One's own voice (autophony) is transmitted to the ears as direct airborne sound, bone conduction, and indirect airborne sound from reflections characterized by overall gain and spectro-temporal features. This study investigates how the spectral profile and gain of simulated indirect airborne sound, quantified as voice support (STV), affect the speaking voice of talkers. Pairs of participants performed a conversation elicitation task in anechoic conditions. The indirect airborne sound was provided in real-time via open headphones that maintain the direct airborne transmission path. Experimental conditions included high-pass, low-pass, and all-pass versions of STV, each presented at three overall gains, and a Baseline condition with no electroacoustic contribution to STV. The results show an overall speech level reduction of 0.22 dB for every additional dB of speech-weighted STV, i.e., a -0.22 dB/dB slope. There was some effect of STV spectrum on speech: slope for the high-pass condition was steeper (statistically significant) and significantly different from the all-pass slope; spectral balance (2-4 kHz vs 0-2 kHz) of speech showed an interaction effect between gender and experimental conditions. This paper's findings may inform acoustic treatments in environments where overall sound reduction is of interest for favorable ergonomics and occupational health for voice professionals.