Best type of metal for turntable platform?


I have someone that owns a CNC machine. And machine for me a metal platform to the dimensions of 16 x 13 x 3. Ive heard aluminum is a good metal vs price for vibration reduction. Does anyone have any recommendations? Any input would help. Thanks. 
deanshias
I always thought copper would be cool. Trying to find a billet that big may be a problem...
I'd try a damping material between two layers of aluminum.
There are so many divergent theories on what an ideal platform for a turtable should do, and how it should be made. I've noticed lately that for high mass and unsuspended tables stainless steel has been popular. What turntable(s) are you going to use on this stand?
If you view this document -  Documentation of damping capacity of metallic, ceramic and metal-matrix composite materials (utexas.edu), it gives an excellent summary of the damping characteristics for metals.  Table III is the one of most interest, and the larger n^ (column to left of Remarks) the greater the damping. 

Aluminum by itself is not that great, so unless you revert to just mass (weight) as @slaw says two layer of AL w/damping can improve the damping considerably.  Also, viscoelastic damping can be any thin film plastic that can stretch at room temp.  Ideally, the two plates are different different thickness (and different stiffness) so that the thinner plate is the constraining layer that along with the viscoelastic damping are what damps the thicker plate.   The viscoelastic damping layer can be as thin as 0.015" and be very effective.  If you then add another layer - its damps even more, but the first layer get you about 85%.
Modellers Clay such as the Brand Newplast  has exceptional damping properties and will be quite valuable as a material when used with 
materials that have structural and mechanical properties.

   
Its not the metal. There are no metals that are good for vibration control. The reason you see all these metal racks is the same reason for all the MDF speakers- these materials are inexpensive and easily machined.

The place where you get the most benefit isn’t the material, it is the design. Straight lines and 90 degree corners, these are used for the same reason as metal and MDF: ease of manufacture. For a one-off project you will get much better results using curves. No straight lines. No parallel shapes. Look at a tuning fork- straight parallel aluminum. Rings and rings all day long. That what you want? No. So no straight lines.

Your best bet will be to incorporate springs into the design. Springs are by far superior to anything you can do with cones, spikes, etc. The trick with springs is to determine the right amount of spring stiffness for the component load. I would get Nobsound springs, as they are small and extremely cost effective, making it easy to add or subtract springs according to whatever load you wind up with.

They are only about 1" high, about 1/2" under load. Then design your shelf. It can be MDF or a sand bed. Using CNC you can machine a sand bed only about 1" deep (thick) to fit within the rack frame so that it looks almost like one piece. The frame itself should then be gently curved across the front, with a tighter radius at the corners. The front, back and side rails should be flat on top but curve like a bridge arc on the bottom.

If you will be using Townshend Pods under your component then you can eliminate the Nobsound springs, incorporate the sand bed into the rack, and make a simple 1/4" plate of aluminum to cover the sand bed. Powder coated this will look rad and work like you won’t believe.

By the way, I have no idea why you're talking such tiny dimensions. Unless your turntable will be on the floor. Which works great, but incredibly inconvenient. If you want a turntable rack that is at normal comfortable height, relatively easy to build and incredibly cost effective, let me know I will tell you how to build this one. https://systems.audiogon.com/systems/8367
At the moment this platform is for a Project RPM3 with Hana SL. Im planning on upgrading both in the future. I have a wooden floor with a lot of play and too many vibrations. Im currently using a maple wood platform at 16 x 13 x 3 on top of SVS subwoofer feet and was going to put the 2nd metal platform on the bottom (maybe on top) of it. Thought if they were same dimensions and flush it would look and sound better. I was planning in putting something in between also. I have a friend with a CNC machine,  so i can pretty much make any design.
Among metals, aluminum is one of the best to dampen resonances.
Are you having footfall problems?
what do you mean by footfall?
If I were to machine a plinth, I’d choose Corian, rather than any metal.      Even if it meant stacking and gluing sheets; to obtain an adequate thickness/depth.      I’ve used the stuff, in a number of installs/applications, for resonance control.      If your tools/CNC router bits are sharp; it machines nicely and can be polished to a beautiful finish.      It’s resonance damping characteristics are much better than any metal.     A thread regarding plinth materials: https://www.diyaudio.com/forums/analogue-source/312473-diy-cld-plinth-design-measured-approach.html
Post removed 
@deanshias,

