What is the reason that instruments in an orchestra are placed the way they are placed?
This is a very interesting discussion on this subject: http://boards.straightdope.com/sdmb/showthread.php?t=608598
Edit: adding some of the above link content on request. I've put the original question in italics, and some of the more interesting answers follow.
I understand the benefits of placing the musicians where they are in the orchestra (eg, all the strings together, all the percussions together, etc.); having similar musicians in the same place so they can all take direction from the conductor, the aesthetics of watching all the violinists' bows moving in perfect unison, etc.
What I don't get is this: strictly from the standpoint of how the music reaches the listeners' ears, does the placement of the musicians matter? If the musicians were seated at random, would a blindfolded listener in the audience be able to tell that something was amiss?
I don't have a citation for this, but I believe (from my years in concert band) that the smaller instruments are in front because they don't project volume nearly as well as the big ones sitting in back. A flautist standing in front of you playing at max volume is unlikely to melt your face off (figuratively of course), but a tuba definitely could. And the percussion section would need to be together to 1) keep time effectively and 2) facilitate the way percussionists have to switch instruments so frequently.
I don't know exactly how the sound waves work, but I think if you put the tubas and drums in front and the flutes in the back that you wouldn't be able to hear the flutes nearly as well. Interference maybe? Or just lack of volume projection.
It does have to do with the dynamics of the instruments. Note that you have 16 first violinists, playing in unison, but only three trumpets. You have eight double basses, but only one tuba. The brass and percussion can play far louder than strings. Woodwinds are in the middle. In order to adjust the dynamics, the orchestra has more strings than anything else, and they are placed near the front.
The set up of the orchestra has been developed over the centuries and is the optimal way to have the correct dynamics (not to mention that the music is composed assuming this setup).
Location of sound sources uses a mix of effects. Phase is one, simple change of relative level between the ears (i.e. like the balance control on a stereo system) is more. When you listen to a pair of speakers in a stereo system these two are what are usefully used to encode position.
If you are seated in front of an orchestra you get to use much better localsisation cues. The Head Related Transfer Function HRTF is the sum of all the effects your ears and head have on the sound heard from each direction on what you finally hear. Our brains learn to decode this to make quite good localisation of sound, beyond what you would reasonably imagine possible given the infinitude of possible solutions mathematically possible. For instance discerning the height of a source, or disambiguating front from rear.
In a good venue the reverbarent sound field accounts for about 90% of the energy you hear. Not the direct sound (i.e the sound that has reflected off at least one surface versus the sound that travelled directly to you.) However the Hass effect is also critical. (This is where the figure of 1ms comes from.) It is the first arrival of the sound that determines location. If subsequent reflections of the sound arrive they merely add to the perceived level (if they are say 5 to 20 ms late) of if they are earlier, they add a sense of space, but still don't ruin the localisation.
Localisation of source in an orchestra is going to depend a great deal on where you sit, and the quality of the venue. But my experience is that once you get a reasonable way back, you lose pretty much all localisation. For reasons I con't quite explain I usually get seats either very close to the front, or the front of the first balcony. The latter position yields a well integrated spacious sound and zero localisation. Front row seats yields a ridiculous separation of sources as the orchestra subtends about 120 degrees across my view. Perfect seats, middle and about row F, yields a nice spread and good localisation, but nothing like the pinpoint imaging so beloved by HiFi freaks (who really need to get out more and listen to live music.) I need to wait for the season ticket holders who get those seats to die before I get them.
One of the critical things about localisation is the harmonics of an instrument or speaker. We have essentially zero ability to localise low frequencies - the waveleght is so long that our head makes no difference to the amplitude, and the period so long that phase differences are useless. But the harmonics of the sound are higher frequency, and due to the quite severe non-linearity of frequency response our ears have in the low frequencies, these harmonics are significant;y emphasised versus the fundamental. A subwoofer should be impossible to localise, however a low quality one isn't to hard to find, because it has quite a bit of distortion, and harmonics that creep into the range we can localise are present. Vent noise (turbulence of the air chuffing in and out of a ported enclosure is a good one.)
Orchestral instruments have quite a lot of harmonic content, that is part of what gives them their character, and interestingly those instruments that boast very low frequency notes may have more output in the harmonics than in the fundamental. The extreme example are organ pipes, where the very low stops may be 10dB down in the fundamental versus the harmonics. Which is part of the reason you can enjoy organ music at all on something less than an insane HiFi system. Horns - even a Tuba, have a remarkable amount of energy in the harmonics. Its what gives a horn its sound. Bowed instruments are essentially a sawtooth wave, so even a double bass has a solid helping of harmonics.
