CLASSROOM AMPLIFICATION: WHO CARES? AND WHY SHOULD WE? James Blair and Jeffery Larsen Utah State University ASHA, San Diego, 2011

Transcription

1 CLASSROOM AMPLIFICATION: WHO CARES? AND WHY SHOULD WE? James Blair and Jeffery Larsen Utah State University ASHA, San Diego, 2011

2 What we know Classroom amplification has been reported to be an advantage to teachers and children in schools Teachers are less fatigued at the end of the day Teachers report students are more attentive Teachers experience less vocal strain Students like it when the systems are used ( I hear better, and don t have to strain to understand. ) When surveyed on what equipment has the greatest direct influence on learning, classroom amplification is ranked as the first or second most important aide.

3 What then are the problems Larsen and Nye (2010) did a systematic review of the literature and found that the research that has been completed fails to demonstrate conclusively that classroom amplification makes any significant difference. The Acoustical Society of America released a position statement in 2006 claiming that classroom amplification, as a general policy, is a bad idea. The concerns expressed are: The systems will amplify bad acoustics The equipment can break down They will add more sound to an already loud room It does not address student-to-student communication and student to teacher communication The recommended solution is to fix the acoustics properties

4 Most new building meet ANSI standards for acoustics, so we studied five Five different classrooms used in the study All were similar in size all 4 th grade 30 to 35 feet deep 32 to 40 feet wide All met ANSI standard for noise and reverberation RT Noise Criteria 32 db Four teachers used classroom amplification, one did not A pass-around microphone was used in one classroom regularly, but either sporadically or not at all in the other three classrooms

5 Procedures A measuring microphone was placed on a tripod, positioned at the level of the child s ear (placed near a child s ear) Measurements were made at 9 different locations in each room (back center, left back, right back, left center, middle center, right center, front right, front left, front center) Measurements were made in 10 minute increments The Time, Energy, Frequency (TEF) system was used to obtain measurements

6 Measured the impact of infrared classroom amplification Obtained signal-to-noise ratios were on average between +13 to +20 dba at every position measured in the rooms One classroom was not fit with a classroom system and all other teachers were asked to turn off their systems for 5 minutes during the data collection The average signal-to-noise ratios were between +2 and +6 dba without amplification

7 Compared amplified to unamplified Teacher asked children to read in a random order around the classroom. Average sound level at the microphone based on distance away from the microphone. 2 feet - 59dB 3 feet - 56 db 6 feet - 55 db 12 feet - 46 db There are times when the sound level is 13 db less intense than at other times.

8 Results: Unamplified Classroom Teacher s measured vocal intensity; Front of the room at nearest student s desk was 58 dba, with a range of 50 to 65 db Middle of the room at child s desk, the level was 52 db, again with a range of 40 to 60 db At the most distant point, this is measured as being 18 feet from the most common place from which the teacher presents information, was 48 db with a range of 40 to 52 db

9 Implications The results indicate that, without amplification, at the front of the room the average signal-to-noise ratio was +15 with a range between +8 and +20 In the middle of the room the S/N ratio was 8 db with a range between +1 and +10 At the back of the room the S/N ratio was 0 db with a range of -15 to +6 db Depending on where the child is seated at any given time changes the amount and quality of input available There are times when everything is audible and other times when information is not audible at all The child who has any kind of hearing problem is getting at best variable auditory input (about 10% of the students) Remember this room meets ANSI standards

10 Amplified Classrooms In these classrooms all speakers were in the ceiling, providing direct sound to the children. No matter where the child was seated in the room they were getting no less than a +10 signal-to-noise advantage. When the hand-held microphone was used the same advantage was present for the children as for the teacher, when not used it was like the results in an unamplified room.

11 The results are startling, but are they reliable? We selected a building that was built 150 years ago, and has been renovated and expanded several times during that time. The school had been fit with classroom amplification twoyears before the research was begun. The amplification systems were installed by the company who sold the equipment when classrooms were empty. The installers set the equipment at levels that sounded appropriate to them. This appears to be a method generally used to install equipment in classrooms.

12 Procedures Measurement were taken in 14 classrooms approximately half-way between the closest and most distant students in the class in the center of students. The measurements were taken at a level that was close to the ear level of an average student in the class. Measurements were taken while class was in session and the teacher was talking to the class. We asked each teacher to talk using the microphone and then to talk while the microphone was turned off. We took measurements every 15 seconds for a period of ten minutes in each classroom. We averaged the sound pressure level in dba for both amplified and unamplified conditions.

