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 Post subject: Re: DIY soundbox / reproducer diaphragm - any tips ?
PostPosted: Wed Sep 09, 2020 5:37 pm 
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Victor II
Joined: Wed Dec 04, 2019 9:31 pm
Posts: 220
Inigo wrote:
Daithi,
Same thickness (apparently, I have no caliber to measure) as the meltrope original, but seems yet thicker than the aluminium used for the hmv 5a/b diaphragms.


Thanks Inigo
I think the HMV 5A and 5B, are thicker in the center and thinner near the edge.


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 Post subject: Re: DIY soundbox / reproducer diaphragm - any tips ?
PostPosted: Wed Sep 30, 2020 4:33 pm 
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Victor Jr
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Joined: Sun Jan 19, 2020 7:27 am
Posts: 43
Location: The south of England
Inigo wrote:
A suggestion for the next step... using the thin aluminium sheet of the food tray. Make the diaphragm larger, and practice using a burin ended in a small ball to make the concentric corrugations, ridges and valleys, passing softly the burin on the diaphragm making circumferences. You can use a towel underneath the diaphragm to make it bend when you draw the circles for the valleys. If you proceed gently you can make pretty high ridges. Then turn the diaphragm to the opposite face to mark the two valleys at both sides of a Ridge, and so on... This way I've achieved a very good imitation of a Meltrope diaphragm that indeed sounded very well. As the ridges and valleys make in the end the diaphragm diameter a bit shorter, that's why you must start with a plain circle of aluminium sheet slightly larger than the desired final size. You can practice several times, and you'll see how soon you get the trick of it. Don't forget to form the central dome!


Thanks "Inigo" that was really useful :D I initially made some 3D printed stampers - but I wasn't happy with the result - however they worked very well in conjunction with your idea to use a tool to impress the ridges and the grooves. I was able to use both stampers to work both sides of the metal, and I used and old phono plug as it had a nice rounded point. I haven't fitted it to my DIY sound box yet - but it is looking hopeful :D

I did do some tests on my DIY sound box with a mica diaphragm designed for an HMV No.4 (54mm) and the video results are here:

https://youtu.be/GwkSmJzJ_bU


Attachments:
File comment: Corrugated aluminium diaphragm in the making, using pie tray aluminium
corrugated_aluminium.jpg
corrugated_aluminium.jpg [ 90.88 KiB | Viewed 247 times ]
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 Post subject: Re: DIY soundbox / reproducer diaphragm - any tips ?
PostPosted: Wed Sep 30, 2020 7:00 pm 
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Victor IV
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Keep'em well oiled
Joined: Mon Dec 18, 2017 2:51 am
Posts: 1000
Location: Madrid, Spain
How nice!
I believe your sounds boxes actually give less volume than the hmv no4 because they are too light, while the diaphragm stiffness and the rest of things are similar.
I'd suggest you to try your soundboxes with two improvements. One, to add mass to them; a pin at the top where you could insert washers, nuts, etc could serve the purpose. Two, to install a flexible rubber coupler between the sb and the tonearm, to avoid the sb body vibrations from reflecting back to the needle. Maybe you should test soft rubber connectors, and slightly harder ones, to find which stiffness produces the best sound.
With these tests you could be surprised, maybe the fund gets rounder and fuller...
Inigo


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 Post subject: Re: DIY soundbox / reproducer diaphragm - any tips ?
PostPosted: Sat Oct 03, 2020 3:37 pm 
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Victor II
Joined: Thu Dec 26, 2013 7:20 pm
Posts: 314
Location: Winfield,Mo
Phonoboy made me an experimental DD type diaphragm for my Exhibition. Don't know how he made it, but it sounds GREAT.


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 Post subject: Re: DIY soundbox / reproducer diaphragm - any tips ?
PostPosted: Tue Oct 06, 2020 2:04 pm 
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Victor IV
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Keep'em well oiled
Joined: Mon Dec 18, 2017 2:51 am
Posts: 1000
Location: Madrid, Spain
What material is it made of? I've heard of diaphragms made of thin expanded polystyrene, pressed to get it harder, that sounds beautifully with diamond discs...
Inigo


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 Post subject: Re: DIY soundbox / reproducer diaphragm - any tips ?
PostPosted: Wed Oct 07, 2020 7:40 am 
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Victor IV
Joined: Sun Mar 15, 2009 6:18 am
Posts: 1158
Location: Luxembourg
Inigo wrote:
What material is it made of? I've heard of diaphragms made of thin expanded polystyrene, pressed to get it harder, that sounds beautifully with diamond discs...


