Basic speaker Q

P

Phil Allison

Guest
Hi to all,


everyone knows the nominal impedance of a cone speaker is slightly greater
than the DC resistance of the wire used in the voice coil. An nominal 8 ohm
speaker will have about 6 or 7 ohms of DC resistance for example.

Where does the extra 1 or 2 ohms come from ?

Seems from recent postings on other NGs that most folk have this one
wrong.



........... Phil
 
The extra power is mostly converted into heat by the rapid flexing the
suspension material while some is converted to sound. Since most speakers
are not even 1% efficient at converting electricity into sound energy nearly
all the extra power is dissipated in flexing the suspension – i.e. the
spider, surround and cone.
Click to expand...
The conversion (electrical/acoustical power) efficiency is greatly influenced
by the acoustic load on the speaker cone. Horn-loaded speakers have been
quoted at up to 80% (Klipschorns) so the amount dissipated by cone-flexing,
suspension flexing etc is probably not in the "99%" region.
Alan
 
"Phil Allison" <philallison@optusnet.com.au> wrote in message
news:3fa2fd70$0$497$afc38c87@news.optusnet.com.au...
Hi to all,


everyone knows the nominal impedance of a cone speaker is slightly
greater
than the DC resistance of the wire used in the voice coil. An nominal 8
ohm
speaker will have about 6 or 7 ohms of DC resistance for example.

Where does the extra 1 or 2 ohms come from ?
Click to expand...

Z=(R˛ + (2*PI*F*L)˛)**˝

Z is the impedance in Ohms
R is the DC coil resistance in Ohms
F is the frequency in Hertz
L is the inductance in Henries

You can see the impedance depends upon frequency.
 
"Lord Garth" <LGarth@Tantalus.net> wrote in message
news:ZkDob.353$Jq.320@newssvr24.news.prodigy.com...
"Phil Allison" <philallison@optusnet.com.au> wrote in message
news:3fa2fd70$0$497$afc38c87@news.optusnet.com.au...
Hi to all,


everyone knows the nominal impedance of a cone speaker is slightly
greater
than the DC resistance of the wire used in the voice coil. An nominal 8
ohm
speaker will have about 6 or 7 ohms of DC resistance for example.

Where does the extra 1 or 2 ohms come from ?


Z=(R˛ + (2*PI*F*L)˛)**˝

Z is the impedance in Ohms
R is the DC coil resistance in Ohms
F is the frequency in Hertz
L is the inductance in Henries

You can see the impedance depends upon frequency.
Click to expand...

** Unfortunately, that is the popular but wrong answer.



.......... Phil
 
"Phil Allison" <philallison@optusnet.com.au> wrote in message
news:3fa2fd70$0$497$afc38c87@news.optusnet.com.au...
Hi to all,


everyone knows the nominal impedance of a cone speaker is slightly
greater
than the DC resistance of the wire used in the voice coil. An nominal 8
ohm
speaker will have about 6 or 7 ohms of DC resistance for example.

Where does the extra 1 or 2 ohms come from ?

Seems from recent postings on other NGs that most folk have this one
wrong.



.......... Phil
Click to expand...
I'll have a go!

Coil in a magentice field, jam some volts on afformentioned coil and it
moves.
But moving coil within said magnetic field makes some volts of it's own.
If jammed in volts is outa phase with generated volts then :
Speaker volts = jammed in volts - generated volts.
This makes it look like a higher resistance to the voltage jammer in device.

So it would seem that the speaker impedance is not a function of the coil
inductance but more a function of the number of turns of the coil, the
strength of the magnetic field and how fast the coil is moving.
Add in a bunch of other factors like cone excursion, magnetic saturation
and a few other power transformer terminologies which are beyond the
scope of this document and call it "nominal" impedance.

Sounds good to me.. :)
Greg the Grog.
 
well, are we going to assume a frequency independent or dependant model?


mark hathaway


"Phil Allison" <philallison@optusnet.com.au> wrote in message
news:3fa2fd70$0$497$afc38c87@news.optusnet.com.au...
Hi to all,


everyone knows the nominal impedance of a cone speaker is slightly
greater
than the DC resistance of the wire used in the voice coil. An nominal 8
ohm
speaker will have about 6 or 7 ohms of DC resistance for example.

