Even It Out
The front-to-back loudness difference is a major issue for a lot of smaller sound systems, and it’s a matter of height. With the edge-of-platform placement, the nearest seats are just a few feet away from the loudspeaker, while the rear seats are much further away. Because sound waves lose loudness over distance, the front ends up much louder than the back.
Figure 2A shows the side view, with the horizontal blue line indicating the ear height of a seated audience. Figure 2B shows the high-frequency coverage from the loudspeaker. Yikes!
The folks in the front are getting blasted. Since each color bar on these diagrams indicates 3 dB of loudness, we can determine that the front seats are 18 dB louder than the rear seats. There’s no way to mix the service at a level that’s comfortable for everyone – that range is just too big.
Figures 2C and 2D show what would happen if we spend $50 on a loudspeaker stand. Much better! By getting the loudspeaker a bit further away from the front seats, we cause a bit of level drop down in front.
Additionally, since the loudspeaker is aimed towards the rear of the seating section, the front seats are on the edge of the coverage pattern, which allows us to take advantage of the fact that loudspeakers lose level as we move off center. Now our listeners are all within a 9 dB range from front to back, which is an incredible improvement just from buying a loudspeaker stand.
The Bottom Line
In summary, support the goal of “putting the sound where the people are” with these three simple steps:
• Give each loudspeaker its own area to cover
• Adjust the horizontal aim through the middle of the section
• Adjust the vertical aim towards the rear seats, getting height where possible
As an added bonus, the division of loudspeaker labor means it’s easy to turn down an amplifier if a certain section is too loud.
One major point to mention here: a loudspeaker should absolutely never be suspended by its handles or by any method other than what is designed, tested, and recommended by the manufacturer. Period.
In virtually every case of rigging failure, human beings have done something they shouldn’t have. This is not a good reason to be on the front page of the newspaper. Rigging work should only be performed by qualified professionals.
