Bob Hairstyles Concave Bob. The concave bob begins with the ends being chipped heavily as it graduates upwards. This creates more volume to the crown of the head. The main difference between concave bob’s and asymmetrical bob’s is that the concave bob has more bangs and layers in the front. While the asymmetrical bob’s are more one length in the front and the sides but shorter in the back as it tapers to the neck. Many of these bobs are created with the use a a straight razor by a professional hairstylist. A side part can be added for a sexier look.