Well after several good conversations with Ian, Tom, Alan and Amie we went out back to look at the testing tower. Its always very pleasant spending time with them and getting caught up.
The tower sure looks like a good 100 ft up close. I had hoped to see a sub being tested but the wind had been picking up since early Friday morning as Ernesto continued its course up the East Coast. Nevertheless I did get a demonstration about the testing procedure.
Here is a shot of the weather instrumentation which goes up before every test. The temperature, humidity, barometric and wind readings are transmitted wirelessly to a metre inside the plant.
The environmental guidelines for successful testing seem to be temperature at no less than 10C, low to no wind, and average humidity. Humidity was not a factor I had given much thought too but apparently a high humidity testing environment can have an impact on results. I want to think about that one as it implies high water content in the air can affect wave propagation.
You can't see it in the above picture but there is a wire about 6ft over the platform which runs parallel. A Bruel & Kjaer mic is suspended over the sub or speaker equidistant from its drivers and ports. The mic can be moved along the wire depending on the subs configuration. Why a B & K mic? Its known to be one of the most accurate mics made and at $5,000 each it better be.
Anyway because of the wind, we just hoisted up the instrument cluster. The procedure was simpler than I thought. No winch. There is a pulley on top of the tower and another at the bottom. The platform is lifted by a 3/8" steel wire which is connected to a golf cart by a hook. Driving the cart backwards raises the platform to the desired height. The cart driver looks familiar.
The long distance of the tower requires a power boost and as a result of 100db appears to be the limit of reliable measurements. That's too bad as I look forward to seeing graphs at max output to get a better idea of the subs behaviour under stress. Perhaps a small generator at the tower itself would help matters. Here is a shot of the platform being lifted along with the electrical wires.
This finicky attention to detail and R & D just impresses the hec out of me.