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Emulating Glasses for Headphone Measurements
- Thread starter amirm
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Yorkshire Mouth
Major Contributor
The pads are hardly touched at all.
Yorkshire Mouth
Major Contributor
Yorkshire Mouth
Major Contributor
Ditto with my normal/distance glasses (the ones I wear when I don’t have my contacts in.
Judging by that particular scenario re glasses type & your face, that would make zero difference to frequency response, but as @RHO pointed out, I can see it could be affected by thicker armed glasses, and perhaps if they were very wide at the front of the skull thereby creating a gap between arms & side of face where the pad might sit (large distance between the arms, which might be indicative of poor glass fitting, eg choosing incorrectly sized glasses, but maybe also down to style of glasses chosen).
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I think that it's important to note that the goal here is less to make an accurate representation of the effect of a pair of glasses on humans (something which is unlikely to ever happen on a GRAS hammerhead fixture anyway), but rather to make a repeatable, standardised test for breach of seal to determine how headphones compare with each others in such instances. There are plenty of other ways headphones may breach seal than glasses (personally that's often caused by the rather significant recess of my skull at the bottom rear of my ears combined with earcups / earpads designs lacking range of motion and compressing unevenly).
For all we care we could be using chopsticks and it would be fine, as long as it's consistent.
For all we care we could be using chopsticks and it would be fine, as long as it's consistent.
I'm not a glass wearer (apart from sunglasses) so I can't comment intimately on this, but I can see the point that @RHO brought up re gap between face and arms(at front of pad seal) of glasses as being an important factor to consider. If not many glasses (that are correctly fitted to a person) exhibit this phenomenon then it wouldn't need to be considered, but if it's quite a common phenomenon then I think it would need to be one of the replications in the test, as the chopsticks you mentioned glued to the side of the fixture wouldn't cover that.
If that's the case then it would make sense to design a test model that is at least representative of what the typical glasses-wearer might experience.
As others have pointed out, there is quite a bit of variation in the size/thickness and clearance of the eyeglass temples (the "arms") from the head. It would be nice to test a variety of different eyeglasses on the gras45 in order to better understand the degree of variation in FR that is attributable. And then choose a model in the middle as the test model.
You'll never get a proper simulation of the impact of an average eyeglasses' arm on an average human (averages which we don't know anyway) to begin with with this sort of fixture. What we want to know is, if we introduce air gap(s) of x(y, z) sizes, what is the impact on the HP's FR ? This won't tell you how the headphones behave on real humans (for that you'll need in situ measurements as Rtings does them), but what it will tell you is how resilient or not the HP's ideal FR is to breach of seal and where the resonant frequency roughly is. We don't specifically need an eyeglasses arm for that.
I don't agree, I think it can be simulated to some degree on a test fixture, I'm not so quick to dismiss it.
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^^
^^^Yes to all this^^^
We could have analysis paralysis for 20 more pages and get nowhere. Velcro the temple pieces to the fixture and carry on.
^^^Yes to all this^^^
We could have analysis paralysis for 20 more pages and get nowhere. Velcro the temple pieces to the fixture and carry on.
Yes, I think you're right. Glasses are certainly not the only way the seal from the pads can be broken.
Testing with some fixed amount of leakage would be fine then. It doesn't have to emulate glasses or any specific type of leak.
I would opt for maybe 3 "sizes" in leaks. Maybe a very small one (5mm²) a medium one (50mm²) and a large one (1cm²). These are all still small, but I don't think really big leaks are common.
You don’t need to do that. Plotting FR for a few representative eyeglasses should be fine to at least understand the variation.
You’re then assuming that the only variable is the size of the hole and not the location of the hole or the effect of the eyeglass temples on the adjacent seal or diffraction/reflection from the temples, etc. I don’t think you know all of these things. Furthermore, how would you know what sizes/shape hole is equivalent to xyz eyeglasses without testing real eyeglasses? For many reasons I also disagree
I think that the advantage of that approach (ie trying to create similarly sized holes) is that it would provide a comparative evaluation between headphones that the current seal breach tests can't fully provide as the HP's pads may deform quite significantly differently when presented with an eyeglasses' arm (or a chopstick). It would allow us to quantify the loss in bass frequencies response per air gap instead of just merely looking at where the resonant frequency is. For ANC headphones with a feedback mechanism it would also tell us at which point the system gives up (when measured with the appropriate signal).