Where does the extra 1 or 2 ohms come from ?

Seems from recent postings on other NGs that most folk have this one
wrong.



.......... Phil
Click to expand...
 
"Mark Hathaway"

well, are we going to assume a frequency independent or dependant model?
Click to expand...


* The nominal impedance of a cone speaker is measured in the mid band -
usually at 250Hz or 400 Hz.

I am not concerned with fake nominal values that are not measurements.

If you test a speaker at 250 - 400 Hz you get a value that is about 20 %
higher than the DC ohms - why ?



............ Phil
 
reactance of the assembly



"Phil Allison" <philallison@optusnet.com.au> wrote in message
news:3fa328ac$0$1089$afc38c87@news.optusnet.com.au...
"Mark Hathaway"

well, are we going to assume a frequency independent or dependant model?



* The nominal impedance of a cone speaker is measured in the mid band -
usually at 250Hz or 400 Hz.

I am not concerned with fake nominal values that are not measurements.

If you test a speaker at 250 - 400 Hz you get a value that is about 20
%
higher than the DC ohms - why ?



........... Phil
Click to expand...
 
"Phil Allison" <philallison@optusnet.com.au> wrote in message
news:3fa3031e$0$497$afc38c87@news.optusnet.com.au...
"Lord Garth" <LGarth@Tantalus.net> wrote in message
news:ZkDob.353$Jq.320@newssvr24.news.prodigy.com...

"Phil Allison" <philallison@optusnet.com.au> wrote in message
news:3fa2fd70$0$497$afc38c87@news.optusnet.com.au...
Hi to all,


everyone knows the nominal impedance of a cone speaker is slightly
greater
than the DC resistance of the wire used in the voice coil. An nominal
8
ohm
speaker will have about 6 or 7 ohms of DC resistance for example.

Where does the extra 1 or 2 ohms come from ?


Z=(R˛ + (2*PI*F*L)˛)**˝

Z is the impedance in Ohms
R is the DC coil resistance in Ohms
F is the frequency in Hertz
L is the inductance in Henries

You can see the impedance depends upon frequency.



** Unfortunately, that is the popular but wrong answer.



......... Phil
Click to expand...
Thanks Phil for enlightening us that it was the "wrong" answer, so how about
sharing your pearls of wisdom and telling us the correct one?

So far the formula above implies that the impedance will vary with frequency
which sounds pretty plausible, but I guess from your comment some or all of
the formula is incorrect. Your learned explanation and the correct formula
would be appreciated.

Cheers,
Alan
 
"Alan Rutlidge" <
Thanks Phil for enlightening us that it was the "wrong" answer, so how
about
sharing your pearls of wisdom and telling us the correct one?

So far the formula above implies that the impedance will vary with
frequency
which sounds pretty plausible, but I guess from your comment some or all
of
the formula is incorrect. Your learned explanation and the correct
formula
would be appreciated.
Click to expand...


** The real answer is simple and not a formula - someone will post it
soon.





......... Phil
 
Phil Allison wrote:
Hi to all,


everyone knows the nominal impedance of a cone speaker is slightly greater
than the DC resistance of the wire used in the voice coil. An nominal 8 ohm
speaker will have about 6 or 7 ohms of DC resistance for example.

Where does the extra 1 or 2 ohms come from ?
Click to expand...
electrical impedance + acoustic impedance

Seems from recent postings on other NGs that most folk have this one
wrong.



.......... Phil
Click to expand...
 
"the swan" <xgswan3x@xbigpond.net.aux> wrote in message
news:eek:dHob.173427$bo1.48253@news-server.bigpond.net.au...
Phil Allison wrote:
Hi to all,


everyone knows the nominal impedance of a cone speaker is slightly
greater
than the DC resistance of the wire used in the voice coil. An nominal 8
ohm
speaker will have about 6 or 7 ohms of DC resistance for example.

