Finally, the program evaluates what would happen if less horns were used. This is explained in the manual on page 14. If the program determines that less horns can be used without exceeding the maximum desirable spacing for 90 dBspl ( up to 75') - AND if the extra spacing that results from less horns will require no more than an additional 0.99 dBspl of output from the horns - then the program makes an automatic adjustment. This is indicated by an asterisk on the resulting configuration screen. The program will not ask if you want this adjustment because the resulting spacing is still within the standard spacing range - if the result of less horns was non standard spacing, the program would prompt you before proceeding.
In this case -
For the 22 foot mounting height, the program determined that increasing the horn output by 0.99 dBspl would allow one less row. This resulted in in 77 total horns.
For the 36 foot mounting height, the program determined that increasing the horn output by 0.99 dBspl would allow one less horn per row AND 2 less rows. This resulted in 60 total horns.
In both cases the horn spacing was less than the maximum desirable spacing for a 90 dBspl ambient noise level.
The key is this, feel free to experiment with different spacings for your design - that's the beauty of computer design. Once you get to the resulting configuration screen, you can enter any spacing that you want to evaluate right on your computer's numeric keypad - or press +/- to increment spacing by +/- one foot. The program will initially pick a perfectly valid configuration - but it's not the only one - and it may or may not be the right one for your application . . .
Question: When I use Option A, the answer refers to a 5 watt horn producing 113.45 dBspl at 4 feet. The 5 watt horn I am using is not that efficient and only produces 107 dBspl at 4 feet. Can I just use a 15 watt horn tapped down to a lower wattage to achieve the suggested 113.45 dBspl at 4 feet ?
Answer: Yes, the important piece of information is the horn's output level, not the horn's wattage. Option A assumes that 5 watt horns produce up to 116 dBspl at 4 feet, 15 watt horns produce up to 121 dBspl at 4 feet and 30 watt horns produce up to 124 dBspl at 4 feet. Check the manufacturer's rating for the horn that you are using. Incidentally, if the manufacturer provides dBspl at 1 meter specs, simply subtract 1.7 dBspl to convert to dBspl at 4 feet (4 feet is a longer distance than 1 meter).
Question: Can I force Option B (ceiling speaker configuration) to use 25 foot speaker spacing ?
Answer: Yes, simply enter a 12 1/2 foot mounting height. The "with background music" solution uses a spacing of twice the mounting height.
