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ASR Getting Into Measuring Headphones!

bobbooo

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They basically took 31 different headphones, measured the FR of each on a GRAS 45, and then REPLICATED each FR curve using EQ and on a single pair of AKG K712 headphones. Each listener "listened" to 8 headphones "virtually" through that K712. The FR match between actual and "virtual/replicated" headphone was only +/- 1dB up to 12khz, and above 12khz, they didn't aggressively EQ. The did validation testing and only found a correlation of 0.85 between actual and virtual ratings.
Honestly, I think it's pretty remarkable that only matching 60% of the frequency response with a +/-1 dB accuracy produced as high a correlation as that, and just goes to show how frequency response makes up the vast majority and most important part of audible differences between headphones, how frequencies above 12 kHz are of much less importantance than below, and how relatively undiscerning the human ear actually is (even those of highly trained listeners), contrary to the outlandish claims of some 'audiophiles' that the human ear is a better acoustic measurement instrument than state of the art man-made equipment.
 
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DualTriode

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@amirm,

What about the APx555 fan noise?

Closed loop the AP can do magic.

Using microphones I do not think that the AP can tell the difference between fan noise and distortion.

Just for grins I took the headphones off the 45CA, turned off the amplifiers and inserted a foam ear plug in the 45CA Left Ear.

Using the optional AP Acoustic Response software the attached is the THD Level plot.

My impression is that a way of isolating the AP fan noise is required.

Thanks DT
THD Level.png
 
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@amirm There a chance to send you earphones and you will measure them as you offer with amplifiers ?
I can send you a kz as16 and CCA ca16. Maybe I can even buy new earphones and send them directly to you, this way there will be only a return shipping cost .I think that this way you will able to measure more earphones without buying them yourself or to loan them from the company .
 
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Wow super incredible.

I'm a relatively new lurker of this site and really respect all the SCIENCE that has and is being done here measuring Amps and DACs and also other audio equipment.

Very cool to see that headphones and earphones are getting the same treatment!
 
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I do agree, thanks for the great work, I'm looking for some headphones to listen to music at night and was highly interested to read these tests of the sennheiser HD800S and audeze LCX... Think I will wait for the next one and wish for one you'll recommend "out of the box" :D
 

laurelkurt

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The heading says it all: we are going to be officially measuring, reviewing and characterizing earphones and headphones (likely more of the latter than the former). Some of you know the evaluation process I went through this summer of the BK 5128 Head and Torso headphone measurement system. The company was wonderful to work with but alas, lack of research using that new system made interpreting the results very difficult. And then there was the cost for which you could buy a luxury car! Post that I evaluated the GRAS 45CA which has been used in research and results were much more encouraging and the cost much lower. So a couple of months ago I decided to put in the order for one and here it is!

View attachment 97136

The fixture is incredibly heavy but that is goodness as it won't move when you try to adjust the headphone. Because the fixture is not a manikin, I actually find it a lot easier to try different positions to get better alignment of the headphone. The unit is stereo so I am able to quickly compare one channel to the other for alignment purposes and also for driver matching.

There are many variations of 45CA. The one I have purchases is the 45CA-10. Options on it are anthropometric pinna (human looking ear), model KB5010, which you can see more clearly here:

View attachment 97138

The old pinna were rigid unlike a real ear. That caused headphones that sat on the ear to sit proud, completely messing up their low frequency response. The pinna as supplied is quite soft -- much like a babies ear. My own ears are more rigid (as they should be for someone as King of Audio!!!). So some variation always remains but at least we are closer.

The other option is the high-frequency ear simulator/coupler (microphone) model RA0402. Traditional couplers were of "711" type and had too much resonance in higher frequencies. The RA0402 has a more muted response in that region. This would avoid the temptation to try to pull those peaks down post measurements as they were likely not matching real ear response. That said, the correction is somewhat arbitrary to so confidence remains low in higher treble region (due to this and reflections inside the cup).

External constant current is needed to drive the microphone pre-amplifiers built into the system. So I had to purchase a GRAS 12AX 4-channel power supply and amplifier (though I will be using it as a 0 dB buffer). The microphones are pre-polarized meaning you don't need a high voltage power supply to drive then as you used to.

The retail cost is around $15,000 so this was another significant investment in our toolset to quantify performance of audio products.

I know some of you think headphone measurements have already been done and other think they are inaccurate so whey bother. I had to resolve both of these issues in my mind before deciding to spend this money so let me give you my justification for proceeding.

1. Measurements have been done. This is indeed true for the most part. It is impressive how the headphone community has embraced measurements to such a degree compared to speakers which was hardly touched as far as proper measurements. Part of this is due to lower cost of measurement gear but still, the effort to measure literally hundreds of not thousands of headphones was not free.

While the data is great, having so many versions of it is not so. There are a number of different fixtures uses resulting in different measurements. Super experienced headphone users know how to wade through these and get the information they need. But it is not for everyone.

