Phonak Audéo PFE 022

This is yet another IEM received from Inks. Once again, thnx for giving me this opportunity, my friend. Please keep in mind that the listed reference response has been obtained with gray filters attached.

PRO: RIGHT ON THE REFERENCE TARGET! Considering its MSRP of $129, the price / performance ratio PFE 022 potentially has is very high. You can even tweak the response with different filters too. Great value for the performance.

CON: There is a lot of harmonic distortion, especially the third harmonics, in the mid-range, at which the human hearing becomes the most sensitive. This is definitely audible, and seems due to the over-equalization done by the manufacturer to forcibly meet the target response. Well, I guess it is a reasonable compromise to take for the low price.

ON SECOND THOUGHT: Although PFE 022's accuracy is right on the target, its practical insertion depth is little too shallow due to the stem being too short. The owner, Inks, also notes that its sound is slightly harsh for him. The magenta-coded plot on the right shows the response with PFE 022 inserted shallow. No wonder it was harsh.

ON SECOND THOUGHT #2: The response of PFE 022 can be tamed, by using filters with various acoustic impedance value. If I was the owner, I'll just stick with gray filters, since they yield the least peaky response.

Yet another oekaki compilation

Well, I've done quite a few drawings with PaintBBS v2.22_8 since the last update. So here comes another compliation.

Yamaha EPH-100

This is yet another IEM offered by my dear friend, Inks: Yamaha EPH-100. According to the manufacturer, EPH-100 is geared up with a super-compact Φ6 mm dynamic transducer, which delivers sound with lower distortion. That sound really intriguing!

Unfortunately, EPH-100's ear sleeves are just too thick to be fully inserted into the ear simulators without tinkering, so measurement data listed below have been acquired sleeveless, fully inserted up to the reference plane. (you can never get to this depth with stock sleeves)

PRO: What a pleasant surprise; Not only EPH-100 delivers a superb sound with virtually no distortion, its frequency range also extends really high.

CON: Left and right channels are slightly mismatched, but it is not big of a deal. Ear sleeves are little too large, even though the IEM itself is very thin. Also, the sub-bass response is just too much with lots of delay. You can say the bass is slow, but at the same time, the delay creates a sound stage of its own.

ON SECOND THOUGHT: In order to properly address the practical aspect of EPH-100's insertion depth, I used  proprietary external ear adapters. The plot on the top shows when EPH-100 is inserted as deep as it can get with stock sleeves. 

The one on the bottom shows the same response on the left channel, with the insertion depth at its shallowest. As expected, insertion depth is not much of an issue here, due to the very low acoustic output impedance of the 6mm driver. This is amazing; the driver is actually working independent from the load(ear canal) impedance!

Fostex T50RP part1: Aesthetics

My friend, Salsal, has been bothering me with this headphone, like, since 2006, by claiming the superiority of the technology Fostex implemented on this headphone.


The packaging

The design

Behold, the king of bulkiness!

Bulky, sturdy, masculine, plastic, and finally, 1980. These are the adjectives that describe Fostex T50RP's cosmetic aspects.

A major upgrade from the first-generation: switching to urethane earpads. While this is still a nice advancement from cheap pleather earpads, there isn't enough thickness to fully seal the ear-driver interspace. With the poor fitting issue of stock earpads, T50RP loses a lot of sub-bass response caused by the radiation impedance. 

Although T50RP's height adjusting mechanism is very primitive, it is built to last: metal joints & a rubber headband.

Such a nice gesture from the manufacturer: A detachable cable not only solves the durability problem, it also satisfies audiophiles who actually care about the quality of the cable, whether it matter or not in terms of affecting the sound quality.

T50RP is a professional studio headphone, and excluding a 3.5mm headphone jack is an understandable circumstance. However, in my opinion, 3.5 mm jack could have appealed to the wider spectrum of customers.

Continued to Part 2, General analysis

Do headphones really need a bass boost?

Die somniantes

SRSLY??? R U **NG KDDNG ME?

For God's sake, it seems Goldenears.net has officially implemented a low-frequency boost in their headphone measurement data, +9 dB for earphone, and +6 dB for headphones respectively, caused by the missing 6 dB effect. And they verified the claim with a comprehensive listening test as well. Wait a minute, the effect has been debunked already!

Previously, GE's contradiction on mannequin measurement data has been discussed. While their idea of a high-frequency attenuation is a reasonable method to minimize possible perceived tonal error for reproducing loudspeaker materials, correlating such subjectivism with mannequin data simply does not work, considering how IEC 60268-7 clearly defines the purpose of a mannequin use.

