This is FOR select high-end speakers. It is an active filter that extends bass response while not affecting the other qualities that make up a speaker's normal excellent performance.KEF Reference series, dependent upon the model, either require such a filter, or have an optional available, to extract the most from the unit. The one's produced by KEF, do extend bass, but based on my experience, slightly compromise the excellent midrange clarity. The KEF filters are called KUBEs.
The "Golden Flutes" not only leave the midrange untouched, but do an even more impressive job on the bass.
B&W, Legacy, and several others can also benefit. Check out JPS Labs on the net. The founder of the company will personally attend to your questions, and ensure you are happy with your purchase. I believe they are available on a trial basis.
A unique product for the audiophile searching for that least bit of refinement, for what are otherwise excellent speakers.