wow. thanksTo understand a scorpion's "hearing" you need to consider what our hearing is. In humans, vibrations enter the ear and cause little hairs in the cochlea to vibrate. Depending on the frequency, different hairs are involved and the brain interprets this as sound. Most of the time, these waves are transmitted through the air, but can be transmitted through water (when we are underwater) or, in the case of fairly low frequencies, through solid objects. The ability of low frequencies to travel through solids so well is why you can stick your subwoofer anywhere in a room, but you need your higher frequency speakers to be pointing at you.
A scorpion doesn't have hearing in this same sort of sense -- but as you can see upon examining them, they do have a lot of "hairs". These actually aren't hairs, of course, but are sensory structures that allow the scorpion to sense vibration. There are also small slits called slit sensila that allow the scorpion to detect mechanical strain. Using these sensory components, scorpions are incredibly adept at detecting vibrations coming through the ground. They can even determine the direction by comparing wave timing among legs. They are also sensitive to airborne vibrations. Using their trichobothria (the much longer sensory hairs concentrated on their pedipalps), it is documented that they can catch prey in mid-flight by picking up on the airborne vibrations they cause. So if you still insist on trying to catagorize scorpion senses based on the human model, the closest comparison would be to say that they have their inner ear spread out across the outside of their body.
Now what does this have to do with Metallica? First off, there is no doubt that your scorpion percieves the music. Unless you have its cage well isolated from the surface it is on, it probably picks up your footsteps when you enter the room, never mind ground-shaking bass. Furthermore, there is no doubt that music that loud is going to cause vibrations in the glass of the enclosure and that will cause vibrations inside the tank. So your scorpion is definitely going to be getting not only the bass (which is all your snakes might pick up) but also the trebble.
Fortunately, there is a thing called habituation. People who live near train tracks quickly stop hearing the train. Likewise, your scorpion probably quickly stopped interpreting the noise as a source of danger. That being said, you have to realize that while you are playing the music that loud the scorpion cannot hunt properly and is gong to be severely inhibited when it comes to navigation. All the little subtle signals it uses to go about its regular life are going to be completely lost. Compare it to someone sticking an incredibly bright light in your face. It will blind you completely, even if after hours and hours the initial discomfort goes away and you can focus on other things. Eventually, when the light is turned off you should go through a recovery period and then be back to normal. If the light is too bright, there may actually be damage and you may become permenently blind or otherwise impared.
Whether or not your music causes any permenent damage (possible, but nobody studies this sort of thing), it definitely is going to cause some stress to your scorpion.
It is up to you to determine the balance between the wellbeing of your charges and the other aspects of your life. Recently, the scorpions on my desk have been subjected to Spoiler NYC at elevated volumes, but the bulk of my collection is at the other side of the house.
http://johnbokma.com/mexit/2006/06/18/centruroides-gracilis-eating-a-moth.html :-Dit is documented that they can catch prey in mid-flight by picking up on the airborne vibrations they cause.
Gracias, senior. Now the next time you see a moth in an enclosure, throw in some Metallica and you have a paired trial.