TECHNICAL SECTION

An improvised amplification device for smartphone loudspeakers J Cubitt, D Williams The Welsh Centre for Burns and Plastic Surgery, Abertawe Bro Morgannwg University Health Board, UK CORRESPONDENCE TO Jonathan Cubitt, E: [email protected]

BACKGROUND

Smartphones are a ubiquitous part of modern day life. However, when used to listen to music in large rooms (eg festive music in operating theatres), the low volume is a significant limiting factor to enjoyment. We have observed that a size 5 adult facemask may be employed to produce a subjective increase in volume from smartphone speakers.

Figure 2 Frequency response curves at 40cm for smartphone loudspeakers with and without improvised amplification device

Reference 1.

Sen SN. Acoustics: Waves and Oscillations. New York: Wiley; 1991.

TECHNIQUE

Once the optimum position for the smartphone within the facemask was identified (Fig 1), a series of experiments were carried out to compare the frequency responses from unmodified and modified smartphones using 34 standard audio test tones ranging from 16Hz to 20kHz (Bink Audio Test CD; HEAnet, Dublin, Ireland). These were measured with a sound pressure level meter application (Decibel 10th; SkyPaw). The modification caused a shift in the resonant frequency from 4kHz to 1.25kHz, with a 10dB gain around 1.25kHz (Fig 2). Further analysis with an audio spectrum analyser application (RTA Lite; Studio Six Digital) showed that the majority of festive tunes, including Merry Christmas Everybody by Slade, produced signals centred around 1.25kHz, with a range of 250Hz to 8kHz. DISCUSSION

The facemask achieves the subjective increase in volume by acting as a substantially parabolic reflector and/or Helmholtz resonator, optimising the output of the smartphone to approximately the centre of the tonal range for male voice and guitars.1 We therefore propose that a size 5 facemask may be employed as an improvised amplifier to enhance enjoyment of festive music.

Figure 1 Smartphone with improvised amplification device. Acoustic effects of the decorative sprigs of holly are unknown

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Ann R Coll Surg Engl 2014; 96: 163–171

Optimisation of intramedullary nail alignment SA Sabah, J Singh, N Heidari Barts Health NHS Trust, UK CORRESPONDENCE TO Shiraz Sabah, E: [email protected]

Intramedullary nailing has been the subject of eight technical tips in the Annals1 and yet none have addressed the problem of malalignment. Our technique uses a modified Poller (ie blocking) system to achieve optimal alignment. A 3mm K-wire is inserted medially across the medullary canal to guide the nail laterally. As the nail advances, it mounts the K-wire and further use of the hammer causes it to bend. The K-wire is then rotated through 90º. The J-shaped kink, with the apex pointing medially, guides the nail into a perfect position (Fig 1). The K-wire is removed after the nail is locked in the sagittal and coronal planes.

Reference 1.

Intramedullary Nailing. Royal College of Surgeons of England. http://www. rcseng.ac.uk/publications/techtips/Orthopaedic%20surgery/Trauma/Intramedullary%20nailing/ (cited November 2013).

Figure 1 Left to right: Tibial nail mounts and bends K-wire. Subsequent rotation of the K-wire steers the tibial nail towards optimal alignment

Optimisation of intramedullary nail alignment.

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