Dynamic Ear Company’s ambient filters: the audiophile’s perspective

INTRODUCTION

Ambient filters are a cornerstone of the musician’s industry. They’re for those instances when you want the hear the stage but your customs do their job a bit too well. Already a customisable option in industry veterans such as Ultimate Ears and Westone, such filters only recently made waves in the audiophile market, first in the form of ADEL (by Asius Technologies, with numerous partners such as 64 Audio, Empire Ears and InEarz), and subsequently APEX by their ex-partners 64 Audio.

In certain cases, the standard -26dB attenuation in custom in-ear monitors is too much, so a mechanism is needed to let the listener hear more of their surroundings. This is achieved in different ways but most commonly with restricted venting and/or acoustic dampers of different resistive values. However, most ambient filters either cause non-linear attenuation that muffles ambient sounds (usually in that higher frequencies are attenuated to a higher degree than lower frequencies) or completely destroy the original signature of the IEM by leaking out too much of its bass frequencies from venting the system. Sometimes both.

Cue stage left, Dynamic Ear Company (DEC) and what they claim to be the solution to this dilemma. They’re offering a set of ambient filters that claims not only to allow you to listen to your surroundings clearly at a lower volume but also retains the IEM’s original bass response. But is it really all it’s propped up to be?

THE HOLY GRAIL: “LINEAR ATTENUATION”

It’s no secret that many musicians consider hearing protection a hassle and a detriment to their own listening experience. Despite the often dangerously high sound levels of their performance environment, a few of the important reasons behind why musicians don’t enjoy wear hearing protection is attributed to changes in timbre, as well as decreased localization ability ¹, i.e. imaging in audiophile terms. This prevents said musicians from adequately monitoring their own performance, especially during parts where dynamics (changes in volume) play a huge role.

Here’s the phrase of the hour: “linear attenuation” — the point in which all frequencies across our hearing is reduced at the same level, resulting in what is (ideally) the exact same sound, just softer. It’s not exactly a novel idea in the industry; Etymotic (a long time giant in professional audio) released their popular ER-15 earplug in 1988 ², boasting linear attenuation for the discerning musician.

That said, Chesky & Amlani (2015), in a measurement-aided study, show that the Etymotic ER-15 does not in fact have linear attenuation and so demonstrates “an urgent need for robust protocols designed specifically for evaluating and labeling earplugs intended for and marketed to musicians”. ⁴ So with the industry giant still unable to fill the void, it does seem that the market is still ripe for DEC to take over if their technology does what it claims to do.

On the other hand, Huttunen, Sivonen & Pöykkö (2011), on the efficacy of the Etymotic ER-15, reveals that its attenuation was actually fairly flat based on their own testing methodology, and so concludes that non-linear attenuation of standard hearing protection is probably not the explanation for its low use among musicians despite the complaints of diminished timbre and dynamics. ³

Though, it is to be noted that Huttunen et. al. still makes use of the REAT (real-ear attenuation at threshold) protocol, the very same testing procedure that Chesky et. al (2015) criticises in their study. Etymotic also uses REAT so as to be OSHA-compliant.

CRESCENDO HEARING PROTECTION

A bit of a side tangent that also serves as a background introduction for DEC, Crescendo Hearing Protection is the commercial brand name for DEC and offers hearing protection products for a wide variety of situations with different attenuation characteristics. Crescendo also provides an interesting tech demo of their various products, though it obviously may not be representative of what you’d experience in real life.

THE DEC AMBIENT FILTERS

DEC ambient filters, built for APEX connectors

The staff at DEC were very accommodating and were willing to send over their ambient filters specifically built for APEX modules so that I may test them. The modules I got were set at -14 dB and -17 dB attenuation respectively and I was planning to test their attenuation and sonic characteristics with my (at that time, still unavailable) 64 Audio N8 custom in-ear monitors.

Unfortunately, for whatever reason, I hit a snag in that the N8 actually has an additional resistive filter built into its module system. This meant that I was unable to test these modules with my unit specifically and had to seek out other 64 Audio universal models to continue with my analysis. This, however, was actually a silver lining as I found out that the modules changed the signature of different IEMs to different extents (more on that later).

