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Impdence Question

In experimenting with an unusual loudspeaker enclosure for which only a certain high-end car speakers fit the design criteria, there is concern about their low impedance damaging the amplifier. Driver impedance ranges from 2.8 ohms to 3.4 ohms. Will this do harm? And if several speakers are used in a 5.1 surround setup, does this increase the load and the chance of damage?

If the low impedance is indeed risky, is their any means of raising it perhaps by placing something in the chain (other than wiring a pair together for series or parallel operation)?

Thank you in advance.
silas
stringreen's avatar
stringreen
6,468 posts
 
When I was fooling around with adding stereo speakers to my 57 Packard in the "good ol' days" I seem to remember that some speakers had transformers attached to them. ( Sweet ride..staight 8, used more oil than gas)
audiokinesis
2,737 posts
 
It looks like my previous answer didn't make it past the moderators. I have no idea why.

Connecting two drivers in series does not lower the amplifier's effective damping factor - instead, it raises it. Damping factor is the ratio of speaker input impedance to amplifier output impedance.

I have some experience working with series-wired drivers.

Duke
dealer/manufacturer
kijanki's avatar
kijanki
4,428 posts
 
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.
kijanki's avatar
kijanki
4,428 posts
 
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
kijanki's avatar
kijanki
4,428 posts
 
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.
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