Basically with the claimed target curve, its "ideal" headphone should have a frequency response with a sound pressure attenuating as the frequency arises, as seen above. It is absolutely true that a negatively tilted room response is ideal for a hi-fidelity loudspeaker reproduction. And although headphone manufacturers know it is not a definitive solution to diminish the association principle mismatch between loudspeaker-headphone acoustics, they still tune their headphones in a similar way, so that their headphones do not sound too sharp and dry. According to Dr. Sear Olive's research from 2009:

"A flat in-room target response is clearly not the optimal target curve for room equalization. The preferred room corrections have a target response that has a smooth downward slope with increasing frequency. This tells us that listeners prefer a certain amount of natural room gain." from: http://seanolive.blogspot.com/2009/11/subjective-and-objective-evaluation-of.html

And GE's target curve closely matches the above description quite well. Well, there is always a catch:

"If the room is acoustically dead with few reflections and/or the directivity of the loudspeaker is quite high, the in-room response will represent a higher proportion of the direct sound, which should be flat. Using a target curve with large downward tilt will make the loudspeaker sound too dull...The only case where a flat in-room response would be desirable was if the room were the acoustic equivalent of an if anechoic chamber and the listener is hearing just the direct sound."
from: http://seanolive.blogspot.com/2009/11/subjective-and-objective-evaluation-of.html

Not to mention even a slight offset of a driver placement on the head causes a night and day difference in the frequency response(extremely directive), considering headphones' transient properties mostly derive from the drivers' own sole mechanical performance, it is only logical to assume the (compensated) frequency response must remain flat on headphones. Should GE's claim verified to be true, typical headphone measurement data must be as complex as in-room loudspeaker measurement data, with various reflective/reverberant characteristics skewing the direct sound. Unfortunately, that is just not the case with headphones; even cogitating a very-reverberant SONY MDR-CD3000's measurement data.


A compensation to no avail

Then how about the listening test? GE say they were able to verify their claim under a reference test condition. As mentioned before, to normal untrained listeners, the low frequency error is still prevalent due to the association principle mismatch. The bottom line is that there is absolutely no way to correctly measure the definitive number for compensation, since it is deriving from an auditory illusional phenomenon after all.

from Olive and Rumsey

One may argue that there is a ~6 dB bass level increment even in IEC 60268-13 conditions, headphones must reflect it as well. According to the above data, this argument seems sound. However, it must not be forgotten that below the Schroeder frequency, at which the room acoustics start to kick-in, there is no absolute 'response target' in regards to 'an ideal bass':

"it is necessary to diminish the importance of the curve at these low frequencies. In fact, we can ignore these effects because they will be merged with, and indeed swamped by, the standing-wave/room resonances active in this frequency region." F. Toole, "Sound Reproduction", Focal Press (2008).

Moreover, there is nothing known about GE's room condition, so it can't be assumed that the sound pressure level difference perceived between speakers and headphones was correctly measured. In other words, even if the frequency responses of both speakers and headphones were well-matched, other factors might have altered the perceived in-room response; there are just too many acoustic variables affecting this frequency region.

"there was evidence of variations in judgments due to irregularities in bass performance. Again, humans seem to be able to adapt to a certain amount of bass misbehavior, but the more extreme the problem, the more difficult it is to completely ignore...there is nothing that can be done in advance of building and setting up a room that has a high degree of certainty of achieving good bass. Probabilities may be improved in some respects of acoustical performance, but not all respects. There is no “magic bullet.” F. Toole, "Sound Reproduction", Focal Press (2008).

Various reference targets do not reflect such hump in the sub-bass region: from B&K, Olive, and Toole.

And how about the discrepancy with earphones? It has been found that the eardrum over-excursion caused by a pressurized ear canal increases the lower frequency response. Since this type of excursion error causes a boost of ~15 dB @ 20 Hz, GE's "test-confirmed" compensation figure of as much as 9 dB can be explained. As the perceived bass of earphones mostly depends on the interpersonal variance of the eardrum's compliance & the amount of air pressure built-up in the ear canal, GE's approach can be interpreted as a case of haste & immature generalization.

Do headphones really need a bass boost?

With all the data I've discussed put into consideration, I would say the answer is definitely 'NO'. A simple amplification in the sound pressure level may reduce the error for normal listeners, but does not solve the source of the problem. Also, it is not simply possible to turn headphones into loudspeakers either, unless an accurate binaural synthesis is implemented.

I think, ironically, headphone enthusiasts' best bet lies in loudspeaker acoustics, by extending the low frequency bandwidth:

"The average bass extension - the low-cutoff frequency - progressively decreases as the fidelity rating increases. The listeners liked low bass - not more bass, in the sense that it is boosted, but bass extended to lower frequencies." F. Toole, "Sound Reproduction", Focal Press (2008).

Then why flogging a dead horse?

I've been wondering, why such objectivism-oriented websites continue to implement rather 'unobjective' test methodologies, when the resulting data can seriously mislead the end-users? Such target curve turns typical headphones' frequency response more favorably to the manufacturers, who simply rely on a pressure level compensation due to the lack of research on their ends. As long as the graph looks good, the product should sell. Since commercial-oriented websites depend on sponsorships, their relationship with headphone manufaturers can be easily understood; They do this for living, in the end. (wait, that is why I can't get a single test sample from any manufacturers! LOL)

SONY MDR-MA900 part 3: In-depth analysis

Continued from part 1 & part 2.


SONY MDR-MA900 is geared up with two vital technologies, which were originally developed for MDR-F1 nearly 15 years ago by the headphone maestro, 投野耕治-san who developed the king of headphones, MDR-R10. The first one is an acoustic bass lens, and the second one is an impedance compensator.

