2aID11 – A transducer not to be ignored: The siren – J. D. Maynard

The siren is a source of sound (or sound transducer) which captures our attention because we know it may emanate from a police vehicle, fire engine, tornado warning tower or other danger warning system. However, there is another reason to heed the siren: it can be a “death ray”! Most of us know of the death ray from science fiction stories which describe a device which can annihilate whole armies silently from a distance. Around 1950 there were newspaper stories which heralded the advent of an actual death ray, with headlines and text such as: “‘Death Ray’ May Be Red [Soviet] Weapon. In the great super arms duel between east and west, has Russia successfully added the “death ray” to its growing arsenal?” (Franklin Johnson, OP, Washington, February 17, 1953) and “US sound ray kills mice in minute. The United States Army has announced the development of a supersonic death ray that kills mice in one minute. In spite of precautions the ray has inflicted burns, dizzyness and loss of balance on laboratory workers.” (American journal, New York, 1947). It may be assumed, and in some cases known, that the death ray referred to in these articles was a high intensity siren which was “silent” because it operated at a frequency above the threshold of human hearing (humans cannot hear frequencies above about 20,000 cycles per second). It was “high intensity” because it operated at a power level which was 10,000 times louder than the level of sound where the sense of “loudness” disappears and pain sets in; at the much louder level, pain becomes death, at least for mice.

A likely cause for the news articles was research with a siren undertaken by acousticians C. H. Allen and Isadore Rudnick, working under H. K. Schilling, Director of the Pennsylvania State College Acoustics Laboratory in 1946. Anyone who knew Izzy Rudnick would hypothesize that his response to the news articles would have been “Rumors of my death ray have been greatly exaggerated”. Indeed, a mouse had to be within about four inches (about 10 centimeters) of the siren in order to be killed, and its death was deemed to be a result of an increase in the temperature of the mouse due to absorption of the sound. In the same manner, the siren was used to heat a cup of coffee, ignite a ball of cotton and pop popcorn. The figure below shows the “trumpet horn” shaped opening of a siren, above which a glass tube is suspended; the lower part of the glass tube contains some popcorn kernels, and the upper part shows some popcorn popping upward.

At close range, a high intensity siren could cause human inner ear problems and deafness, and could set your hair on fire, but it could never be a real death ray. For the most part, the siren has received serious study by acousticians so as to make it a more efficient and longer range danger warning device.

Figure. A high intensity acoustic siren being used to pop popcorn.

 

J. D. Maynard
Department of Physics
The Pennsylvania State University
University Park, PA 16802

Popular version of paper 2aID11
Presented Tuesday morning, October 28, 2014
168th ASA Meeting, Indianapolis

4aSCb8 – How do kids communicate in challenging conditions? – Valerie Hazan

4aSCb8 – How do kids communicate in challenging conditions? – Valerie Hazan

Kids learn to speak fluently at a young age and we expect young teenagers to communicate as effectively as adults. However, researchers are increasingly realizing that certain aspects of speech communication have a slower developmental path. For example, as adults, we are very skilled at adapting the way that we speak according to the needs of the communication. When we are speaking a predictable message in good listening conditions, we do not need to make an effort to pronounce speech clearly and we can expend less effort. However, in poor listening conditions or when transmitting new information, we increase the effort that we make to enunciate speech clearly in order to be more easily understood.

In our project, we investigated whether 9 to 14 year olds (divided into three age bands) were able to make such skilled adaptations when speaking in challenging conditions. We recorded 96 pairs of friends of the same age and gender while they carried out a simple picture-based ‘spot the difference’ game (See Figure 1).
Hazan1_fig
Figure 1: one of the picture pairs in the DiapixUK ‘spot the difference’ task.

The two friends were seated in different rooms and spoke to each other via headphones; they had to try to find 12 differences between their two pictures without seeing each other or the other picture. In the ‘easy communication’ condition, both friends could hear each other normally, while in the ‘difficult communication’ condition, we made it difficult for one of the friends (‘Speaker B’) to hear the other by heavily distorting the speech of ‘Speaker A’ using a vocoder (See Figure 2 and sound demos 1 and 2). Both kids had received some training at understanding this type of distorted speech. We investigated what adaptations Speaker A, who was hearing normally, made to his or her speech in order to make themselves understood by their friend with ‘impaired’ hearing, so that they could complete the task successfully.
Hazan2_fig
Figure 2: The recording set up for the ‘easy communication’ (NB) and ‘difficult communication’ (VOC) conditions.