There are several reasons for why the instruments of an orchestra are placed the way they are.
Instruments with lower frequencies are usually located on the audience's right and instruments with higher frequencies are located on the left.
I don't believe that the official design decisions are documented anywhere, so I'll list all the justifications that I can think of.
Percussion instruments need to be at the back because:
It depends on various factors ranging from ease of communication and performance to the acoustics of the performance space.
If musicians from the same group of instruments are seated together, it helps you to listen to each other and keep playing together as a section, working as a team, which is invaluable in an orchestra. It also improves communication between the section, particularly in circumstances where there may be a problem, for example, one quite regularly sees a problem involving someone's instrument and the section can usually sort it out amongst themselves, even during a concert. Of course, everyone is seated facing the conductor, which helps, of course.
As regards to acoustics, there are various accepted seating plans for different purposes and different concert halls and most conductors seems to have their own preference. Although the above is pretty much the most common set up, there are several things which need to be taken into consideration, for example, projection of the instruments and balance.
I, personally, very much favor the two violin sections to be facing each other, with the concert master to the direct left of the conductor and the principle 2nd violin the direct right. Then the violas come next to the 1st violins and the cellos next to the second violins. This produces a better balanced sound, in my opinion, since the 1st violin part is the more harmonically important part of the two, and the 1st violin will project much better towards the audience from this angle. The second violins, when facing the 1st violins will almost project inwards which means they don't project outwards as loudly, which means that they can play more freely since they don't have control their playing as much and that they don't worry about overpowering the 1st violins. The cellos project forward much better from this angle as well. Also, there is much more freedom of communication between section principles which helps.
As regards to the percussion, that varies from piece to piece, but very often, I will have them on the far right behind the cellos and 2nd violins or right at the back behind everyone. If it's a big piece for percussion, I'll have them right at the back but personally, I prefer the sound when the double basses are right at the back behind and above everyone else though, but the percussion section and the double bass section are interchangeable. I think, in a good acoustic, the double bass sound bounces off the back wall and projects out over the orchestra which has a nice effect and provides a much needed 'oomph' from the back.
I will have the french horns on the far left and the tuba/trombones/trumpets on the far right, seated on the same tier, but much further over. It should be noted that the horns are generally seated on two separate tiers, with the 1st and 3rd in front and the 2nd and 4th behind. 1st and 3rd are the 'high' horn parts and the 2nd and 4th the 'low' ones, so those respective players work together more often, hence the seating plan. I have the woodwinds in between the horn section and the tpts/trbns/tuba section. They are seated as on that image, with section principle seated on the conductor's left. This helps communication between double reeds and flutes/clarinets.
In my experience, the sound is considerably better the above way in terms of balance, and it is easier for the conductor to cue, etc. This set up is becoming more and more common. The Vienna Philharmonic and Prague Phil have accepted this seating plan, and UK orchestras which use this plan include the Hallé and the Liverpool Phil (sometimes).
I will add some small tidbits of experience here focusing on the winds. Playing bassoon and contrabasson, but started on the trombone.
It of course goes down to tradition, but also to practical matters.
I want the wind instruments to sit close to each others when possible. Often the wind instruments play sections together and will want to phrase the same way. This is much easier if you can hear each other. One good setting is front row having flutes and oboe in front row with 1st players in the middle. Right behind you have clarinet 1st and bassoon 1st next to each others.
Keep the horns to the (audience) left and in the back. The sound goes backward and to the (player) right. If you end up sitting in the chair next (player) right to the horn player playing bassoon, you simply will not hear what you are playing. This goes similarily to sitting right in front of loud trumpets and with your head right text to the timpani (you may imagine why I know). Bass trombones are extra loud, so it helps if they are a way off from me. When possible I want to play without hearing protecting, but often enough it is not possible.
Next is, never put the horns right in front of the trombones. They will play into each others bells which can really hurt your lips (again, ask me why I know).
Sometimes first bassoon and concertmaster violin plays the same phrasing. It helps if I can see the concertmaster bow. Even more often the bassoon plays together with the cellos, and it then really helps if sitting close to the cellos to get the same intonation and phrasing. (In my experience, cellos and the basson tend to "naturally" intonate differently and need to hear each other when playing the same tones which is quite common in some music styles).
I guess there are similar experiences in seetings for other instruments not known to me.