there are lots of simple ways these days to do sound like this cheaply. this is just a canned solution for those that dont want to bother tinkering.
there are scads of little mp3 players these days dirt cheap. some will have enough headphone umph to drive a small speaker with lower impedance giving more volume, but more distortion. there are very simple amplifier circuits that will let you boost it if you need more speaker power. or go for those cheap little battery powered speakers (they have a little amplifier circuit in them) you can get for mp3 players and supply them with your own power instead of battery power.
most cheap mp3 players will let you loop all your files so you can sequence up a bunch using the file names and just put them on loop or just create a long audioscape audio file to play and or loop. only issue with these systems (including an ipod or computer) is at power on you will almost certainly have to hit a few buttons to put the player into the right mode. also its better if you can plug in a flash card rather than plug the unit into a computer with a usb cable to load files onto onboard flash memory. once installed somewhere it might be tougher to connect to the computer, but flash card equipped units can be more expensive.
there are some good digital audio boxes you can buy for $50-200 that will give you 2-4 channels of digital audio off mp3 files on a flash card and enough power per channel to drive small speakers. there are a couple that are made and marketed for train layouts. there are others that are used in general exhibit and public presentation systems as well that have more options as well like triggered playing with a switch closure that allows easy triggering from other events or a button on the layout for users to push to get something.
there are super cheap little $2 10second record playback devices. they are pretty wimpy though, i have to work on mine some more, first quick tests showed it was not very loud, but they are cheap and triggerable by a switch closure. i need to check the batteries as they may have been shot. i also want to give it a direct signal in for recording instead of the mic as that may be crap too.
http://www.ebay.com/itm/10-Sec-Talking-Sound-Music-Recordable-Module-Card-/120811519069?pt=LH_DefaultDomain_0&hash=item1c20ed7c5d#ht_2544wt_1126ive been tempted to try one of these, for $9 might be ok, but the recording aspect is a pain, so much easier to dump an mp3 file onto a unit to fiddle than have to record it, also limited length, but these i think are much better quality than the little greeting card units for $2 that are pretty crappy.
http://www.ebay.com/itm/Audio-Module-Record-board-Playback-Module-ISD1820-C62-/270777424369?pt=LH_DefaultDomain_0&hash=item3f0b9799f1#ht_1816wt_892i picked up a remote control relay recently that i want to hook up to something like this to do a few remote audio triggers like goji roaring. so when someone is bending over close to goji i can hit the remote in my pocket to make him roar at him. other fun things like a dog barking in a scene near the edge, etc.
similar situation here with the mp4 video players, the more consumer stuff will allow easy additions of files with mp3, flash cards, etc, but have obnoxious setup and play back things that will need to be done each time its turned on. you can get more basic circuits like the one above, that have no setup needs once programmed, but they lack the features of playing mp3s etc. to get something that has mp3s, flash card, go to your program at power on, etc then you end up having to spend some money unfortunately.
eventually im sure there will be some nice boards made with arduino to do this via programmable triggering, there are some basic boards out there now but you have to build them.
cheers
jeff
