No speaker, monitor or hi-fi sound system, regardless of the design principle or cost, has a completely flat frequency response; all speakers color the sound to some degree. Monitor speakers are assumed to be as free as possible from coloration. While no rigid distinction exists between consumer speakers and studio monitors, manufacturers more and more accent the difference in their marketing material. Generally, studio monitors are physically robust, to cope with the high volumes and physical knocks that may happen in the studio, and are used for listening at shorter distances (e.g., near field) than hi-fi speakers, though nothing precludes them from being used in a home-sized environment. In one prominent recording magazine, "Sound on Sound", the number of self-amplified (active) studio monitor reviews significantly outweighs the number of passive monitor reviews over the past two decades indicating that studio monitors are predominantly self-amplified, although not exclusively so. Hi-fi speakers usually require external amplification.