13 Results While we found that on the average across all classrooms the average difference between the amplified and unamplified teacher s voice was a +13 db. This is about what we would like to see for a signal-tonoise ratio. However, the averages between classrooms was +5 to +23dB. In other words some teachers voices were well above the recommended signal-to-noise levels and others were considerably below. Parenthetically, those teacher whose output was only +5 db reported that they did not see any advantage to using the system, while those who were above +12 db all reported that they believed that the students responded better to them when they used the system compared to when they did not.

14 Implications There needs to be someone in the school who can adjust the system so that the teacher s voice level is consistently 12 db louder than the noise floor during instructional periods. Speech-Language Pathologists are in a position to influence their school districts to implement this procedure Since the children we serve in the schools have speech, listening, or language problems it is critical that they all have access to clear, intelligible speech all day every day.

15 Summary We need to do better in helping kids have an acoustic environment where they can have the best chance for success The current debate between whether its better to modify classrooms to improve classroom acoustics or put a classroom amplification system is a distraction we need both We need more and better research to optimize all options to help remove the classroom as a barrier to learning We need to have advocates in the schools that understand the critical value of classroom amplification and do a better job of making sure that classrooms are amplified appropriately and that teachers know how to use the systems effectively.

16 Some other classroom amplification issues we have been looking at Different loudspeakers Loudspeaker placement Why current published evidence is not compelling enough and what we need to do about it

17 Loudspeaker characteristics Two-way loudspeakers Woofers and tweeters Results in an increasingly directive beam of sound with increasing frequency Flat panel loudspeaker Multiple excitation points Spreads high frequencies well Not as great for amplifying low frequencies

18 Distributed Mode Loudspeaker Several trade publications claim the DM loudspeaker should produce diffuse and uniform spread of energy (Azima, 2004; & Day, 2008) Only one scientific study comparing a single DM to a single TW (Prendergast, 2001) DM produced higher mean speech discrimination scores (66% vs. 58%) > or = speaker output at 44 of the 48 measurement locations Design Flaw

19 Comparison of loudspeaker types Measures were made in an anechoic chamber and in a classroom chosen for its acoustic characteristics Classroom characteristics: 0.7 Reverberation time 38 dba ambient noise (unoccupied) Included a CA system utilizing 4 TW loudspeakers Measurements were made every 10 in the front horizontal plane (180 ) 1 meter from the speaker Measured 500 Hz, 1000 Hz, 2000 Hz, 3150 Hz, & 4,000 Hz

20 Anechoic Chamber Measurement 1000Hz

21 Anechoic Chamber Measurement 4000Hz

22 Classroom Measurement 1000Hz

23 Classroom Measurement 4000Hz

24

25

26 Conclusion 1 to 1 comparison the DM outperforms the TW in terms of spread of energy and frequency response (Most likely speech as well) DM great option if portable system is needed or if only 1 speaker is desired More research to see if it can replace a 4 TW system or even a 2 TW system Educational Audiologist role is vital when determining preferential seating

27 Loudspeaker placement Anderson & Goldstein (2004) compared the performance of children with hearing loss with amplified speech through a loudspeaker in the classroom, loudspeakers on the desks of the children, and through the personal FM systems attached to the children s hearing aids The results showed that the children performed best with the personal FM system, then next best with the loudspeakers on their desks, and then the loudspeaker placed in the corner of the room What made the difference in performance? SNR? Speech quality? Critical distance?

28 The placement of speaker debate Choices: Speaker in the front of the room Speakers on the walls Speakers in a cluster Speakers in the ceiling

29 What we found Any speaker is better than none Provided they are turned up loud enough to improve the signal-to-noise ratio The best placement is in the ceiling so as to be over the head of the children. This arrangement provides the most consistent sound to every child in the room. Other arrangements provide variable intensity as the child is moved away from the speaker If only one speaker is going to be used it would be better to place that speaker in the back of the room rather than the front

30 Why is our current evidence not enough? Larsen & Nye (2010) Stephenson (2007) Each found that the scientific validity of the studies was lacking in sufficient strength Heeney (2007) dissertation demonstrated global benefits of classroom amplification The number one problem with most studies is that they did not report the one factor that makes the difference in any study of classroom amplification how the classroom amplification changes the signal-to-noise ratio at the ears of the listeners

31 SUMMARY Who cares about classroom amplification? Well, we do (obviously) Why should anyone care? Because we don t want poor acoustics or insufficient sound to hold kids back in school these are problems we can solve

32 CONCLUSIONS Classroom amplification does work when it is done right Doing it right is not hard, but it does take some effort Thinking about the details like where to put the loudspeaker, what kind of loudspeaker to use, and how close do they need to be to the kids are not trivial details Having someone verify that the intensity is set for optimal results is worth the effort Trained professionals can do this and do it well