I hate that effect (IIRC it's called the occlusion effect), and thus I'm not a fan of IEMs. I would rather have earbuds (the kind that don't have a sealing tip) than IEMs if I can't wear over-ear headphones. Sure, those earbuds lack the seal and thus the bass suffers, but in headphones/earphones, comfort is king, and I'd rather live with less bass than live underwater. I've heard that foam tips rather than silicone tips lessen the effect.