help with this V-spring desing

[fanelx]

Hello! I’m currently working on a DIY embossing cutterhead. After researching extensively on this forum and using every AI tool I could, I managed to gather enough information to start building one. I’m now on my third prototype, but I’ve run into some issues: I’m getting a complete loss of definition in the sound — no high frequencies, everything turns into a muddy low-end mess, and the volume is very low.

After some investigation, I found that this might be caused by the stiffness of the V-spring combined with a very high moving mass. All of this puts a lot of stress on my drivers. I’m currently using cheap AliExpress resonant speakers, 4 Ω and 25 W each. I’ll upgrade them in the future, but for now my main concern is the V-spring.

I’m sharing a video where I show my design.
Please excuse my English — my native language is Spanish, so don’t laugh at my mistakes hahaha.

VIDEO HERE
[YouTube2]https://www.youtube.com/watch?si=bWvIPH4xqGZVvAph&v=bnXgNWXhENs&feature=youtu.be[/YouTube2]

[fanelx]

Here some photos

[Semar]

Hello, maybe waiting for other answers than mine but i think that the tube that is screwed to your spring is very too loud ...

[Fela Borbone]

Hello,

The V-spring is meant to restrict the movement of the torque tube only in the direction that the coils push and pull, preventing it from twisting.

Regarding stiffness, you have to consider the overall stiffness of the system (coil support and V-spring), which will determine the resonance of the cutter head. Resonance is the musical tone you hear when you strike a drum or any other percussion instrument, for example. In a cutter head, you ideally want this resonance around 1 kHz, because it is "the center of the spectrum." It will cause a strong peak in the frequency response, which you may need to tame with EQ (if not using feedback). To maintain this, you need stiff coil supports and V-springs, though this requires more energy to drive.

Another factor that can shift the resonant point upward is reducing the mass. This will make the system require less energy.

Therefore, try to save every 0.1 gram of weight you can, and you may be able to use less stiffness.

To determine the resonant frequency of your head, you can connect the speaker as if it were a microphone, tap or pluck it with a guitar pick, and record the result. You will get a fast-decaying sine wave, possibly with some harmonics, which can give you a good clue of where you are.

[fanelx]

Hello,

The V-spring is meant to restrict the movement of the torque tube only in the direction that the coils push and pull, preventing it from twisting.

Regarding stiffness, you have to consider the overall stiffness of the system (coil support and V-spring), which will determine the resonance of the cutter head. Resonance is the musical tone you hear when you strike a drum or any other percussion instrument, for example. In a cutter head, you ideally want this resonance around 1 kHz, because it is "the center of the spectrum." It will cause a strong peak in the frequency response, which you may need to tame with EQ (if not using feedback). To maintain this, you need stiff coil supports and V-springs, though this requires more energy to drive.

Another factor that can shift the resonant point upward is reducing the mass. This will make the system require less energy.

Therefore, try to save every 0.1 gram of weight you can, and you may be able to use less stiffness.

To determine the resonant frequency of your head, you can connect the speaker as if it were a microphone, tap or pluck it with a guitar pick, and record the result. You will get a fast-decaying sine wave, possibly with some harmonics, which can give you a good clue of where you are.

Hello Fela Borbone,
Thank you so much for the detailed explanation regarding the trade-off between stiffness and mass. It makes perfect sense now why reducing the moving mass is so critical to pushing the resonant frequency up without needing excessive driving power. I will definitely aim to shave off every 0.1g I can from the assembly.
Regarding the "guitar pick" method to measure resonance, I want to make sure I understood the setup correctly to avoid damaging anything:
Do you mean connecting the cutterhead terminals directly to an audio interface input (like a microphone preamp), and then physically plucking the stylus/torque tube? I assume the idea is to capture the "back EMF" generated by the coil movement and look for the dominant frequency in a spectrum analyzer (or simply measure the sine wave period in the DAW). Is that correct?
Also, regarding the V-spring material: Besides 3D printed parts or standard spring steel, do you have any recommendations for "scavenger" or recycled materials that work well for this? I’ve read about people using piano wire or even parts of feeler gauges. I am looking for something accessible that offers good torsional stiffness.
Thanks again for your help!

[Fela Borbone]

Well, Spring steel or alike is easy to find in many old devices, (like the ribbon that rolls back the cable of vacuum cleaners). But is brittle, if you want to machine it, first heat red hot and let cool slowly. Then is easy to machine. If then heat again, but cool it fast in cold water or oil, becomes spring like again.
Piano wire or spring wire is used to tie the end of torque tube (and v spring) to the frame, so is not dragged forward when cutting the groove.

[Fela Borbone]

A dynamic microphone and a speaker are more or less the same thing, coil ,magnet, membrane... only size and impedance change.In fact, and old DJ trick is to plug the headphones in the mic input and speak thru them. So, you use the speakers as microphones,record in a computer, tap or pluck in the moving parts. Have a look of the recording wave. Check the time lapse between peaks, thats the period(T), the inverse of frequency (T= 1/F)

[Thelatheofus]

There are many elements in a cutterhead, and the least you have, the easier you can test every component separately.
A v-spring like that is hard to do because there are many parameters at play : its shape, the material, the material thickness, how it's connected, does it need to be dampened...
Also as Fela Borbone pointed out, there needs to be a piano wire connected at the end of your torque tube to limit movement back and forth.

I would advice to try with a simpler type of suspension : the souri cutterhead style, or to hold the torque tube in rubber (like the gorooveguy cutter head or the TKV ones do that aswell if I'm not mistaking). Or just a piano wire and no v-spring to begin with.

As semar pointed out, that torque tube looks a bit big. It might be too heavy. It's not aluminium, is it ? What diameter ? Also I guess it's better to avoid weird resonances if it is a rod, and not a tube. And that screw you are using to connect it to the v-spring is certainly too heavy too. This is causing your lack of highs issue.
Distortion probably comes from lack of suspension. So either the suspension inside your speakers, or your v-spring, or both.

Also, I used AI for a lot of stuff when building a lathe, like coding, calculations etc.. but for record cutting it is really not knowledgeable. Try asking here instead or searching the forum, AI could lead you totally in the wrong direction.