If your problem is a flexible floor, then the term footfall relates to the very low frequency (<4Hz) vibration that occurs as you walk across the floor.  In this case, mass & resonant damping with metal or anything else is not going to work unless you add so much mass (weight) that the floor is loaded sufficient not to bounce - but you may overload the floor.  

So what @millercarbon recommends with springs (or air bladders) is the best way to solve footfall unless you can stiffen the floor from underneath or avoid the floor entirely and shift to a wall mount.
YES! I have both of those issues, especially footfall. One because of the flexible floor and the other from surrounding vibrations. I have to tiptoe to avoid woofer flutter. and because of limited space I have to keep the whole setup in this area. I was ultimately never able to use a subwoofer with the turntable because the floor is so sensitive. I don't use a sub with 2 channel but sometimes I want to crank of the bass. Cannot do wall mount in this area. That was my first choice.
  If I were to machine a plinth, I’d choose Corian, rather than any metal.  

I would use the Panzerholtz, I prefer it of all.
Yes, I live in an old home, with ‘flexible’ floors as well. Had similar issues, and tried all types of things (which worked to some degree or another) before I got my SOTA Sapphire.

As I always say now, get a SOTA, problem solved 😉

But, first off, is your TT on the first floor with a basement below? Is the basement unfinished below the turntable? If so, a cheap way to add rigidity to the floor is to get a few 2x4’s, cut them to slightly more than from the top of your basement slab and bottom of your floor joists, locate then under the turntable area, and along a couple of floor joist spans, and use the 2x4’s to reinforce the area by simply hammering then tightly in place. If the 2x4’s bow a little, that’s fine, that means there is tension. No need to nail them to anything, simply friction fit.

Yea, technically you should use treated limber, but 2x4’s are cheap, so if they ever start deteriorating against the concrete, replace them. Unlikely to happen unless they are there for years.

You might still have to do more, but that is a great start if you can do it.
There's crawl space under my floor. SOTA has came up many times for my situation, but I do really like this TT and want to make it work. Even if I wall mount I feel that the flexible floor vibration will creep into the wall.
I even replaced the bottom of my whole BDI audio rack with 2 types antivibration pads (one rubber and one with cork) that are for washer/dryers and it really didnt do anything.
There’s crawl space under my floor. SOTA has came up many times for my situation, but I do really like this TT and want to make it work. Even if I wall mount I feel that the flexible floor vibration will creep into the wall.

Well, you could still do it, just not as easy. Dirt or gravel floor in the crawl? Or concrete? If dirt or gravel, you could get 12x12 concrete block as a simple ‘footer’ sitting on top the dirt or gravel, and then brace the 2x’s off of that.

Your problem is the floor joists were undersized for their span, or at the limit of acceptable design, which equals ‘bounce’. Not unusual in an older home. Fine for most folks, but not for most turntables, except the SOTA, of course. 😁

if you can brace the floor, your solution at the table will be greatly minimized.
Look... I'm not knocking the SOTA (except for its looks :). If I dont solve this, then I might consider it. I just didnt want to be limited to ONE turntable in this room. I was considering a VPI Prime Signature in a year or two as the next TT. But with this room the way it is, I dont see that happening. the concrete blocks/wood as a footer does sound like the logical thing to do... So there's noooo other way to deal with a footfall im assuming? Is this why im getting woofer flutter/pumping with almost anything I do?
The point is, you might have to spend a lot of money on a localized audiophile bandaid solution instead of a few bucks by minimizing the actual problem. 
You don't need CNC, unless you yourself make it a requirement. What you need to eliminate footfall problems is a two stage approach. First stage, mass eliminates large amplitude low frequency footfall type vibrations. Second stage, springs isolate the turntable from the smaller amplitude higher frequencies that get past the mass. 

