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 Post subject: Re: Tracking Weight of acoustic gramophones.
PostPosted: Wed Dec 02, 2020 5:05 am 
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Victor IV
Joined: Sun Mar 15, 2009 6:18 am
Posts: 1256
Location: Luxembourg
Daithi wrote:
I'd love if you could measure the weight every time you found a satisfactory play just to see how they group and within what range they fall?
Would that be possible, am I asking too much?


Unfortunately I do not have a scale that reaches such high weights, I only have one made for modern turntables with 10 grams as upper limit.


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 Post subject: Re: Tracking Weight of acoustic gramophones.
PostPosted: Wed Dec 02, 2020 10:09 am 
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Victor II
Joined: Wed Dec 04, 2019 9:31 pm
Posts: 259
CarlosV wrote:

Unfortunately I do not have a scale that reaches such high weights, I only have one made for modern turntables with 10 grams as upper limit.


This is the one I am using.

https://www.ebay.ie/itm/0-01g-x-200g-Gr ... 2749.l2649


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 Post subject: Re: Tracking Weight of acoustic gramophones.
PostPosted: Wed Dec 02, 2020 3:43 pm 
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Victor Jr
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Joined: Fri Mar 27, 2020 5:58 pm
Posts: 25
Location: London UK
Daithi wrote:
I'd love if you could measure the weight every time you found a satisfactory play just to see how they group and within what range they fall?
Would that be possible, am I asking too much?


As Carlos says, it's the force applied by the needle that matters rather than the weight of the reproducer. I have a cheap digital scale:-

https://www.ebay.co.uk/itm/1kg-0-1g-LCD ... 3749392231

that can weigh up to 1Kg.

By positioning it so that it is at the same height as the disc, the force can be accurately determined. The geometry of the combined tone arm and reproducer alters the force. This will vary with different tone arm designs. In the case of my Expert, a 217.4 gram 4 spring reproducer only applies a 172.6 gram force when mounted on the arm. This can be further reduced with the sort of counterweight that Carlos is using.

I have been experimenting with making 3d printed reproducers (based on the dimensions of the Expert 4 spring). The one shown is mostly made of nylon (with an Aluminium diaphragm and part steel needle bar). This only weighs 31.8g but, perhaps surprisingly, applies a force of 49.9 gram when mounted on the arm. This appears to be sufficient to get good tracking and sound on my Expert. The tone arm bearing on the Expert is well engineered. More force may be necessary to get good tracking on less well engineered systems.


Attachments:
expert_reproducer.JPG
expert_reproducer.JPG [ 614.04 KiB | Viewed 247 times ]
nylon_reproducer.JPG
nylon_reproducer.JPG [ 606.29 KiB | Viewed 247 times ]
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 Post subject: Re: Tracking Weight of acoustic gramophones.
PostPosted: Wed Dec 02, 2020 3:56 pm 
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Victor V
Joined: Mon May 13, 2013 2:04 pm
Posts: 2569
physicist wrote:
Daithi wrote:
I'd love if you could measure the weight every time you found a satisfactory play just to see how they group and within what range they fall?
Would that be possible, am I asking too much?


As Carlos says, it's the force applied by the needle that matters rather than the weight of the reproducer. I have a cheap digital scale:-

https://www.ebay.co.uk/itm/1kg-0-1g-LCD ... 3749392231

that can weigh up to 1Kg.

By positioning it so that it is at the same height as the disc, the force can be accurately determined. The geometry of the combined tone arm and reproducer alters the force. This will vary with different tone arm designs. In the case of my Expert, a 217.4 gram 4 spring reproducer only applies a 172.6 gram force when mounted on the arm. This can be further reduced with the sort of counterweight that Carlos is using.

I have been experimenting with making 3d printed reproducers (based on the dimensions of the Expert 4 spring). The one shown is mostly made of nylon (with an Aluminium diaphragm and part steel needle bar). This only weighs 31.8g but, perhaps surprisingly, applies a force of 49.9 gram when mounted on the arm. This appears to be sufficient to get good tracking and sound on my Expert. The tone arm bearing on the Expert is well engineered. More force may be necessary to get good tracking on less well engineered systems.


When are you going to sell them ?


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 Post subject: Re: Tracking Weight of acoustic gramophones.
PostPosted: Wed Dec 02, 2020 8:30 pm 
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Victor IV
Joined: Sun Mar 15, 2009 6:18 am
Posts: 1256
Location: Luxembourg
physicist wrote:


I have been experimenting with making 3d printed reproducers (based on the dimensions of the Expert 4 spring). The one shown is mostly made of nylon (with an Aluminium diaphragm and part steel needle bar). This only weighs 31.8g but, perhaps surprisingly, applies a force of 49.9 gram when mounted on the arm. This appears to be sufficient to get good tracking and sound on my Expert. The tone arm bearing on the Expert is well engineered. More force may be necessary to get good tracking on less well engineered systems.


I like the Inexpert branding! It does not seem to have the springs at the needle bar, how did you achieve the required compliance?


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 Post subject: Re: Tracking Weight of acoustic gramophones.
PostPosted: Wed Dec 02, 2020 8:33 pm 
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Victor II
Joined: Wed Dec 04, 2019 9:31 pm
Posts: 259
soundgen wrote:
When are you going to sell them ?


