Recently, a new open photoacoustic cell (OPC) has been developed for the determination of both optical and thermal properties of the sample. The OPC can also be applied for the determination of photosynthetic parameters as energy storage and oxygen evolution for in vivo and in situ plant leaves. However, the membrane of the microphone used in this cell inserts a spurious component in the photoacoustic signal of non-opaque samples such as plant leaves. The membrane signal is added to the sample signal, making the analysis more complicated. In the present work, we discuss this problem and propose a simple method to eliminate it.2641700209219