So, I acquired a couple of defective 6,5 inch midbass units, made by the German company Accuton. Really high quality and somewhat decent construction. The basket and magnet are very rigid, the cone however is not 😉
This is one of the four woofers I have. It is pretty much intact, I glued a piece of one of the other cones to it, to make it work again. This is my reference.
I proceeded to measure the radius of the cone, fortunately this really was a radius, and made a plastic dome in the same shape. The material of the dome is Poly Ethylene, so it should not stick to epoxy, in theory 😱
The plan is to make the cone out of woven glass fibre with epoxy resin. I ordered the thinnest glass mat I could find and started making a laminate with epoxy. I thought 3 layers would be sufficient, but the cone was really flexible after curing. I added another 5 layers, so I now have a cone made of 8 layers glass fiber. The cone is still just 0,3mm thick. It is fairly rigid, though not as rigid as the ceramic cone obviously.
The dome/form/mold in the background, with the newly made cone on top of the original speaker. The cone itself weighs 5,5 grams. As I have no full cone apart from the assembled original speaker, I don't have a clue what it weighs... I assume it is light.😀
The new speaker fully assembled. Centering the voice coil was very difficult. I have refoamed and reconed lots of speakers, but this time I had no access to the air gap as it is covered by the speaker cone!
The resonance frequency of the woofer increased to 44Hz, comparing to the original speaker which was 36Hz. I used a new rubber surround from the Vifa 17WP200/P17WJ, as it is identical in size. I think this is the main reason for the rise in resonance. The mass is supposedly the same, maybe slightly heavier.
I then proceeded to listen to the speaker. The bass is really tight, the mids however are horrible. 🙁 That was a little disappointing.
This plot is from the original woofer, in a sealed enclosure without any crossover.
This plot is from my speaker in that same enclosure.
The cone seems to have a really bad resonance at 1200-2000Hz. This is due to the cone not being stiff enough I think.
I can do two things, start again with a thinner cone, so it will dampen itself, like most paper cone speakers do. This is not really my favorite method I think...
Or, I can add more layers, making the cone stiffer. This will make it more like a piston that moves, but the mass will increase which will lower the efficiency. Efficiency is not really a problem for me, I just want them to sound smooth. Making the cone stiffer will move the bad resonance to a higher frequency, but then it should be higher than 3kHz, as that is the goal frequency I want to be able to reproduce... I hope it will move to 5-6kHz or something like that, if I add a few extra layers.
What should I do? Any of you ever made your own, very stiff, speaker cones? 😕
This is one of the four woofers I have. It is pretty much intact, I glued a piece of one of the other cones to it, to make it work again. This is my reference.
I proceeded to measure the radius of the cone, fortunately this really was a radius, and made a plastic dome in the same shape. The material of the dome is Poly Ethylene, so it should not stick to epoxy, in theory 😱
The plan is to make the cone out of woven glass fibre with epoxy resin. I ordered the thinnest glass mat I could find and started making a laminate with epoxy. I thought 3 layers would be sufficient, but the cone was really flexible after curing. I added another 5 layers, so I now have a cone made of 8 layers glass fiber. The cone is still just 0,3mm thick. It is fairly rigid, though not as rigid as the ceramic cone obviously.
The dome/form/mold in the background, with the newly made cone on top of the original speaker. The cone itself weighs 5,5 grams. As I have no full cone apart from the assembled original speaker, I don't have a clue what it weighs... I assume it is light.😀
The new speaker fully assembled. Centering the voice coil was very difficult. I have refoamed and reconed lots of speakers, but this time I had no access to the air gap as it is covered by the speaker cone!
The resonance frequency of the woofer increased to 44Hz, comparing to the original speaker which was 36Hz. I used a new rubber surround from the Vifa 17WP200/P17WJ, as it is identical in size. I think this is the main reason for the rise in resonance. The mass is supposedly the same, maybe slightly heavier.
I then proceeded to listen to the speaker. The bass is really tight, the mids however are horrible. 🙁 That was a little disappointing.
This plot is from the original woofer, in a sealed enclosure without any crossover.
This plot is from my speaker in that same enclosure.
The cone seems to have a really bad resonance at 1200-2000Hz. This is due to the cone not being stiff enough I think.
I can do two things, start again with a thinner cone, so it will dampen itself, like most paper cone speakers do. This is not really my favorite method I think...
Or, I can add more layers, making the cone stiffer. This will make it more like a piston that moves, but the mass will increase which will lower the efficiency. Efficiency is not really a problem for me, I just want them to sound smooth. Making the cone stiffer will move the bad resonance to a higher frequency, but then it should be higher than 3kHz, as that is the goal frequency I want to be able to reproduce... I hope it will move to 5-6kHz or something like that, if I add a few extra layers.
What should I do? Any of you ever made your own, very stiff, speaker cones? 😕
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