With a superior product like Townshend Pods your table will probably be fine even with your existing rack. People who have PM'd me about problems like this tried Pods and they work great in situations much like yours. They work even better in situations like mine, which is why it is still a good idea for you to build a sturdy low profile rack with a massive sand bed. As described above. 

You really should as a general principle ask the question you want answered. You came here asking about metal when really it is about footfall problems with your turntable. At least that is what it seems to be. Until it changes yet again....?
@best-groove:     A plinth could be more a work of art*, made of that.        If cleverly equipped with an air bladder; very efficacious against footfalls.                                                               * Some Panzerholtz laminates are leg-wetter gorgeous!
Well.. yes.. the original question was for the platform.. but since someone else brought up footfalls.. which was always a bigger problem.. why not ask to get as much help on it. Ive asked about it in the past but the info you guys are giving is better than anything ive hearf in the past. Again.. i do have a friend with a CNC machine that can make almost any type of metal platform.. so yes.. any info does help with that.
I'll add my two cents: the kind of metal that isn;t metal.  Do a constrained-layer dampening plinth, and suspend it on whatever you want. Look it up - surprisingly easy and surprisingly effective.
You want something that will not resonate within the audio band (or anywhere it is likely to beat into the audio band)
Alum is best. metal rings.
"There's crawl space under my floor."

Then...

When weather permits crawl in and use basic/inexpenisve items to support the floor under your TT.

You would need to lift the joists (scissor jack form your car?) maybe half an inch, or so, and then block/support them with cinder blocks/and perhaps suitable non-compliant shims allowing gravity do it's job once the joists are lowered.

Hate crawl spaces myself, but once done (depending on the lower/ground surface) the remedy should last years, if not decades.

I used to place my TT's in closets (including unused Murphy bed closets) in old rental units due to to the added bracing/structure those specific areas afforded.

Curent TT is also in a closet (along with all the electronics), but for other reasons.

I now use specialty shelving, upturned brass spikes, et cetera, however my floor is quite stable (aside from the occasional earthquake and/or Air Force afterburner flyovers/drills).

A stable floor is the main goal, if it can be accomplished within reason/budget. 

DeKay
Soft lead is a good material for a platform.  Lead also works well when added to a well-damped platter to add mass.  VPI's best turntable platters were the 25 lbs acrylic-lead ones.    

Unfortunately, lead is considered unsafe and does not meet RoHS requirements.    
Ok.. yes.. as much as i said i can never handle my crawl space and would never go under there.. if its for the love of getting rid of vibration for the ultimate analog bliss.. im gonna do it! Im gonna lift this freaking house up. Do i move out as much furniture, etc., out of the room before lifting it? 
foot fall is when you walk up to the turntable and it starts skipping because the floor is bouncing under you.
A well isolated turntable will not be bothered by anything. This requires a suspension. If you really want to isolate an unsuspended turntable you get a MinusK platform. They are the best. But , if you get a properly suspended turntable you can put it on a foldable card table and it will not care. Examples are the SME turntables, Sota turntables, The Avid Actus,
The Kuzma Ref 2, Basis turntables, Dohmann turntables, Oracle turntables and probably a few I do not know about. You can put almost any turntable on a MinusK platform and get excellent isolation.
Don’t go crazy, but dekay has a reasonable idea. When actually leveling a floor, you have to know what your are doing, and do it fractions at a time, for a variety of reasons. All you want to do is reinforce, stabilize, and provide support at the joists along the area where your turntable is. Thus, if you use a jack, I would not raise the area more than a 1/4”, put a couple 2x4’s, or perhaps get some treated 4x4’s, stand them in place (on a 12x12 concrete block as a ‘footer’) and lower the joists back down upon the vertical 4x4 with the jack. Pretty easy actually, but depending how much crawl height you have, can be cramped, so scope everything out, precut the lumber, etc. There is no real need to make full height pilasters out of block for what you are doing and trying to achieve, that would be overkill.

