Damping Factor
Aug 9, 2014 at 10:23 PM Post #76 of 168
I posted Ty'll page since it's the only page I know of that gives you some insight into Orthos that I know of.  Tyll says the magnet has very strong magnetic field and current is applied to the diaphram to move it back and forth.  Diaphram is very light.  The magnets are permanent, it's not like a motor's inductive coil causing significant Back EMF.  This is why I thought know how of the drivers is pretty insightful.  Also the impedance graph shows no resonance.
 
Aug 9, 2014 at 10:37 PM Post #77 of 168
  Here is an AES paper describing an equivalent electrical circuit model for electrodynamic transducers. Of particular interest to this discussion is the introduction which outlines the equivalent electrical circuit for an electrodynamic driver including the origin of impedance variation with frequency in dynamic drivers and how the back emf generated by transducer motion fits into the picture.
 
 
Cheers


Well, looking at google image of drivers of Audeze and Oppo, I couldn't even find the "moving coil" to begin with this paper..
 
Aug 9, 2014 at 10:52 PM Post #79 of 168
 
 
so the idea I get from this:
Quote:
don't underestimate the power of the force! (at least for higher frequencies, but I don't know the formula to turn the quantity of midichlorian into force).
 
seriously I remember several people over time who mentioned on the interwerrb that for high freqs there was some effect that actually helped the driver maintain a fast enough movement (something to do with the air vibrating at the frequency kind of helping the membrane keep it's speed?) if someone knows what I'm talking about I would appreciate some light on this(don't know if it has a place in here, but if it impacts how long a movement is kept alive I guess it's part of it).
 
also again it might not seem directly related, but amps usually behave better when the damping ration is good. I don't remember reading much about an headphone amp that had better measurements with a 8ohm load vs the same amp with 150ohm load.

 

 
tongue.gif

 
What you are describing kind of sounds like someone was talking about the acoustics of the speaker's enclosure. Certainly how the speaker is coupled to the space it's driving affects the performance. Does anything in that article ring a bell?
 
Cheers
 
Aug 9, 2014 at 10:56 PM Post #80 of 168
Stop replying within quotes. All I'm able to quote from all that is "Cheers."

se

My apologies. I've edited that last post to bring it all out of the quotation dialog. Hope this helps! 
smily_headphones1.gif

 
Cheers
 
Aug 9, 2014 at 11:02 PM Post #81 of 168
 
Well, looking at google image of drivers of Audeze and Oppo, I couldn't even find the "moving coil" to begin with this paper..

The "coil" is the trace etched into the membrane.
 

 
 
Here is the picture from Innerfidelity's ortho post with the trace on the membrane pointed to by the red arrow.
 
Cheers
 
Aug 9, 2014 at 11:15 PM Post #83 of 168
I found this on a webpage called, "Headphones for Dummies"  
biggrin.gif
  http://hfddrivers.blogspot.com/2012/06/how-dynamic-driver-works.html
 

How A Dynamic Driver Works

 


Dynamic drivers are by far the most commonly used technology in speakers and headphones as they are easy to manufacture and they are cheap as well. Almost all headphones in the $10-$500 over ear headphones  use the dynamic driver principle. For speakers, well lets just say anything that has a cone in it uses a dynamic driver. I can guarantee that you have used a device that uses a dynamic driver sometime in your life. The speakers attached to your computer or integrated into your laptop, they use dynamic drivers. The Apple earbuds that come with your iPod or iPhone, those use dynamic drivers, dynamic drivers are everywhere.
A dynamic headphone driver

HOW DOES IT WORK?

Dynamic drivers use magnetism and electromagnetism to create the movement necessary to create the sound. The dynamic driver in a headphone consist of three parts: A neodymium magnet and a voice coil which is attached to a diaphragm. The neodymium magnet is in the shape of a ring with a gap which allows the voice coil to move up and down. A dynamic driver in a speaker has a few more parts that help it keep it's shape because of it's size and overall mass of the diaphragm.
 
A Diagram of a Dynamic Headphone Driver

A dynamic driver works by making the voice coil an electromagnet which interacts with the magnetic field created by the permanent magnet below it. The voice coil is made of copper meaning that without a charge, it will not be attracted by a magnet meaning it will not move in a neutral position, but once you send a current into the voice coil you make it a solenoid which will create a magnetic field heading north in one direction and south in the other. In a headphone the current alternates which means the flow of the current can change, in turn changing the direction of the magnetic field. In a dynamic driver, the magnetic field created by the voice coil interacts with the magnetic field created by the permanent magnet which creates motion as the voice coil is repelled and attracted towards the permanent magnet. This will cause the diaphragm attached to the voice coil to move and displace air, creating sound.
 

Volume

The motion created by the voice coil can be controlled by providing a larger current or a smaller current which in turn will strengthen or weaken the magnetic field the voice coil creates. By controlling the current that goes into the voice coil you can control how far the voice coil is repelled or attracted towards the permanent magnet, this allows you to control how much air the diaphragm displaces. Going back to the introduction, the larger the larger the amount of air displaced, the outer the volume.
 

