Building new plinth

[fromans4]

OK, so I am going to replace the plinth on my TD-160 as part of an overall turntable rebuild project and I wanted some suggestions. I was thinking I would use two different hard woods laminated, mainly because I thought it would look cool. Is there any reason, from a performance point of view, not to do this? Are there things I should consider when designing the new plinth that would improve how the turntable would sound? Below is a picture I found on the website "theanalogdept.com" that shows kinda what I am thinking of -



I'm looking to make mine slightly larger then this but this is the basic concept.

Any suggestions or concerns regarding the desighn and build?

Thanks in advance for any help,

[aardvarkash10]

I'd layer hardwood and softwood to better dam pa range of resonances, but otherwise, look fabulous!

[rkernell]

Would you post photos as the project progresses?

Rick Kernell

[fromans4]

I had planned on opening a thread when I started the project showing progress. I am waiting for an arm I got off fleebay, an SME 3009 II shipping from England. It should be a lot of fun and I am hoping it will also be a big improvement over my little Yamaha P-450.

[satanfriendly]

It is better you work in a harder wood as it makes it easier for clean and accurate joints. it also goes a long way if you are intending to add some form of 'fluting' effect or similar using a routing machine. Consider strengthening the corners with additional bracing or brackets. I used the top plate to 'tension' the plinth.

Does it make a difference? I think so, improving the overall sound and adding (as suggested) some dampening in to the structure.

As aardvarkash highlighted, it will look the B******s.

I did a similar project with an Ariston and the personal rewards were very satisfying, both looks wise and sonically.

http://www.vinylengine.com/phpBB2/viewtopic.php?t=20453

I would love to do the same with my 160 in due course as it is such an easy TT to work with.

Good luck with your project and look forward to seeing your end product.

[zharca]

The one in the picture looks stunning. If you can make something like that you will have a really terrific deck.

[cats squirrel]

contrary to urban myth, common natural wood has very little damping, so if you are getting a good sound now, making something out of natural wood is not going to change things much, unless you mount the arm differently.

Modified wood is another matter. From a sonic point of view, mdf is too undamped, plywood a little better, and chip board not bad at all. Bamboo is very good, but best of all, from a damping perspective, is panzerholz.

Of course, when making a plinth, stiffness and mass are important too, an area where panzerholz scores highly.

Making your own ply from many woods would be OK, but it would have little intrinsic damping.

[john guest]

Hi there,

I made mine out of solid beech ,it was difficult, as I decided to but the ends together at the sides to give a nice looking gain effect . It took 3 attempts , if the sides are not at a perfect 90 degrees , when stuck together the whole frame warps and cannot be straightened.after the 3rd attempt it worked and looks great . I found the beech to be good to work with and to me with the extra weight sounds really good .






If you look closely at the sides you can just make out the joint butted together . The picture does not do it justice , on how nice it looks when you look at it at an angle
Best Regards
John Guest.

[fromans4]

Of course, when making a plinth, stiffness and mass are important too, an area where panzerholz scores highly.

I have never heard of this material, where would I go to get a look at it or buy some if need be? I could always use real wood veneer if it doesn't look that great.

[Bigears]

MDF does in fact have damping properties...thats why Pro-ject use it for their platter material and why many TT manufacturers use in in plinths. Most speaker cabinets are also manufactured from MDF. Its pretty dull on its own though. One advantage of it is that its very easily worked. I used three layers of 19mm MDF for my Garrard motor plinth and surrounded it with a ardwood, not unlike the end effect of John Guest's plinth. My finished deck:





On refelction though, I would have used a laminated timber fore the outside shell in place of the hardwood planking (shiny though it now is) and cut it larger than it neede to be for visual aesthetics but I'd still have stuck with a MDF layered sandwich for the motorboard as it does a great job of damping out the motor vibrations. I'd also recommend mounting the motorboard on four sorbothane feet sat within the outer shell.

[cats squirrel]

nope, mdf has no damping properties, another urban myth. The property that describes the damping property of a material is the damping factor, Greek letter eta (n). I have measured n for lots of materials. Anything above 0.07 is said to be damping, anything above 0.1 is a good damper. Here are the results of some of the materials I have measured:

mdf 0.0174
Russian 7 ply 0.040
chipboard 0.101
slate 0.0172

panzerholz 0.387

just for the record (sorry ) here is a scan of an mdf panel, struck percussively, measured with an accelerometer, upper trace z axis (out of the panel) and x axis (along the panel)


© Cat's Squirrel 2010

The axis along the top is in seconds, you can see mdf rings for over half a second, when struck.

The reason that mdf is used as a platter material is that it is slightly better than rigid metal (Al, n = 0.0043) and the reason it is used for loudspeakers cabinets is because it is very cheap and can be machined, not for its sonic qualities, which we all have to suffer.

[Bigears]

Fascinating stuff cats squirrel. Perhaps the misnoma lies then in mdf's behaviour of harmonics, where resonances are not as pronounced at certain frequencies as some hardwoods? Have you any data on harmonic frequency response? Its still a good choice for general plinth building etc as it can easily be damped. My layered mdf motorboard is far deader than the old wooden one it replaced (and this was chipboard) so I'm happy enough with the results. I guess understanding resonance at certain frequencies is the key...

[cats squirrel]

Fascinating stuff cats squirrel. Perhaps the misnoma lies then in mdf's behaviour of harmonics, where resonances are not as pronounced at certain frequencies as some hardwoods? Have you any data on harmonic frequency response? Its still a good choice for general plinth building etc as it can easily be damped. My layered mdf motorboard is far deader than the old wooden one it replaced (and this was chipboard) so I'm happy enough with the results. I guess understanding resonance at certain frequencies is the key...

it is usual to talk about modes of vibration, rather than harmonics, the vibrations of a plinth will only be harmonically related if the width to breadth dimensions are related (so best to use a 'golden ratio' 0.6:1.0:1.6) from that viewpoint. Because mdf has a low damping factor (n) and as n = 1/Q (at a resonance) the resonances of mdf will be high and narrow bandwidth, compared to chipboard, which will be more rounded and broader.

This will change the waveform in different ways. For periodic forces (read sound vibrations) acting on the plinth, if the fundamental or harmonic frequncies of the sound coincide with the plinth's resonances, an increase in output at that frequency will be the result. One can appreciate that the more resonances the plinth has, and the higher the Q (amplification) the higher the output of the plinth, the more colouration in the final waveform.

It is difficult to guess at a materials damping properties by just a knuckle test, I've been wrong in my guesses so many times I've given it up

[NickT]

Wood is an excellent resonator - that's why guitars have been made out of it for hundreds of years. Better solid body guitars have always used denser woods such as ash, mahogony & maple. I'm with Cats Squirrel on this one, MDF is cheap and can be machined, that's the only reason it's used.