Originally Posted by SoundSparks
Could you please help me to understand if the sensitivity quoted at “2.0 volts, free air” is the same as quoted at “2.0 V at 3.3 ft, free air”, is the same as quoted at “1 W at 1 m”, and in case of the 210RT’s is 95 dB?
Actually, this is a very tricky question thanks to the marketing departments of large manufactures. The 1w doesn't tell you how many volts was applied. If the sensitivity spec is 1w than it could be based off the average impedance or the normalized impedance. The "normalized" impedance is based off the minimum resistance and is used to properly match an amplifier to a speaker. The minimum impedance shouldn't be less than 70% of the normalized impedance (4 ohm = 2.8 ohm). So, if you see a speaker that is rated at 8 ohm but has a minimum impedance of 3.1 ohm than it's really a 4 ohm speaker even though is might have an 8 ohm average impedance. If a speaker has a normalized 4 ohm impedance than 2.0 volts would normally be 1 watt however if that normalized 4 ohm speaker has an average impedance of 10 ohms than 3.16 volts would equal an average of 1 watt (2.5 watts at 4 ohm).
Speakers benefit from boundary gain. If a speaker is rated at ground plane (1/2 space) than the measurement would be 6db higher than a free air (full space) measurement. Just to throw a wrench in the mix, some manufactures are using an "axial" spec which is 3db more than free air and 3db less than ground plane.
So, a 2.0 volt, free air spec will result in the lowest number of all other ways of rating the sensitivity of a 4 ohm speaker which is why customers have noted that the Noesis 212HTR (101db/1m/2.0v, free air) was more sensitive than speakers with a 104db/1w/3.3ft rating (1m = 3.3ft).
Even still, JTR is going to adjust its specs. The Noesis 212 was measured at 105db, 2.0v, halfspace by Data-Bass which would be 99db, 2.0v, free air or 102db, 2.83v, free air or 102db, 2.0v, axial or 105db, 2.83v, axial. The Noesis 215 was measured at 100db, 2.0v, halfspace by Data-Bass which would be 94db, 2.0db, free air or 97db, 2.83v, free air or 97db, 2.0v, axial.
To be the most transparent, I think we are going to list several different ratings so that people can compare them to others.