Equalizing a loudspeaker response can worsen off-axis sound quality.

Evidence

In practice, there are always limitations to how appropriate rigorous equalization is. Figure 4.5 illustrates an example of a loudspeaker response and several equalized responses (Karjalainen et al., 1997). Higher orders of EQ filters flatten the response increasingly, finally practically flattening the equalized response. However, one must remember that the equalized magnitude responses shown are valid only along the main axis of the loudspeaker in a free field, and that in other directions the response may be worse than the original unequalized one. In addition, equalization increases the movement of the loudspeaker diaphragm at amplified frequencies, which may also amplify some non-linear distortion components. Furthermore, in some cases, such frequency-specific amplification may also amplify unwanted noise originating from some earlier part of the signal chain. — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 523

Categorization

• QUESTION: Interesting that flattening magnitude response along one axis makes off-axis response worse — worth understanding why and whether it’s ever worth doing.
• corroborated: 2 independent passages support this claim — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 523