Thank you for your reply.

Obviously I am a little disappointed that the soundfield system is not back in use yet but I understand the practical reasons. You raise a number of issues that are not unusual but which we are very keen to understand. You could say that we are biased in wanting our systems to be helping students since we manufacture them but feedback from nearly all users is that the systems are a great help to all students and the teachers using them. In the few cases where reactions have not been 100% positive it has been mostly due to teacher attitudes, finger trouble, poor setting up or poor system management. Occasionally, of course, as with any equipment, there are faults in the systems themselves but they are rare and we deal with them as soon as we are notified. Time and again various studies and user reports have shown that soundfield systems can be of great benfit when used properly so we are keen to help users understand and gain maximum benefit from their systems. What value the users place on their systems seems to depend on how effectively they are able to use them.

I came across the 'research' suggesting that the simultaneous use of soundfield and radio aids was less desirable than radio aids alone in November 2003. It was presented by Liz Wood from the University of Southampton coclear centre. I challenged her about this and it turned out that the conclusions were drawn rather hastily without considering all the relevant data. Unfortunately the results had already been presented in the public domain. This issue has come up, to my knowledge, a couple of times since at the FM Working Group hosted by the NDCS. Further research by other groups has indicated that the order of benfit for HI students is:

1 Least: HA alone
2 HA + soundfield
3 HA + radio aid
4 Best: HA + radio aid + soundfield

However, it depends on what basis the 'improvement' is judged as there are pros and cons for each. E.g. where a soundfield is used, there are benefits for all classroom occupants and all occupants can hear each other well when a roving microphone is also used. Clearly the 'best' combination, considered in isolation from any other factor, would be the HA + radio aid alone, but that is only true if the HA microphone is off and the user is listening solely to the transmitted signal from the teacher with no intrusion of background noise. If the HA microphone is on, background noise will be more intrusive but the user can listen to their neighbours. Of course they will have difficulty hearing sounds or voices from further away (i.e. not via the radio aid) without the assistance of the soundfield system. Since this is the most usual case, one must then consider whether there is any detrimental effect on intelligibility when the live HA microphone picks up a good signal from the soundfield speakers at the same time as receiving the direct transmitted sound via the radio aid. As there is a nominal 10dB FM advantage via the radio aid, one would expect that the additional soundfield signal would not significantly degrade intelligibility and this has been borne out in more recent studies. Any degradation of the sound due to the combinination of the two signals would be a result of phase addition and cancellation of the two signals (since they arrive at the listener's ears at slightly different times). This is a normal occurrence anyway and is the process that 'colours' the sound in a particular environment to make it sound the way it does. Unless the physical layout of the environment is dynamically changing or the listening and/or sound source positions are moving, then even a normally hearing listener will not be aware of any signal phase addition or cancellation.

I should be pleased if you would keep us updated on your 'saga' as things progress.

If it would be beneficial for you and your colleagues to receive further presentations or training then please let John, David or myself know and we will gladly pencil you in for a visit next time we are up your way.

Best wishes,

Gareth Pont
Design Director

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