Two loudspeakers \(42.0 \mathrm{~m}\) apart and facing each other emit identical \(115 \mathrm{~Hz}\) sinusoidal sound waves in a room where the sound speed is \(345 \mathrm{~m} / \mathrm{s}\). Susan is walking along a line between the speakers. As she walks, she finds herself moving through loud and quiet spots. If Susan stands \(19.5 \mathrm{~m}\) from one speaker, is she standing at a quiet spot or a loud spot?