MADflyer

While fully respecting the traditional views of attire for these sorts of occasions one of the positive sides promoted by relaxing the dress code is that the events are more accessable to a broader audience.

I was often amazed at first in Stockholm at the mix of attire but then really came to appreciate it. They now sell heavily discounted student tickets to all perfornances except for the first row but it used to be they would fill all the remaining seats at the last minute with students in all sorts of attire for around $5 if I recall. They still have 'listening seating' for around $6 for all performances.

Madrid needs to add a section to their website as they have in Stockholm where they state as follows:

Klädsel
Det finns ingen ”dresscode” på Operan. Det är helt valfritt hur man vill klä sig. Det är vanligt att man klär sig elegantare på premiärer än andra föreställningskvällar. Klä dig så att du själv känner dig bekväm!

Translated
There is no 'dresscode' at the Opera. It is totally up to you how you choose to dress. It is the norm that people do dress somewhat more elegant for Premeirs than for other performances. Dress in a way that you yourself will feel comfortable!

In their own English translation they add... 'though to dress up might make the evening more special' ... not in the Swedish text.