Brain gone dead - question on drivers in series

[Henry8]

I have two identical drivers at 91dB and 4ohms.
If I connect them in series the overall impedance is 8ohms.
But what is the overall sensitivity?

[wintermute]

Overall sensitivity I believe will be the same. From memory (best check) two drivers results in 3db increase in spl. 8 ohms instead of 4 ohms (seen by the amp) results in 3db decrease in spl so overall the end result is the same spl as a single driver at 4 ohms, ie 91db.

Power handling should be better and amp will be working less.

Tony.

[speaker dave]

Originally Posted by wintermute

Overall sensitivity I believe will be the same. From memory (best check) two drivers results in 3db increase in spl. 8 ohms instead of 4 ohms (seen by the amp) results in 3db decrease in spl so overall the end result is the same spl as a single driver at 4 ohms, ie 91db.

Power handling should be better and amp will be working less.

Tony.

Close.

Two drivers in series will both share half the voltage. That is a 6dB drop in each. On axis they will sum in phase so that will double pressure for a 6dB gain. Net effect is the same sensitivity, still 91dB for the stated voltage.

Did the efficiency change? You get the same output with half the current so the wattage halves, but you have increased the directivity index 3dB at upper frequencies, which accounts for the hf difference. At low frequencies there really is a 3dB efficiency increase.

David S.

[domtweaker]

One more thing

You will change the damping of the whole system too.

I was told not to do it by Skanning boys unless you really have no choice.

You could run one of the woofers Active as lower bass .

cheers

[speaker dave]

Originally Posted by domtweaker

One more thing

You will change the damping of the whole system too.

I was told not to do it by Skanning boys unless you really have no choice.

You could run one of the woofers Active as lower bass .

cheers

No, since both woofers have identical impedence curves they always split the voltage in half. Damping doesn't change.

David S.

[SY]

I don't see how the damping is changed as long as the drivers are the same. The drive voltage has to be equal across each driver by symmetry.

edit: crossposted with Dave, sorry!

[domtweaker]

I have two identical woofs too and I was advised not to do it .

better to use sep amps two 4 ohm loads instead of series 8 ohm ?

That comes from Audio Technology guys ? I dont think they would be steering me wrong?

[domtweaker]

so what benefits do you get ?? From series hook up ??

[SY]

If you have something like a tube amp where you can change transformer taps, you have twice the efficiency and reduce the transformer turns ratio by 30% or so. Or if you want to keep sensitivity constant for matching with other drivers. or if you want to avoid low impedance dips, series may be a viable option.

[speaker dave]

Originally Posted by domtweaker

so what benefits do you get ?? From series hook up ??

For me it was always about doing slim tower speakers with 2 woofers. How do you connect them? If the impedance is on the high side then parallel them and cut it in half. If it is low to begin with then series connection is your only choice.

I will concede that series connected woofers can have slight issues if the woofers aren't fairly well matched in impedance. They might also be more prone to DC offset (in opposite directions) especially if they share the same cavity. But series connection, or series parallel connection, is pretty common.

(Hey Sy, great minds think alike...)

David S.