Then there is our method of doing things. You could have found electronic and speaker measurements elsewhere but we have managed to not only catch up but leave behind many other sites that do this type of work. There is a "style," method and even attitude that goes into my reviews that is unique and works for both me and the readership. This combination does not exist elsewhere as it is unique by nature of it. Indeed the few headphone reviews I have done created a ton of interest. Importantly for me, they quantified the performance of the headphones I tested beyond what I had read elsewhere. Maybe that is my issue but again, how to clearly communicate what a piece of audio is about is what I specialize in. And will bring the same to headphones.

2. Why bother to measure headphones as data is inaccurate. This is what led me last year to invest in speaker measurements than headphones. The research about speakers is far more conclusive and measurements a ton more standardized. But something changed when I got the GRA 45C evaluation system. I measured, saw the deficiencies, applied judicious EQ that resulted in incredible sonic improvement in these headphones. This demonstrated that the objective data is indeed highly instructive. And that just a bit of EQ transforms the performance of any headphone, making them not only more accurate but far more enjoyable. As I type this, I am listening to AEON Flow closed headphone post EQ and it sounds so nice. In some respects, it is outperforming some of the best speakers I have tested!

Yes, you have to be careful how you approach the measurement data. I am not a fan of hugging a target curve to the max and spitting out 10 EQ bands to apply to them. The measurement data is not that reliable to enable this. But a softer approach works and works wonderfully.

A bonus of measuring headphones relative to speakers is speed. I am able to characterize the frequency response of a headphone in 5 seconds. Same process takes hours with speakers and lugging around heavy boxes around.

Ultimately I thought I had no choice but to test and review headphones. They are part and parcel of my own music listening and countless audiophiles. We have to treat them as well as we do other audio products, Leaving their testing to others did not make sense leaving a hole in our arsenal of bringing the best sound to everyone.

The main barrier was of course the cost. The capital investments in this effort have long gone the crazy land even when I purchased my Audio Precision analyzer let alone the Klippel speaker measurement system. I don't know when I am going to recoup those dollars. So investing even more did not at all seem logical. But I just decided to hell with it and proceed. Asked my wife what she thought and she could tell in my eyes there was not a "no" in what I was expecting from her. :)

As with our other measurements, there will be some growing pains as we develop and mature our measurement suite for headphones. I will as always carry a hard line in listening to complaints. :) But I will internalize some and will make them more perfect as time goes. I ask you to leave negativity behind and work constructively to get more data under our belt about this super important transducer. Last thing I need is dealing with food fights on this subject in addition to new workload of testing headphones.

So there it is. I am poorer financially but am confident I will be far richer emotionally to bring more data to our collective audio life.

P.S. I picked up the 45CA in person from Audio Precision headquarters since they are the sister company to GRAS. Alas, half way down the check engine line came on in our Mercedes Sprinter RV. :( Read the code and it is two emissions (NOx) sensors going bad. Hear huge horror stories about how expensive such repairs are at Mercedes. Have a call into them to see if they are covered under emissions warranty (the van is 4.5 years old with only 18,000 miles). I got home only to see a message from them that the power supply had just arrived and was not in the box I picked up! So I had to wait a week for that to arrive. Not a good start but hopefully things will change from here on.

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Any donations are appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
 
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amirm

amirm

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Thread Starter #268
@amirm There a chance to send you earphones and you will measure them as you offer with amplifiers ?
I can send you a kz as16 and CCA ca16. Maybe I can even buy new earphones and send them directly to you, this way there will be only a return shipping cost .I think that this way you will able to measure more earphones without buying them yourself or to loan them from the company .
It will be a similar process but let's wait a bit on that. I want to make sure I have a proper protocol for IEMs before accepting more.
 
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amirm

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Thread Starter #269
@amirm,

What about the APx555 fan noise?
It is an annoyance to be sure. For now, set the playback level high enough that it dominates the AP noise. Also, I have my AP inside of an enclosure which quiets it down some. I also have isolation under my Gras 45CA which helped with low frequency transmission through the fixture itself.

I will probably build a quiet box in the future for it but it makes the workflow much slower. Right now I have the headphones right next to me and can make quick adjustments. With a large soundbox it would have to be somewhere else, slowing down the process.
 
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Would love to see the ZMF Verite closed to get measured, heavily considering to buy a pair. They’re the most highly regarded closed back out there.

Actually interested in any ZMF headphones being measured and let’s see if they fare better than the Abyss and Focal.
 

Hayabusa

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There are many variations of 45CA. The one I have purchases is the 45CA-10. Options on it are anthropometric pinna (human looking ear), model KB5010, which you can see more clearly here:

View attachment 97138


Any donations are appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
Hi Amir, I was just thinking about thia experiment: It would be nice to see what the transfer function of the 45CA-10 is if the source would be from a set of speakers setup in a typical stereo setup/listening distance.
This could be done by using the speakers as source and then measure the difference between the FR with the 45CA-10 and a calibrated mic at the same position.
This should give some kind of inverse version of the Harman curve isn't it?
 
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