[KinGensai]

Something interesting has come to my attention, and I've been thinking about what is going on here and why the pieces aren't matching. For context, the data in question is below.

Happy holidays tip-rollers! I did some experiments on my ghetto measurement rig, trying to understand how different factors impact the sound of eartips in the most controlled environment possible, and to understand my own listening impressions. All using my Final E500; they are open-back, which is a plus for this experiment. The factors I'm interested in are:

1. Sound bore width.
   • For this experiment, I decided to go with Tanchjim T300T (wide) vs T300B (narrow), two tips that, to my bare eyes, are identical up to the bore diameter.
2. Sound bore glossy-ness / matte-ness.
   • For this experiment, I decided to go with Tennmak Whirlwind vs KZ Whirlwind. I might make post about how to differentiate them at some point, but for the purpose of this post, Tennmak Whirlwind visibly has a more glossy soundbore than KZ Whirlwind. Another candidate for this would be JVC SpiralDot FX9 vs FX10, but those two are more different in their materials than in their textures.
3. Sound bore length.
   • A natural candidate for this is Sedna (Original) vs Sedna Short, but for this purpose of being comparable to other results, I decided to go with the approach of adding a 1mm o-ring to the end of the E500 nozzle to shallow-fit the Tennmak Whirlwind and to simulate a longer sound bore length. Note that this effectively increases the eardrum-to-driver distance by adding extra length via eartip's sound bore.
4. Fit depth.
   • For this experiment, I vary the depth in which the E500/Tennmak Whirlwind is inserted onto my measurement rig. This would be equivalent to going a size up to shallow-fit or going a size down to deep-fit your IEM into your ear canal. Note that this effectively changes the eardrum-to-driver distance by adding/subtracting length via ear canal.

Here are the results. Surprisingly, they all agree with my listening impression.

1. The effect of sound bore width (unnormalized & normalized at 1kHz)
   • 
     
   • No surprise that the overall absolute volume are roughly the same between narrow bore and wide bore, although narrow bore can be perceived to be louder due to it being louder in the midrange. Narrowing the sound bore has two effect: boosting the upper-midrange and creating a dip in the treble. Depending on the depth in which you fit your IEM, this dip can happen at the mid-treble or upper-treble. In my case, it is the upper-treble and translates to a narrower soundstage and faster instrument decay. The boost in the upper-midrange is very noticeable too, but less so than the most extreme Final E tips. This translates to a more intimate presentation of images in the midrange.
2. The effect of sound bore glossy-ness / matte-ness (unnormalized & normalized at 1kHz)
   • 
     
   • A matte sound bore sounds like a treated room and a glossy sound bore sounds like an untreated one. That's basically it. Like in a two channel system, treatment or the lack thereof isn't always better. It depends on the speaker, the room and the bass response you are trying to achieve.
   • I have a theory that oddities inside the sound bore (e.g. the ridges in SpinFits and Spring Tip, the dots in SprialDots) sound like furniture in a room, but there isn't a pair of earips in my collection that enables me to do a controlled experiment on this. SpinFit fans, any suggestions?
3. The effect of sound bore length (unnormalized & normalized at 1kHz)
   • 
     
   • The "front o-ring" means deep fitting the eartip onto the nozzle (short sound bore) and the one without means shallow fiftting the eartip onto the nozzle (long sound bore). Sorry for the confusion. The shorter the sound bore, the darker the treble.
4. The effect of depth of fit (unnormalized & normalized at 1kHz)
   • 
   • The deeper the fit, the more absolute volume/energy you are getting in the midrange, especially upper-midrange, extending into lower treble. On the contrary, the shallower the fit, the more bass and treble extension you are getting. The increase in treble overwhelms the increase in bass. Depending on the smoothness of your IEM's treble response, this can translate to extra sibilance and/or a bigger soundstage, when combined with the more distant midrange.
5. Bonus: Tennmak Whirlwind vs T300T, two of my favs
   • 

My main area of concern is the sound bore size effects in this data set, as they seem to contradict my understanding of the physics at play (acoustic impedance) and my direct experience of the tips in question (Tanchjim T300 tips here). I find them to present sound as advertised, whereas here the data set Edric collected and his reported experience is contrary to mine for reasons I'm trying to comprehend.