Sound 1: Here, you will hear an excerpt from the diapix task between two 10 year olds in the ‘difficult communication’ conversation from the viewpoint of the talker hearing normally. Hear how she attempts to clarify her speech when her friend has difficulty understanding her.


Sound 2: Here, you will hear the same excerpt but from the viewpoint of the talker hearing the heavily degraded (vocoded) speech. Even though you will find this speech very difficult to understand, even 10 year olds get better at perceiving it after a bit of training. However, they are still having difficulty understanding what is being said, which forces their friend to make greater effort to communicate.

We looked at the time it took to find the differences between the pictures as a measure of communication efficiency. We also carried out analyses of the acoustic aspects of the speech to see how these varied when communication was easy or difficult.
We found that when communication was easy, the child groups did not differ from adults in the average time that it took to find a difference in the picture, showing that 9 to 14 year olds were communicating as efficiently as adults. When the speech of Speaker A was heavily distorted, all groups took longer to do the task, but only the 9-10 year old group took significantly longer than adults (See Figure 3). The additional problems experienced by younger kids are likely to be due both to greater difficulty for Speaker B in understanding degraded speech and to Speaker A being less skilled at compensating for this difficulties. The results obtained for children aged 11 and older suggest that they were using good strategies to compensate for the difficulties imposed on the communication (See Figure 3).
Hazan3_fig
Figure 3: Average time taken to find one difference in the picture task. The four talker groups do not differ when communication is easy (blue bars); in the ‘difficult communication’ condition (green bars), the 9-10 years olds take significantly longer than the adults but the other child groups do not.

In terms of the acoustic characteristics of their speech, the 9 to 14 year olds differed in certain aspects from adults in the ‘easy communication’ condition. All child groups produced more distinct vowels and used a higher pitch than adults; kids younger than 11-12 also spoke more slowly and more loudly than adults. They hadn’t learnt to ‘reduce’ their speaking effort in the way that adults would do when communication was easy. When communication was made difficult, the 9 to 14 year olds were able to make adaptations to their speech for the benefit of their friend hearing the distorted speech, even though they themselves were having no hearing difficulties. For example, they spoke more slowly (See Figure 4) and more loudly. However, some of these adaptations differed from those produced by adults.
Hazan4_fig
Figure 4: Speaking rate changes with age and communication difficulty. 9-10 year olds spoke more slowly than adults in the ‘easy communication’ condition (blue bars). All speaker groups slowed down their speech as a strategy to help their friend understand them in the ‘difficult communication’ (vocoder) condition (green bars).

Overall, therefore, even in the second decade of life, there are changes taking place in the conversational speech produced by young people. Some of these changes are due to physiological reasons such as growth of the vocal apparatus, but increasing experience with speech communication and cognitive developments occurring in this period also play a part.

Younger kids may experience greater difficulty than adults when communicating in difficult conditions and even though they can make adaptations to their speech, they may not be as skilled at compensating for these difficulties. This has implications for communication within school environments, where noise is often an issue, and for communication with peers with hearing or language impairments.

 

Valerie Hazan – v.hazan@ucl.ac.uk
University College London (UCL)
Speech Hearing and Phonetic Sciences
Gower Street, London WC1E 6BT, UK

Michèle Pettinato – Michele.Pettinato@uantwerpen.be
University College London (UCL)
Speech Hearing and Phonetic Sciences
Gower Street, London WC1E 6BT, UK

Outi Tuomainen – o.tuomainen@ucl.ac.uk
University College London (UCL)
Speech Hearing and Phonetic Sciences
Gower Street, London WC1E 6BT, UK
Sonia Granlund – s.granlund@ucl.ac.uk
University College London (UCL)
Speech Hearing and Phonetic Sciences
Gower Street, London WC1E 6BT, UK
Popular version of paper 4aSCb8
Presented Thursday morning, October 30, 2014
168th ASA Meeting, Indianapolis