The theory of more stuff.

Vibration isolation in audio is a subject surrounded in mystery half truths and any number of wild theories. As an engineering exercise, the explanation is quite straight foreword and may be explained by the “Theory of more stuff”.

Take a surface, be it the floor or a table, on which your hi fi component is placed and it is desired to reduce the vibration from the support to the equipment. The way this is done is to put “some stuff” between the equipment and the supporting surface. There are three possible outcomes.

1 The vibration in the equipment is more than the vibration in the support.
This is not possible as if it were; the energy crisis would be solved! More
out than what is put in. Free power forever! Unfortunately, this scenario
contradicts the first and second laws of thermodynamics, so is not
possible.

2 The vibration in the supported equipment will be the same as in the case of no stuff. The chances of this are one in a million because something has been changed… it may be the same, but that is extremely unlikely, therefore, the only possibility is,

3 The vibration will be attenuated, to a greater or lesser degree, and this is the case.

There are many products out there that do in fact attenuate vibration. Be it spikes on glass, wood and slate, aluminium spikes in cups, ball bearings in cups, solid plates separated by compliant sheets, lead, Bluetack, sand, marble, concrete, the list is endless. It is also known that multiple combinations of the above produce better results because there is more stuff. E.g. multiple platforms stacked really high.

The engineering approach is to get the best result in the simplest manner by optimizing the “stuff” and way back about two centuries ago the Victorian engineers came up with the solution…. the spring! The spring may be anything “springy”, from elastic, rubber, coiled steel, straight steel, air-bladders to flexible wooden strips. As long as it has sufficient spring or compliance, when optimised with an appropriate mass, a mechanical low pass filter is realised.


The ideal is to have the resonant frequency as low as is possible, ideally around 2Hz in both the horizontal and vertical planes and with a damping ratio of about 0.16. This will give an attenuation of about 25dB at 10 Hz increasing at 20dB per decade above. This will ensure excellent isolation for the deleterious audio system vibrations which are from 5Hz to 500Hz.

 


if you can brace the floor, your solution at the table will be greatly minimized.
+1 @bkeske 

Good to see you taking the advice. Install a concrete plinth directly beneath the turntable for maximum stability. I ended up in the concrete basement such was the improvement in sound quality over suspended floors, live walls, and all manner of vibrations.
Personally, my choices wouldn’t include a metal plinth at all. Instead, ordered by decreasing preference: heavy marble or other stone slab; a leather bag filled with buckshot; concrete; glass; thick acrylic or Lucan, HDPE, or a couple layers of heavy rubber, like lSorbothane sheeting. 
Butcher block acoustics makes affordable and good looking isolation platform made of wood, maple or walnut. Been using them for years to good effect. Can be bought with or without metal threaded inserts for the feet of your choice, which they also sell. My latest in maple replaces an existing wood shelf that came with my turntable wall mount, so no inserts and no feet required, as the isolation rubber feet are integrated into the turntable wall mount. The wood is very hard and so I can do without the tip toe discs on the turntable. Wood is a far more "dead" material than metal. Not sure why one would consider metal. Between the added butcher block, the dual plinth design of the turntable, the TT tip toe feet, and the fact the shelf is bolted to a concrete outside wall which faces the back of house, and away from "possible" street/traffic induced vibrations etc....not sure I can better my set up much. Plus the shelf is up high, eye level when standing....well above speakers. I tend not to worry about so called seismic vibrations, unless there is a 6 on the richter scale. 😁
Townsend is the clear winner. I’ve been saying this for almost 2 years now.
I have a vpi classic 3. It’s extremely heavy. The plinth is made out of steel. I would find out what type because even if you tap hard on the player there is no skipping. You can even tap it hard with your hand. Truly amazing. It weighs 65lbs. 
@deanshias,

