1. DOCK Box Acoustic Speaker for iPhone: This speaker is made out of plywood and amplifies sound so you don't have to put the volume on your iPhone up too high. It and other plywood speaker designs are available at the Etsy store IndexDrums.
2. Eco-Amp by Eco Made: This acoustic speakers is made out of a sustainable paper-based material, and it folds completely flat until you need it. It's something handy to slip into your bag, when you don't have room for anything powered.
3. Change the Record Speaker: Designer Paul Cocksedge's passive speaker is quite striking and beautiful. He deforms an old vinyl to get this interesting shape, which works well for passive amplifying.
4. Passive Non-Powered Speakers for Smartphones: If you like speakers that look like pieces of art, then you'll be happy to see all of the ones we've found for you in this post. They come in all shapes, sizes and colors, and there are plenty to choose from.
5. Simple Acoustic Speakers for Your iPhone: In this post, find even more speakers that will power your tunes without consuming any electricity. MORE SPEAKERS & HEADPHONES ON APARTMENT THERAPY: • The Portable Boombox • Loud Luggage: Powered Suitcase Speakers • These Earbuds Always Stay In (Images: as credited above)