1. Acoustic bass lens
2. Impedance compensator

The effects these technologies inflicting on MDR-MA900's sound signature will be discussed.


1. An economical, yet effective technique

On the user manual of MDR-F1, there is a brief description on this bass-enhancing technology:

"On the front side of the driver unit of the MDR-F1 is an "Acoustic bass lens", a box shaped chamber covered by an acoustical resistor material. The acoustical resistor material allows high frequency sound to pass through and filters the low frequency sound. Consequently, the low frequency sounds are concentrated to the center part of the driver unit, and sufficient bass sound is delivered to the listener. At the same time, frequency response is controlled by the "Acoustic bass lens" to provide mild yet extending high frequency sound."

And according to SONY's patent, 特開平10-032892, while the low frequency bypasses the inertance(Me) of a non-woven fabric intact, the frontal cavity compliance(Ce) and the fabric(Re) effectively damp peaks in the mid frequency range. The high frequency response can be attenuated as well, by decreasing the pore size(Me). Regrettably, since SONY has not disclosed any of relevant data, such as the acoustic resistance of the fabric, or the volume of cavities, to estimate the effect of the lens, no calculation can be made.

In short, this bass lens is an acoustic low-pass filter, accompanied with partial damping of the sound using a porous material.

Still doesn't ring a bell?

This is a well-known acoustic tuning technique, and is actually quite primitive to be called as a 'technology'. As this 'lens' is easily applicable due to its lower manufacturing cost compared to other techniques, it can be easily seen on headphones from other manufacturers as well. Yet, it does not mean the technique is just a commercial gimmick; they are very effective in evening out peaks.

D: far from the ear / N: close to the ear / E: N with acoustic bass lens 

Going back to the patent, there is no need for identifying each curves; It is obvious which one is the result of the lens.

The developer of MDR-MA900, 松尾伴大-san, describes acoustic bass lens this way:

"By utilizing an acoustic damping material, the low-frequency response is first concentrated, and then radiated to the pinna directly. This acoustic focusing technique has been used previously with MDR-F1, and consequently, the low frequency response should be perceived more or less the same by any listeners."


2. A resistive voltage divider within

Although there is a mention about the impedance compensator on the user manual of MDR-F1, the description is just too vague to correctly identify what it is.

"In full open air type headphones, impedance around f0 fluctuates, thus the output impedance of the audio player affects the sound reproduced by the headphones...Conventional full open air type headphones need to be connected to speaker output terminals or to be driven by a special amplifier in order to reproduce intended quality sound. The MDR-F1 does not need special connections because they have impedance compensator which eliminate the variation of sound quality created by amplifier output impedance."

So the compensator's role is to help maintain linearity in the low frequency, regardless of the source impedance of which the headphone is connected to. Basically, SONY is claiming that MDR-F1 and MDR-MA900 operate free from damping-related response errors.

In order to further investigate the technology, with a friendly advice from my dear friend, ソノベ-san, the very patent that deals with this compensator has been tracked down: 特開平09-307980. 

According to SONY, the impedance compensator is simply a resistive voltage divider with a pair of 22 Ω resistors installed in parallel on each channel. With a simple formula, a consequential source impedance can be calculated:

Zo = (R1 * R2) / (R1 + R2)

And this is why MDR-F1 & MDR-MA900's rated impedances are both 12 Ω.

So how does it work? With this voltage divider, a source impedance of 470 Ω becomes 21 Ω, and the consequential damping error on MDR-F1's output decreases almost in half, from 7 dB to 3.8 dB. While this seems like a brilliant way to minimize the effect of damping, the filter still adds 11 Ω to even a 0 Ω source. That means an expensive, dedicated pure voltage source will be completely wasted: Sound quality compromised for the sake of circumstantial variables. Having an unnecessary resistive voltage divider in an acoustic signal transmission is definitely not a good news for audio enthusiasts, IMO.

Furthermore, this filter totally screwed up my impedance measurement data; the reference load of 100 Ω on my impedance measurement jig has been compensated too! It was measured 17 Ω, which is not correct.

In order to correctly figure out MDR-MA900's true impedance value, a frequency-dependent attenuation calculation shall be applied. By comparing differences between the level of attenuation with a serial resistor loaded/unloaded, MDR-MA900's original impedance comes out to be 8 Ω on each channel.

response error of 2 dB @ f0

In conclusion

SONY MDR-MA900 is like an old-innovation revisited. Even with all the sleek looks, the technology the manufacturer utilized is quite classical. Although these core technologies have been passed down and revamped on later models many times, it seems the designer, 松尾伴大-san, truly wanted to revitalize his master, 投野耕治-san's underrated work, MDR-F1.

So did 松尾-san get what he wanted? Maybe. MDR-MA900's acoustic uniqueness shines off among other open-air headphones for sure. I was not impressed with the original MDR-F1, but MA900 is such a pleasure to listen to. However, he should have considered the fact that most of us audiophiles actually own a dedicated headphone amplifier with an output impedance less than 1 Ω. Considering the MSRP of $299, who would most likely be potential buyers: Audiophiles? or normal users?