The CEP website has some photos, but essentially the earplugs are very similar to a set of in-ear stereo earphones, with soft foam expanding tips which provide excellent passive noise attenuation - the end of the earphone cable has a SMB connector. A small hole is drilled in the helmet towards the bottom on one side, and a recessed SMB jack inserted and wired in parallel with the helmet speakers. You put in the earphones, put on the helmet, then plug the end of the earphone cable into the jack on the outside of the helmet. Works very well. If you don't like the sound of drilling a hole in the helmet (note there are already holes drilled for the existing cabling, visor bungee studs etc) there are versions with a smaller trailing SMB connector lead wired into the helmet, but most people use the external jack. CEP use the Comply foam tips, and you can buy these from a non-aviation source at about half the price charged by the aviation sources.
A more expensive solution is to have custom-made gel plugs made from a mould of your ear canal, but this comes in at about £300, whereas the CEP kit is about £75.
Last edited by eharding; 8th April 2008 at 17:13.