Article: 3D Printing and Audio.....or.....how can I implement 3D printing into my Audio interests? Part 1.
Pucks (record weights) and clamps: Because ABS plastic has many attributes which indicate potential mechanical uses, I chose to explore the possibility of printing out my own record weight in ABS. Physical attributes such as tensile strength, compression strength, mass density, elasticity and acoustic impedance...... all of these prompted me to explore the potential for a record weight that would carry multiple chambers filled with lead shot. While the ABS material has a very low density, and therefore doesn't weigh much at all, it has enough strength to carry lead shot, as is used in shotgun shells.
Acoustic Impedance? Yes, sound waves travel through solid materials. Sound waves travel through liquids. Sound waves travel through the Earth's atmosphere. When traveling through solid materials the sound waves encounter resistance to the forward flow. Just how much resistance to this forward flow depends upon the material in question. Different materials have different acoustic impedance values. Turntable designers, when designing platters and platter mats, will pay heed to this when they select a material that has an impedance value that is very close to that of the vinyl record. For instance PVC (vinyl) has an impedance value of 2.99 to 3.27 while ABS has an impedance value of 2.31 - 2.36. Thus it follows that vibrations traveling through the vinyl record should easily flow into the ABS material of my ShotPuck. Given this much food for thought, it might seem that another good material for a record puck, or platter mat, would be the same material as that of the vinyl record.
Why lead shot: It is the same idea as a sand box isolator shelf, or a dead-blow mallet. Or a leather shot bag that holds position on smooth curvy surfaces. The large mass of loose shot serves to dampen vibration energy as it enters into the volume of the shot. Other examples of lead shot chambers can be found in plinth design and also in -some- high mass platter designs.
left: I called this version 1a. I printed two of these. I chose not to produce it in numbers because the design requires quite a lot of post-print deburr and surface smoothing in hard-to-reach locations. Otherwise, it is robust, passes the drop test and does improve record playback sound quality.
left: I called this version 1b. This one failed the drop test. Upon impact with the concrete floor one chamber burst open, letting the #9 lead shot escape. And so the design was abandoned.
left: initially this was my third version, but because of its simplicity and overall attributes it became Shotpuck Model One. Its weight is just over 1/2 lb. Its flexibility allows it to pass the drop test.
left: the fourth design. This version was meant to carry a larger load of shot so that I could get puck weight up over 3/4 lb. It turned out to be successful. I printed one version. It was replaced because I felt I had a design I liked better....like this next one...
This, which became the product ShotPuck 2. I felt that this version would allow much simpler post-print clean-up and I liked the overall look better than the first version above. SP2 has a total mass of .83 lbs and 85% of its total mass is lead shot. It is a more efficient use of ABS, I feel. I have produced test versions of this design with and without silicone cone footers. Presently feel that SP2 , without the foam foot pads allows better sonic improvements. However these are purely subjective listening observations.
With some feedback from one of my field testers, I chose to look into designing a puck that could clamp over the spindle pin, thus having the ability to press the record down further without the need of greater weight. Below is my initial design.
Note: Thorens belt drive models from that period when they manufactured in Lahr, Germany are notorious for having slightly 'fat' spindle pins and are also a tad short. In reality the Thorens spindle diameter met the RIAA specification that controls Lp record production for hole diameters in the record. However Lp record spindle holes are often slightly smaller than the spec due to accumulated wear on the stamper. So....most turntable manufacturers produced their spindle pins a 'thou' or so smaller to anticipate stamper wear. Nevertheless, Thorens chose to make theirs exactly to spec. Fine, we can live with that, mostly. But then the spindle pin does not protrude very far above the platter mat which makes the spin less adaptable for use with record clamps.....sigh.
Most of my puck designs just function as record weights in that the actual weight of the clamp is used to press downward over the record label, pushing the Lp deeper against the platter mat. However I have experimented with a puck design that also clamps. As follows.
This design takes advantage of the elasticity and spring-back properties of the ABS material to obtain some clamping action over the turntable spindle pin. Note the slot within the spindle bore. In its relaxed state the size of the bore is just slightly smaller in diameter to the pin it fits over. To fit the clamp, hold the clamp in one hand with a thumb between the two shot chambers adjacent the slot, press thumb deeper between the two chambers. This has the effect of opening the diameter of the bore so that the clamp fits easily over the turntable spindle pin. Then remove thumb when the clamp is in position over the Lp label. And the result is that the puck clamps down on the spindle pin, holding its vertical position relative to the record. To release, use one hand again, and lightly press your thumb between the two adjacent chambers relative to the slot...this releases the clamping action so that the clamp may be lifted off the platter.
Sequence below: A Thorens TD126 mkIII turntable gets to test this version clamp design.
Left: A Boston Audio graphite Mat 2. (BAMat2) It is 5mm thick. The stock Thorens rubber mat for this model is 3.7mm thick. I choose to use the somewhat thicker BAMat2 because it is a superior isolator and gives audibly better sound reproduction. And...negatively, this gives me 1.3mm less spindle pin height to hold the record.
Yet, there is just enough for the record clamp to register over the pin and remain fixed while turning the record. Ah, but.....yes the clamp does locate over the pin and spins true, but.....there is not enough pin there for the clamping action of this puck design to actually make grip. Still, I can use a record weight. However, with thinner records like most normal ones, the clamp will function per design.