Speaker resistance and sound energy

[M. Hamed]

I was reading the ARRL handbook (2010) and on page 4.7 there was this sentence:

"it can be said that any device that dissipates power has a definitive value of resistance"

This made me think. I always see speakers modeled 8 Ohms. And this is probably their DC resistance value. But shouldn't the conversion to sound be accounted for somehow since it's a sink on energy delivered?

I thought maybe an inductance should be added to the model but then an inductance is lossless, so where does the sound producing energy come from?

 

[John Fields]

On Sun, 24 Mar 2013 10:47:49 -0700 (PDT), "M. Hamed"
<mhdpublic@gmail.com> wrote:

I was reading the ARRL handbook (2010) and on page 4.7 there was this sentence:

"it can be said that any device that dissipates power has a definitive value of resistance"

This made me think. I always see speakers modeled 8 Ohms. And this is probably their DC resistance value.

---
No, it's their nominal _impedance_.
---

But shouldn't the conversion to sound be accounted for somehow since it's a sink on >energy delivered?

---
The conversion of the power delivered to the voice coil by the AC
source and the acoustic power delivered to ambient air by the
loudspeaker cone is accounted for by the cone's being physically
attached to the voice coil and the magnetic field being generated
around the voice coil by the AC source which interacts with the
permanent magnetic field generated by the field magnet, causing the
cone to move back and forth and either compress or rarefact the
ambient air.
---

I thought maybe an inductance should be added to the model but then an inductance is lossless, so where does the sound producing energy come from?

---
It comes from the AC source pushing current through the voice coil,
which generates the magnetic field which interacts with the field
magnet's fixed field.

--
JF

 

[Ken]

On Sun, 24 Mar 2013 10:47:49 -0700 (PDT), "M. Hamed"
<mhdpublic@gmail.com> wrote:

I always see speakers modeled 8 Ohms. And this is probably their DC resistance value.

No.

 

[John Larkin]

On Sun, 24 Mar 2013 10:47:49 -0700 (PDT), "M. Hamed" <mhdpublic@gmail.com>
wrote:

I was reading the ARRL handbook (2010) and on page 4.7 there was this sentence:

"it can be said that any device that dissipates power has a definitive value of resistance"

This made me think. I always see speakers modeled 8 Ohms. And this is probably their DC resistance value. But shouldn't the conversion to sound be accounted for somehow since it's a sink on energy delivered?

I thought maybe an inductance should be added to the model but then an inductance is lossless, so where does the sound producing energy come from?

DC resistance is usually a healthy fraction of the rated AC impedance, like 3/4
maybe. Which indicates that speakers are pretty inefficient.

Of course, impedance is usually a wild function of frequency, not a steady 8
ohms. And if there's a crossover, there will be series capacitors that will look
open to an ohmmeter, and inductors too.

Sound is produced by the voice coil moving in the magnetic field, with a
component of the motion being mechanically lossy because of the sound produced.
It's like a motor driving a load, where the mechanical load reflects back as
electrical resistance.


--

John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators

 

[John Fields]

On Sun, 24 Mar 2013 14:19:23 -0700, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Sun, 24 Mar 2013 10:47:49 -0700 (PDT), "M. Hamed" <mhdpublic@gmail.com
wrote:

I was reading the ARRL handbook (2010) and on page 4.7 there was this sentence:

"it can be said that any device that dissipates power has a definitive value of resistance"

This made me think. I always see speakers modeled 8 Ohms. And this is probably their DC resistance value. But shouldn't the conversion to sound be accounted for somehow since it's a sink on energy delivered?

I thought maybe an inductance should be added to the model but then an inductance is lossless, so where does the sound producing energy come from?

DC resistance is usually a healthy fraction of the rated AC impedance, like 3/4
maybe. Which indicates that speakers are pretty inefficient.

Of course, impedance is usually a wild function of frequency, not a steady 8
ohms. And if there's a crossover, there will be series capacitors that will look
open to an ohmmeter, and inductors too.

Sound is produced by the voice coil moving in the magnetic field, with a
component of the motion being mechanically lossy because of the sound produced.
It's like a motor driving a load, where the mechanical load reflects back as
electrical resistance.

---
No, it's like a voltage source driving a motor which is driving a load
where the mechanical load reflects back as electrical resistance.

--
JF

 

[Phil Allison]

"M. Hamed"

I was reading the ARRL handbook (2010) and on page 4.7 there was this
sentence:

"it can be said that any device that dissipates power has a definitive
value of resistance"

This made me think. I always see speakers modeled 8 Ohms. And this is
probably their DC resistance value.

** Not exactly.

8 ohms ( or whatever) is the"nominal impedance" of the speaker - usually
measured with a 250 or 400Hz tone.

The DC resistance of the voice coil is about 80% of that number or about 6.4
ohms.

The impedance of most ( bass or full range ) speakers in the range of 250 to
400 Hz is RESISTIVE too.

So, we have two resistances that dissipate heat, one the copper wire and the
other due to losses in the moving suspension, magnet assembly and sound
radiation.

Sound radiation accounts for barely 1% of the input power, in most cases.