CAVEATS AND LIMITATIONS

Due to the difference in build between the APEX connectors and DEC’s own connectors, the comparison between my findings and the actual final product will most likely not be a true one-to-one comparison. This is due to the fact that DEC did not account for the attenuation of the 64 Audio universal housings and the different volumes between the modules creating different attenuation effects.

My isolation measurements should also be taken with a HUGE grain of salt as my setup for this specific use case is extremely rudimentary, amateur, and not checked against any industry standards such as REAT, though is performed similarly to the procedure highlighted in Chesky et. al’s (2015) research (except with a closed-back headphone rather than speakers).

ANALYSIS OF THE INTERNALS

When looking at the internals, I refer to European Patent No. EP3169290B1 and Netherlands Patent No. NL2015947B1 for the -14 dB and -17 dB modules, respectively.

-14dB “Mushroom” module

The -14 dB module (referred to as the “Mushroom” for semi-obvious reasons) utilises a fine mesh as an acoustic filter. Per point 10, “the mesh is preferably a woven mesh, i.e. precision woven. It is found that the sound filtering characteristics of a mesh can be particularly beneficial for attenuating relatively low to midrange sound pressure levels, e.g. below 100 dB. The characteristics of the mesh can be determined e.g. by the many openings formed between a woven grid of the mesh. Typically, several hundred openings can be formed which however provide a relatively low total cross-section”. ⁵

The mesh structure is somewhat visible under bright light.

Fig 1 of Patent EP3169290B1

Interestingly enough though, the patent calls for an additional perforated rigid disc (on the diagram as point 4 and 5) on top of this mesh structure to act as a barrier for impulse sounds, but I can’t find such a structure in my own mushroom module. Perhaps it is a separate design choice or a misinterpretation on my part, or maybe they’ve reversed the position of the perforation at the end of the module rather than at the opening in order to accommodate the APEX connection.

The -17 dB module is an interesting one, using rigid foil pieces with slits punched into it acting as acoustic channels to filter out ambient noise with small holes punched in at the top acting as impulse filters. Van ‘t Hof, et. al. state this particular filtering system also has the added benefit of being easier to manufacture and install into the module compared to precision-woven meshes whilst having “similar acoustic performance”.

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  The slit membrane
  

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  Bottom view of module
  

Slit positioning highlighted in Patent NL2015947B1

CLAIMS VERSUS REALITY

Legend at the bottom of the graph (it’s tiny)

I did my own measurements out of curiosity, so interpret the data how you will. I am not very confident with the data myself so I don’t think you should read into it too much anyways. There are measurements provided on DEC’s patent, also to be taken with a grain of salt.

Source: Patent EP3169290B1.
71: Response for an open artificial ear
72a: Response for a mesh with 20 pm holes (total diameter of the mesh 1.6 mm)
72b: Response for a mesh with 6 pm holes (total diameter 4 mm)
73: Response for a 200 pm diameter hole

According to the patent, the above graphs illustrate that the mesh (-14 dB module) provides an improved (flatter) acoustic transfer function, more similar to the open ear than the plate with a single hole.

Ignoring measurements for a second, let’s dive into subjectivity. The DEC modules are definitely a solid middle ground between going completely “naked” versus using the M15 and M20 modules (both of which aren’t too different in terms of isolation, really). I can definitely hear more of my environment compared to the stock APEX modules, but there’s still some isolation, unlike the experience of having no modules installed.

How about linear attenuation? Well, it’s not quite there. Outside sounds still come in a bit muffled, though it does seem that bass frequencies are attenuated at a slightly lower degree compared to the stock APEX modules which does make ambient noise sound a tad more balanced and clear. The -14dB modules are the better of the two in my opinion, having a noticeably more linear attenuation (though still not exactly linear in an absolute sense) whereas the attenuation characteristics of the -17 dB modules are almost the same as the stock APEX modules, isolation-wise.

Considering that I don’t have the equipment to prove or disprove DEC’s claims, I won’t make any black-and-white statements. At least for the -14 dB module, it does seem like it has some potential to be an adequately linear ambient filter on a subjective scale.

THE AUDIOPHILE’S PERSPECTIVE

It’s hard to be completely objective in this case considering that these filters were meant to be built alongside the IEM itself from the ground up, rather than as an alternative solution for pre-existing APEX/ADEL-compatible IEMs. Therefore I shall switch the perspective of my investigational question: for existing audiophiles, are the DEC ambient filters a decent alternative to ADEL and APEX in changing an IEM’s sound?