Pitch and Frequency

When you want to play a note at a certain frequency, the driver must create a certain number of vibrations per second which can be done by alternating the current at a certain speed. This will cause the voice coil to be attracted and repelled at a certain speed creating a sound wave at a certain frequency.


 
Aug 9, 2014 at 11:17 PM Post #85 of 168
  The "coil" is the trace etched into the membrane.
 

 
 
Here is the picture from Innerfidelity's ortho post with the trace on the membrane pointed to by the red arrow.
 
Cheers

But doesn't seem like it will exhibit similar physical properties as moving coils in dynamic drivers.. not sure how you can apply same fomulas on it
 
Aug 9, 2014 at 11:22 PM Post #86 of 168
There is some information from a website of the 3 headphone types:  http://headfonics.com/2011/05/dynamic-vs-orthodynamic-vs-electrostatic-which-is-which/

comparisons of brands of headsets or specific units, but lets talk about the actual engineering and construction of headphones and how they work and what works for you and why?

Currently in the market we have 3 standards:

1. Dynamic
2. Orthodynamic
3. Stax or electrostatic


These categories base the headphones on the type of technology used to create their sound. The difference between the two types is in the transducer principle used; that is, how the headphones convert the electrical signal from a media player into sound waves that can be heard.

1. Dynamic

emon_head-fi16.jpg
Dynamic Headphones

Dynamic headphones work just like two miniature speakers. The signal is transmitted through a connection to a standard jack. Once the electrical signal reaches the earphones, a magnet forces a voice coil to vibrate rapidly inside a diaphragm — a paper, fibrous or plastic cone-shaped object. The inner works are then lifted up and down much like a piston, often faster than the eye can see. This rapid vibration is what stirs the air and creates vibrations called sound waves which are then picked up by our eardrums.

Headphone Transducer

Dynamic headphones are by far the most common type used by the average music listener, musicians and professional studio mixers alike. The most popular manufacturers in the music industry all make dynamic headphones, including Sony, Beyer, Sennheiser, Grado and Audio-Technica. They can cost $8 or $800 US Dollars (USD) upwards and can be wired or wireless, open-air or closed-back, ear buds or studio-quality.

2. Isodynamic (aka orthodynamic)

The KH-85B

Orthodynamic headphones were very popular worldwide (if not so much in the US) in the 1970s. Several companies manufactured such headphones or the parts for them, and numerous others contracted with those Original Equipment Manufacturers (OEMs) to make parts or complete headphones for them to sell under their band names. Fostex and PMB OEM heaphones are by far the most common.

Manufacturers include Audeze, Fostex, Hifiman, Kenwood and Dual.

Isodynamic drive headphones have drivers with flexible plastic film diaphragms into which a flat voice coil (spiral or serpentine in shape– see photos below) is embedded or glued on for even distribution of the drive force. That is, the diaphragm is driven more or less equally over its entire surface at once, obviating the need to make the diaphragm rigid so that it can therefore be as lightweight and agile and nonresonant as possible. Isodynamic diaphragms are either lightly tensioned or corrugated to supply restoring force.

Orthodynamics

Magnetic assemblies (bar magnets or perforated disc magnets) on both sides of the diaphragm supply the magnetic field against which the voice coil’s varying magnetic field reacts, which makes the diaphragm vibrate.

Isodynamic diaphragms are more massive than electrostatic diaphragms, but the equal-force drive principle allows them to move very quickly and in a coherent, uniform way, so provided there is sufficient mechanical damping, an isodynamic headphone gives excellent transient response and a sound quality not unlike that of an electrostatic

3. Electrostatic

Electrostatic drivers consist of a thin, electrically charged diaphragm, typically a coated PET film membrane, suspended between two perforated metal plates (electrodes). The electrical sound signal is applied to the electrodes creating an electrical field; depending on the polarity of this field, the diaphragm is drawn towards one of the plates. Air is forced through the perforations; combined with a continuously changing electrical signal driving the membrane, a sound wave is generated. Electrostatic headphones are usually more expensive than moving-coil ones, and are comparatively uncommon. In addition, a special amplifier is required to amplify the signal to deflect the membrane, which often requires electrical potentials in the range of 100 to 1000 volts.

Es_spk.gif


Due to the extremely thin and light diaphragm membrane, often only a few micrometers thick, and the complete absence of moving metalwork, the frequency response of electrostatic headphones usually extends well above the audible limit of approximately 20 kHz. The high frequency response means that the low midband distortion level is maintained to the top of the audible frequency band, which is generally not the case with moving coil drivers. Also, the frequency response peakiness regularly seen in the high frequency region with moving coil drivers is absent. The result is significantly better sound quality, if designed properly.

stax-sr007.jpg


Electrostatic headphones are powered by anything from 100v to over 1kV, and are in proximity to a user’s head. The usual method of making this safe is to limit the possible fault current to a low and safe value with resistors.

