Concert venues in Cardiff: the halls

Both host classical concerts, and treating them as interchangeable is the commonest mistake a visitor to Cardiff makes.

The difference is acoustic and it is decided at the drawing board. A concert hall and an opera house solve two incompatible problems, and no building has solved both well. That is why the Wales Millennium Centre, having built a theatre for Welsh National Opera, then had to build a second and separate room, the BBC Hoddinott Hall, before an orchestra could work there properly.

What makes a room a concert hall rather than a large room

A concert hall is a room tuned to a reverberation time, which is the number of seconds a sound takes to decay to inaudibility after the source stops. Orchestral repertoire wants roughly 1.8 to 2.2 seconds when the seats are full. That is long enough for the strings of an orchestra of 80 to 100 players to blend into a single body of sound, and long enough for the last chord of an Elgar symphony to hang in the air rather than stop dead.

An opera house wants something much drier, in the region of 1.2 to 1.5 seconds, because a singer has consonants to deliver and a libretto to be understood. Put an orchestra in an opera house and it sounds thin and close. Put an opera in a concert hall and the words dissolve. Everything else about hall design follows from that single number: the volume of air per seat, the material of the walls, the depth of the balconies, the presence or absence of a fly tower over the stage.

Four other things separate a real concert hall from a hall that merely holds concerts:

• The platform is raked and stepped, so that brass and percussion at the back are physically above the strings and can be heard without being forced.
• The surfaces are hard and irregular, in plaster, timber and stone, because flat soft surfaces absorb the high frequencies that make an orchestra sound alive.
• The audience is wrapped closer to the players than in a theatre, which shortens the distance the first arriving sound has to travel.
• The get-in, the loading route from the street to the platform, is wide enough and level enough for a concert grand, a timpani set and a double bass trunk, a mundane requirement that quietly rules out most beautiful old buildings.

The halls of south Wales, and what plays in each

The halls below are the rooms in which most professional orchestral and operatic performance in south Wales takes place. Capacities are given where a figure is established; where it is not, the row states the scale of the room instead.

Shoebox against vineyard: the two arguments about plan

Shoebox and vineyard are the two plans a concert hall can have, and the argument between them is about a century and a half old. The shoebox is the older answer: a plain rectangular box, narrow and high, with the platform at one end and the audience facing it, as at the Musikverein in Vienna of 1870 and the Concertgebouw in Amsterdam of 1888. Narrowness is the point. Sound reaching a listener from the side walls within a few thousandths of a second of the direct sound is what the ear reads as envelopment, and a narrow room delivers those early lateral reflections for nothing.

The vineyard plan came in 1963 with Hans Scharoun's Berlin Philharmonie, which broke the audience into terraced blocks surrounding the platform at different levels, like plots on a hillside. The gain is intimacy: nobody is very far from the orchestra, and 2,000 people can be seated without the back row being 50 metres away. The cost is complexity, because every terrace wall has to be angled deliberately to throw sound back rather than swallow it. St David's Hall is a polygonal vineyard hall derived directly from Scharoun's model, and its acoustic reputation rests on that decision.

Two buildings, two answers to the same question

St David's Hall and the Wales Millennium Centre were built 22 years apart by different bodies for different purposes, and the contrast between them is the clearest illustration in Wales of what hall design decides. St David's Hall, by the Seymour Harris Partnership, is a single-purpose concert hall dropped into the middle of a shopping street in central Cardiff, with a concert organ behind the platform and a plan borrowed from Berlin. It is a listed building, which for a British concert hall of the 1980s is unusual, and it is the resident home of the Welsh Proms, founded in 1986 by the conductor Owain Arwel Hughes, who has been its artistic director since.

The Wales Millennium Centre, by Jonathan Adams of the Percy Thomas Partnership, is a different proposition: a building in Welsh slate, steel and glass in Cardiff Bay, housing eight resident arts organisations, of which Welsh National Opera is the largest. Its main auditorium, the Donald Gordon Theatre, has the fly tower, the orchestra pit and the drier acoustic that opera requires. Its inscription, by the poet Gwyneth Lewis, is formed of windows and lit from behind at night, in Welsh and English.

The organ, and why so few halls have one

A concert organ is the single most expensive fixture a hall can carry, and the decision to install one is made before the building exists, because the instrument is structural. It occupies the wall behind the platform and cannot be retrofitted into a room that was not planned for it. St David's Hall has one, which is why the organ repertoire of Wales, from William Mathias onward, has a home there and an Organ Prom in the summer season. The Donald Gordon Theatre does not and could not, because the space behind an opera stage is occupied by scenery.

That is the whole logic of the two buildings in one detail. A hall is not a neutral container that music is poured into. It is an instrument, chosen once, expensive to change, and audible in every note played inside it.

Also in this programme

• Wales Millennium CentreWhat is inside it, and who works there
• St David's HallThe national concert hall of Wales
• Edward ElgarThe Enigma Variations, the Cello Concerto and the symphonies