While few of us have the training and skill to design a fine performance hall, we can draw from others' experience in spotting a design that may be successful.  This is extremely important in light of some flagrant disasters of recent years.  Generally the most successful performance halls of the past and of recent years have had simple, traditional shapes and proportions.  Many of the departures from conservative design have led to severe problems, in several cases necessitating complete rebuilding of the interiors!  The experience of New York and San Francisco is notorious; both of those cities had to spend large amounts of money to correct serious acoustical deficiencies in new concert halls.

That a fine concert hall can still be built in the 21st century is demonstrated by several beatiful examples from the past few decades.  The twin cities of Minneapolis and St.  Paul were blessed with two superb new concert halls.  Even the small city of San Luis Obispo, California (population about 45,000) showed great resourcefullness in constructing one of the finest concert halls that appeared anywhere in the world in the 1990's.  That large amounts of money alone are not a key to success is demonstrated by the fact that San Luis Obispo is located far from the major centers of wealth in the Los Angeles and San Francisco areas.

The four essentials for a good performance hall are

1. good acoustics,
2. satisfactory sight lines,
3. comfortable seating, and
4. adequate circulation.

Circulation
Beginning with the last item, circulation is more important than generally realized.  Efficient ingress and egress are obviously important.  But, even more vital to a performance center are the social interactions promoted by comfortable lobbies and circulation areas.  The circulation space must promote relaxation during intermissions; no performer wants an audience that is drowsy and uncomfortable.  The success of many events is determined by personal interactions during and after the performance.  The circulation areas must be spacious, well ventilated and attractive.

The access to the seating area impacts both the circulation and the comfort.  The so-called "European" type seating, with long rows of seats with aisles only on the extreme sides has been popular in recent years, largely because everyone has more-or-less equal sight lines and acoustics.  It doesn't provide any greater seating capacity because the pitch of the rows has to be increased to provide easy access to the innermost seats.

The Alberta Bair Theater (see below) in Billings, Montana is an example of an otherwise excellent facility that is hampered by inadequate circulation space.  The fault is attributable to the conversion of a former movie theater.  Movie theaters are not very demanding of circulation space because movies seldom have intermissions; the audience is expected to spend nearly all their time in their seats.

Comfort
Comfortable seating is relatively easy to provide.  The best seats have firm backs and moderately firm seat cushions.  For the average person, some of the most comfortable seats are among the most economical, and are used in the auditoriums of many schools.  There is no reason, except a false sense of luxury, to install elaborate, old-fashioned seats with deep cushions and backs.  The San Francisco Opera House and the old New York Metropolitan Opera House were notorious for luxury, and also notorious for dozens of patrons who spent their evenings dozing in soft seats.

The principal comfort criterion is how long a person can sit without having to adjust his position; overly soft seats generally fail this test even though they may seem comfortable at first.

Sight Lines
Good sight lines pose a challenge to architects because they depend on the three-dimensional geometry of the finished building.  The geometry may not be fully conveyed by a floor plan.  Extreme designs, such as circular theaters, usually have poor sight lines from a large fraction of the seats.  A circular plan or semicircular plan can provide a sense of intimacy for the few who are lucky enough to have seats near the stage, but some spectators see only the performer's backs.  Those plans are best suited to cabarets, small popular music performances, and ceremonial rituals.  One of the more extreme examples below was designed to serve Masonic rituals (Masonic Hall, San Francisco), which it may do very well, but it is seriously flawed as a venue for other events.

The two general plans that have been found to have the best sight lines for the largest portion of seats are the traditional rectangular box, and the moderately broad fan.  The rectangular box gives everyone a view from roughly the same direction, but, in halls seating more than 1200, may place some at too great a distance from the stage.  This was overcome in the traditional European opera house, and in some recent, very successful examples, by placing the spectators in the back in several tiers of shallow horseshoe-shaped balconies.  The fan is well suited to halls where balconies are unsuitable.  A broad fan brings everyone in close, but the audience on the sides may have impaired sight lines, as with the semicircular plan.  An extremely broad fan shaped hall is also complex to lay out with a traditional stage having sufficient depth for large productions (see the example below from San Jose); otherwise a considerable portion of the stage may be obstructed for people sitting at the sides.

Acoustics
Good acoustics are extremely difficult to achieve without drawing on both extensive experience and thorough knowledge of acoustic principles.  Good acoustics can be the critical factor that determines the success of a hall.  Despite common misperceptions, acoustics are vital also to speech and to situations where electronic amplification is necessary.  The architects' greatest challenge is to build-in good acoustics, without the need for extensive "tuning," or even reconstruction.

