You have to look at ALL of the specs, inch by inch. If they spec "at one watt", the spl levels are directly comparable regardless of impedance. If they spec "at 2.83 volts" and are a relatively lower impedance speaker, they are playing games. This takes into account that they are "averaging" the spl level over the "midband" frequency range and not just picking some arbitrary frequency that may produce a slightly higher peak SPL.
With a speaker that is "nominally" 8 ohms, 2.83 volts is equivalent to one watt of power. Applying the same amount of voltage into a "nominal" 4 ohm speaker is NOT one watt of power. That is because, even though the voltage is the same, current is doubled due to the speaker having half the resistance. The 4 ohm speaker may appear to be more efficient or as efficient, but in reality, it is sucking up measurably more power to obtain those spl levels.
Another little known trick is to spec the speaker at 3 ft instead of at 1 meter. While this is only a matter of 3.5" or so, taking the measurement a little closer and "fudging" the figures can help them out a bit. Combine the distance factor with a higher current level into a low impedance load can make things seem quite a bit "sweeter" than they really are.
So, to compare apples to apples, you have to have the same reference level i.e. X amount of wattage into the speaker and measured at the same distance. Otherwise, you can end up with more power ( same voltage but more current ) measured at a closer distance.
Even with all of that in mind, you need to realize that different types of speakers ( dynamic "cone" drivers, planars / ribbons / e-stat's, horns, etc...) will produce different spl levels at various distances EVEN if they may produce the same spl at 1 meter. This all has to due with how they load into the room, their individual dispersion characteristics and radiation patterns, etc...
Like anything else, there are TONS of ways to create specs, interpret specs and "bamboozle" the unsuspecting. That is why so many "old timers" say things to the effect that specs are relatively useless. Even with the few rules that the FTC has created to "protect the consumer", those rules have some BIG loop-holes in them. Your best bet is to keep your eyes and ears open and try to experience as much for yourself as you can. First hand experience can be a HELLUVA teacher... Sean
>
With a speaker that is "nominally" 8 ohms, 2.83 volts is equivalent to one watt of power. Applying the same amount of voltage into a "nominal" 4 ohm speaker is NOT one watt of power. That is because, even though the voltage is the same, current is doubled due to the speaker having half the resistance. The 4 ohm speaker may appear to be more efficient or as efficient, but in reality, it is sucking up measurably more power to obtain those spl levels.
Another little known trick is to spec the speaker at 3 ft instead of at 1 meter. While this is only a matter of 3.5" or so, taking the measurement a little closer and "fudging" the figures can help them out a bit. Combine the distance factor with a higher current level into a low impedance load can make things seem quite a bit "sweeter" than they really are.
So, to compare apples to apples, you have to have the same reference level i.e. X amount of wattage into the speaker and measured at the same distance. Otherwise, you can end up with more power ( same voltage but more current ) measured at a closer distance.
Even with all of that in mind, you need to realize that different types of speakers ( dynamic "cone" drivers, planars / ribbons / e-stat's, horns, etc...) will produce different spl levels at various distances EVEN if they may produce the same spl at 1 meter. This all has to due with how they load into the room, their individual dispersion characteristics and radiation patterns, etc...
Like anything else, there are TONS of ways to create specs, interpret specs and "bamboozle" the unsuspecting. That is why so many "old timers" say things to the effect that specs are relatively useless. Even with the few rules that the FTC has created to "protect the consumer", those rules have some BIG loop-holes in them. Your best bet is to keep your eyes and ears open and try to experience as much for yourself as you can. First hand experience can be a HELLUVA teacher... Sean
>