I heve had good luck using computer speakers just remove them from the box and use them with a box in the tank made with card board. Most of them i have found soung alot better and are plenty loud just hooked to the hl board. All the henglong gearboxes i have had needed to be rebuilt by drilling the shaft holes out oblong to remove the slop and soldering in place then shims then valve compound then take apart and clean after that they run ok.