15 ohm speakers yea or nay?

In the 1950’s all amplifiers were tube, and many loudspeakers 16 ohm (nominally). The move to solid state amps and lower impedance loudspeakers at the same time (mid-to-late 60’s) was not a matter of coincidence.

One reason the QUAD ESL sounds better with tube amps is because of it’s insane modulus of impedance. Nominally 16 ohm, but up to 32 ohms at low frequencies, down to 1 ohm at high. Used with a typical tube amp (with their relatively high output impedance, and resultant frequency response deviations), the ESL is missing high frequencies, used with solid state missing bass.

@rodman99999 Great article. Once seen it before, however paid greater attention to it this time.  Used the info to determine needs for my Tannoy Sterlings. The recent review of them in Stereophile did raise some concerns.  I am thinking they may need more power (as current)  than I originally thought.  

Thanks.

@yogiboy These days sensitivity (2.83V/1 meter) is how speakers are measured. There was a time when efficiency (1 Watt/1 meter) was the spec instead- back when tubes were King.

2.83 Volts into 8 Ohms is 1 Watt. That is why the seemingly arbitrary number.

When you cut the impedance in half to 4 Ohms, 2.83 Volts is now 2 Watts (which is a 3dB increase). So the impedance makes a difference! You have one speaker that is 6 Ohms and the other is 15. If the sensitivity is the same, for each doubling of impedance the efficiency is increased. So by my calculations the 15 Ohm speakers should sound about 4.5dB louder because they are 4.5dB more efficient.

When you are talking tube amps, because they can’t double power as impedance is halved (like many solid state amps do) the efficiency spec is more important. That means you have to derive it from the sensitivity spec and the impedance of the speaker. How I arrived at my numbers above is 6 is halfway between 8 and 4 Ohms so that’s a matter of 1.5 dB instead of 3 dB (which it would be if the 6 Ohm speaker were 4 instead).

The difference between 8 and 16 Ohms is its doubled, meaning another 3dB difference. I added the 1.5 to 3 dB to get my answer. Its not quite right since the speaker is really 15 Ohms, but its close enough for government work.

Hi Ralph,

Thanks for the great explanation of why the 15 ohm Falcons play louder than the 6 ohm Harbeths. You are a real asset to the Audigon community!

Yogiboy