Jerry,
The speaker is like a LC circuit and it has a resonance. The frequency is
dependant on the
mass of the cone and the elasticity of the suspension (including the
enclosure air).
The for formula is the same as LC resonance.
To determine the mass I used to measure the first a peak in voltage and
then attach a
know weight like 1gram and get a second peak. Using these two we can
calculate the
mass of the cone and with that know the elasticity.
I used to change the resonance by spray painting the cone a little! I
have seen woofers
that had paint and sand type particles on the cone to increase its
mass!
In bass reflex the box and the duct has it own resonance which shows up
in the tests.
Raj
At 22-03-18, you wrote:
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Interesting, though raises more
questions than it gives answers to.
The graphs show different speaker responses, mostly for no particular
reason.
At the start he defines resistance and impedance as two different things
(probably should read resistance and reactance),
then in the graphs it properly shows complex impedance as ohms of
impedance with a phase angle,
which is the combination of resistance and reactance.
More puzzling to me, he shows a self resonance at 130 hz or so in the
first graph,
and the phase angle flips there from positive to negative just like an LC
circuit.
But "impedance rise due to voice coil inductance" in the second
graph doesn't take over till 1khz and beyond.
What exactly is going on at self resonance??? That's a central
concept here, and left unexplained.
And seems a resonance at 150 hz would be extremely disruptive to the
sound spectrum we hear.
He shows a base-reflex speaker's impedance to have two peaks (at two
different frequencies),
then claims that if they are the same height (same max impedance on both
peaks)
then the "resonant frequency of the speaker matches the resonant
frequency of the box".
But the frequencies certainly don't match.
Not sure I trust anything in the writeup now, but that second graph is
interesting.
Shows his nominally 4 ohm speaker to have a dc resistance of 3.2 ohms
and a resonance at 30hz of about 31 ohms.? At resonance, it's far
from 4 ohms.
Conclusion:? A 4 ohm speaker can have drastic variations in
impedance
over the audio frequency range.
Jerry, KE7ER
On Thu, Mar 22, 2018 at 06:03 am, Raj vu2zap wrote:
- Worth reading this page.
-
Raj vu2zap