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Why do we have amps and headphones with large resistance levels? - Page 3

post #31 of 46

I am describing how the principle/definition is used by designers, manufactures of motors when communicating with other engineers - it is assumed the constant total conductor cross section, swapping wire size for turns/length with ideal transformer relations can be applied to get "the same" motor that works at differing I,V ratio that the user may want

 

this just is the industry standard engineering assumption - and if you want to talk with motor designers you need to learn it, not start arguing that you have a personal interpretation of "thinner wire" that means less mass, lower efficiency

 

wire size, resulting headphone Z is a "free variable" because you can design the voice coil motor with voice coil conductor material, cross section area and mass - and set all electro-acoustic parameters to the design goals

 

then you can select wire size, number of turns that fits the geometry for any electrical Z within a range, limited by packing factor/coil dimensions/layers/fraction of area wasted in minimum practical insulation thickness

 

this can be seen in practice with dual voice coil loudspeaker drivers, and that some loudspeaker drivers are offered with the same model #, same response with different Z; commonly 4, 8, sometimes 16 Ohms 

 

 

if you want to talk differences in motor designs that give different efficiency, damping, bass resonance frequency, other electro-acoustic properties then it is worth learning what motor design engineers use as design factors

 

for dynamic drivers with voice coil motors Thiele-Small parameters are widely accepted, used - even by thousands of amateur/hobbyist speaker builders

 

 

googling BL product gets the Wikipedia Thiele-Small article as 1st hit - I do try to provide enough info that interested people can get to the background material

 

 

http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magfor.html is the fundamental

 

then you move to the practical implementation - say you can fit one length L of some wire into a voice coil in the magnet gap - then calculate the force/A

or you could use 1/2 diameter wire, which fits 4x L into the same voice coil cross section - now you have 4x force/A - but your wire can only carry 1/4 of the current at the same loss from resistance

so the net result looks just like you included an ideal electrical step-up transformer in series with the 1st 1 L design's electrical terminals


Edited by jcx - 7/14/13 at 11:19am
post #32 of 46

Thanks for taking the time to help us out, JCX. I know it takes lots of time to write it up. 

 

Hmm... I can indeed tell why my specifying "thinner wire" ended up seeming wonky, given the assumptions the engineers put along with it... So I think I should have said something like "thinner cross section wire while keeping the same number of turns" or something like that...  

 

Reading your link right now... Quite educational indeed...

 

 smily_headphones1.gif


Edited by Chromako - 7/15/13 at 1:41am
post #33 of 46
Quote:
Originally Posted by jcx View Post

I am describing how the principle/definition is used by designers, manufactures of motors when communicating with other engineers - it is assumed the constant total conductor cross section, swapping wire size for turns/length with ideal transformer relations can be applied to get "the same" motor that works at differing I,V ratio that the user may want

this just is the industry standard engineering assumption - and if you want to talk with motor designers you need to learn it, not start arguing that you have a personal interpretation of "thinner wire" that means less mass, lower efficiency

wire size, resulting headphone Z is a "free variable" because you can design the voice coil motor with voice coil conductor material, cross section area and mass - and set all electro-acoustic parameters to the design goals

then you can select wire size, number of turns that fits the geometry for any electrical Z within a range, limited by packing factor/coil dimensions/layers/fraction of area wasted in minimum practical insulation thickness

this can be seen in practice with dual voice coil loudspeaker drivers, and that some loudspeaker drivers are offered with the same model #, same response with different Z; commonly 4, 8, sometimes 16 Ohms 


if you want to talk differences in motor designs that give different efficiency, damping, bass resonance frequency, other electro-acoustic properties then it is worth learning what motor design engineers use as design factors

for dynamic drivers with voice coil motors Thiele-Small parameters are widely accepted, used - even by thousands of amateur/hobbyist speaker builders


googling BL product gets the Wikipedia Thiele-Small article as 1st hit - I do try to provide enough info that interested people can get to the background material


http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magfor.html is the fundamental

then you move to the practical implementation - say you can fit one length L of some wire into a voice coil in the magnet gap - then calculate the force/A
or you could use 1/2 diameter wire, which fits 4x L into the same voice coil cross section - now you have 4x force/A - but your wire can only carry 1/4 of the current at the same loss from resistance
so the net result looks just like you included an ideal electrical step-up transformer in series with the 1st 1 L design's electrical terminals

Nice!
I learned something!

