What is the sound pressure level at 1 m for 1 W of power under anechoic conditions?
A20 – Conventionally the sensitivity of a speaker is defined as the sound pressure level SPL that would be obtained at 1 m if driven with 2.83 Vrms at its terminals. This corresponds to 1 W input power if the terminal impedance is 8 ohm. The voltage sensitivity has been estimated (Design Models – I) for the PHOENIX as 90 dB SPL for the tweeter, 103 dB for the midrange above 250 Hz which drops to 96 dB at 100 Hz, and for the woofer as 95 dB at 100 Hz decreasing to 85 dB SPL at 30 Hz for a constant 2.83 V across the driver terminals. Since the actual terminal impedances are not 8 ohm, and since each driver is only used over part of its frequency range, because the active crossover limits the range that each amplifier has to cover, the effective load impedances become approximately 4.5 ohm for the tweeter, 3.5 ohm for the midrange and 6.5 ohm for the woofer. Thus in each case it takes more than 1 W to obtain the 1 m SPL given above. The SPL at 1 m for 1 W of power into the effective termi
