Headphone Fundamentals

[solderdude]

I am very curious to hear the response to the question John Yang raised, and it would be interesting to see a plot with the other units of sensitivity.

There is only dB/mW and dB/V and this is what John mentioned.

Here is a list (that also is not always correct) with basic headphone specs of a lot of headphones.

I also made a list but isn't upto date anymore and not interactive.

 

[AudioStudies]

@solderdude - thanks so much for those links. It looks like I did pretty well with my headphone purchases. The 650 after it had become cheap, and the Sine was used but arrived in like new condition.

 

[RayDunzl]

I am not sure about the impedance rating of the Audeze Sine, but I think it is quite a bit less than the other one.

Impedance 18 ohms
Sensitivity 97 dB/1mW (at Drum Reference Point)

https://www.audeze.com/products/sine

 

[Hipper]

As solderdude suggests comfort is an important factor in headphones. In my view the most important. What's the point of having the best sounding headphones if you can't have them on your head for more then a few minutes?

And, again as solderdude said, if the ear pieces alter the shape of your pinnae it will likely have an impact on the sound for you. That's why I'm so fond of the HD800 headphones. They have larger then normal earpieces that do not distort my pinnae. This also makes them more comfortable. The only other headphones I've tried with no pinnae distortion were the Jecklin Floats which were designed specifically for this reason.

 

[AudioStudies]

Leaving town tonight, will be on a trip for a few days. When I return, I will renew my study of headphone issues. Yes, I will bring headphones on my trip, the Audeze Sine, and play music with my newly acquired Olympus LS-P4. Everyone have a great Labor Day.

 

[AudioStudies]

Got back home to Lakewood, CO from my trip to Yellowstone. The Olympus LS-P4 performed well as my playback source into the Audeze Sine. This was the first time that I used the Audeze for such an extended period and there was some discomfort after extended listening sessions, but overall things worked out well. The Olympus is starting to grow on me, I have grown accustomed to the tiny controls, and it sure is nice having something so small that it can fit into the pocket of blue jeans. In a very limited fashion, I tested its recording capabilities, recording some of the geysers at Yellowstone, and it performed admirably, much better than any mobile phone. In playback, the Olympus and the Audeze are likely not a perfect match, as I need the volume turned up pretty high to reach my desired listening level; however I have yet to find an album or song wherein I cannot reach my desired level. Yes, I could playback from a phone, but the advantage of having the Olympus is that if some interesting or unusual sounds occur, it can quickly assume recording duties. Unusual among portable recorders, the Olympus can record to FLAC. I thought I had read somewhere that it can take SD cards up to 128 GB, but I want to double check that.

 

[AudioStudies]

In reviewing the Headphone Fundamentals document, I think it might be helpful to expand on the list of headphone manufacturers, to distinguish a bit regarding what each of the companies is noted for -- as an example I think Audeze is noted for planar magnetics. Also, it may be helpful to distinguish which companies are pushing the state of the art with high end headphones, are the big three in that department Audeze, HiFiMan and Focal? Additionally, some distinctions among mass market headphones, because I see a clear difference between higher quality mass produced headphones from companies like Sennheiser versus lower end Bose headphones. Lastly, I haven't mentioned anything about wireless headphones yet, and am curious about the technologies that signals can be sent wireless to headphones. I know Bluetooth is one of them, and I have heard that the latest version of Bluetooth (number ?) has improved substantially over previous versions. How does the best wireless technology available compare with wired headphones?

 

[solderdude]

Here is a not complete list of headphone 'brands'
https://reference-audio-analyzer.pr...php?&sp_1=1&sp_2=2&sp_12=12&trp1=hp#gsc.tab=0

How does the best wireless technology available compare with wired headphones?

They are all lossy or bandlimited codecs.
For listning to music most will do fine.
I wouldn't want to use BT when I was playing hi-res or DSDx4 or something to a HD800. Wouldn't use BT for that. Chances are you cannot tell the difference using a good codec but it's the idea that counts.
Technically wired is always better.

What's the idea of your document ?
To have some relevant info in a nutshell or to have a really nice paper describing all aspects. ?

 

[AudioStudies]

What's the idea of your document ?
To have some relevant info in a nutshell or to have a really nice paper describing all aspects. ?

