Q: why is it that an ensemble with many instruments in the high range can often sound great, but having more than one bass player is often disastrous?
A: the harmonic series is really like a tree. the branches get smaller as they go up, so there can be more of them. but 2 trunks would really never work. play 3rds on a piano starting from around middle C, and get lower and lower. you will hear them stop working at a certain point. this will be about 1 octave above the point where 5ths would stop working, and it would be about 2 octaves above the point where single notes stop working, which is usually the end of the instrument (like around low A on piano, or in my opinion B or C) i've found that the harmonic series actually illustrates this exactly. you'll see thirds appear 2 octaves above the source note. so in otherwords if you play thirds in a certain range, the amount of 'mess' it makes is equal to the amount of 'mess' it would make if you played 5ths an octave below that. or a single note 2 octaves below. that's why heavy guitar riffs often use 5ths, and the bass usually plays the same thing 1 octave below, but in a single note. if you try to play 5ths there it just sounds like an earthquake. another interesting way of illustrating this is if you put distortion on and play 5ths, it often sounds exactly like a single note, 1 octave down. it even works if you play 4ths with distortion. it often sounds like a single note 2 octaves below the highest note. again agreeing with the harmonic series that your 2 notes are a part of