[Pseudoscience-is-malarkey (OP)]

If you're analyzing something made from wood, such as a chair, desk, piano, etc, by knocking on it and mentally measuring the feel and/or echo, can you tell what kind of wood it is?

[charles1948]

If you're analyzing something made from wood, such as a chair, desk, piano, etc, by knocking on it and mentally measuring the feel and/or echo, can you tell what kind of wood it is?

This is an interesting question.  Nowadays, wood has fallen into some neglect.  Having been largely replaced by more predictable metals and plastic.

In the past it was different.  In those days, variegated wood was an essential material. So the individual  properties of different kinds of wood were carefully studied.

For example, ships were made of "Oak" wood,  and archery bows, were made of "Yew" wood.   For good reasons.

Because the difference between the properties of the two kinds of wood were important. They varied in density, yield and tensile strength.  And you might detect the variations by a simple technique such as "knocking" on them.

But these days, "wood" is not a material that most people encounter.  They don't know what it is.

So to answer your question, Pseudo, I'd say:  Nobody on these forums can tell what kind of wood it is, by knocking on it.  Unless they build model aeroplanes.

[evan_au]

Unless they build model aeroplanes.

One of the moderators builds wooden musical instruments.... that might qualify?

[charles1948]

Unless they build model aeroplanes.

One of the moderators builds wooden musical instruments.... that might qualify?

It might indeed qualify, if he builds instruments such as Xylophones, where you need scientific precision in measuring the mathematically precise rectangular bars.  To get the right note.  But instruments like violins are less scientific, because their body shapes seem  more subject to fashion than mathematics.

 Actually, I'm slightly disturbed that a moderator should be building any form of artistic musical instrument at all.  Instead of a  more scientific instrument, such as a telescope.

Do you think that moderators like that should be on here?
 

 

[evan_au]

a  more scientific instrument, such as a telescope

I'm not that practical.
- I bought one from the telescope shop.
- When I was younger, I bought a guitar from the music shop.

[charles1948]

a  more scientific instrument, such as a telescope

I'm not that practical.
- I bought one from the telescope shop.
- When I was younger, I bought a guitar from the music shop.

  I once bought a guitar for my brother, but was never interested in it myself.  I like telescopes and binoculars!
My flat has masses of them, stacked on shelves, and on the floor, and in the airing-cupboard!  Also microscopes, and magnifying glasses, cameras, any instrument with a lens!  I love glass lenses. They have magic.

[Bored chemist]

Nobody on these forums can tell what kind of wood it is, by knocking on it. 

I'd expect to be able to tell a softwood like yew from a hardwood like oak.

[evan_au]

One of the moderators builds wooden musical instruments

I understand that the acoustic characteristics of the wood are modified by the way it is aged, and the kind of lacquer used.

Musicologists continue to analyze old Stradivarius violins, to see what made them sound so magical
- But some double-blind experiments found that expert listeners couldn't tell the difference between a Stradivarius and a high-quality plastic violin, when played by an expert violinist.

[alancalverd]

Don't knock wood as a structural material!

You can exploit its anisotropy in all sorts of ways and the best light aircraft ever, the wooden Robin DR400, is still being manufactured, with laminated spars and steamed ply leading edges. It's relaxingly quiet compared with American spam cans, easier to repair than carbon fibre, and handles like a fighter if you are that way inclined.

A few years ago a friend built a photographic studio with laminated wooden roof beams because the insurance was cheaper than unprotected steel and the construction less hazardous than fireproofing  RSJs.

[Colin2B]

Sorry missed this one, been a bit busy. Have been grabbing a few days away so have some time to reply.

It is possible to tell quite a bit from the resonance of a block of wood, but you have to prepare it very carefully and do some quite involved calculations in order to measure Young’s modulus using the frequencies. The problem is that a particular species of wood can have a significant range of, say, longitudinal Young’s modulus. For example, with Sitka Spruce used for steel string guitar soundboards it can vary between 9 and 13GPa which takes it across the range of many other softwoods and quite a few hardwoods.

