set different volumes inside app

Question

i'd like to set the volume inside the touchesBegan action on half the volume of the IBAction.

- (void) awakeFromNib {
 [super awakeFromNib];
 engine = [[Finch alloc] init];
 E = [[RevolverSound alloc] initWithFile:PATH(@"E.wav")rounds:9];
}

-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
 UITouch *touch = [[event allTouches] anyObject];
 CGPoint location = [touch locationInView:self.view];

 if(CGRectContainsPoint(Edrop.frame,location)){  
  [E play];
 }
}

- (IBAction)bass:(id)sender {
 if(CGRectIntersectsRect(finga.frame,e.frame)){
  if(finga.center.y <= e.center.y)
   [E play];
 }
}

thanx, blacksheep