As others have said , Townsend knows what he talks about. But, let me if I can expound upon what he said. If you view Figure 7 of this Fundamentals of Vibration (newport.com) , when your designing a vibration isolator, the resonant frequency needs to be less than the Hz you are trying to isolate. At resonance (and all vibration isolators have one), any vibration is amplified and this is called the transmissibility. The damping factor reduces the transmissibility peak, but reduces how quickly (the slope) the vibration is reduced after the resonant frequency. So when Townsend say a damping factor of 0.16 - that is near optimum. Townsend may very well have a curve that looks like Figure 7; and each design is limited to a range of supported weights.

Because of the low frequency (foot fall) you are trying to isolate, which has a lot energy associated with it you have an engineering problem that the number of solutions is pretty limited. You can dismiss as you wish; and spend all the $$$ you wish; but your up against some very hard truths. Good Luck.

Antinn gave you good advice. Constrained layer damping is an important element in most plinth designs - it’s often absent and that’s always obvious.

If you want an easy solution, I use Delignit panzerholz B25, which costs about $1000 a sheet. In my plinth, constrained layer is partly in the plies of beech wood in the panzerholz, and partly from a top layer of carbon composite.

Rigidifying your floor is even more important. My floor is concrete - it’s great - and as others have suggested, try to make your floor as much like concrete as possible.

Good luck!
If you're dead set on using an aluminum plate for a plinth, then the alloy makes a big difference. Alloy 2024 is recommended by some who have experimented, and the temper does not seem to matter much; all tempers seem to have about the same loss modulus, which is a lot better than alloy 6061.
I need some feet under a TT plinth (which just nothing fancy, just about 6" stack of Baltic Birch ply) and was thinking of trying the Townsend Pods. Would I divide my roughly 100lb load by 4 and use 4x pods that accommodate roughly 25lb each?
To remove the Floor Bounce issue and Vibration Transmission to the 
TT.
A TT Wall Shelf can be used.
It will be at it most effective if a Wall is Bricks and Mortar Structure, if  other structural materials are used, it will be best to seek out the ideal fastening to secure the TT Shelf.

When Looking a a fastening for a Wall Shelf, Do Not ! just delect a fastening as you are familiar with it.
Seek out the ones that has the best Kg Loading for the substrate to be fastened to.
I found mine on Youtube and when fastened into Cinderblock, they are 250Kg per fastening.
There is nothing like such reassurances.  

A DIY Sub Plinth can be made that can control various effects from Vibration.
A low profile 'Side Wall'  1 1/4" (30mm) Tray can be made that is to contain a approx 5/8" (15mm) Depth of Kiln Dried Sand.
This box can be sat on Sorbothane or Similar Footers.

An additional Box will be made, that fits snuggly into the Kiln Dried Sand Tray, a 1/8" (3mm) clearance all round between each boxes 'Side Walls'
should be ample space.

A base can be cut for this Box, that is 1/4" (6mm) smaller that the inside dimension of the Trays 'Side Wall'.

The following is a Crude Version of a early Townshend Design.
It works on par with any type of design using the concept.
 
This Box will be a Housing for a Inflatable Inner Tube, a Side Wall will have a Vertical Slot cut in,  to allow the Valve to exit the internal space.
The Slot allows the Valve to elevate freely when inflating.

The Height of the Side Wall will need to be determined by how much inflation is chosen for the Inner Tube.
When the ideal inflation is discovered  the Inner Tube can be placed on the Kiln Dried Sand, a Dimension can be taken from the base of the of the box that will be approx 10mm above the Kiln Dried Sand
(The inner Tube should be close to 10mm above the Side Wall when inflated, do not make a excessive dimension, as the 10mm will allow the assembly to find a resting place in a controlled manner if a inflation is decreased over time ).
Place the Box with inflated Inner Tube onto the Sand, with the Inner Tube seated on the Sand.

