Here's what Seymour Duncan say about the Woody XL Soundhole Pickup:
The Woody XL (SA-3XL) is a passive, noiseless, magnetic soundhole pickup with adjustable pole pieces that delivers a full spectrum acoustic tone that is great for everything from jangly strumming, to quiet fingerstyle playing. It gives you a great balance that combines the fat bottom of the HC version, with the sparkly top end of the SC version all with no 60-cycle hum. The individually adjustable pole pieces enable you to really fine tune your sting-to-string balance.
All of the Woodys are available in our custom maple, walnut or black stained housing, and are double potted to keep them resistant to feedback. It mounts instantly into your soundhole, with no modification of any kind needed to the guitar and can easily be removed at a moments notice. It comes with a 14-foot low capacitance, studio quality cable that will plug directly into your favorite amp, PA, direct box, or console. Fits all standard soundholes (3.75″ (94mm) to 4.0″ (100mm). Great for all standard types of steel string acoustic guitars.
NOTE this is a magnetic pickup, and will not work with nylon stringed instruments.