Those are very good questions. I tend to get sidetracked from my audio hobby at times and get involved in other things. Then, when I come back to audio, I realize that I have forgotten where I left off, so to speak. So I want to have detailed notes for myself. I find the best format for those notes is my own personal "white papers" that can help me remember things, if say for two years I get involved in other things. I guess the best answer to your question is that I do want to have a really nice paper describing all aspects; however it might have more detailed information in the areas of most interest to me. Those interests include playback of 16 bit / 44.1 kHz wav files (no DSD or High Res) and learning more about high performance headphones before I shell out more money for my next set of cans. Very happy with the two cans I do own, but will likely make a jump to the $1000 - $1200 level within the next year. This new purchase would be for at home listening only, not travel, so right now I am leaning towards open-back planar magnetics. High impedance would be OK, because I can drive them with my RME dac/headphone amp combo, or I can feed my Topping D90 into my Atom El Amp II then to the headphones. As a secondary purpose, I like having these white papers, as a convenient way to help friends who want to get into the hobby.

 

[AudioStudies]

What is the scoop on WiFi headphones, I guess they are relatively new to the party? How would the WiFi option compare with Bluetooth?

 

[MC_RME]

I also made a list but isn't upto date anymore and not interactive.

I use your list regularly for years and already wanted to ask you if an update might come. Several of the headphones that I use for testing are missing as they came out around or after 2016. This list is too good to not keep it alive!

 

[solderdude]

I really should update the list.
So many new headphones in the last 4 years.
It is a very time consuming job though... gathering all the info ...

 

[AudioStudies]

I have been reviewing some of the links provided by BooBoo, taking notes, and then preparing segments to add to my white paper. This is the latest that I have come up with:

Headphone sources, such as mobile phones or dedicated headphone amplifiers, exhibit an output impedance. The differences in these source output impedances is a very common reason the same headphones can sound different, depending on the source used to power the headphones. Regrettably, the output impedance of sources is not often specified by manufacturers; yet it can significantly affect sound quality and is a key parameter that determines the compatibility of particular headphones with the source. A source output impedance under 2 ohms will work well with nearly all headphones on the market.

In audio systems, including those with headphones, the damping factor is ratio of the resistive portion of the speaker impedance to the resistive portion of the source impedance. Higher damping factors are preferred, and the damping factor should be taken into consideration when choosing the combination of source and headphones that vary widely in impedance, typically in the range of 16 Ohms to 600 Ohms. There are three primary reasons for choosing a source with low output impedance:

• The greater the output impedance of a source driving headphones, the greater the voltage drop when driving headphones with low impedance loads. If this voltage drop is too great, the low impedance headphones cannot be driven to appropriate listening volume levels.

• In many cases of headphone design, the headphone impedance changes with frequency. If the source output impedance is too high, then the voltage driving the headphones will likewise be frequency dependent. Thus the greater the output impedance of the source driving the headphones, the greater deviation in frequency response affecting tonal balance.

• Electrical damping is reduced as the source output impedance is increased, and this can result in subpar bass performance of the headphones, with boomy (less controlled) bass sounds. Additionally the transient response is compromised and the bass will roll off sooner and not go as deep.

Regrettably, the only Standards for source output impedance are severely out of date and inappropriate for modern headphone sources.

Question: So if the manufacturers often don’t provide output impedance ratings for source amps, where is the best place to look for such information? The list provided will prove helpful, but are there other sources? Is this something an amateur equipped with an electrical meter can measure easily?

 

[AudioStudies]

@bobbooo NvAvGuy article provided a link to a Wiki site that defined electric damping factor, in terms of "resistive part of impedance" - However, the Benchmark white paper just defines damping factor as Load Impedance / Source Impedance. Why the apparent discrepancy? Also, why not just call the "resistive part of impedance" resistance?

 

[solderdude]

• Electrical damping is reduced as the source output impedance is increased, and this can result in subpar bass performance of the headphones, with boomy (less controlled) bass sounds. Additionally the transient response is compromised and the bass will roll off sooner and not go as deep.

I have never seen this in any of my measurements.
The 'boomy' bass is caused by voltage division and the usual boost in the lows.
EQ it down to the same level and there is no boomy bass anymore.
Damping factor thing for headphones is a bit of a nonsensical thing.
My reasons are explained here (+ read the posts after it)
Damping factor with woofers and motors etc. is a thing.

