Sennheiser has expanded its line of full-sized HD headphones with the release of the HD 428, HD 438 and HD 448. The latter of the new releases offers the highest-quality sound of the group, while the HD 438 features a more natural sound. The HD 428 provides better lower frequency quality and is intended for bass response. Each model utilizes a gold-plated quarter-inch stereo adapter and a closed-b
