[owners] are choosing to reinvest in their current aircraft, given market conditions.”
Skandia offers soundproofing kits for more than 80 different aircraft models, from Bombardier Globals down to turboprops and Cessna piston aircraft.
“The key is the frequency from 63 Hz to 8,000 Hz; those are the ranges we need to neutralize,” said Kambiz Avval, a Skandia acoustic engineer and specialist in aerospace soundproofing. “As material scientists, we look at what material is best for which frequency range.”
Dampening low frequencies (63 Hz-250 Hz) requires heavy material, but given the need to keep empty weight down, “We have to do optimization and integration, creating a matrix of different materials, each layer for a dominant frequency harmonic wave we hear in an aircraft,” Avval said.
The thermal/acoustic barrier includes insulating strip blankets, overframe blankets and carpet padding, made from fibrous cell foam, fabric and felt-based materials, all meeting the radiant flammability test for Part 25 aircraft.
The installations can be complex; a Global Express soundproofing system has more than 1,200 pieces, and accurate positioning of the material is critical for proper functioning. Skandia provides precise diagrams and instructions with its kits as well as training to ensure proper installation.
But each aircraft cabin has its own unique noise signature, and the most effective soundproofing solutions are customized. For such projects, Skandia uses handheld devices to record ambient sound at various points in the cabin aboard the aircraft when it’s at cruise power at its typical cruising altitude.
The equipment measures both the dB(A) level–the perceived loudness across the entire audible frequency range–and the dB(SIL) level, which measures the difficulty of hearing speech, in the 1,000-, 2000- and 4,000-Hz range. The dB(SIL) scale “is the sound level perceived as most annoying to the human ear,” Avval said.
The cabin recording data is downloaded, the dominant harmonic waves and the aircraft’s “noise profile” are reviewed, and the soundproofing system is designed around the results. Following installation, Skandia conducts a second in-flight recording to document the changes in cabin sound levels.
The dB (decibel) scale is exponential; every 3 dB reduction in sound is the equivalent of a perceived 50 percent reduction in cabin noise level. Skandia’s systems reduce cabin sound levels by 3 to 10 dB, Triplett said.
As an added bonus, a soundproofing retrofit often reduces weight as well. “The older generation materials tend to be on the heavy side,” said Triplett. With current-generation materials, engineers can achieve an equal level of soundproofing with just two thirds of the weight of the old, he explained.
Triplett declined to provide pricing for the soundproofing kits, but said “more often that not, costs are not the deciding factor” in the retrofit soundproofing decision. EBACE attendees are invited to Skandia’s display to hear more about their cabin-quieting capabilities.
Source: AIN Online, to read more click here.