You're absolutely right, but I think that seeking to simulate how a pair of HPs would behave in terms of seal breach on real humans with a GRAS hammerhead style fixture is a fool's errand and better served by Rtings' approach of measuring HP's bass response on five real humans, which, as low a sample size it is, already is a start.
The above approach would at least provide new information that we currently don't have (ie the quantifiable aspect in terms of FR magnitude).
Yorkshire Mouth
Major Contributor
But it’s impossible to spectate the two.
By definition, your glasses may sink into your face enough that they don’t break the deal at all. 100 goes into your face, 0% into the pads.
If Amir devised a test with a dummy head with flat, solid sides, so that 100% goes j to the pads and 0% ever goes into the face, that completely invalidates the process.
Even if in real life just 20% of the hit us taken by the face, the fact that 0% is taken by the dummy head would completely skew the results.
There is one way the experiment were to be valid. If it showed no difference, even on a solid head with no give.
There’s no dummy head on the GRAS used by Amir.
We can add an objective data point to the measurements by agreeing on a standard thickness of the gap.
Or we can keep asking for subjective reports by people wearing all kind of glasses over all kind of heads.
On the former, please keep in mind we’re asking a single person, albeit very passionate, to produce those measurements, so I would take into consideration how much of an hassle will be to actually do it, and how many times.
Of course the beauty of a 3D print is that it can be easily reproduced, a version with a different clamp could also be made to use the same gaps with different GRAS models, like the one used by @Resolve, which has a single “ear”.
It‘s good to keep thinking about how and what we want to measure, but we should stay real over what’s possible, practical and, above all, can be standardised and reproduced by as many people as possible.
We can add an objective data point to the measurements by agreeing on a standard thickness of the gap.
Or we can keep asking for subjective reports by people wearing all kind of glasses over all kind of heads.
On the former, please keep in mind we’re asking a single person, albeit very passionate, to produce those measurements, so I would take into consideration how much of an hassle will be to actually do it, and how many times.
Of course the beauty of a 3D print is that it can be easily reproduced, a version with a different clamp could also be made to use the same gaps with different GRAS models, like the one used by @Resolve, which has a single “ear”.
It‘s good to keep thinking about how and what we want to measure, but we should stay real over what’s possible, practical and, above all, can be standardised and reproduced by as many people as possible.
Use the very thin armed glasses.
No need to measure for the majority or popular frames as the average person isn't going to care.
Measure for the person who does, and is willing to wear minimalist glasses.
No need to measure for the majority or popular frames as the average person isn't going to care.
Measure for the person who does, and is willing to wear minimalist glasses.
OP
- Thread Starter
- #79
Not that I look forward to this 
, but we could built multiple glass emulators and test them all. From very little to large -- sort of how I do the distortion tests. Then you can look at the trend and make some conclusions. For this, it would be nice if whatever we come up with can be modified with some mechanical means without changing its position or require remounting. Maybe some kind of cam that you rotate?
, but we could built multiple glass emulators and test them all. From very little to large -- sort of how I do the distortion tests. Then you can look at the trend and make some conclusions. For this, it would be nice if whatever we come up with can be modified with some mechanical means without changing its position or require remounting. Maybe some kind of cam that you rotate?
I agree it could be done by measuring on real humans, but I also think it can be done on the GRAS unit. To be fair, if we really wanted to work it out we could put the "same" glasses on the GRAS and also on an array of humans and compare the differences - if the GRAS unit accurately reflected the bass leakage of the humans then you could then say for sure let's use the GRAS (in which case you don't have to track down 5 humans for each headphone test!).
EDIT: or if the GRAS didn't reflect the bass leakage on the humans then you could change the thickness of the glasses on the GRAS to equal the corresponding results on the humans - a calibration if you like. That way you could say a certain thickness of arm measured on a GRAS is equal to a certain thickness of arm on an average human, and that way you could calibrate your results this way, thus enabling you to create valid measurements on the GRAS.
@amirm , this is getting your family & interns involved - the 5 subjects to calibrate the GRAS!
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