Hi there i understand polyrhythms and such but i am just wondering what the correct term is if i were to say have a bar of 4 against a bar of 3 but i stretch the bar of 3 to the same length of the 4 by changing the tempo so they last the same amount of time in seconds but have totally different feels?

cheers

carl
The term is polytempo. However, for a situation as simple as what you describe, it might be easier to just notate the music using tuplets. For example, a bar of 4 quarter notes in 4/4 against a bar of half note triplets in 4/4. The resulting rhythm is the same and you don't have to worry about two different tempos.
it's right, you have different feels. That's the thing.
As far as I know:

Polytempo - two or more tempo's going on at the same time, eg. 100bpm and 150bpm.

Polymeter - two or more time signatures going on at the same time, eg. 3/4 and 4/4.

Polyrhythms - two or more rhythms going on at the same time, eg. 4 crotchets per bar against 3 triplet crotchets (in 4/4 for example). Polyrhythms are usually with, i'm not sure the correct term, contradictory rhythms (if anyone apart from me gets what that means).

A cool example of polytempo is Piano Phase by Steve Reich (http://www.youtube.com/watch?v=AnC5DhNqZ6w). The two pianists start of playing a two bar ostinato at the same tempo but after a while the second one accelerates to a slightly higher tempo (then continues to play at that tempo).

You hear the two parts go out of time with each other until the second pianist has moved so far ahead that his first note now coincides with the first pianists second note. At this point the second pianist drops to the first's slower tempo again, and they play at the same tempo for a while (although the 2nd one now starts on the 1st's second note). The second one then accelarates again... and the pattern repeats itself.

It is of course very difficult to play at a slightly different tempo to someone else because you can hear yourself going out of time with them but not (I'm told, I still can't do it) as impossibly hard as it first seems.

PS, the opening riff seems quite flashy but it can be playing quite easily on a piano. With your left hand you play the notes E, B, D (going upwards) and with the right F# C#. However, you play the left hand for one note then the right, then the left, then the right.

Once you've got that down you get the ostinato of E F# B C# D F# E C# B F# D C#. Then the entire thing starts again.