I've just started to learn how to play slap bass, but I'm having a little problem.

When I slap, its a lot quieter than when I finger/pluck, obviously I expected this coz theres less vibrations, but my whenever I slap the A string its A LOT quieter than when I slap the E string.

Now is this due to my technique? (I'm using the technique everyone uses, thumb joint etc) or is it due to my string height? I've lowered it a bit, but if I lower it anymore, the strings buzz when I play it normally.
Its even more quieter when I play notes (instead of open string).

Any hints and tips?

It's got nothing to do with your string action (height), man. It's most likely your technique. A compressor pedal should in theory help you out quite a bit with your problem, as suggested above.
ok, cheers. I changed my technique slightly. So instead of just 'bouncing off' the string, I kinda 'bounce down' so it hits it a lot hard and gives a louder sound.
Dunno if its correct, but it still sounds like slap.
Slapping should be a hell of a lot louder than fingering. It is possible that its the string height, to high or too low and you start cutting sustain and volume.

Loosen up your thumb, it shouldn't be like you're hitting the string with a stick.
Well, they call it SLAP for a reason. Maybe you just need to work on technique? I slap and pop and it's waaay louder than fingerstyle, and I keep my action super low.
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