I understand that the acoustic characteristics of the wood are modified by the way it is aged,

Young’s modulus is one of the key properties that affect resonance in soundboards and that changes with drying. For example, longitudinal Youngs modulus for a sample of Engleman Spruce was 7GPa green, 9 @ 12% (considered dry); Sitka Spruce came in at 8 and 11 respectively. Moisture in the cells also affects the damping factor of the wood.

and the kind of lacquer used.

Ah, the varnish, mmmm lots of myths & legends. Depends on the instrument. Lutes with gut strings often had a protective layer of egg white to seal the surface, don’t want to deaden the resonance. Handbuilt classical guitars are often given a thin french polish whereas factory steel string will take heavy nitrocellulose lacquer and still put out a lot of sound. Traditional varnish for the bowed instruments is an oil and resin varnish on a pumice (or similar) ground - I use mica.

Musicologists continue to analyze old Stradivarius violins, to see what made them sound so magical

Lots of people seem to think varnish, but analysis suggests not. The guild system in Italy meant that you could not make your own and all the makers (and most furniture makers) had to get it from the apothecary. Nothing special about Stradivarius varnish, except that he clearly took care in applying it and used a very attractive orange-red colour.
It’s worth remembering that what you hear today is nothing like the original sound. He made baroque instruments with gut strings, fine for chamber orchestras and consorts in churches and palaces. The 19C saw a big rise in the merchant and later industrialist classes who wanted to show off their wealth and be seen in all the right places eg opera, concerts. That meant louder instruments for larger halls. So, many of the earlier instruments were de-baroqued to support the extra tension of, mainly, steel strings; the neck was replaced with a longer one and its angle changed, bridge and tailpiece replaced, the body was strengthened with a larger bass bar and soundpost, in some cases the belly was reprofiled to make the edges thinner.
In his time Stradivari was a successful maker with his own label. He was also an experimenter and in his so called golden period produced instruments with thicker backs than earlier makers, eg Amati,  and this would certainly help support the higher tension of steel strings. He also used a lower arching on these instruments.

But some double-blind experiments found that expert listeners couldn't tell the difference between a Stradivarius and a high-quality plastic violin, when played by an expert violinist.

I’ve seen results against instruments made by top current makers and same is true, often the listener appears better at recognising the player than the instrument.
Certainly the player is one of the biggest influences on the sound and these instruments are rarely played by novices. It is a point of some irritation to many professional players that people go to a concert to ‘hear the violin’ and comment on how amazing it is.
Another factor that has a big influence is the set up. Small changes to the soundpost position and bridge shape, thickness etc can have a big effect on the sound and these instruments are looked after by highly skilled luthiers.
It might surprise non players to know that the bow can have a big influence on sound. When our daughter, now a professional player, was choosing a bow we went to help as listeners. The listening room was lined with cabinets of bows, thousands. The bows were not arranged by price but by a combination of length, weight and hair width, so there would be bows costing a few hundred next to bows of 10k+. We selected without looking at price and were very surprised how much difference in sound there was between bows, and it didn’t correlate with price (when we finally looked).
So, a top professional player has a lot of tools in the bag to get a good distinctive sound and skill is certainly top of the list. Many of the modified Strads and modern instruments are often described as responsive, which for a less experienced player means hard to play. It takes a skilled player to get the best and varied tonal range from these instruments.

[Bored chemist]

Somehow this

It is a point of some irritation to many professional players that people go to a concert to ‘hear the violin’ and comment on how amazing it is.

reminds me of this
https://www.independent.co.uk/sport/olympics/pentathlete-horse-jump-medal-olympics-b1898551.html

And this

The listening room was lined with cabinets of bows, thousands. The bows were not arranged by price but by a combination of length, weight and hair width,

reminds me of this
https://www.queensinclosure.hants.sch.uk/_site/data/files/files/learning%20from%20home/year%20f/summer/week%205/3B8B2DBFAEFC936356481508A4004EA7.pdf

[Spamname 250921]

There are different types of wood, each of which is made from different trees and has different applications in industry, including shipbuilding, aircraft construction, wooden tools and accessories, and more.
That by tapping on a stick we can tell what kind of wood it is. Perhaps in terms of strength or fineness, it is possible to determine the strength of wood. But to be able to say exactly what the name of that wood is, of course, requires knowing the wood. One who does not know the type of wood can not give an answer, but one who knows the wood can give a definite opinion.