A Night at the Volksoper

by Lance Meister

My wife and I recently took a trip to Europe to visit her family and get some culture.  We spent three days in Vienna, and one night we went to the opera to see La Boheme.  We went to the Volksoper (the people’s opera), which could be classified as the second best opera house in Vienna, after the Stadtoper (the state opera).  This was definitely a classic opera house, with the red velour seat covers and the boxes up both sides of the stage.

We took the U-bahn (the subway in German) to the opera house.  Interestingly, it looks like the Vienna subway is a wide gauge (the distance between the rails, the standard is 4′ 8 1/2″, and it looks like Vienna might be 5′).  When we got off the train, about a block from the opera house, we saw a streetcar running down the street next to the Volksoper.  It’s impressive to see how much public transit European cities have.

We went in and found our seats in the balcony.  (Interesting acoustics note:  If you’re down in the lower seats close to the stage, you might be able to see better, but the seats in the balcony have some of the best acoustics in the house.  They’re also cheaper.)  The opera started, and almost immediately I noticed a very low-frequency rumbling noise.  At first, I thought it might be a thunder-type sound effect from the orchestra, but even with my limited knowledge of both German and opera, it didn’t fit the scene.  The sound went away, but then it came back about 5-10 minutes later.  I realized that what I was hearing was ground-bourne noise (or GBN as we call it) from the streetcar on the street outside.  Now, I’ve been in the business for many years, but I think this was the first time I had really experienced GBN, and been seriously bothered by it.  The noise, even when the orchestra was playing and the singers were singing, was clearly audible, due mainly to the very low frequency of the noise.  It was definitely interfering with my enjoyment of the performance.

Now, you may ask, what is GBN, and how could the streetcar be causing it?  GBN is caused by ground-bourne vibration.  Vibration propagates from the steel wheels on the steel rail, through the ground, into a building, and causes room surfaces to shake and radiate noise; much like a speaker generates noise by vibrating the diaphragm.  Because vibration is very low frequency, the radiated noise is also low frequency, and produces a very low rumbling sound.  Most of the time, this GBN is inaudible, and is masked by airborne noise.  However, in  two cases, GBN may be heard.  One is when the train is in a tunnel, and there is no airborne noise to mask the GBN.  The other is when a building is very well insulated against airborne noise, such as a recording studio, a theater, or… an opera house!

What really surprised me was than in a place like Vienna, where they value their cultural spaces, and where noise and vibration is taken seriously, they wouldn’t have solved this problem a long time ago.  Both the opera house and the street car appear to have been there for a long time,  so this has to have been occurring for many years.  However, GBN is a relatively easy problem to solve. While GBN is low frequency noise (100-400 Hz), it is caused by what we consider high frequency vibration.  Vibration  (and GBN) mitigation is almost universally effective at higher frequencies (above 60 Hz), so most types of mitigation would be effective at reducing the annoyance from the GBN in the opera house.

So for me, the tragedy was not the death of the heroine at the end of the opera, but the fact that the performance was spoiled by a GBN problem that could be solved relatively easily.

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