Adventures in aerospace acoustics

In early January we received a call from the University of Salford's Acoustic Test & Calibration Laboratory asking for assistance with a demanding acoustic simulation for an aerospace contractor, following personal recommendations from some of their lab staff. Working to a very specific brief with only a few days notice to design, test and implement a system very different from the norm, our staff worked with Salford's world-reknowned acoustic labs to create a truly monstrous system capable of recreating the intense environments experienced by pilots of modern aircraft to assist in the design of new helmet technologies. Unfortunately contractual obligations prevent us from detailing the full design specification and response plot that needed to be reproduced, but needless to say it was a task far beyond the needs of your average rock 'n' roll concert; particular highlights being the requirement for 115dB of SPL at an incredible 20Hz frequency and no less than 20 points of parametric equalisation needed to achieve the exact opposite of the traditional 'flat response'.

We deployed a horizontal array of 8 of our largest custom-built touring subs, the Void Acoustics Psyco Sub, reaching wall to wall in the intended test chamber so that the truly subharmonic frequencies could be assisted by boundary effects (commonly known as 'corner loading'). These were complimented by a pair of Void Acoustics Stasys Prime mid-high packs, chosen for their ability to reach very high SPL levels with minimal ringing, distortion or beaming. Void Acoustics Infinite 8v2 amplifiers were used due to their ability to bypass the 20Hz subharmonic filter put in place to prevent over-excursion and damage to speakers in normal use.

This system would normally be at home entertaining over 500 people in an open air arena, and admirably reached the target of 104dB at an eye-watering 12.5Hz, but to rise to this exemplary task further assistance was still required!

We called upon our friends at OHM UK, based just down the road in Knutsford as this was a perfect opportunity for them to truly test their latest 'INFRA' addition to the their long established TRS range of loudspeakers. Utilising a push-pull slot loaded ported design, extremely long excursion 18" woofers and a tuning frequency in the mid-20Hz region, this is a true 'sub' cabinet and gave the additional brute force needed to maintain consistent 115dB output (±3dB) at 20Hz with pink noise for the duration of the testing.

The far from normal input EQ in Armonia software

Several visits were made by our staff over the duration of the test period, not only to assist in the testing procedure itself but to ensure that this seriously intense workout wasn't putting undue strain on the cabinets, drivers or amplifiers. All equipment held up with not a single failure, despite being required to maintain this truly punishing signal for upwards of 20 minutes at a time, for several days; a testament to the British manufacturing and design involved in creating the equipment used.

Needless to say, the client was incredibly happy with the system design and the test results achieved, and our staff relished the chance to do something a little off the beaten path.