I'm not a subject matter expert in either acoustics or materials science, so I would like to explore this topic in depth. I believe that there might be an inconsistency between the T300B and T300T in flange design that could cause this sort of unintuitive contradictory effect in a measurement rig, but I might be wrong and I want to get to the truth of this matter.

 

[Edric Li]

Something interesting has come to my attention, and I've been thinking about what is going on here and why the pieces aren't matching. For context, the data in question is below.


My main area of concern is the sound bore size effects in this data set, as they seem to contradict my understanding of the physics at play (acoustic impedance) and my direct experience of the tips in question (Tanchjim T300 tips here). I find them to present sound as advertised, whereas here the data set Edric collected and his reported experience is contrary to mine for reasons I'm trying to comprehend.

I'm not a subject matter expert in either acoustics or materials science, so I would like to explore this topic in depth. I believe that there might be an inconsistency between the T300B and T300T in flange design that could cause this sort of unintuitive contradictory effect in a measurement rig, but I might be wrong and I want to get to the truth of this matter.

There are many physics at play here, all of which can give varying/contradicting predictions. One such physics that supports my finding of wider bore being more bassy is end correction. It states that the wider the pipe, the lower the resonance frequency.

 

[KinGensai]

@Edric Li
As I understand it, end correction is an additional variable in the calculation of resonant frequencies in a pipe, which does take the diameter of the pipe into consideration for calculating the location of the nodes and antinodes. So (n/2)λ=L+2e given e is the same at both ends of the pipe.

the length of a 100Hz waveform is approximately 3430 mm give or take a bit for barometric pressure variations, which is still far too long a waveform for such minute differences like these to affect in terms of resonant frequencies.

Again, not my area of expertise, so I'm probably missing something, but I don't see how end correction can cause a significant enough difference to attenuate the bass response of the B variant vs the T variant, especially compared to an acoustic impedance analysis.

 

[Edric Li]

@Edric Li
As I understand it, end correction is an additional variable in the calculation of resonant frequencies in a pipe, which does take the diameter of the pipe into consideration for calculating the location of the nodes and antinodes. So (n/2)λ=L+2e given e is the same at both ends of the pipe.

Yes, end correction says that a wider pipe has the same effect on the resonance frequency as a longer pipe. Unclear whether it is due to resonance frequency, but you can see in my post that increasing the bore diameter indeed has a similar effect on the FR as decreasing the insertion depth. If you'd like to read more FR measurement of eartips, check out this youtube channel.

the length of a 100Hz waveform is approximately 3430 mm/s give or take a bit for barometric pressure variations, which is still far too long a waveform for such minute differences like these to affect in terms of resonant frequencies.

Not sure what you mean but if you can hear 100Hz in music in your IEM, you can hear a 100Hz resonance in your eartip. In any case, end correction is no more valid than an impedance analysis. It is a theory that supports my observation, that's all.

In my listening experience with eartips in general, I've found that the narrower the sound bore, the more energetic and more intimate the sound is. Wide bores sound more relaxed and spacious. This likely can be explained by something along the lines of acoustic impedance. I believe the change in FR is a result of this change in intimacy vs spaciousness, as opposed to the other way around. It took me a while to realize that more energy and intimacy does not equal more bass quantity. Outside of this anecdote, take everything from me as an uneducated guess.

 

[KinGensai]

What I mean by the second point is that tips are too short to resonate with bass frequencies, so I was just asking for elaboration on how end correction factors in to the attenuation of frequencies below 300Hz in the B variant.

My experience with tips tends to accord with what you describe too, just not in this particular instance of the T vs B variants. I am trying to understand if my perception is being colored by bias or if there's something else happening with the data set.

 

[Edric Li]

What I mean by the second point is that tips are too short to resonate with bass frequencies, so I was just asking for elaboration on how end correction factors in to the attenuation of frequencies below 300Hz in the B variant.

Oh that's not how sound waves work. The wavelength of a 100Hz sound wave is 3 meters but you definitely can hear it from an IEM sitting millimeters away from your eardrum. There too *will* be resonance in an eartip. Those resonance frequencies *will* be lower in the wider pipe. The question is whether we can hear the lowered resonance of a 1.5mm end correction, and whether other physical phenomena happening in this tiny space will overwhelm its effect.

