For the past few months, fans of live music have watched their favourite musicians on patchy livestreams from their phones and laptops. The novelty of peering inside the stars’ living rooms soon wore off, and the virtual experience hasn’t quite been the same as enjoying a visit to a local music venue. But there’s hope! Gradually, some countries and regions are exploring the music scene in the wake of COVID-19. They’re re-opening venues at lower capacity, with strictly assigned seating and social distancing measures in place. But not only will attending a show in a half-empty venue be a completely different experience than it was in the long distant past of four months ago, but – thanks to physics – the music will even sound slightly different.
In Europe, where many countries are past the first major peak of the COVID-19 outbreak, music venues have found creative ways to reopen. There are no huge stadium shows or crowded festivals yet, and no large international tours, but some smaller venues and local performers have gone back to work, cautiously following their country’s new rules and guidelines. In Portugal, seated concerts are now allowed to take place at 50% capacity; Indoor events in Germany are capped at 300 people; The Netherlands is planning to carefully reopen venues as long as visitors can stay 1.5 meters apart.
Even though the reopening of music venues is following different timelines and guidelines around the world, many of them have one thing in common: Initially, these spaces will not be full. Those half-empty venues are not just interesting from an economic point of view, but they will also effect the music itself.
Acoustic experts have studied the effect of audiences on the sound in performance space for decades. Back in 1962, Leo Beranek published a book called Music, Acoustics, and Architecture, in which he described and analysed the acoustics of 55 concert halls around the world. The book has been republished several times over the years and now covers twice as many venues.
Research such as this is useful for designing new performance venues, or for fixing any sound problems in existing buildings. But when engineers take audience reverberation into account, they’ll often assume that the venue will be at capacity, not that it’s mostly empty with people spread several feet apart. Yet that is exactly the situation in some concert halls and theatres at the moment. In Vienna, the Wiener Philharmoniker performed for only 100 people earlier this month. Munich’s Bavarian State Opera has allowed 20 people at a time to attend performances. In the Netherlands, the Ziggo Dome, which normally hosts international megastars for audiences of 17,000 is now hosting tiny gigs with only 30 people in attendance.
With a smaller audience spread out across the space, there are fewer bodies to absorb the sound. It doesn’t make much of a difference for the sound that comes directly from the stage or the speakers, but without audience in the space that sound also bounces off the walls, floors and structures in the room. An empty room sounds more echo-y than one that’s filled with people. In acoustics terms, the audience absorbs reverberation.
This also depends somewhat on the design (and carpeting) of the room itself, but several studies over the years have shown that the audience definitely makes a difference. The music will sound different in a partly filled room because fewer of the reverberations are absorbed.
In a full music venue the audience doesn’t just absorb the soundwaves from the music, they also interfere with the sound by adding their own noise. Whether it’s a crowd singing along or moving around at a rock gig or a whispering, shuffling, program-page-turning audience in a classical venue, the audience creates their own noises that form part of the overall sound in the room. It’s usually not detrimental to the music, and it even adds to the experience. But with so many empty seats this background noise will also sound different.
Ultimately, the pandemic will pass. Once we have a vaccine, it’s likely that music venues will gradually be allowed to open at capacity (if they survive), and the music will sound just as it did before. But until then, live music in mostly empty venues will have its own unique acoustics.