well there are wastes and energy usages during production, but if you're considering when they are connected to your computer then it's different. All electronics are inefficient and produce some waste heat but it would be less than a larger stereo, which also has its own chip which uses power to process inputs and produce sound. while your speakers are not in use they also draw electricity if they are left on because while the power is on they still make a slight vibration, even if you don't have anything playing. so turn them off when not in use. Also the power adapter which converts ac to dc will always use some power while plugged in.
