Bruce Liu plays Chopin at Wigmore Hall on July 14 [Bartek Barczyk]

IT sounds crazy – a piano quartet playing in Trafalgar Square, in competition with the wail of passing sirens and the grind of buses. Nobody would hear a note.

But when it happens this coming Saturday, July 13, there will be a significant adjustment to help out, in the form of 70 or so extra musicians. Because this will be an orchestral enlargement of Brahms’s 1st Piano Quartet (or at least, the Gipsy Rondo from it), made originally by Schoenberg and performed by the London Symphony Orchestra as part of their annual outing to the foot of Nelson’s Column.

It’s entirely free to access, because BMW pay the costs, and always a big, bustling event that draws an audience of thousands. So although the start time is 5pm, you might want to get there early for a decent place – a lion’s paw would do nicely if they let you perch there – and take an umbrella.

Other items on the bill include Stravinsky’s ballet score Petrushka, whose thudding rhythms will give the buses a run for their money. And there’s a new piece by composer Joanna Lee written for the LSO to be joined onstage by young musicians from East London schools. Democracy in action, think of it as a salute to the ideals of a welcome new government. Details: lso.co.uk

• Annoyingly there’s a rival attraction on Saturday when tenor Nicky Spence, soprano Mary Bevan and pianist Joseph Middleton give what sounds more like a party than a concert to celebrate Noel Coward. It happens at Wigmore Hall, 7.30pm, so more dedicated (and athletic) concert-goers might just be able to sprint it from Trafalgar Square and take in both events. And it celebrates the genius of Coward’s songs alongside those of contemporaries like Britten, Poulenc and Walton – no doubt treading carefully with the Walton in that Coward’s wickedly funny send-up of his Façade generated mutually directed vitriol with Edith Sitwell, author of the texts. Expect an evening of high camp and waspishness. wigmore-hall.org.uk

• More seriously at Wigmore Hall on Sunday, July 14, the beyond-glamorous young pianist Bruce Liu – recent winner of Warsaw’s Chopin Competition – plays what should be a sell-out recital. He’s not short of fans. And his programme, unsurprisingly, includes Chopin. wigmore-hall.org.uk

• Pop-baroque programmes of Pachelbel and Vivaldi aren’t often anything to get excited about. But the one at St Martin-in-the-Fields, on Friday, July 12, has interest in that it’s given by the visiting forces of the Oxford Philharmonic: a band not often heard in London, capable of good surprises in the quality of what it does. St-martin-in-the-fields.org

• When opera companies stage I Pagliacci, the classic melodrama about murderous clowns, it usually comes on a double-bill with Cavalleria Rusticana, about murderous Sicilians. But Opera Holland Park are pairing Pagliacci with something else: the not so well-known comedy Susanna’s Secret by Wolf-Ferrari.

The secret here is that Susanna smokes: a daring habit for a lady at the time when the piece was written, and unknown to her husband who smells tobacco in the house and assumes she’s harbouring a secret lover. Yes it’s froth, but entertaining. And as the piece is rarely done, you might want to seize this opportunity. Runs Jul 17-Aug 3. operahollandpark.com