Effect Ohms Have on db and Speaker Sensitivity

I'm not sure if this is why you could be confused, but some driver manufacturers do offer 2 versions of the same woofer: an 8 and 4 Ohm.

The 4 Ohm allows twice the current to flow in the coil, which means 2x the power for the same V will be dissipated. The advantage in this particular case, everything else being equal, is the 4 Ohm version gains 3 dB of sensitivity.

It is only in this type of situation, where everything except the voice coil impedance is the same, that we can generalize and say that 4 Ohm versions are more sensitive. We cannot take this and compare drivers in general even within the same manufacturer. The magnetic strength, gap, weight, cone diameter, suspension, all come into play.

Thank you for all the feedback.

Thanks to Almarg for the math lesson.

Maybe I should have started by stating my issue:

I have speakers with 97db efficiency into nominal 6 Ohms. I'm running a pair of 300B mono amps......about 8 watts. 

I thought that 97db speakers at 6 Ohms would be efficient enough for the 300B's to really "sing,"  however, they lack the bass depth and slam that we all enjoy.

I may need a bit more power, or a speaker that is 97db into 8+ Ohms.

Try the 4 ohm taps if it's got them. 

8 Ohm taps only.....unfortunately.

There are a many possible causes of the symptoms you have described that are more likely to be responsible for the issue than the fact that the speakers have a 6 ohm nominal impedance instead of an 8 ohm nominal impedance. One such factor being how the impedance of the particular speaker varies from its nominal value over the frequency range. Another possible factor being the output impedance of the particular amp and how it interacts with the variation of speaker impedance over the frequency range.  Another possible factor being an impedance incompatibility between the preamp and the amp.

More power may not be the answer either.

What I suggest is that you indicate the specific make and model of the speakers, the amp, and the preamp or other component that is driving the amp. Some idea of the kind of music you listen to, how loud you listen, room size, and listening distance may also be helpful. Hopefully that information will enable us to provide suggestions that focus on your specific situation.

Regards,
-- Al