I'd argue it is audible: notice in the formula that end correction is a linear effect. This is saying that widening the sound bore by 1.5mm has the same effect of decreasing the insertion depth by x*1.5mm. If you have adequate size o-rings, you can easily check with your ear that even 0.5mm change in insertion depth is very audible, with an IEM that goes reasonably deep. If you've heard the change going from S to M to L with the same model eartips, you've heard the change in 0.5mm insertion depth. How large this x is? I don't know, I don't have a degree.

My experience with tips tends to accord with what you describe too, just not in this particular instance of the T vs B variants. I am trying to understand if my perception is being colored by bias or if there's something else happening with the data set.

My suggestion would be to try more eartips and do more extreme comparisons. For one, the Tanchjim tips are frankly quite unique. The T and B have noticeably more bass than other eartips at the same diameter. I haven't quite figure out whether it is due to them having a smaller opening than sound bore, or the glossy and hex-shaped sound bore themselves. Plus neither the B or the T are particularly wide or narrow. Try, for example, Final E vs Tannmak Whirlwind, or Acoustune AET08 vs BVGP W01, to really get a sense of the contrast.

 

[KinGensai]

Oh that's not how sound waves work. The wavelength of a 100Hz sound wave is 3 meters but you definitely can hear it from an IEM sitting millimeters away from your eardrum. There too *will* be resonance in an eartip. Those resonance frequencies *will* be lower in the wider pipe. The question is whether we can hear the lowered resonance of a 1.5mm end correction, and whether other physical phenomena happening in this tiny space will overwhelm its effect.

I think you are misunderstanding my argument. My argument, according to the equation, is that tips are nowhere near long enough to resonate with low frequencies because the node and antinode are too close together whether you add 3mm or not to the length, thus the difference in amplitude of the low frequencies are not affected by constructive or destructive phase interference from resonance in particular. (7128Hz is my result assuming l+e=12mm since the pipe is effectively a stopped pipe).

Edit: I'm doing some more reading on this, and I think I'm understanding what you are getting at here. As the bore diameter increases, the fundamental resonant frequency shifts downward, so more of the sound becomes affected in theory. I still don't think this particular point is involved with bass because of how far removed the fundamental resonance is from the low end, but maybe you know something about this I don't.

Another thing I notice in regards to this is that bore size doesn't seem to have as much of an effect as material density does, the Divinius Velvet delivers more bass response than either of the T300 variants as an example.

I'd argue it is audible: notice in the formula that end correction is a linear effect. This is saying that widening the sound bore by 1.5mm has the same effect of decreasing the insertion depth by x*1.5mm. If you have adequate size o-rings, you can easily check with your ear that even 0.5mm change in insertion depth is very audible, with an IEM that goes reasonably deep. If you've heard the change going from S to M to L with the same model eartips, you've heard the change in 0.5mm insertion depth. How large this x is? I don't know, I don't have a degree.

It does play a difference, but it's mainly in the treble region that I can discern. Bass region seems more resistant to change based on insertion depth.

 

[Edric Li]

I think you are misunderstanding my argument. My argument, according to the equation, is that tips are nowhere near long enough to resonate with low frequencies because the node and antinode are too close together whether you add 3mm or not to the length, thus the difference in amplitude of the low frequencies are not affected by constructive or destructive phase interference from resonance in particular. (7128Hz is my result assuming l+e=12mm since the pipe is effectively a stopped pipe).

You could be right. I really don’t know.

Another thing I notice in regards to this is that bore size doesn't seem to have as much of an effect as material density does, the Divinius Velvet delivers more bass response than either of the T300 variants as an example.

I tested the bore surface smoothness and indeed it affects bass. I also believe material density makes a difference, especially at loud volume. I just didn’t have a controlled experiment in mind to test for it, besides perhaps JVC FX9 vs FX10.

It does play a difference, but it's mainly in the treble region that I can discern. Bass region seems more resistant to change based on insertion depth.

The change in treble is more drastic than the change in bass, per my measurement. As I postulated in my post, one factor could be how your IEM is tuned. A change in bass is more audible when your IEM is subjectively bass shy than when it is bass heavy. Going from just enough to not enough is a more drastic change than from abundant to plenty, if that makes sense.

In any case, I encourage you to pay attention to the midrange in stead of bass and treble. Does the midrange sound more distant and relaxed going from B to T, while the sub bass impact stays similar? If that’s what you hear, then we are hearing the same.