Where does the extra 1 or 2 ohms come from ?

electrical impedance + acoustic impedance
Click to expand...

** The electrical impedance at 250 or 490 Hz is all we are able to
measure.

The DC resistance is part of it - the extra bit is due to what
exactly?





........... Phil
 
not hostile at all.


the equation for Z is as follows


Z = (R^2 + X^2) ^ (1/2)




"Phil Allison" <philallison@optusnet.com.au> wrote in message
news:3fa32f8b$0$2239$afc38c87@news.optusnet.com.au...
"Mark Hathaway"


reactance of the assembly


** Huh ?

Is this like a hostile senate ?




........ Phil
Click to expand...
 
"Mark Hathaway" <markhathawayREMOVEME@bigblue.net.au> wrote in message
news:bnvhcf$1grq$1@news.ausix.net...
not hostile at all.

the equation for Z is as follows

Z = (R^2 + X^2) ^ (1/2)
Click to expand...


** Lord Garth beat you to that one hours ago.



........ Phil
 
popular but wrong hey?

I'd love to see your source, or is this your own theory?


I checked my answer against a few publishments, I'd love to see you
contradict them.



Mark

"Phil Allison" <philallison@optusnet.com.au> wrote in message
news:3fa356e3$0$28123$afc38c87@news.optusnet.com.au...
"Mark Hathaway" <markhathawayREMOVEME@bigblue.net.au> wrote in message
news:bnvhcf$1grq$1@news.ausix.net...
not hostile at all.

the equation for Z is as follows

Z = (R^2 + X^2) ^ (1/2)



** Lord Garth beat you to that one hours ago.



....... Phil
Click to expand...
 
"Phil Allison" <philallison@optusnet.com.au> wrote in message
news:3fa2fd70$0$497$afc38c87@news.optusnet.com.au...
Hi to all,


everyone knows the nominal impedance of a cone speaker is slightly
greater
than the DC resistance of the wire used in the voice coil. An nominal 8
ohm
speaker will have about 6 or 7 ohms of DC resistance for example.

Where does the extra 1 or 2 ohms come from ?

Seems from recent postings on other NGs that most folk have this one
wrong.
Click to expand...
back emf?

ross
 
"Mark Hathaway" <
I'd love to see your source, or is this your own theory?
I checked my answer against a few publishments, I'd love to see you
contradict them.
Click to expand...

** Go ahead - post them.

Make my day......



.......... Phil
 
"Phil Allison" wrote

everyone knows the nominal impedance of a cone speaker is slightly
greater
than the DC resistance of the wire used in the voice coil. An nominal 8
ohm
speaker will have about 6 or 7 ohms of DC resistance for example.

Where does the extra 1 or 2 ohms come from ?

***** Skin effect,Brian Goldsmith.
 
Phil Allison wrote:
"the swan" <xgswan3x@xbigpond.net.aux> wrote in message
news:eek:dHob.173427$bo1.48253@news-server.bigpond.net.au...

Phil Allison wrote:

Hi to all,


everyone knows the nominal impedance of a cone speaker is slightly

greater

than the DC resistance of the wire used in the voice coil. An nominal 8

ohm

speaker will have about 6 or 7 ohms of DC resistance for example.

Where does the extra 1 or 2 ohms come from ?

electrical impedance + acoustic impedance



** The electrical impedance at 250 or 490 Hz is all we are able to
measure.

The DC resistance is part of it - the extra bit is due to what
exactly?
Click to expand...
I am intrigued as to how "nominal impedance" is measured?
I am only guessing that it is the impedance of the driver when mounted
on an "infinite" baffle with a generator (amplifier) output impedance of
0 ohms.
The total acoustic resistance is then:

Rat = Ras + (((B.l)^2)/(Re.Sd^2)

where: Ras = acoustic resistance of driver suspension
B = magnetic flux density in driver air gap
l = length of voice coil conductor in magnetic field of air gap
Re = DC resistance of voice coil (the "6 or 7 ohms")
Sd = effective projected surface area of driver diaphragm

But then again, it could all be bollox :)

.......... Phil
Click to expand...
 
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