Conclusions?

So with this short introduction out of the way I have to say owning various of each there is no definitive camp to sit in and this a good thing in my mind. The old adage ‘horses for courses’ come to mind and whilst dynamic has the lion share of the market it really does not have the lion share of sq. For that stats and orthos can punch way above their market share weight. You just have to spend a bit more and this is where dynamics win with their lower cost to performance ratio.

Of course the choice is yours and there is a platform for whatever budget you have. The Fostex range can go as low as $100 or less for an ortho and the Baby Stax SR001 mk2 (now discontinued) could be had for around $350 but at the end of the market things get very competitive between the 3 standards. Its only when you decide to go north of $500 do you get real separation in terms of distinct platform qualities.

 
Aug 10, 2014 at 12:01 AM Post #87 of 168
No. This is a simplified circuit. The AES paper I linked to in a previous post shows the equivalent circuit for a speaker:


I don't give a crap about the AES paper regarding dynamic drivers.

Here is the reality.



Magnitude: FLAT

Phase: FLAT (save for a bit of a rise at high frequencies due to the self-inductance of the voice coil)

FLAT magnitude and FLAT phase mean a RESISTIVE load.



se
 
Aug 10, 2014 at 12:29 AM Post #88 of 168
  But doesn't seem like it will exhibit similar physical properties as moving coils in dynamic drivers.. not sure how you can apply same fomulas on it

 
It more or less does.
 
The fundamental difference between dynamic and orthodynamic drivers is the layout of the magnets and the voice coil. As illustrated in @SilverEars' posts, dynamics have a single magnet with the voice coil winding in many loops around the single magnet. Here, current i through the wire loop with total length L runs perpendicular to the magnetic field B, thus a force perpendicular to both is generated (F = (L*i x B)).
 
 
 
Here is illustration from a magnetism website

 
 
Orthodynamics work using the same principle (F = (L*i x B)).
 
 
Here's one of the images SilverEars linked above of the magnetic field in an ortho headphone

 
You can see in that the arrangement of the magnet array generates many regions where the magnetic field lines run horizontally between alternating poles. It is through these regions that the serpentine trace of the ortho's voice coil would run through (in this case into and out of the image). Again, this forces the diaphragm perpendicular to both the current and the magnetic field lines, hence (F = (L*i x B)).
 
In both cases, the magnitude of the force on the diaphragm is F = B*L*i and when the diaphragm moves through the magnetic field, a back EMF is generated V = B*L*u as we've covered in the previous posts.
 
This back EMF is the source of electrical damping and the magnitude of its effect on the diaphragm dynamics depends on the damping factor, which is the topic of the thread.
 
What we are fleshing out now is how important this effect is depending on specific headphone parameters based on a first principles approach, and trying to rectify that with the observed electrical characteristics that people have measured with different types of headphones.
 
Cheers
 
Aug 10, 2014 at 12:42 AM Post #89 of 168
Found this from another thread:
 
Damping factor:

Resonance is another issue concerning speakers, and too much of it can cause distortion. Since the speaker basically consists of a coil moving back and forth in an magnetic field, it will generate a back EMF, or back current by Faraday's Law. This induced current will restrict the coil movement, making it slower or less responsive.

Now looking from the speaker side, if the speaker generates a voltage, the amp is the load. If the load has lower resistance it'll allow more current to pass through, hence the back emf can be dissipated easily, controlling the unwanted oscillation at resonant frequency. This is known as a 'High Damping Factor'.

Most speakers have this happening near the lower frequency regions, so a High Damping means the Amp can control the speaker movement tightly.

But beware of damping marketing ploys. If amps have near zero output impedance, Damping is no longer a problem.
 
 
  1. Impedance - What does it really mean?  A general discussion on impedance, damping, etc.
 

More links on Damping:

http://sound.westhost.com/impedanc.htm

http://sound.westhost.com/project56.htm

http://sound.westhost.com/project70.htm

http://sound.westhost.com/z-effects.htm
 
Aug 10, 2014 at 12:50 AM Post #90 of 168
I don't give a crap about the AES paper regarding dynamic drivers.

Here is the reality.



Magnitude: FLAT

Phase: FLAT (save for a bit of a rise at high frequencies due to the self-inductance of the voice coil)

FLAT magnitude and FLAT phase mean a RESISTIVE load.



se

 
Yes, I am well aware how orthodynamic headphones measure. I'm not sure what your point is?
 
The topic is damping factor. Can you please relate these observed electrical characteristics to the electro-mechanics of a dynamic driver? It isn't clear to me how the impedance of a dynamic driver being predominately real over the audio frequency range decouples the driver dynamics from the damping factor. Either that result can be derived (say, from the model given in the AES paper), or we need to add additional restrictions to arrive at such a result. (Or there is no such result)
 
Cheers
 

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