What BassZen said points to an important point... if you're playing a chord on bass you need to choose the notes carefully, as too many notes any where on the fretboard will get muddy.
Pick out the chords tones that give the chord it's flavour - usually the root, 3rd and 7th and drop the 5th. The sound of the perfect 5th in a most chords just adds to the muddyness and doesnt actually give the chord any stronger or more unique sound.
I wouldn't agree with Copyu specifically, but there is a good point there also,,, some places on a bass neck are good for chords and some aren't.
Usually below the 7th fret or so on the E, A & D you're getting into muddy territory, but equally above the 17th fret on the E and A can be messy too.
Try stick to the areasof the neck where tones are clear and more bell like - that way you can hear the harmony better.
In many cases you can play the root, then other chords tones (e.g. 3rd & 7th) as a double stop (two note chords specifially on stringed instruments) to imply the chord without having to play three notes together and get all muddy.
12th fret harmonic - and other natural harmonics are also real handy for a nice clear chord.
