Turntable needles, or more specifically the stylus (the little diamond point on the end of the needle) come in different shapes. Not all are created equal. The overall goal of turntable needles is to be in as much contact with the groove on the record as possible. To understand this goal, a basic understanding of surface area is required.
Consider a man laying on a bed of nails. He is able to lay on these nails because the sum of the surface areas of all the nail heads is quite large. Therefore it is better if the man is in contact with as many nails as possible in order to have as much surface area to lie on as possible. Laying on a bed of 50 nails, for example, would not be a pleasant experience, whereas laying on a bed of 1000 nails would be much more easily achieved.
Turntable needles that achieve a high degree of contact with the groove reduce stress on the stylus. Turntable needles move very fast, and larger surface area reduces the stress on the needle. Higher surface areas also reduce the wear on the groove, helping your records last longer.
Three Tips for Buying Realistic Turntable Needles
1. The shape of turntable needles determines the contact they can achieve within the groove of a record. The more contact the better the sound. Conical or spherical stylus shapes are not the best option. A groove on a vinyl record is triangular in shape, and spherical turntable needles do not fit well in to this shape. Elliptical is a good option for reasonable cost.
2. The type of material the stylus is made out of matters. Most turntable needles these days are made out of diamond. Diamond is the premium material and anything else should be avoided as it will wear out faster and damage your records more rapidly.
3. The size of turntable needles is important, and smaller sized turntable needles will fit in the groove more easily. The deeper in to the groove that turntable needles get, the richer the sound the system puts out. The sizing is measured in mil and will be listed as 0.3 x 0.8 or something similar. A notable exception to the smaller is better rule is with 78s. Turntable needles designed for playing 78 rpm records are around 2.5 to 3 mil, so if you are planning on playing 78s then you will need a separate stylus.
The best turntables on the market are likely to already come with a high quality turntable needle. However, vintage turntables are likely to have turntable needles that need replacing. Spend the right amount of money for your setup: there is not much point buying premium turntable needles for cheap turntables, and vice versa.