1000 Violins? 500 Cellos? 300 Trumpets?
You get the idea. Is there a limit? I’m sure conducting such a behemoth would be difficult.
current (?) record
I don’t see why there would be an upper limit.
Possible? Wouldn’t the answer be… every person on earth gathered at one location, and each with an instrument?
Doesn’t the fact that at the speed sound travels mean a lag in the instruments sound further away? Kind of like a reverberation?
Yes, which is why I was thinking more than, say, a fifth of a sound-second might be problematic. But you could fit a thousand performers into a circle of that diameter (about 70 yards).
Yes, and then the record won’t be able to be broken for a very long time.
Every person on earth can’t play a musical instrument. Many can, but few are professional musicians, symphony qualified. I should have clarified this in my OP.
Still, this leaves us with thousands of musicians. 101 Strings? Nah. How about 10001 strings? 
As a data point on how long a delay you can have before it causes problems. I was taking a course on digital communications and the instructor was discussing a project he had worked on for wireless microphones for musicians. He said that one of the requirements was that the delay be less than 10ms otherwise their experience was that musicians would complain that the delay was noticeable and would cause problems with performances.
Even in a normal sized orchestra the players have to compensate for time differences. The aim is a coherent time as heard in the audience. Inside the orchestra the time differences are perceptible, and in order for the sound to be coherent the winds need to play ever so slightly ahead. The conductor keeps the time, but the players know where to sit their playing relative to him.
A 5 metre distance front to back is about 15ms. Which is on the edge of the Hass effect’s cutoff. Thus not playing with a slight delay would create a noticeable change in the sound as the brain integrates what is heard.
There are examples of coordinated playing with much bigger delays. A common one is an orchestra plus choir or organ (or both). The organ console can often be quite remote to the orchestra, and the organist needs to maintain visual sight of the conductor (often now done with closed circuit video) and also needs to compensate for the distance from the organ to the audience.
Thus a very large orchestra is possible, but within the constraints that not only will the players need help maintaining sychrony with the conductor, they will need to play ahead of the conductor’s beat by the amount of time it takes the sound to reach him. With a very large orchestra this may be a problem, especially if the time difference approaches the period of a subdivision of the rhythm. Orchestras already play with time lags across their locations, and thus play in a situation where no-one gets a coherent whole except the conductor - but if you want a very very large number of players it will get harder. If you want to set a world record you may need technological help.
The obvious example of musicians who have to cope with delay problems, as a matter of course, are marching bands.
Largest one on record included:
76 trombones
110 cornets
over 1000 reeds (claimed, no verified count)
Only partial details are available as to other instruments present.
Moved to Cafe Society.
Colibri
General Questions Moderator
I’ve taken part in “mass band” events. Basically, you fill the space available on a football field with people standing holding instruments.
It sounds about as terrible as you’d expect, but it’s possible.
Been there, done that. (UC Berkeley “Battle of the Bands”) You’re right we (And about 30 other high school bands) stunk!
Mr. Vaughan, your post was very informative! Thank you for your reply.
I heard about that. Must have been shockingly imbalanced though as, for all the trombones and bassoons, there was just the one and only bass.
If you’re willing to stretch the definition of “orchestra”—an entire city.
As is often the case, I’d like to recommend a performance of 4’33".
Don’t forget fifty (50) mounted cannon.
Not to mention the strings.
I remember seeing Schoenberg’s Gurre-Lieder, and they had to combine two orchestras (Montreal Symphony and McGill Symphony) to get enough people. 150 instrumentalists and 200 singers, Wikipedia says. Mahler’s 8th symphony (Symphony of a Thousand) may require more. (Never seen a performance of that, although it seems to be played more often than the Schoenberg.) In the Mahler, it’s even suggested that some parts be doubled to be heard above the huge mass of sound.
The Wikipedia article on Havergal Brian’s “Gothic” symphony states, “The orchestral forces for this symphony are commonly thought to be the largest employed in the symphonic repertoire.”
What about virtual? Have you heard of the Virtual Choir?
5905 singers in one ‘choir’.
The time delay issue seems easily solvable: the performers all wear headphones to monitor all the other performers, and everyone plays into a mic. Attach all that to the hugest mixing board ever and everyone hears everything at the same time, no delay. The ensemble members could even be far distant from each other. The audience would need to listen to the music over amplified speakers, not acoustically, to hear the performance correctly.