One very minor little nit pick:
96 dB @ 1 mW is efficiency rating
106 dB @ 1 Volt is sensitivity rating
post #34 of 46

dB SPL re 1 mW is called sensitivity too - and it could be argued that fully proper "efficiency" would be (power out)/(power in) and SPL isn't really a power unit- converting it to power requires several added assumptions: of some reference acoustic load, radiation condition, integration region

post #35 of 46
it could be argued that a number like 1 mW @ 96 dB SPL expresses the efficiency of the conversion of electrical energy into acoustic energy.

assume we are using pink noise:
if speaker system A was 90 dB SPL @ 1 W @ 1 m, and speaker B was 100 dB SPL @1W @1 m then we would conclude that speaker B was more efficient than speaker A

let the endless discussion of semantics continue!
post #36 of 46

But, but, efficiency is usually dimensionless and specified as 0.0 to 1.0 or in percent! tongue.gif

post #37 of 46
Quote:
Originally Posted by Chris J View Post

assume we are using pink noise:
if speaker system A was 90 dB SPL @ 1 W @ 1 m, and speaker B was 100 dB SPL @1W @1 m then we would conclude that speaker B was more efficient than speaker A

 

Unfortunately, this is not true. You are only measuring the sound pressure level at a single location. If speaker A was a tiny, spherical transducer and speaker B was a very very large speaker (or better yet, an array of speakers) in an infinite baffle, then speaker A would radiate sound equally in all directions, with the SPL falling off like 1/distance^2 whereas speaker system B could focus its sonic energy at the location where you were measuring SPL. I that case, it's entirely possible that speaker A is actually converting more electricity into sound energy, even though the loudness at the location you are measuring is lower than B.

 

Here's a link on directional sound

 

Originally Posted by Chris J View Post
let the endless discussion of semantics continue!

how did I do? biggrin.gif

 

Cheers!


Edited by ab initio - 7/18/13 at 6:05pm
post #38 of 46
Quote:
Originally Posted by ab initio View Post

Unfortunately, this is not true. You are only measuring the sound pressure level at a single location. If speaker A was a tiny, spherical transducer and speaker B was a very very large speaker (or better yet, an array of speakers) in an infinite baffle, then speaker A would radiate sound equally in all directions, with the SPL falling off like 1/distance^2 whereas speaker system B could focus its sonic energy at the location where you were measuring SPL. I that case, it's entirely possible that speaker A is actually converting more electricity into sound energy, even though the loudness at the location you are measuring is lower than B.

Here's a link on directional sound
Quote:
Originally Posted by Chris J View Post

let the endless discussion of semantics continue!
how did I do? biggrin.gif

Cheers!

Well played!tongue.gif
You'll fit right in with the rest of us pedantic idiots on the Science Fiction Forum!

In this case, I add another assumption!
Assume both loudspeakers have the same radiation pattern!
post #39 of 46
Quote:
Originally Posted by Chris J View Post


Well played!tongue.gif
You'll fit right in with the rest of us pedantic idiots on the Science Fiction Forum!
 

Thanks smily_headphones1.gif

 

Quote:
Originally Posted by Chris J View Post

In this case, I add another assumption!
Assume both loudspeakers have the same radiation pattern!
Quote:
Originally Posted by Chris J View Post

assume we are using pink noise:
if speaker system A was 90 dB SPL @ 1 W @ 1 m, and speaker B was 100 dB SPL @1W @1 m then we would conclude that speaker B was more efficient than speaker A

 

Assuming we know the radiation pattern, I think we now have enough information to define a proper efficiency as the ratio of one power to another power. And now, yes, I think that comparing the SPL levels would be equivalent to efficiency!

 

Cheers!

post #40 of 46
Quote:
Originally Posted by ab initio View Post

Thanks smily_headphones1.gif


Assuming we know the radiation pattern, I think we now have enough information to define a proper efficiency as the ratio of one power to another power. And now, yes, I think that comparing the SPL levels would be equivalent to efficiency!

Cheers!

efficiency = Watts / Watts !

No stinking units for us! tongue.gif or is it mad.gif ?
post #41 of 46
Quote:
Originally Posted by Chris J View Post


efficiency = Watts / Watts !

No stinking units for us! tongue.gif or is it mad.gif ?

 

Personally, I find working without units a tongue.gif.  Whenever somebody tries to discuss a problem in dimensional form it makes me frown.gif

 

Besides, what the heck is a Jiggawatt anyways?

 

Cheers!

post #42 of 46
Quote:
Originally Posted by ab initio View Post

 

Personally, I find working without units a tongue.gif.  Whenever somebody tries to discuss a problem in dimensional form it makes me frown.gif

 

Besides, what the heck is a Jiggawatt anyways?

 

Cheers!

 

At this point I recommend that we pick apart each other's grammar, spelling and sentence structure! Also critique each other's literary style! A JiggaWatt is a measurement used to quanify ONE BURST of phasor fire!
post #43 of 46

Or let's just get real again and acknowledge that sensitivity does not equal efficiency. tongue.gif

post #44 of 46
Quote:
Originally Posted by jcx View Post

dB SPL re 1 mW is called sensitivity too - and it could be argued that fully proper "efficiency" would be (power out)/(power in) and SPL isn't really a power unit- converting it to power requires several added assumptions: of some reference acoustic load, radiation condition, integration region

Or use the same anechoic chamber when comparing two loudspeakers..........................which have the same, or similar radiation patterns.

post #45 of 46

I'm confused because you guys are correct, yet you guys are correcting each other.

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