can you do preacher curls with straight bar
Try it for yourself and with proper form you will be able to understand what exersice works what. The preacher curl by far with proper form (all the way down IMO) works the lower bicep. That you can feel. The straight bar works more the medial and upper part of the bicep. I personally do them both on arm days, it gives me a good all around bicep workout. Try it.