Impdence Question

"The only practical way to increase driver impedance is to either wire two drivers in series or use a transformer."

Do not connect speakers in series because it will lower damping by amplifier (speakers isolate each other from the amp) - poor bass definition.

Audiokinesis - JBL in users manual for GT4 car subwoofer system states:

"We recommend that you avoid
connecting separate woofers in
series. The amplifier-damping
factor (the amplifier’s ability to
control the motion of the woofer
is expressed as a ratio of termin
impedance (the sum of speaker
impedance, wire resistance and
the D.C. resistance of any
crossover coil connected to the
woofer) to amplifier-output
impedance. Therefore, connectin
separate woofers in series
reduces the damping factor of
the amplifier to a value less
than 1. This will result in poor
transient response. "

and the link is here: http://manuals.harman.com/JBL/CAR/Owner's%20Manual/15515%20GT4%20Man_ENG.pdf

Of course they might be wrong.

Sorry - link got shortened in my last post - here it is again:

http://manuals.harman.com/JBL/CAR/Owner's%20Manual/15515%20GT4%20Man_ENG.pdf

System doesn't like long links and shortens them.

The way I see it speakers is controlled when EMF generated by the speaker is
shorted. Just take speaker and move/press its membrane - it moves freely.
Now try to repeat it with speaker shorted by wire - membrane won't move.
When you have two speakers in series one sees impedance of another in
series. No matter what will happen with EMFs of two identical speakers
impedance of another speaker won't disappear.

DF is defined as speaker (and not the speaker box) impedance over amps
impedance. If my 8 ohm woofer has 0.1 ohm inductor in series inside of the
box DF will drop to 80 even if amplifier's output impedance is zero.

As far as I know speaker with identical woofers have them always in- parallel.
There are even bass players forums where they mention poor definition of in
series wired speakers.

Duke - I like your example wit divided coil, but I think that the difference is that EMF of both coils reacts with the speaker membrane motion while in case of two separate speakers it doesn't - even if they are driven with the same back EMF (same signal). What might happen is that total EMF voltage will be sum of them but impedance each of them sees will be 4 ohm and not sub-ohm amp's output. Two separate speaker coils are just not the same as one coil.

My practical experience tells me that woofers in series have "wooly" sound, but it was long long time ago and my memory is fuzzy. I tried to find something more on the internet to support my point but found instead that opinions are divided. Sweetwater (music store) FAQ agrees with your position - I have to thing about it.

Oops - should be "I have to think about it" - my english is bad but not that bad.

Duke - I'm leaning toward your view. I think that my previous experience with in-series woofer connection might have to do with other factors. One of them is doubling inductance in the circuit while another is getting stronger resonanses since they might be slightly different, power being proportional to square of the increased voltage on the speaker.

As for "winning" - I have met here many "scientists" with extremely high credentials that prevented them from learning.