkrugs second book "Lautsprecher Aufbau Nachbau Umbau" is very good, too.
At the time some years ago where I did measurements I could not find big differences in frequency response.

But waterfall measurements showed cleaned up resonance behavior of alu sandwiched paper cones.

I rarely did distortion measurements.

Some measurements can be found here in the thread. Just look it carefully through.

Usually I treat fullrange drivers with aluminum foil and apply dsp linearization (= auto EQ in the near field with Behringer DEQ2496 or Minidsp plus measurement system). Together you get a real high end loudspeaker because the cone makes the sound.
Either use fullrange drivers with Faraday rings or use transconductance amplifiers to minimize distortions originating from the voice coil and magnet assembly.

So feel free to try out this kind of tweak and make measurements of your own. With your own equipment and loudspeakers. At the end a listening test in A/ B comparison is valuable, too. A report from a second party would be a benefit.
One secret of good sound with aluminized paper cones is that in this construction the core is the damping paper. And the foil is mellow household alu not duraluminium and hard polystyrene like DA Barlow used it in the mid sixties.

Or KEF in their famous B139 woofer.

All these break up in hard resonances as they strive for maximized stiffness.

They even never thought about using sandwich construction for fullrange loudspeakers!

For a good impulse response you do need a compromise between all parameters so the sandwich of alu paper alu gives you diaphragms which can have reduced resonances.

If there is left one dominant resonance it can be DSPed out by only linearizing the f response leaving a clean waterfall response.
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Comparison of waterfall measurements.
My measurements of Fane Sovereign 15 300tc with both sides household aluminum foil. Whizzer cones one sided. Small cone with thin alu foil.

First measurement on axis, second off axis
Fane Sovereign 15-300TC waterfall Arta 10cm.png

Fane Sovereign 15-300TC waterfall Arta 15cm 30 degree off axis.png

Measurement of the smaller Fane 12 250tc

15 300tc
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I have here measurements of a 38cm bass loudspeaker with and without aluminium foil

and with and without added copper rings

(other thread here in DIY Audio Forum I made "How to diy / add a faraday ring to a loudspeaker", but have no access to my old Win XP Laptop with ATB PC measurements system to open the files at the moment.

Downloaded the Demoversion on Kirchner Elektronik de but it cannot open the specific XFT files without Dongle or registration.....

So you have to wait

Although you do not need to trust me (=trust only your own measurements!) - everything I did was measurement assisted and is evidence based.

From the waterfall measurment I did on the 38cm / 15 inch of the aluminized Fane Sovereign you can certainly derive that it looks pretty good for such a big driver up to 2 or 3 Khz. Above this frequency there are the resonances from the dual cone / triple cone construction (whizzer cones).

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From post

in this thread here some fotos of a measured aluminium sandwiched fullrange loudspeaker system - you can search a long time to find a 25cm fullrange loudspeaker with such a nice waterfall.

Irrespective how the paper cone looked before putting aluminium on it - the aluminium sandwich foils of thick quality (3x thicker than household alu foil) did not add resonances in the middle tones.

Here you can see a 10 inch driver fullrange going down to 35 Hertz in Reflex, dsp corrected, both sides of the diaphragm is aluminium covered. Dustcap is aluminium hand made. It is not optically perfect but acoustically its o.k.
The ringing in the high frequencies (burst decay) is inaudible so I left the aluminium dust cap untreated.
I is phase linear from approx 200 Hertz to 8 Khz. This is due to the point source - always perfect time response after linearizing the frequency response.
Frequency response of this 10 inch fullrange sandwich driver:
Blue curve on axis
brown curve is 45 degrees off axis
red is bass reflex
There are no tweeters active. It is a fullrange driver.
Burst decay is measured down to -25db

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From post

in this thread here some fotos of a measured aluminium sandwiched fullrange loudspeaker system with SABA greencones.

Here you find the so much seeked for before / after measurements, so original, one sided and both sides (sandwich) aluminium paper cone with aluminium of very thin quality from the gold smith (several times lighter than household aluminium foil).

You really end up with posting everything several times because people are too lazy to click on links.

Saba Greencone without aluminium.png
Saba Greencone one sided aluminium.png
Saba Greencone both sides aluminium.png
SABA Familie aluminiumbeschichtet_www_onewayspeaker_com.jpg
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Thanks a lot Freedom. No hurry and Im glad you agree that before and after helps us to better judge when the mod pays of mostly. Also to have better basis for suggestions to potential alternative methods/improvements of the procedures.
Also thank you overall for sharing your discoveries.
No hurry or heavy reasons for that Freedom. My suggestion is to post before and after measurements when surcomstances allow it, when you modify in the future. Also to refrain from posting measurements without before. I aknowledge that they are not completely useless, but it would save you from spending time on answering to critzisism like mine 😄.
Its my thoughts on it and best advice I can come up with, but I might not be right. Don't worry, and don't spend too much time going through back-catalog to satisfy my curiosity 😊
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Measurement of Beyma 8 ag/n in marble reflex box with Arta in the near field 15cm with aluminized whizzer with thin foil and the paper cone sandwiched with household alu foil.

There is no measurement of the raw unmodified driver.


burst decay Beyma 8agn.jpg

FR Beyma 8agn sandwich.jpg

Really the Beyma due to a very stiff corrugated paper surround does not do anything below 100 Hertz.

Maybe the driver will get more response after long time break in, who knows.
Reminiscence / commemoration of Rudy Bozak using aluminium foil on loudspeakers in the early age of loudspeaker manufacturing (besides Dr Emil Podzus in Germany who used alu foil already in the 30ies)

Citation from wikipedia

"The original midrange and tweeter cones were paper. In 1961 the B-209 midrange cone was changed to a radical new design. The material was very thin spun aluminum which took much of its strength from its curvilinear profile along the radius. The cone received a thin coating of latex in order to damp the surface reflections that otherwise would occur on a metal surface which is vibrated rapidly. The design was patented and was largely responsible for the superb transient response of the Bozak B-209B and B-209C midrange."


First two Fotos Bozak loudspeakers, next two Podzus Görlich