Families often watch TV together, but what happens when one member has hearing difficulties? Usually the result is a compromise on listening volume that doesn’t really satisfy anyone. In my research, I have been designing highly directional acoustical radiators, commonly known as loudspeaker arrays, which are aimed to increase the speech intelligibility of hearing impaired TV listeners.
Fig. 1. Sound field created by a 4 source line array.
Loudspeaker arrays are made up of sets of drivers a certain distance apart. The acoustic waves they generate arrive at a certain spatial point at the same time i.e., in phase, creating a constructive interference and summing in intensity, whilst at points where the sound waves do not arrive in phase, a destructive interference is created, with a consequence reduction in intensity. An example is given in Fig. 1, which shows the soundfield created by a line array of four drivers. By the use of these radiators, a boosted version of the TV audio is sent towards one spatial location, where a hearing impaired TV listener is present. This hearing impaired TV listener is clearly beneficiated from the highest volume provided by the array, and now has a greater speech intelligibility, whilst other TV listeners with healthy hearing are placed at positions in where the radiation of the array is minimum, and do not listen to the amplification provided by the array.
Fig. 2. Line arrays used to increase speech intelligibility. The lower one is the newest version of radiator, aimed to reduce reflections from floor and ceiling.
The performance of loudspeaker arrays grows proportionally to the number of sources used. However, a greater number of sources need more electric power and a greater computational cost for the array to operate. Part of my research recently published in the Journal of the Acoustical Society of America introduces the use of phase-shift sources in a line array, which reduce the number of sources needed. This corresponds to the upper array shown in Fig. 2. Thanks to the work performed on it I was awarded the IOA-IAC young person’s award for innovation in acoustical engineering in 2013.
The directional characteristics of a line array are greatly reduced, however, when the array is introduced in a room, due to reflections from the walls. My most recent research is centred on understanding how and how much is the performance of an array reduced due to reverberation, and how it can be improved. This has led to the design and construction of a new array, of planar configuration, which reduces the radiation towards floor and ceiling. This array, which is shown at the bottom of Fig. 2, has been presented in some conferences, winning the Spanish Acoustical Society (SEA) Andrés Lara prize for young scientists in 2013.
My first contact with acoustic was during my undergrad, in the Universidad Politécnica de Madrid, where I obtained a BSc in telecommunications engineering. After that, I decided to continue with my studies, and having not done Erasmus I thought about doing a masters abroad, which took me to the ISVR. Here, I performed a MSc in Sound and Vibrations Studies in 2010, an experience I greatly enjoyed, both in the academic/learning side and in the friendship/personal side. I really liked the time working in my MSc Project, and this persuaded me to start a PhD. In October 2011 I started a PhD under the supervision of Professor Stephen Elliott, funded by the University of Southampton.