Danley of Sound Physics Labs began working on a three-way multiple entry horn, bringing the SPL-td1 to market in 2000. The design used seven drivers, with one high frequency driver at the horn's throat, four mid-frequency drivers near the throat and two low frequency drivers ported closer to the horn mouth. In 2001, Tom Danley began developing the "Unity" horn for Yorkville Sound, patenting the improvement in 2002. Following the 2003 release of Yorkville's Unity line, Danley formed Danley Sound Labs and developed a significant improvement over the SPL-td1 called the "Synergy" horn, yielding substantially better phase and magnitude response along with smoother polar pattern. The synergy horn design promises greater power output achieved from a smaller loudspeaker enclosure. Because the design retains pattern control through its crossover regions and over a large range of its total bandwidth, and because the acoustic center of the design is near the rear of the enclosure, it is more easily combined in arrays for public address applications. Waveguide horns The term "waveguide" is used to describe horns with low acoustic loading, such as conic, quadratic, oblate spheroidal or elliptic cylindrical horns. These are designed more to control the radiation pattern rather than to gain efficiency via improved acoustic loading. All horns have some pattern control, and all waveguides provide a degree of acoustic loading, so the difference between a waveguide and a horn is a matter of judgement. Quadratic-Throat Waveguide In 1999, Charlie Hughes of Peavey Electronics filed for a patent on a hybrid horn he called Quadratic-Throat Waveguide. The horn was basically a simple conic section but its throat was curved in a circular arc to match the desired throat size for proper mating to the speaker driver. Instead of increasing the horn mouth size with a flare to control midrange beaming, a relatively thin layer of foam covering the mouth edge was found to suit the same end. The QT waveguide, when compared to popular CD horns, produced about lower levels of second harmonic distortion across all frequencies, and an average of lower levels of the more annoying third harmonic distortion. Being without a diffraction slot, the QT waveguide was free from problems with apparent apex, making it arrayable as needed for public address purposes. Oblate spheroid waveguide Oblate spheroid waveguide (OSWG) horn designs improve directivity pattern control above 1 kHz, provide a lower frequency of directivity to better match the