I know this is a silly question but it's something that's been puzzling me.

Why don't opera singers deafen each other?

In one of the numerous clips of Pavarotti that have been on recently, he's standing on stage and singing with his head six inches from his partner's ears.

Now this is a voice that can reach the back rows of an opera house, right?

How loud is that voice when you're just six inches away from it? Surely that's got to be painful!

Yes, I've found it a bit deafening on a couple of occasions (at private recitals in small rooms) when I was sitting in opera singers' direct line of fire, as it were. Maybe having a larger space makes a difference, as Ruth says.

I used to live with a rather operatic mezzo-soprano and yes, a singing voice at close quarters can be damn loud. Fortunately it's quite directional though - if it's pointed at you a voice can be loud enough to cause quite a bit of discomfort (depends what she's saying of course ) but if two singers are standing shoulder to shoulder it's fairly painless (for them, at least) however loudly they're going for it.

This might be interesting...

http://www.gcaudio.com/resources/howtos/loudness.html

The figures aren't directly comparable though, some coming from different studies which don't specify the distance from the source. I wouldn't be surprised if that figure for the voice is on the low side. I shall search further.

I spend more time than I care to calculate standing next to opera singers    As Ollie rightly said, it's extremely "directional", and a lot of the carrying power relies upon making the upper resonances of the voice do the work...  it's not brute force.  (In fact bellowing and shrieking noises tend to get lost in the orchestral soup).  That "golden" sound (sometimes also called the "olive oil" sound) we associate with Pavarotti's voice is a perfect example - all of the "carbohydrate" is stripped out of the sound, and it's "pure protein".  This is basically the technique of singing known as "bel canto"...  which refers principally to the physical means used to produce the sound (and only incidentally to the repertoire of music written for singers who did and do so).

They don't deafen each other because - unless they are doing it wrong - they should always be angling themselves so that they are singing into the auditorium,  rather than "at" another singer (from where the sound would then disappear into the wings).  A well-staged production should usually position any soloist with much to say to another upstage (and to one side) of his/her collocutor,  so that the soloist can "open fire" directly into the hall whilst the other singer appears to listen.  In that positioning then yes - it can be pretty bloody loud for the other performer involved    (This is what opera production is actually about - and not, as often suggested, sitting in coffee-shops "conceptualising"     Conversely singers shouldn't be placed so far upstage that the sound becomes masked by the prosc, or that they are blocked by other performers further downstage.  All singers should be restrained from their natural tendency to creep downstage towards the edge of the pit and stand there making that "I am displaying an imaginary watermelon in my left hand" pose they so dearly love).

I thought the double-bass was supposed to be the noisiest thing in an orchestra, btw?

Well, I was working with a soprano a couple of days ago, and when she belted out her top C I can confirm that it was loud enough to bring a rush of blood to my head, if you know what I mean - exciting, in other words - but from approx 3 feet away it wasn't too uncomfortable on the ear (I didn't ask her to do it any closer!) That was in a room in my house.

Another time, last year, I was rehearsing with a baritone in a dance studio, and from a few feet away the sound was sometimes really, uncomfortably loud. This led me to believe that quite a large proportion of the sound one hears is actually reflected, rather than direct. The dance studio, which had a very bright acoustic, seemed to emphasise the higher frequencies caused by the vibrato, so the voice may not have been too loud, but the reflections certainly were in that space. On the stage, therefore, I think the voice up close may not in actual fact be as loud as it might seem to be from the auditorium, where it benefits from all the reflections of the sound. That's my theory, anyway. Also, in theatres that are not particularly well designed for opera (like the Royal Lyceum in Edinburgh for example) a lot of the voice is absorbed by the surfaces of the theatre (and the bodies of the audience) rather than reflected, so that the sound does not project so well.

I second Reiner's comments about opera production, by the way.