I am rational and humane despite having declawed cats. And so is my father-in-law who was a practising vet for about 40 years and has declawed thousands of cats. If you have evidence to the contrary, please present it rather than relying upon moral proselytizing with value judgements that others may not share.
In addition to the helpful and humourous comments above, here is some potentially useful information based upon biological facts, rather than personal values.
Cats will scratch. It is an instinct. Even a declawed cat will knead its paws as if scratching. Scratching is used to sharpen their claws to facilitate hunting and eating, just as a bear or a big cat will scratch a tree trunk. Domesticity has repressed it to a certain extent, but you cannot totally stop it. In order to assist in the sharpening, it is useful for the surface to have a bit of texture to provide resistance to the claw. A particularly good scratching post is one covered with thick rope knots. It feels more "natural" to the cat, like a tree trunk. However, if your cat is domesticated and has never used its natural scratching posts, it will have developed the habit of using something else. It may then become so used to this "something else", that it will not use other things. So even if you bring in a "better" scratching post, the cat may not use it. You can try, but it won't work 100%. Smooth surfaces are less likely to be scratched, but again, if that's what the cat got started on, it will continue to use it. So smooth surfaces are also not 100% effective.
Another alternative is conditioning. Like a rat or pigeon in a Skinner box, you train it not to use the speaker as a scratching post by negative reinforcement. You need not harm the cat, merely provide an unpleasant stimulus. For example, bang a tin plate or shoot it in the back or haunches with a water pistol when it attempts to scratch the speaker. This can be effective, but it requires constant negative reinforcement until the behaviour is extinguished. This is not practical. You cannot be with the cat 24/7. Remember, they're nocturnal so while you're sleeping, kitty will be downstairs scratching up the speaker to sharpen its claws in anticipation of a night of mousing.
Placing the speaker higher up on a stand will do nothing to stop the cat from scratching. It will just cause the cat to scratch the stand instead of the speaker. This may be fine but also consider that cats like to climb. They feel safer higher up. For example, leopards live most of their lives in trees. They even drag their killed prey up if they can. They do this so they don't get killed by lions. Lions, which do not climb too much, live in the same habitat as leopards. Lions view leopards as competitors and will kill a leopard if they get a chance. Domestic cats have this climbing instinct and may try to get up on the speaker. It may even use the speaker cable to assist or jump from nearby furniture such as a couch or an equipment rack. If it does try to jump on the speaker, it will naturally use its claws to grab hold of the speaker while it climbs on.
There is always the possibility that you have a cat that has no desire to scratch a speaker, as opposed to something else. However, the odds are that it will want to explore something new brought into its environment and it may give the speaker a test as a scratching post.
The only 100% effective method is to keep the cat away from the speaker. Do not give the cat access to the room unless you are there and within arm's reach to grab it. Or have it declawed. Anything else is a gamble that you will lose at some point. Declawing is the compromise cats have to pay to live with us. Or scratched furniture is the price we have to pay to live with cats. Take your pick. Your values, not somebody else's.
In addition to the helpful and humourous comments above, here is some potentially useful information based upon biological facts, rather than personal values.
Cats will scratch. It is an instinct. Even a declawed cat will knead its paws as if scratching. Scratching is used to sharpen their claws to facilitate hunting and eating, just as a bear or a big cat will scratch a tree trunk. Domesticity has repressed it to a certain extent, but you cannot totally stop it. In order to assist in the sharpening, it is useful for the surface to have a bit of texture to provide resistance to the claw. A particularly good scratching post is one covered with thick rope knots. It feels more "natural" to the cat, like a tree trunk. However, if your cat is domesticated and has never used its natural scratching posts, it will have developed the habit of using something else. It may then become so used to this "something else", that it will not use other things. So even if you bring in a "better" scratching post, the cat may not use it. You can try, but it won't work 100%. Smooth surfaces are less likely to be scratched, but again, if that's what the cat got started on, it will continue to use it. So smooth surfaces are also not 100% effective.
Another alternative is conditioning. Like a rat or pigeon in a Skinner box, you train it not to use the speaker as a scratching post by negative reinforcement. You need not harm the cat, merely provide an unpleasant stimulus. For example, bang a tin plate or shoot it in the back or haunches with a water pistol when it attempts to scratch the speaker. This can be effective, but it requires constant negative reinforcement until the behaviour is extinguished. This is not practical. You cannot be with the cat 24/7. Remember, they're nocturnal so while you're sleeping, kitty will be downstairs scratching up the speaker to sharpen its claws in anticipation of a night of mousing.
Placing the speaker higher up on a stand will do nothing to stop the cat from scratching. It will just cause the cat to scratch the stand instead of the speaker. This may be fine but also consider that cats like to climb. They feel safer higher up. For example, leopards live most of their lives in trees. They even drag their killed prey up if they can. They do this so they don't get killed by lions. Lions, which do not climb too much, live in the same habitat as leopards. Lions view leopards as competitors and will kill a leopard if they get a chance. Domestic cats have this climbing instinct and may try to get up on the speaker. It may even use the speaker cable to assist or jump from nearby furniture such as a couch or an equipment rack. If it does try to jump on the speaker, it will naturally use its claws to grab hold of the speaker while it climbs on.
There is always the possibility that you have a cat that has no desire to scratch a speaker, as opposed to something else. However, the odds are that it will want to explore something new brought into its environment and it may give the speaker a test as a scratching post.
The only 100% effective method is to keep the cat away from the speaker. Do not give the cat access to the room unless you are there and within arm's reach to grab it. Or have it declawed. Anything else is a gamble that you will lose at some point. Declawing is the compromise cats have to pay to live with us. Or scratched furniture is the price we have to pay to live with cats. Take your pick. Your values, not somebody else's.