Sound, DCC and locomotives

The last entry on the locos provoked a comment about sound wagons.   I've actually got two of these although only one is DCC but pictures of both will serve to illustrate the principles.  

First up is an official LGB product.   In pre DCC days they obviously made a number of factory converted "sound wagons" so those with smaller engines could enjoy sounds.  I'd have to read the instruction book to see if track magnets would trigger additional sounds, but on DC it makes a steam train sound.  The wires out the front left connect to the power supply socket on the rear of the (DC) loco and as the track power is increased (thus meaning more speed), the chuff increases.   The speaker is floor mounted.  I bought the coach because I wanted the style of 4 door coach and the price was right (excluding sound) on German ebay.  

 The 9v battery will serve to provide power in the event of track failure, such as going across points or an isolation track.  

Next up is what somebody lovingly crafted and I bought with the Spreewald.  A standard LGB DCC sound module has been fitted inside a (resprayed) goods wagon.  This has a digital decoder fitted and thus has its own ID - currently set to number 1 (it should be possible to change this).  When placed behind a loco with the same ID, then the sounds increase as the loco increases speed and the other sound functions (bell, whistle etc) are also available (in reality the same message is being sent to two decoders with the same ID number).

With its own DCC ID then it is possible to have this wagon sitting on its own making noises as if it was a loco: so it really needs to stay permanently behind the loco.  One of the problems with sound - in all scales I suspect - is finding place and a suitable mounting for the loudspeaker.  Recent technology has produced a range of thin, almost flat loudspeakers which are idea for mounting in the cab roof of a loco which seems to be a favoured place.  Power pick up is via the track (see wires to take power off the wheels, but again some sort of buffer (Capacitors?) have been fitted so that in the event of isolation (e..g point frog etc) the sounds will continue to play.