Architects in the eighteenth and nineteenth centuries had a relatively easy design task, because they had only a small number of traditional designs to draw upon, which could be readily adapted to a new hall.  They were also limited in their selection of materials, which usually worked to their advantage.  The interiors of most halls were constructed of wood and plaster, both of which have excellent acoustic characterists.  Architecutural preferences favored "classical" rectangular shapes, which often provided fortuitously fine acoustics.  Only after the time of Wagner and his gargantuan Festspielhaus have architects felt compelled to tinker with the shape and general features.

Some designs have been found to be much more likely than others to yield good acoustics.  The traditional rectangular box has served well from the eighteenth through the twentieth century.  There have been acoustically fine halls that departed from the traditional; but an alarmingly large number of non-traditional halls have provided dreadful acoustics for a large proportion of the audience.

Several dangers are well known.  Unsuitable materials, such as exposed smooth concrete, generate harsh sound reflections.  Walls that are not supported firmly enough, especially when covered with cheap gypsum board or thin wood paneling, can act like the skin on a drum, yielding undesirable resonances.  As in the eighteenth and nineteenth centuries, wood, plaster, and fabrics still have safe and predictable acoustic properties.

Extreme proportions, particularly very high ceilings or very wide halls, can lead to unsatisfactory acoustics.  One standard rule (of which many architects and builders in the past seem to have been unaware) is to avoid concave curved surfaces.  Despite the misleading example of the Tabernacle in Salt Lake City, concave surfaces and ceilings can focus the sound in unpleasant ways.  That building has relatively benign acoustics mainly because of fortuitous combinations of materials and a relatively absorbant ceiling.  If the tabernacle had been build in the twentieth century of reinforced concrete, it might have been an acoustic disaster.

Stage Design
The shape of an auditorium has much to do with its acoustic properties.  Here is a sketch of the cross section of an idealized performance hall.  Notice first that the seats are raked to give everyone a good view of the stage.  The rake in the back also affects the acoustics if the hall is well designed.  The dashed lines indicate the paths of the sound, as it reflects off the walls and ceiling.  The convergence of the ceiling and seats in the tiers keep the sound from being absorbed before it reach the rear.

The traditional stage, set behind a proscenium arch, leads to special acoustic problems.  Some of the sound is lost in the high loft unless a shell is erected completely surrounding the performers.  Musical groups have learned to perform with a shell whenever they must use a traditional stage.  Even with a shell surrounding the performers within the stage, the proscenium opening can lead to poor acoustic coupling between the stage and auditorium.  Splay panels or sound reflectors, both on the sides and ceiling can compensate for a high ceiling, and greatly improve the distribution of sound.

Notice that the sketch above does not show an overhanging balcony.  Overhanging balconies are always inimical to good acoustics.  They are frequently found in older theaters, especially movie theaters, but even there the audience members under the overhang find the sound dull and muffled.  Where balconies are needed to provide a large seating capacity, shallow balconies or "horseshoe" balconies are far preferable.

A technical note
The problem with stages and prsceniums is a matter of acoustic coupling or impedance matching.  Some of the terminology is borrowed from electrical engineering.  In transmitting an oscillating signal between two electrical circuit elements, losses can occur if the impedances are not well matched.  For example, a TV antenna is most efficient if the elements are comparable in size with the wavelength of the signal.

Acoustical Impediance matching is important in the design of musical instruments.  The problem arises because the vibrating element is usually much smaller than the wavelength of the sound it generates.  The solution for wind instruments is to provide a large flared bell for the exit of the sound waves.  The solution for stringed instruments is to provide a large sounding board.

Many of the finest halls, such as the Boston Symphony Hall the Troy Savings Bank Music Hall, the San Luis Obispo Performing Arts Center, and some of the classic halls in Europe have been constructed with open platform stages - sometimes in front of a proscenium stage.  This can greatly minimize the problems associated with the coupling between the stage and auditorium.  The trade-off is in the elimination of the stage machinery desired for opera, musical theater, and plays.

An open stage can be particularly beneficial to orchestral music.  Unfortunately, some of the worst halls in recent years, such as the Avery Fischer Hall in New York, Boettcher Hall in Denver, and Louise Davies Concert Hall in San Francisco, have also been built with open platform stages.  The problems there stemmed from a combination of poor proportions, such as a too-high ceiling, and too great a depth between the front of the stage and the sound-reflecting wall at the back of the stage.  Sometimes the acoustics can be improved after a performance hall is completed by installing sound reflectors over the stage, but this is usually an inadequate corrective solution.

Small performance spaces usually exhibit one or more echoes within less than a tenth of a second after the sound.  Such echoes are generally harmless, and appear only because of the finite time the sound takes to diffuse through the room.

See examples and analysis