The True tone diaphragms that Larry makes are incomparably better than the original Edison ones, and bring forward a sound quality out of the diamond discs that cannot be produced with the extant original designs. This is not to say that Edison design is poor, but that the materials used degraded with time and made them brittle and hard. Larry's diaphragm is made of some kind of foamy plastic material. The one that Wyatt makes is also a vast improvement over the original, but it is made of a different material.


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 Post subject: Re: DIY soundbox / reproducer diaphragm - any tips ?
PostPosted: Tue Oct 20, 2020 5:03 pm 
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Victor Jr
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Joined: Sun Jan 19, 2020 7:27 am
Posts: 43
Location: The south of England
Inigo wrote:
How nice!
I believe your sounds boxes actually give less volume than the hmv no4 because they are too light, while the diaphragm stiffness and the rest of things are similar.
I'd suggest you to try your soundboxes with two improvements. One, to add mass to them; a pin at the top where you could insert washers, nuts, etc could serve the purpose. Two, to install a flexible rubber coupler between the sb and the tonearm, to avoid the sb body vibrations from reflecting back to the needle. Maybe you should test soft rubber connectors, and slightly harder ones, to find which stiffness produces the best sound.
With these tests you could be surprised, maybe the fund gets rounder and fuller...


Thanks Inigo :) . I've now fitted this to my DIY soundbox and made a video comparing it against the mica diaphragm - and also just the plain sheet aluminium I had previously used.

https://youtu.be/mK1bGhanqf4

Yes the weight of this soundbox is only a little over half of that of the No.4 - but in a very basic test which I did with the mica diaphragm fitted - the volume was comparable to the No.4 (its about 6m 35s through the video below)

https://youtu.be/GwkSmJzJ_bU

Its also not easy to see - but there is an O ring isolator between the back of the soundbox and the main body of the soundbox. In future designs I may make this a much bigger and thicker isolator - as I doubt it is very effective currently

Thanks :D


Attachments:
File comment: O ring isolator in my DIY soundbox (sorry don't have a better picture)
isolatorring.jpg
isolatorring.jpg [ 132.85 KiB | Viewed 41 times ]
File comment: Corrugated aluminium diaphragm fitted to my DIY soundbox
corrugated_aluminium.jpg
corrugated_aluminium.jpg [ 314.37 KiB | Viewed 41 times ]
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 Post subject: Re: DIY soundbox / reproducer diaphragm - any tips ?
PostPosted: Tue Oct 20, 2020 5:15 pm 
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Victor IV
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Keep'em well oiled
Joined: Mon Dec 18, 2017 2:51 am
Posts: 1000
Location: Madrid, Spain
Ok, ok... But let's see if I can explain it better. With a stiff diaphragm, compared to the weight of the sb, the needle vibrations tend to move and vibrate the whole sb instead of forcing the diaphragm in and out. With a light sb you should better fit a much lighter and flexible diaphragm. If you use mica or aluminium diaphragms of stiffness comparable to the standard ones, you should make the sb mass much greater, so the mass reacts against the vibration, and then it has a comparatively softer way out by moving the diaphragm. It's a matter of relative impedances between the mass of the sb and the stiffness of the diaphragm.
Inigo


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 Post subject: Re: DIY soundbox / reproducer diaphragm - any tips ?
PostPosted: Tue Oct 20, 2020 7:22 pm 
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Victor Jr
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Joined: Sun Jan 19, 2020 7:27 am
Posts: 43
Location: The south of England
Inigo wrote:
Ok, ok... But let's see if I can explain it better. With a stiff diaphragm, compared to the weight of the sb, the needle vibrations tend to move and vibrate the whole sb instead of forcing the diaphragm in and out. With a light sb you should better fit a much lighter and flexible diaphragm. If you use mica or aluminium diaphragms of stiffness comparable to the standard ones, you should make the sb mass much greater, so the mass reacts against the vibration, and then it has a comparatively softer way out by moving the diaphragm. It's a matter of relative impedances between the mass of the sb and the stiffness of the diaphragm.


Ok - yes thanks - I understand. The soundbox needs to be heavier so it doesn't vibrate instead of the diaphragm. The next version should be much heavier - the sort of weight of a No.4 (I think about 130g). Maybe one day I will be able to machine components out of metal (I do have a lathe but the not the skill to do this yet) - but for the moment I intend to build in more metal weights (washers) into the 3D printed parts. There are already washers adding about 30g - but bigger washers will be better (although of course all metal components would be even better) Thanks :)

This video is about the mica diaphragm but from about 4m in - I talk about the washers I intend to use and also the sizes/weights)

https://youtu.be/ZdJ9mAAJn6I


Attachments:
washers.png
washers.png [ 1.3 MiB | Viewed 29 times ]
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