A KNOP for the VMS?

[evildrome]

Hi All,

When I was building the half scale VMS I realised that I would need a cutting head.

I was impressed with the KNOP head and I bought two bodies (one pla & one resin) and all the other necessary parts.

Only later did I realise that the KNOP head would be too big for the half scale VMS.

In my defence, the full scale VMS is huge so imagining that the KNOP head would fit something half that size wasn't as dumb as it might seem.

Anyway, I'm left with enough bits to make at least one head so I thought that if I'm going to have to make a head for the VMS, I may as well make the KNOP head first as a learning exercise.

Initial thoughts...

1) Everything has to be weight balanced. Any sprung mass on one side has to be the same as the other.

Yes, lightness is desirable but I think more important is that the mass being driven by the tweeters must be the same.

So what does that mean?

It means that I need a way to replicably cut down the perfume funnels to the same size and weigh them.

I need a way to add the same amount of adhesive to both otherwise weight matching them is pointless.


2) It should be easy to dismantle therefore, anything that can be screwed together should be and quick connects should be used where possible.

Ideally, I'd want the ability to withdraw the tweeters from the back but that would mean redesigning the head (not such a big deal) and creating a way to connect and disconnect the tweeter from the push rod/torque tube (a bigger deal).

First things first. Cutting the funnels to length.

That's going to need a fixture for the lathe.

The first one I made, just to roughly check the geometry worked but was... nasty.

SORRY about the image orientation... if you click on an image it will open in the correct orientation.

IMG_9960.JPG

The second one was nicer but because it had a better surface finish, it didn't want to let go the funnel afterwards.

IMG_9969.JPG

Trying to pull the jammed funnel out using a tap as a screw extractor.

IMG_9959.JPG

So in the end I had to modify it to incorporate a "jack out" ring where the outer section screws off, thereby releasing the workpiece.

IMG_9970.JPG

IMG_9971.JPG

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Its still not right though and marks up the funnel so I'll probably have to re-do it out of nylon rather than aluminium.

Here's a mock-up of my idea for connecting up the tweeters and heater wire.

Screenshot 2024-10-10 125937.jpeg

[Thelatheofus]

Nice work ! Let us know how the tests go !

[evildrome]

Long way from that as yet.

I remade the funnel cutting jog from nylon bar and the result is good.

The funnels as cut are well matched weight wise

matched-funnels.jpg

and they are not all marked up like the earlier ones I made using the aluminium funnel holding jig.

marked-up-funnel.jpg

[Thelatheofus]

I think matching the length is more important. Those funnels are not made with great precision, some are thicker than others (some are not really round etc...), so an equal weight won't mean necessarily equal length.

I must have had a little weight difference on my left and right cones when I tried a replica of this design but I didn't notice a difference between left and right in the tests because of that. The tweeter's slight differences in frequency responses (because they are cheap chinese speakers) has more impact on the sound than 0.05g weigh difference

Alignement and the quality of the connection between the different elements seem much more crucial to me.

[farmersplow]

Great work! Keep up the good work! I'm already curious to see what happens next.