Speakers in series

[BobbyN]

I wrote this just out of curiosity. Sometimes funny things can happen "acoustically." To answer one person's question, I meant the speakers, not just a driver.
One of these days when I have lots of ambition (moving heavy speakers takes ambition) I may give it a try just for the halibut.

 

[bowtie427ss]

Is there no BSEE out there that can state what the electronic effect will be?

If it adds weight for you, the engineer's name is Barry Ferrell. He's been at QSC since 1990.

The following from a loudspeaker, and amplifier engineer:

When a loudspeaker is connected to an amplifier output, the amplifier provides better control of the speaker motion and the speaker has a flatter frequency response if the output impedance of the amplifier is a lot lower than the impedance of the speaker. This is most often specified as the “amplifier damping factor” into 8 ohms, rather than the actual amplifier output impedance. If the amplifier has a damping factor of 250, the output impedance is 8 ohms divided by 250, or 0.032 ohms. With such a low output impedance, the frequency response of the voltage supplied to the speaker is very flat and the amplifier maintains good control over the cone motion at low frequencies.

If a second speaker is placed in series with the first speaker, each speaker is driven by the combined impedance of the amplifier plus the impedance of the other speaker. Instead of a damping factor of 250, it now drops to slightly less than 1, since the new impedance seen by each speaker is 8.032 ohms (the other speaker plus the amplifier output impedance). It gets even lower when speaker cable resistance is added in. The frequency response is affected by any mismatch in the impedance curves of the two speakers.

 

[swechsler]

If a second speaker is placed in series with the first speaker, each speaker is driven by the combined impedance of the amplifier plus the impedance of the other speaker. Instead of a damping factor of 250, it now drops to slightly less than 1, since the new impedance seen by each speaker is 8.032 ohms (the other speaker plus the amplifier output impedance). It gets even lower when speaker cable resistance is added in. The frequency response is affected by any mismatch in the impedance curves of the two speakers.

OK, so this would also appear to also affect woofers in series in a single cabinet, which contradicts what was written earlier. So what gives?

 

[bowtie427ss]

So what gives?

Identical drivers in the same pass band, wired in series, will be seen electrically as a single load within the speaker system. The resultant parameters are calculable.

I suspect that when all the nits are sorted out, there are probably specific drivers that fare better than others in a series arrangement, or at least certain parameters that make a driver more or less desirable for series wiring.

As mentioned earlier in the thread, it's likely that a 2-way speaker with a simple 1st order filter on the tweeter is going to play better when wired in series than speaker systems having more complex networks and steeper filters.

 

[w3jn]

Speakers connected in series, madness. Try connecting two light bulbs in series and turn it on!

Incandescent lightbulbs are resistive loads, do not generally have inductors/capacitors in series or parallel with the load, are not a reactive load, and do not care about their source impedance. Apples and oranges. The answer is more complex and it would depend largely on the makeup of the crossover and the amplifier. But you're most likely not gonna ruin anything by trying.

 

[C Hart]

If it adds weight for you, the engineer's name is Barry Ferrell. He's been at QSC since 1990.

Hmm. I'm sure it must be correct since he knows way more than I do, but it is still puzzling. Why isn't the impedence of the system (8 ohms + 8 ohms) / 250, or .064 ohms? How is a 2x8 ohm load different than a 16 ohm load? Would a nominal 16 ohm speaker cause the same issue? Re damping, isn't that just a concern at resonance, i.e. to prevent coil-generated current in the circuit, so how would it affect sound at non-resonant frequencies?

Perhaps we've beaten this to death, but I too am curious and might do the experiment.

 

[bowtie427ss]

Perhaps we've beaten this to death

No no no, you raise valid points and questions to which i would also like definitive answers.

 

[Nyjblbob]

questions to which i would also like definitive answers.

To complicate matters even more,
Back to My buddies -4 ohm Alon speakers, and when playing through his Tube Amp, a Cary Sla-80
80 watt, pentode, 40 wpc in triode with both 4 ohm and 8 ohm taps.
He says he Likes the 8 ohm tap better, better bass. "Correction"
and obviously with 86db speakers in the more powerfull 80 watt mode.
Yet on the SS Marantz Av receiverand Alons, it's a NO Fly Zone.
Probably due to the Massive hunk of Iron in the power supply with the Cary.

 

[bowtie427ss]

Yet on the SS Marantz Av receiverand Alons

I would guess that the mid level Marantz has(price point engineered) current limiting in it's design. Current limiting, and speakers that present a nominally low and dynamic impedance curve are almost never going to make for a happy marriage at anything above library listening levels. Put a pair of easy to drive JBL's or Altecs(or Klipsch) on the Marantz, and i'll bet it sounds surprisingly good.

The Cary would be much more robust top to bottom and care a lot less about what's strapped to it's terminals.