 

[AudioStudies]

Damping factor with woofers

Makes sense, larger drivers. When I blend the segment into the main document, I will remove the thing about electrical damping. There are already enough reasons to keep source impedance low, anyway. I will post a few more segments in the coming days. Thanks solderdude for keeping a close eye on this thread. The NvAvGuy appears to be a smart guy, but it looks like he got this one wrong. My recollection tells me that impedance can consist of any combination of resistance, capacitive reactance, and inductance. If I understood NvAvGuy correctly, most headphone circuits have a significant amount of inductance, and capacitive reactance to a lesser degree. I would suspect the amount of inductance relates back to the transducer technology used in the design.

 

[bobbooo]

@bobbooo NvAvGuy article provided a link to a Wiki site that defined electric damping factor, in terms of "resistive part of impedance" - However, the Benchmark white paper just defines damping factor as Load Impedance / Source Impedance. Why the apparent discrepancy? Also, why not just call the "resistive part of impedance" resistance?

Just to make clear that impedance (Z) is a complex quantity (in the mathematical sense), defined as Z = R + iX, where X is the reactance (due to inductance and capacitance). In practice the reactance effects are negligible in these cases so impedance and resistance are sometimes used interchangeably.

 

[AudioStudies]

Reactive Loads

Headphones typically do not exhibit the behavior of pure resistors; rather inductance is prevalent in most headphones, and to a lesser degree capacitance. Most headphones exhibit reactance, opposition to electrical current attributable to inductance or capacitance (or both), when connected to a source amplifier. This reactance represents a complex impedance. In situations of reactive loads, the capacitive and inductive elements in these headphones causes the impedance to change with frequency. Audio signals containing music are transmitted in AC current, thus impedance, rather than resistance, is how headphones are rated for use. Calculations involving reactive loads involve more complex mathematics than the simple forms of Ohm’s Law that can be used in circuits that are purely resistive and DC current only.

Reactance is similar to resistance in the sense that the greater reactance, the smaller the current for a given voltage. However, there are significant differences between reactance and resistance. Consider that reactance changes the phase, power is stored rather than dissipated in a purely reactive element, reactance can be negative, and reactance in a circuit element is frequency-dependent.

Phase is the time difference between the peak voltage and the peak current. A phase shift occurs in reactive circuit elements such that the current through the element is shifted by a quarter of a cycle relative to the voltage.

The transducer technology chosen for a headphone design is related to the reactance and thus the impedance. ??Can anyone elaborate???

 

[AudioStudies]

Voltage Division

A voltage divider is a passive linear electronic circuit that exhibits an output voltage, Vout, that is a fraction of the input voltage, Vin, applied to the circuit. Two resistors in series circuit is an example of a voltage divider, when Vin is applied across the pair of resistors, and Vout is taken from the connection between the two resistors. Voltage division is the result of distributing the input voltage among the components of the divider. The output voltage of a voltage divider varies with respect to the current supplied to an external load.

Resistor voltage dividers can create reference voltages, reduce the magnitude of a voltage to enable measurement, and may also be used as signal attenuators at low frequencies.

In DC current applications, with relatively low frequencies, a voltage divider comprised solely of resistors may be sufficiently accurate. Conversely, where frequency response over a wide range is required, a voltage divider has capacitive elements added to compensate the load capacitance. A low-pass RC filter is an example of a voltage divider consisting of a resistor and a capacitor in series with the output voltage taken between these two circuit elements.

In headphone circuits, voltage division is the reason that amplifier output impedance is required to be significantly lower than the impedance rating of the headphone. The change in headphone sound when the impedance varies is attributable to voltage division.

 

[AudioStudies]

In general, a low impedance headphone requires more current and less voltage; whereas a high impedance headphone requires more voltage and less current. The voltage is the driving force that produces current, and this driving force needs to be greater to overcome higher impedance loads. Conversely lower impedance loads do not require as much voltage to drive through the impedance, but the current requirement will be greater because there is less impedance resisting the current.

At the maximum amplitude in an AC circuit, power, P, is defined as the product of voltage and current: P = VI. It is therefore possible that a low impedance headphone and a high impedance headphone could have the same power requirements. Additionally, a low impedance headphone may have a greater power requirement than a high impedance headphone. Therefore, impedance alone is not a determinant of how much power is required to drive a headphone to appropriate listening volumes.

Clearly, sensitivity also plays a role in determining how much power is required to drive a headphone. The very hardest headphones to drive are those with low impedance and low sensitivity because of great current requirement due to the low impedance combined with the voltage requirement to overcome the low sensitivity and achieve listenable volume levels.