Oct 19, 2012 1:42 PM, By Bob McCarthy
When are they needed?
MORE FIELD EXAMPLES
The next hall is another (see Figure 2) single balcony. In this case, the over-balcony area is much deeper than the under-balcony. Both levels have a shape factor of around 3.5 and therefore we see under- and over-balcony systems. Because the shape factor is so high we will need to cover as large an area as possible. The limiting factor is how far the delays can go before getting too loud in the closer rows. The over-balcony speakers are power scaled for the much longer distance they need to cover. After the delays are added, the shape factor for the mains is reduced to around 1.3, which means no second set of delays is needed.
A third hall has an easy call for the U/B system (shape factor 3.5), but the over-balcony area is just over the edge at 2.4. The result is a small-scale delay system to cover the last rows.
These are not hard and fast numbers, but the trend lines can help to give the designer confidence in their decision on whether or not to go through the trouble and expense to add a U/B system. See more pictures of example systems and the complete chart that shows the ratios for the many designs I studied on my blog at www.bobmccarthy.wordpress.com.
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