Birth of a Classroom Active Speakers System

“Can you help me find a winning sound system for the classroom?” was the briefing from a distributor who wanted to access the education audio market with active speakers.

Their in-house installation company used a sub-woofer with satellite speakers but the speakers were to be mounted either side of an interactive whiteboard so this was not the ideal solution. We had a photo of their sub-woofer and that of a competitor’s but not a lot more to go on.

The challenge was to design an active speakers system for interactive whiteboards that met the acoustic needs of an average classroom with only the minimum of customer input.

We researched the acoustic qualities expected of an average UK classroom, which was not good being a 10 metre by 6 metre room often with concrete floor and walls with windows on one side and full of desks and children. The distance from the whiteboard to the rear of the class was typically 6 metres and average background noise level of around 60dB, mostly expected from the pupils. Research suggest that the signal to noise ratio needs to be at least 15dB above the general noise level. So we were looking to design an active speaker system that was loud enough to be heard, could amplify different sources from the teachers equipment and stand up to the “rough and tumble” of a classroom environment.

We approached several manufacturers to see if they had products that met our developing specification and the target price. We tried and tested two “off the shelf” models but the suppliers did not meet our standards for manufacture and one sample failed on extended testing and they were not suitable for the classroom. We had a favoured manufacturer in mind, they were relatively large which meant they would only be interested if the production volumes were high but they had the engineers and quality systems to get our new product into manufacture. 

The design progressed with steel speaker grilles, special security wall brackets and a wired remote control so that the teacher could control the unit without climbing up a chair to adjust the volume. When we tested a prototype in an anechoic chamber the sound levels at the speaker at 1 metre were fine but at 6 metres the sound level was far far too low, were our calculations wrong?. Then it struck me that a classroom was nothing like a well designed anechoic room with sound absorbing walls. We found a room resembling a UK classroom with concrete floors, walls and ceiling of about the right dimensions. The result a resounding success and the choice of wood cabinet paid off with a better than expected sound quality.

Jennie Zheng is an author who writes articles for EdisAV makers of active speakers

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