The strings on the bass, are most likely, the major factor in the sound of your bass. If you have a really good bass, and the strings are old, gunked up with sweat and flesh (yep, that is what it is…), then your bass sound has definite limits, unless that is the type of sound you are going for today.
However, most situations, will require a cleaner type of sound. Even though the bass is primarily a low frequency instrument (30Hz-500Hz), you can get frequencies from the overtones of the strings as high as 5000-7000Hz.
Mid range frequencies are very important in bass playing (900Hz – 2.5KHz). Remember, the human ear does not hear sounds in a linear fashion. Most humans hear sounds at 1500Hz – 2500Hz the best.
Then our hearing drops off on both sides (Low frequencies and High Frequencies). In most cases you will need some of these mid and high frequency sounds, to help with clarity. Generally, you need a brighter sound than you think you will, especially if you are playing a live gig.
Those high frequency sounds will fade away as you move away from your speaker system. You mid and high frequency sounds will also be competing with the other instruments in the band and will be diminished. (See Sound Shaping for more information)
There several different types of Strings for the bass. There are FlatWounds strings (1960s vintage), there are black nylon strings (60s and 70s sound), there are RoundWounds (70s to the present) which are most commonly used types of bass strings.
Then there are half breed types such as ground wound (round wounds ground to a flat wound feel, but brighter than flat wounds and punchier than round wounds). There are also half wound/half ground types, where the ground wound is usually over the fingerboard area, and the round would is from the end of the neck to the bridge.
There are bare core types, where the center wire is exposed at the bridge heel, to reduce false overtones of the string. There are tapered wound ends, which attempt to have better control at the tuners and place less stress coming out of the machine head slot.
All bass players eventually develop a preference for certain gauges and string types.
To get more life out of your strings see the Get More String Mileage page. For a list of suppliers and resources for bass guitar strings see the Resources page.