OFFICIAL27 Why does the professor discuss the growth cycle of trees?

[00:00.00]NARRATOR: Listen to part of a lecture in a history of musical instruments class.[00:05.76]MALE PROFESSOR: So, musical instruments evolved in ways that optimized their acoustical properties, how the instrument vibrates and sends those vibrations through the air to our eardrums.[00:18.88]Now, professional musicians are very particular about their instruments. They want instruments that help them fully express the intent of the composer...which, of course, translates into a more enjoyable listening experience for the audience members. [00:34.71]Yet, most audience members probably aren't even aware of how much the instrument matters. [00:41.35] I mean...OK, think about the last concert you attended. [00:46.05]When you applauded, what went through your mind? [00:49.33]FEMALE STUDENT: I recently heard a violinist who totally blew me away. [00:54.11] Uh so, when I applauded, I guess I was showing my appreciation for his skill, the hours of practice he must've put in.[01:01.23]MALE PROFESSOR: And his violin...?[01:02.18]FEMALE STUDENT: Didn't really think about it. [01:04.13] It looked exactly like mine, uh, which is inspiring, in a way, knowing my violin could also produce such beautiful tones, that maybe I'll sound that good someday.[01:13.61]MALE PROFESSOR: I hope you do. [01:14.86] But if your violin isn't as good as his...[01:17.79]FEMALE STUDENT:Y'mean he might not sound as good playing my violin?[01:21.68]MALE PROFESSOR: As I said, tone quality differs from instrument to instrument. [01:26.65]The question is...why? [01:28.39] Why does one instrument sound more beautiful than another, even if they look identical?
[01:34.61]There's a particularly interesting case with an extraordinary generation of violins made in northern Italy...in the city of Cremona, back in the late 1600s, early 1700s.[01:47.08]These vintage Cremonese violins are considered the best in the world. [01:52.31]But it's not like the makers of those violins were any more skilled than their modern-day counterparts; [01:57.66]they weren't. [01:58.41] Today's top violin makers can pretty much replicate all of the physical attributes of a Cremonese violin. [02:04.95] But it's generally thought that the acoustical quality of modern violins doesn't live up to the quality of the vintage ones.
[02:11.80]FEMALE STUDENT: So, what of the old violins have been replicated?[02:17.05]MALE PROFESSOR: Oh, their dimensions, shape...their fingerboard height, uh, general craftsmanship. [02:22.61] For a long time, people thought the varnish used to coat and protect the violins was special. [02:28.59] But research showed it was the same ordinary varnish used on furniture. [02:32.93]However, researchers have discovered that there's something special about the wood the violins were made from, [02:40.39]and recently, they've been able to replicate that, too.[02:43.97]FEMALE STUDENT: How...unless the trees the Cremonese used are still alive....[02:48.41]MALE PROFESSOR: The trees weren't replicated, just the wood...specifically the wood's density. [02:53.64] Density's determined by how trees grow. [02:56.96] Trees, all trees that don't grow in the tropics, grow seasonally. They grow faster early in the year, in the springtime, than they do later in the year. [03:06.76]So early-growth wood is relatively porous; [03:10.40] late-growth wood is denser, less porous. [03:13.48]And this variation shows up in the tree's growth rings.
[03:17.82]The denser layers are generally darker than the less-dense layers. [03:22.65]We call this variation the "density differential."[03:26.78] MALE PROFESSOR: Variations in wood density affect vibrations, and therefore, sound. [03:32.87]When scientists first analyzed the wood of vintage Cremonese violins and compared it with the modern violin wood, they calculated the average density and found no difference. [03:43.73] Later, other researchers measured the density differential and found a significant difference: [03:50.86]modern violins had a greater variation... larger differential.
[03:56.23]FEMALE STUDENT: So you mean the density of the wood in the Cremonese violins is, is more uniform?[04:02.97]MALE PROFESSOR: Correct.[04:03.91]FEMALE STUDENT: But northern Italy isn't in the tropics![04:06.40]MALE PROFESSOR: No, but climate matters. [04:08.67]Turns out the Cremonese violins were made from trees that grew during a "little ice age," a period when temperatures across Europe were significantly lower than normal. [04:19.96] So the trees grew more evenly throughout the year, making the density differential relatively small.[04:27.29]FEMALE STUDENT: But you said someone replicated the Cremonese wood.[04:30.64]MALE PROFESSOR: The density differential was replicated.[04:33.88]FEMALE STUDENT: What did they do, [04:35.02]try to simulate an ice-age climate in a greenhouse and grow some trees in there?[04:39.44]MALE PROFESSOR: No. What happened was a materials scientist figured out a way to process wood to make it acoustically similar to the Cremonese wood. [04:49.03]He basically exposed the wood to a species of fungus, a mushroom. [04:54.67]In the forest, fungi are decomposers; [04:58.09]they break down dead wood. [04:59.84]But this particular fungus nibbles away only at certain layers in the wood, leaving other layers alone. [05:07.65]As a result, the density differential of the fungi-treated wood approached that of the Cremonese wood.