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Design: Loudspeaker support Part 1 – Setting the scene

Because design is central to engineering it is also central to developing engineers' eyes. Here is your first encounter with it.
Your first design task is to decide how to safely suspend a heavy loudspeaker above an auditorium. You can pause the video at various points and work things out for yourself, or you can just watch us do it. Either way, it’s a practical application of how two forces acting at a point share a load. The task is to specify the cables and shackles that will suspend the loudspeaker. Performers will be underneath, so it is vital that it is secure, but you don’t want to waste money on items that are bigger than they have to be. To participate, you’ll need pencil, paper, and a scientific calculator. Here is the setup. The loudspeaker will be below a large air conditioning duct.
Two cables have been arranged as shown in the diagram. In fact, it will require two pairs of cables– one pair at the front and one pair at the back. You must specify the size of the front cables and the size of the shackles that will connect them to the loudspeaker. Why two sets of cables? The manufacturer specifies that the front pair of cables must be able to take all of the load by themselves. The main task of the rear pair is to tilt the loudspeaker to the required angle. As you can see, the rear cable runs through a pulley. This way, each cable takes its proper load and the rear support can be adjusted to tilt the loudspeaker.
Each cable of the front pair will be at the same angle, so that the loudspeaker hangs square. The manager of the concert hall would like the loudspeaker to be as high as possible, so the cables have been arranged to be as close to horizontal as possible. This increases the load in the cables. The loudspeaker manufacturer has requirements, too. They provide the mass of the system, and they also specify that we apply a safety factor of 10 - based on breaking load for the cables and the shackles. To simplify the calculations, assume that each pair of cables lies in a vertical plane, like this.
To make it simpler still, assume that the main front pair of cables takes all the load. This could actually be the case if the rear cable is slacked fully off. That’s the task. The next video will guide you through the steps required to select the cables and the shackles.
Because design is central to engineering it is also central to developing engineers’ eyes. Here is your first encounter with it.
You will select components that will meet a requirement safely and at minimum cost.
This video will lay out the problem for you.
The next video will guide you to a design solution.

Talking points

  • Where have you seen loudspeakers suspended above an audience or performers?
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Through Engineers' Eyes: Engineering Mechanics by Experiment, Analysis and Design

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