Place the TT on the Box/Sub Plinth and check the TT for Level.
Footers under the Plinth will assist with achieving the levelling that is required, as well as offer a further Vibration Control.

Footers are also going to attenuate the sound, so finding a ideal one is a
personal experience and down to ones preference.
My Footer of choice in direct contact with a TT Plinth is 
 Solid Tech 'Feet of Silence', these were put into Service after using
AT-616.
As said the choice becomes personal.         

Note: The Box with the Inner Tube can be seated in reverse with the Boxes Sub Plinth being seated on to the Sand.

This will allow for 'different material Sub Plinths' to be seated onto the Inner Tube, this is another way to fine tune attenuation to suit a personal preference.

This assembly can be achieved at a reasonable cost and a allocation of ones time, it will offer a vast improvement over a conventional Support/Rack that is in direct contact with floor.

The cosmetics for the finishing will be a little more to be added to the parts used, if the raw honesty is not desirable. 

Apologies for the Long Mails, I'm living in a Lock Down, so Coffees and Keyboard are part of the Day Filler. 
  
Hello,

I remember audiophile discuss we had during  the vinyl  " golden age" from middle of seventies to eighties"
We had discovered the " sound" of the turntable highlighted by the audio litterature ( Ivor tieffenbrun Linn sondek)

In general two approach have been acknoledged for the structure design

The ratio of mass
- plinth -platters-tonearm-cartrige tracktability( high or low)
A)
High mass plinth 
High mass platter
High mass tonearm
Low cartridge tracktability

In this configuration the transmission of the energy of vibration is balanced
B)

Low mass plinth
Low mass suspended (or not) platters
Low mass tonearm
Low tracktability cartrige

In that case, the ratio of mass structure between  the elements is also balanced

So, what ever the platter structure is the " bell"  effect must be be reduced keeping in mind that each component have specific " sound" never neutral..

I own two vintage turntables  whitch are complying  perfectly  these rules as example
- Thorens TD 124 II 
( injected aluminium & cast iron)
- sme 3012/2 & DL103)

-Walker Cj 55
Wood and suspended platter in tufnol ( the most neutral backelit phenolic component to be used in aircraft for years)
Colin walker was engineer who used to work for castle engineering in the seventies and launched the linn sondek and Ariston RD11s in uk, Usa and australia inthe seventies...

Sorry fpr this backward looking story !
It is just my experience to be shared...

Raymond





+1 +1 +1 noromance

You sure got it correct.
Concrete is the answer to vibration and indeed marble and stone, and plenty of it.

OP has a suspended floor above crawl space and bare earth below. Great start.

Rolls Royce solution:  Take up the floor, dig out a bit if required, lay new DPC, in-fill with concrete screed, lower floor level to get more ceiling height if desired.  According to taste, re-lay boards except where equipment and speakers are to stand.  Or lay carpet.
OK there is a cost, but it will be worth it.

Use marble or stone blockwork for equipment supports, standing on spikes (PLEASE NOT SPRINGS - BOINNGGGGG...GGG...GGG!).  All you equipment will be rock steady, no vibration.  It is mass-loaded to Planet Earth.  Infinitely mass-loaded as I have said.  OK, not quite infinite but the mass of the earth is quite large.

This is absolutely excellent for turntables and speakers, good for CD players and amps benefit too.  There is no ground-borne vibration (except in California) and the mass damps away all air-borne waves.

I have implemented this construction in my sound engineered basement listening room.  Improvement to SQ is much bigger than many component changes.
Target wall mount TT stand fastened to a load bearing wall.  $150 and you are done.  
Best to fasten 3/4 plywood to the wall studs for the Target TT platform. Gives more positioning options and more peace-of-mind.
I would use a run-of the-mill Technics turntable as a plinth... completely immune to footfall.

What's the next problem?

BTW, there are plenty of round things that are designed to vibrate and resonate...look at bells, cymbals and drums. 

Going square is probably fine. Just decouple it and add mass (that doesn't have a very uniform grain structure). How about good old concrete?