A good circuit model for a loudspeaker is not a simple one, it would have
many inductances, resistances and capacitances involved - plus the
resistances would each have temperature co-efficient.


.... Phil

 

[default]

On Sun, 24 Mar 2013 10:47:49 -0700 (PDT), "M. Hamed"
<mhdpublic@gmail.com> wrote:

I was reading the ARRL handbook (2010) and on page 4.7 there was this sentence:

"it can be said that any device that dissipates power has a definitive value of resistance"

This made me think. I always see speakers modeled 8 Ohms. And this is probably their DC resistance value. But shouldn't the conversion to sound be accounted for somehow since it's a sink on energy delivered?

I thought maybe an inductance should be added to the model but then an inductance is lossless, so where does the sound producing energy come from?

Speakers are rated in impedance a combination of resistance and
inductive reactance. And a real speaker would have different
impedances at different frequencies, air density, cabinet design, cone
compliance, magnet design, etc..

I think I remember reading somewhere that speakers are rated in
impedance at 1,000 cycles - but doubtless that wouldn't hold true for
a tweeter... would it?

 

[M. Hamed]

Thank you for the thorough explanation. As it often happens my false assumptions led to false conclusions.

I remember a couple years ago I created a toy speaker out of magnet wire and a strong magnet. I remember how I carefully wound the coil to measure 8 Ohms DC. How naive I was

 

[John Larkin]

On Thu, 28 Mar 2013 01:00:36 -0700 (PDT), "M. Hamed" <mhdpublic@gmail.com>
wrote:

Thank you for the thorough explanation. As it often happens my false assumptions led to false conclusions.

I remember a couple years ago I created a toy speaker out of magnet wire and a strong magnet. I remember how I carefully wound the coil to measure 8 Ohms DC. How naive I was

You were only about 20% off. In audio, that's high precision.


--

John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators

 

[amdx]

On 3/28/2013 10:42 AM, John Larkin wrote:

On Thu, 28 Mar 2013 01:00:36 -0700 (PDT), "M. Hamed" <mhdpublic@gmail.com
wrote:

Thank you for the thorough explanation. As it often happens my false assumptions led to false conclusions.

I remember a couple years ago I created a toy speaker out of magnet wire and a strong magnet. I remember how I carefully wound the coil to measure 8 Ohms DC. How naive I was

You were only about 20% off. In audio, that's high precision.


You trying to start an audiophoolery fight?

Mikek

 

[Fred Abse]

On Sun, 24 Mar 2013 18:17:45 -0500, John Fields wrote:

No, it's like a voltage source driving a motor which is driving a load
where the mechanical load reflects back as electrical resistance.

I like the way they used to (maybe still?) describe horn loudspeaker
transducers as "motors".

--
"For a successful technology, reality must take precedence
over public relations, for nature cannot be fooled."
(Richard Feynman)

 

On Sun, 31 Mar 2013 11:25:18 -0700, Fred Abse
<excretatauris@invalid.invalid> wrote:

On Sun, 24 Mar 2013 18:17:45 -0500, John Fields wrote:

No, it's like a voltage source driving a motor which is driving a load
where the mechanical load reflects back as electrical resistance.

I like the way they used to (maybe still?) describe horn loudspeaker
transducers as "motors".

The "motor" part of a loudspeaker is the linear motor, not the entire
assembly.

 

[John Larkin]

On Sun, 31 Mar 2013 11:25:18 -0700, Fred Abse <excretatauris@invalid.invalid>
wrote:

On Sun, 24 Mar 2013 18:17:45 -0500, John Fields wrote:

No, it's like a voltage source driving a motor which is driving a load
where the mechanical load reflects back as electrical resistance.

I like the way they used to (maybe still?) describe horn loudspeaker
transducers as "motors".

Or drivers.


--

John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators

 

[Fred Abse]

On Sun, 31 Mar 2013 18:28:59 -0400, krw wrote:

I like the way they used to (maybe still?) describe horn loudspeaker
transducers as "motors".
^^^^^^^^^^^

The "motor" part of a loudspeaker is the linear motor, not the entire
assembly.

See above

--
"For a successful technology, reality must take precedence
over public relations, for nature cannot be fooled."
(Richard Feynman)

 

On Mon, 01 Apr 2013 13:16:00 -0700, Fred Abse
<excretatauris@invalid.invalid> wrote:

On Sun, 31 Mar 2013 18:28:59 -0400, krw wrote:

I like the way they used to (maybe still?) describe horn loudspeaker
transducers as "motors".
^^^^^^^^^^^


The "motor" part of a loudspeaker is the linear motor, not the entire
assembly.

See above

The cone is part of the transducer (the entire loudspeaker). It is
not part of the motor.

 

On Mon, 01 Apr 2013 13:16:00 -0700, Fred Abse
<excretatauris@invalid.invalid> wrote:

"For a successful technology, reality must take precedence
over public relations, for nature cannot be fooled."
(Richard Feynman)
Richard Feynman is a man for whom I have great respect. I have learned

much from reading books by Feynman, and much more from watching videos
of his lectures. Yet still I see quotes of things Feynman has said,
which I had not seen before, that are valid today, years after his
death. Thanks.
Eric