Review on Hudson Hi-Fi Silicone Isolation Feet - 4 Pack, Firm Block 150lb Capacity (Non-Adhesive) - Enhance Audio Quality & Stability by Robert Carter

They work but make sure you understand the measurements before you buy. This is not affected by subwoofers on carpet. I've used them to stack two identical subwoofers on top of each other and they work great for that. They can also be used for components without feet. The problem is they don't come with glue. If you plan to keep an item in the same place for a long time and you can put it on top of that, that's fine, but if you want to put a large component on top of it, it's basically impossible because they don't have glue. They're solidly built, just know what you're getting and how big they are.