Yes, and how much ?
Although 50 grams sounds crazy light.


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 Post subject: Re: Tracking Weight of acoustic gramophones.
PostPosted: Thu Dec 03, 2020 8:38 pm 
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Victor Jr
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Joined: Fri Mar 27, 2020 5:58 pm
Posts: 25
Location: London UK
CarlosV wrote:

I like the Inexpert branding! It does not seem to have the springs at the needle bar, how did you achieve the required compliance?


Thanks for the appreciation! I'm taking advantage of the properties of some modern materials. I have used a similar pivot system as Ginn used - there are steel points that the needle bar assembly rests on. The bar assembly is retained with flexible nylon screws that allow very free motion of the bar. I also have used silicone rubber "washers" to further increase flexibility in some samples.

soundgen wrote:
When are you going to sell them ?


I started this during idle time in the first UK covid lockdown and I'm still at the experimental stage, investigating the effects of different diaphragm (and needle) materials.


Daithi wrote:
Yes, and how much ?
Although 50 grams sounds crazy light.


I have no idea about cost - what would be fair for something that takes a couple of days work (and some materials) to manufacture?

The weight may be too low for some tone arms. It is also too low for stiffer diaphragms - I have some lead weights that I have been using to cope with this and to investigate what effect weight has on sound and needle wear.

The attached image shows a few samples. Some have plastic diaphragms, some painted paper, some aluminium and some titanium. The different materials result in considerable variation in frequency response and volume.


Attachments:
reproducers5.jpg
reproducers5.jpg [ 335.67 KiB | Viewed 202 times ]
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 Post subject: Re: Tracking Weight of acoustic gramophones.
PostPosted: Fri Dec 04, 2020 5:23 am 
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Victor III
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Joined: Mon Jul 02, 2012 9:57 am
Posts: 783
Location: Hampshire, England.
So wonderful to see all this R & D going on in this area ! Some comments and videos on the audio results in due course would be really fascinating ! Many congratulations on this work which will be of huge interest and benefit to us all. No pressure.....!!


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 Post subject: Re: Tracking Weight of acoustic gramophones.
PostPosted: Fri Dec 04, 2020 12:14 pm 
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Victor II
Joined: Wed Dec 04, 2019 9:31 pm
Posts: 259
physicist wrote:
Some have plastic diaphragms, some painted paper, some aluminium and some titanium. The different materials result in considerable variation in frequency response and volume.


If you could please discuss briefly the differences in diaphragm materials.
If you have not already done so.
I think you did talk about this in a previous post but it seems to me that you are much farther down the road now in your investigations.
This is sooo exciting. The idea of a super light and responsive modern soundbox.
Wow!!!!!!


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 Post subject: Re: Tracking Weight of acoustic gramophones.
PostPosted: Fri Dec 04, 2020 5:46 pm 
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Victor Jr
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Joined: Fri Mar 27, 2020 5:58 pm
Posts: 25
Location: London UK
Daithi wrote:
If you could please discuss briefly the differences in diaphragm materials.
If you have not already done so.
I think you did talk about this in a previous post


Any previous discussion was not mine. Forgive me if in re-stating the obvious.


For a low tracking weight to work, a highly compliant path between the record groove and the diaphragm is desirable. You also need a compliant diaphragm. The length ratio of diaphragm -to- pivot over needle tip -to- pivot. is very roughly 1.5 which means that the centre of the diaphragm should be able to easily displace by about 1.5* the amplitude of the groove vibrations. If there is too little compliance the lateral forces of the groove on the needle will push it up the side of the groove, initially introducing distortion and ultimately jumping into an adjacent groove.

The edge of the diaphragm is constrained by the rubber tubing so the displacement of the centre is achieved by flexing of the diaphragm. The contouring of the central part (and/or "spider" additions on some diaphragms) makes this more rigid so most flexing occurs at the boundary between the flat outer part and the circular border of the contoured part. The mass of both the needle bar and the diaphragm are, presumably, factors so the lightest material is desirable provided sufficient stiffness can be achieved in the relevant places.

Aluminium appears to have been Ginn's material of choice. The ones I have are about 0.1mm thick which, coincidentally is very similar to the thickness of various fizzy (and/or alcoholic) drink cans. This is reasonably stiff (especially when formed). It's density is about 2.7g/cm3. There are, of course, different aluminium alloys with a range of properties that might be better...

Plastic sheet is less dense (~ 1g/cm3) so the material can be thicker for the same mass but it is much softer so the central region is not going to be as stiff. There are lots of different plastics so there is (unfortunately) scope for a lot of testing here. A first impression is that there is less response at high frequency - not surprising for a softer material.

Paper of a similar thickness to the aluminium and formed to the same shape, impregnated with spray paint to waterproof it and stiffen it a bit is better than I expected but rather fragile.

Titanium is a little denser (4.5g/cm3) than aluminium but appreciably stiffer. I have some 0.1mm thick Ti sheet some of which which I have also etched down to about 0.05mm so the diaphragm can be lighter than an aluminium one.

Other factors (e.g. transmission line impedance) come into play when the reproducer is attached to a horn and the behaviour of the combined system may have different resonances and compliance. I suspect that it's resonance in the mid range that makes the Expert soundbox seem so loud.


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