When it comes to reproducing the sound of an 18th/ 19th century Classical orchestra, there are a number of things to take into account, most notably - 1) Evolution of the instruments from then until now, 2) Performance halls, and 3) Performance practice. Taking them in order: 18th century instruments were significantly different between the 18th c and today. They were about halfway on the evolutionary scale from Stradivarius' time and now. When Stradivarius created his incomparable violins (and other stringed instruments) In the 17th century, the Baroque era, the bridge was curved, the bow had a bigger curve and looser hair, and the strings were "catgut," made from the intestines of animals. There were other structural differences as well. By the 18th c Classical era, the violin was approaching the instrument we know now, with the biggest difference being that gut strings were still being used. One of the enduring benefits of the industrial revolution was the easy creation of wire, allowing violins to be strung with wire strings, which gave the instruments a louder and brighter sound. The higher string pull between the head and the tailpiece also required that the instruments be reinforced. This is the violin that we have today, and it remains essentially unchanged since the end of the 19th century. All of those old Strads that are coveted so much today have had to be significantly reworked, with flatter bridges (easy) and reinforcing to handle steel strings (not so easy). There is at least one Strad that is still in its original condition and has never been played to any great degree. There has been even more evolution in wind instruments. Classical era brass instruments were all without valves, which weren't introduced until the end of the 19th century (the industrial revolution once again). There was the occasional keyed trumpet, which utilized keys like we see on saxophones of today. French horns (just known by players as "the horn") had no keys or valves, and today we refer to it as the "natural horn." The player changed notes by sticking his hand into the bell and by changing the shape of the fist and stuffing it farther in, could approximate a chromatic scale. Mozart's four concertos for horn were composed with such an instrument in mind, and there are a numerous recordings of them played with a natural horn. Listening to them performed like this is interesting because every note has a different tonal quality. Notes sounded without the hand in the bell sound full and open, while notes requiring the hand to be stuffed deep in the bell sound muffled. The trombone, with its long slide remains essentially unchanged. Woodwinds were all generally still wooden, including the flute. They generally had fewer keys that now. Eventually flutes would be made from metal and clarinets and oboes would be cast in bakelite or some other hard plastic, although some are still wooden. Then there are the instrruments that no longer exist, like the serpent or ophieclide. This was a low sounding instrument made of wood with keys, but with a cup mouthpiece like a trombone. Eventually it was replaced by the tuba after the introduction of valves. So an 18th century orchestra would require violins with gut strings, valveless brass, and simpler wooden woodwinds. The string section would also be smaller, but that is more of a performance practice issue. 2) Performance halls: the major difference here is in size. Classical-era orchestras were generally smaller, and the instruments less powerful, so a smaller hall would be required because an orchestra would not be able to fill a large hall. Amplification is not a concern. A true professional orchestra never relies on amplification in their home hall (although they usually do in their summer outdoor spaces, which is why I stay way from summer shed performances - I can listen to an orchestra through speakers at home). One notable example of a currently used 18th century performance hall is the Drottningholm Palace Opera Hall in Sweden. Built in the 18th century to replace a 17th century hall that had burned down, it was closed after the king died in 1792. It was left alone until it was restored to its former glory in the early 20th century, and continues to employ some of the operatic stage effects from its earliest days. It is probably the most authentic Classical-era performance hall in the world. Peformance hall acoustics have evolved greatly since the 18th century. Halls today are "tuned" through the use of wall treatments and ceiling treatments, floating reflectors above the audience and orchestra, baffles behind the orchestra, etc to aim a balanced and pleasant sound out to the audience. So a truly authentic 18th century performance would have to take place in a smaller theater with less emphasis on acoustical enhancements. 3) Performance practice: This is probably the hardest part of the equation. The history of music is filled with little tricks, nuances, customs, traditions, etc that have never been written down, and in the days before recording, how did one know about them? If there were no recordings today, how would guitarists 200 years from now understand the playing of Jimi Hendrix? The only way was to pass them from one generation of musician to the next, a game of "Telephone" stretching across centuries, with a predictable result of change. Sometimes there are little clues in the music, or from critics who wrote about performances, or in the writings and letters of the composers themselves. We know that 18th c orchestras often split their violin sections, with the first violins to the left and the second violins to the right, with the violas and cellos in the middle, giving the orchestra more of a stereo effect, and composers would sometimes compose for that ping pong effect, an effect that would be lost when the two section are placed side by side like they are today. Sometimes the limitations of these early insturments can give clues as to the tempo or volume of a piece. Composers would often conduct from the keyboard, even in works that today don't include a piano, the conductor improvising an accompaniment that would reinforce important melodies or harmonic sequences. 18th century pianos were far different from today's pianos, with gut strings and fewer strings per key, so they were quieter, with an action that wasn't nearly so fast. Performance practice is where numerous conductors have made their reputations as early music experts. Nikolaus Harnoncourt and Gustave Leonhardt were aming the first, but they generally stuck with the Baroque era and earlier. Eventually conductors started making progress into the music of the Classical era, and even later. For instance, I was never much of a fan of the Brahms symphonies until I heard a recording of them performed by the Mannheim Orchestra. Mannheim gave the premieres of those symphonies, and theI recording used the same size forces that Brahms used when he premiered them - far smaller than today's forces. I was used to hearing plodding, thick, lugubrious performances of Brahms orchestral works, but with Mannheim's smaller forces combined with a tradional knowledge of the works handed down from musician to musician, Brahms' works take on a fleetness and clarity that were reveletory. THIS was why Brahms had such a reputation during his own lifetime. So a true 18th century performance would have to include all 18th century instruments (fairly easy) an 18th century hall (fairly easy), and 18th century performance practices (not so easy). More on reddit.com

Two things. First of all, when well played, they really do sound beautiful for baroque or classical period music (up to 1820 or so). It's subjective, but there is a clean purity of string sound, woody transparency with the woodwinds, and roughness of the brass that is different and, in the opinion of many, nicer for that music. Second, they bring you closer to the sound the composer would have been familiar with, which is interesting and enlightening. The sound of a modern piano or a modern orchestra would have been unfamiliar to Bach or Mozart, and to understand their music, it's helpful to hear what the instruments of their period would have sounded like. That's not to say that performances on modern instruments can't be beautiful (indeed, I find the best players of modern instruments preferable to most period instrument performances), but period instruments have their place, and I encourage everyone interested in music up to (say) Berlioz, to give them a try. More on reddit.com

I disagree. Baroque/Renaissance music is at its most beautiful when played on period instruments. More on reddit.com

Define better? That said, some of the flute sonatas attributed to JS Bach, esp Eb, are easier on the ear when played on the modern boehm flute. The Vivaldi piccolo concerti are also pretty rad on a modern picc, when played well. More on reddit.com