The DEC modules do manage to at least retain the SPL of lower frequencies, but I wouldn’t say that the original signature of the properly sealed IEM is completely intact. There are quite a few changes here and there that are, to an audible degree, definitely the biggest changes induced by the -14 dB “Mushroom” module.

Is that a bad thing? For those ultimately looking for reduced attenuation with virtually no change in the original sound, no. However, from my perspective as a crazy audiophile looking for any way to tweak the sound of my transducer, quite the opposite.

Courtesy of Music Sanctuary, I tested the DEC modules with various 64 Audio models such as the U18Tzar, the U12t, the A6t, the A2e and even the N8 universal (which doesn’t have the resistive filter built into the module connection for whatever reason). Across the board, the decreased isolation and increased “venting” increases the sense of “space” in terms of soundstage width, overall contributing to more realistic stereo imaging qualities compared to the standard APEX modules. This matches my personally observed trend of venting having a positive effect on soundstage and spatial cues on transducers, such as on the Sony MDR-EX1000 and the Audeze in-ear planars.

The effect on tonality (or frequency response, depending on your definition) is interesting as the changes aren’t necessarily always positive depending on model. I absolutely loved the U18 Tzar when paired with the -14 dB mushroom model, livening up the signature by reducing the lower-mid bloat yet retaining bass impact.

Module effects on the 64 Audio U18Tzar

The same goes with the A6t, with the DEC modules resulting in a change that tightens its relatively slow transients and makes it sound more defined and clear. I can see someone not liking this change as it diminishes the smooth, almost wet nature that the A6t is known for, though in my case I’d say it’s an improvement.

Module effects on the 64 Audio A6t

On the flipside, the effect of the DEC modules on the 64Audio U12t wasn’t very positive to me. The U12t was already edging on thinness in terms of note weight, and with the reduction in the lower mids and slight boost in the upper mids it was a change that took it a little too far. For the U12t specifically, I’d rather it be completely sealed. But, of course, your mileage may vary.

Module effects on the 64 Audio U12t

The other interesting thing is that even with the universal N8, with no resistive filter installed in its APEX module, is still almost completely unreactive to module changes. Even on the mushroom module, while there’s less attenuation, there’s basically no change in its original sound signature. It’s an odd mystery.

CONCLUSION

For DEC’s original goal of linear attenuation, based off my current subjective impressions, I’m a bit skeptical of its claim, though it remains to be seen if an IEM that was built from the ground up with the proper modules would live up to expectations.

On the other hand, as a tool for any audiophile with APEX (and potentially ADEL) compatible IEMs, it’s an extremely viable alternative to fine-tune your sound. Perhaps there’s another untapped market for this, because I can definitely see myself recommending DEC filters for those wanting specific changes to their IEMs without the use of EQ.

References

1. Laitinen, H., & Poulsen, T. (2008). Questionnaire investigation of musicians’ use of hearing protectors, self reported hearing disorders, and their experience of their working environment. International Journal of Audiology, 47(4), 160-168.
2. Etymotic (2013) 30 Years of Research & Development 1983-2013. Retrieved from: https://www.etymotic.com/media/publications/er_30_years_timeline_2013.pdf
3. Huttunen, K. H., Sivonen, V. P., & Pöykkö, V. T. (2011). Symphony orchestra musicians’ use of hearing protection and attenuation of custom-made hearing protectors as measured with two different real-ear attenuation at threshold methods. Noise and Health, 13(51), 176.
4. Chesky, K., & Amlani, A. M. (2015). An acoustical analysis of the frequency-attenuation response of musician earplugs. Commun Disord Deaf Stud Hearing Aids, 3(127), 2.
5. Van ‘t Hof, Pieter Gerard & Wilmink, Engbert (2014) European Patent No. EP3169290B1. Retrieved from: https://patentimages.storage.googleapis.com/d7/14/6d/f4d751dbb67b6c/EP3169290B1.pdf
6. Van ‘t Hof, Pieter Gerard & Wilmink, Engbert (2015) Netherlands Patent No. NL2015947B1. Retrieved from: https://patentimages.storage.googleapis.com/1c/65/27/cc7ded98e2fdc2/NL2015947B1.pdf