 

[castleofargh]

I did not read everything, sorry if I bring up something already explained.
Before anything else, how the measurements are done? How much is showing the tips and how much is showing the measurement?
- I can't think of a reason for the low frequency to change that is related to the inside diameter of the tip. Seal quality is almost always the reason for bass change in reality. A few other things could affect measurements like low SPL measure with noisy environment, but that can be tested with a different SPL or in the hopefully quiet nighttime. Do you know what causes the wiggly crap at low freq(is this done with noise instead of a sine sweep)?
- The high frequency seems to show a small shift from insertion difference. Is there still much to see if the alignment(hard to do manually) is more accurate?

End correction is real, but shouldn't it be relevant at the end of the tube? I might be missing something here, but be it on a coupler or in the ear, the tip is no longer out in the open.

 

[Edric Li]

I did not read everything, sorry if I bring up something already explained.
Before anything else, how the measurements are done? How much is showing the tips and how much is showing the measurement?
- I can't think of a reason for the low frequency to change that is related to the inside diameter of the tip. Seal quality is almost always the reason for bass change in reality. A few other things could affect measurements like low SPL measure with noisy environment, but that can be tested with a different SPL or in the hopefully quiet nighttime. Do you know what causes the wiggly crap at low freq(is this done with noise instead of a sine sweep)?
- The high frequency seems to show a small shift from insertion difference. Is there still much to see if the alignment(hard to do manually) is more accurate?.

This is done with pink noise, not sine waves.

Outside of that, my general response is that I’m but a random dude on the internet. I technically cannot convince you of anything I’ve done, respectfully. I can say that the experiment is controlled and done in a way that it convinced myself about the subject of study. And I still feel the same way after reading your suggestions.

End correction is real, but shouldn't it be relevant at the end of the tube? I might be missing something here, but be it on a coupler or in the ear, the tip is no longer out in the open.

I don’t have a degree, but I can assure you that’s not what end correction is. I’d suggest you to scroll up.

 

[BS5711]

Here is an interesting one that someone with technical savvy might explain to me.

I took a few sets of silicone tips that fit well, seal well and sound good. They were KBear 07, Divinus Velvet and Spiral Dots.

I had some tips with foam inserts inside silicone, these never worked for me, just never sounded right.

I took the foam inserts out and put them inside the three tips listed above then tried them on my Letshuoer S12 Pro.

No part of the foam is exposed to my ear canal or an area of sound waves being entirely within the cavity between the stem and the dome, for all practical purposes it is on the outside of the tips with them in ones ears.

In every case the foam changed the sound robbing energy from the bass as I recall. I didn’t listen for long as the effect was an obvious backward step but long enough with each to hear a significant change in sound.

For me conventional foam tips also reduce the bass on the S12 Pro but I didn’t expect the encapsulated foam to do something similar.

I struggle to imagine the physical damping of the silicone by the foam doing anything with such low energy drivers but I can’t think of any other reason why the foam would change the sound.

 

[KinGensai]

@Edric Li
Is it possible you switched the names of your measurements of the T300s? I listened to the tips on my V14 again, and looking at your graphs, switching the names makes the data make sense in conjunction with my experience.

Here is an interesting one that someone with technical savvy might explain to me.

I took a few sets of silicone tips that fit well, seal well and sound good. They were KBear 07, Divinus Velvet and Spiral Dots.

I had some tips with foam inserts inside silicone, these never worked for me, just never sounded right.

I took the foam inserts out and put them inside the three tips listed above then tried them on my Letshuoer S12 Pro.

No part of the foam is exposed to my ear canal or an area of sound waves being entirely within the cavity between the stem and the dome, for all practical purposes it is on the outside of the tips with them in ones ears.

In every case the foam changed the sound robbing energy from the bass as I recall. I didn’t listen for long as the effect was an obvious backward step but long enough with each to hear a significant change in sound.

For me conventional foam tips also reduce the bass on the S12 Pro but I didn’t expect the encapsulated foam to do something similar.

I struggle to imagine the physical damping of the silicone by the foam doing anything with such low energy drivers but I can’t think of any other reason why the foam would change the sound.

IIRC, silicone tends to absorb bass energy and reflect mids and treble, so the thickness of the silicone changes how much bass is reflected vs absorbed. The foam might be stabilizing the silicone and absorbing more bass than normal. Maybe lower density foam could help highlight this behavior compared to the harder foam that's in the Symbio tips.