[DrGroove]

I'm currently shopping through CIEMs, but I'm a bit confused by some of this stuff and have some questions and concerns.
 
1. If an ER4-S/PT can be so good and clear (though lacking bass) with a single BA driver, why can't you get a perfectly tuned IEM with a single low and single high driver setup?
 
2. What is the technical advantage of adding more drivers? I haven't been able to find a direct answer to this. It seems to me that adding more crossovers and drivers would confine each driver to a smaller frequency range and lower the overall distortion, but is this significant? Does a single or dual BA setup have audibly more distortion than 6 or 8 drivers? It also seems like adding more and more crossovers adds a great deal of complication when creating smooth tuning.
 
3. What is the purpose of having more than one driver in a given frequency range? If I'm understanding correctly, many of the 6 driver CIEMs use 2 crossovers with a dual low, dual mid, dual high setup. The CustomArt H8 Pro is especially confusing to me because it has 2 full range drivers, which would be 3 drivers active on a given frequency range. You don't see speakers designed this way, and it seems like drivers outputting the same thing would drastically increase distortion even if they were physically phase aligned.
 
Please tell me how wrong I am, I'm just trying to figure all this out before I drop a lot of money.
 
I'm looking for a really neutral and high clarity CIEM. So far I'm mainly considering some mid-range reference sets around $4-500, or going all out with a TOTL setup.
 
Main contenders
CustomArt Pro 300v2
Aclair reference
Earwerkz Supra 2
 
CustomArt H8 Pro
Earwerkz Legend R

 

[billybob_jcv]

This is one of the oldest and greatest debates in head-fi. Back in the early days, it was the ER4P/S against the dual & triple driver IEMs from Westone, Shure and Ultimate Ears. IMHO, there's no right answer - every good headphone designer sets out to create the best headphone they can within the design constraints they are given by the product marketing department. Those constraints might include a cost target, or a use case such as being suitable for stage musicians, or in the case of TOTL & statement products - they might be given absolutely no constraints whatsoever.

The ER4P is not perfect. Many people would say the bass is too light, or the cable is too microphonic, or that they can become sibiliant or that they are simply uncomfortable. Like Westone, Etymotic has its roots in traditional audiology and hearing research - not in audiophile products. JH Audio and many of the more recent CIEM manufacturers have a different background and have chosen a different path. They came from the music & audio industry, and music reproduction has always been their only focus. I'm not saying that makes one better or more capable than the other - I'm just recognizing that they have very different histories.

Are there pros and cons to the number of drivers? Of course. I suspect delivering a coherent sound from 14 drivers is really, really difficult. I also suspect that modern computer aided design and simulations of both the circuits and the housings make this possible. It's up to you, the listener, to decide if they have succeeded.

 

[ProtegeManiac]

 
1. If an ER4-S/PT can be so good and clear (though lacking bass) with a single BA driver, why can't you get a perfectly tuned IEM with a single low and single high driver setup?

 

Because any time you introduce any driver more than one, you have to deal with crossover design issues. A crossover doesn't cleanly "cut" the frequencies going into each, as much as that's usually the term used (especially in car audio, where we manually mess around with active crossovers). What they actually do is attenuate the frequencies: the "slope" determines how steep the drop is below or above the chosen frequency. 

 

In a speaker application, you have the added problem of timing differences - depending on where your head is, there might be enough variance in the distance from your ears to the tweeter vs the midwoofer, and you hear one before the other, so the sound isn't well integrated. This gets more complicated when you have for example multiple bass drivers - in a small enough room that tends to pull the bass downwards. In some cases they design a huge speaker with a "mirrored" set up of the drivers just to avoid that, at the cost of making an absurdly large cabinet that is hard to sell because people tend to not have the kind of room that can maximize it, increasing its price since it can't sell more units (look at Dynaudio's more expensive models). Others just angle each driver differently (look up Focal's Utopia series, or any speaker with a slanted baffle).

 

In an IEM integration isn't as big a problem in terms of timing but it's still a problem with the crossover, plus that crossover needs to fit inside an IEM shell along with the drivers. That's why JH Audio released IEMs that had their on active crossover+amplifier units (crossover is applied before the amps, as on serious car audio systems). The problem there is that it's a closed system, and I'm not even sure if you can use that as a transportable since AFAIK they don't work with iOS or Android devices. Then there's all those cables going into the IEM - they would need to be extra thin or they'd be too thick and likely won't go around the ears and stay there properly.

 

Personally, I'd rather use a single generally large dynamic driver. It has a wider response, and can do bass very well (hell, all of these drop off past 12khz anyway, including fullsize headphones; it's just a question of how steep that dive is or if it sharply goes back up). Of course, there's a reason why they would even bother with BA drivers and crossovers. On the business side of it, notice how these BA driver manufacturers aren't originally hi-fi manufacturers - before all these other hi-fi IEM manufacturers came out the original CIEMs were made by hearing aid manufacturers, who need to tune the sound (as hearing loss can be a severely bad EQ effect than a uniform attenuation) and they also make specialized communication equipment like those used by racing teams (which basically need a good fit, and need to reproduce only the human voice).

 

On the technical side, there's always a downside to any design, and in the case of dynamic drivers they need a lot of air space inside the enclosure - just look at how large a speaker enclosure has to be vs a planar speaker (heck, the planars might be free air, but look at how large they are - and yet some need a dynamic bass driver, or a dedicated planar bass driver as with Magnepan). Big dynamic driver IEMs tend to be bigger too - some can't even wear them properly. In some cases the driver is too big that there's some bass imbalance that the drop off in the treble is made even worse by the added bass response (like my Aurisonics ASG-1).
 
Basically, all these transducer designs are here for a reason: there is no perfect transducer design, and manufacturers have to use designs and end up with compromises they can live with, including size and price.
 

 
2. What is the technical advantage of adding more drivers? I haven't been able to find a direct answer to this. It seems to me that adding more crossovers and drivers would confine each driver to a smaller frequency range and lower the overall distortion, but is this significant? Does a single or dual BA setup have audibly more distortion than 6 or 8 drivers? It also seems like adding more and more crossovers adds a great deal of complication when creating smooth tuning.

 
 

Aside from distortion (in terms of making a driver play less of what might be too low or too high for it), you can also control it and use the driver for only the range where its response is relatively smoother/flatter. Of course, there's that problem with crossovers - and in low impedance dynamic drivers like speakers that usually means the speaker as a system would need a bit more current due to the complexity of the load (I think it enhances impedance swings, but I'm not sure). BA drivers are generally not as susceptible to that kind of complexity as far as the load on the amp is concerned, but all the others - like how to design the crossovers to still end up with just enough overlap for drivers to compliment each other instead of producing peaks where they meet - are still there. Hence the price might in parts is a lot lower than the R&D man-hours involved.

 

 
 

 
3. What is the purpose of having more than one driver in a given frequency range? If I'm understanding correctly, many of the 6 driver CIEMs use 2 crossovers with a dual low, dual mid, dual high setup. The CustomArt H8 Pro is especially confusing to me because it has 2 full range drivers, which would be 3 drivers active on a given frequency range.

 

I'm not sure about those specific IEMs, but in cases with say more three bass, two midrange, and one treble driver for example it has to do with the individual efficiency and/or introducing a particular balance. Look at a speaker for example - there are a number of tower speakers with one tweeter, one midrange, and two bass drivers - tweeters usually have the highest efficiency at well over 90dB, followed by the midrange, then the bass drivers. In some speakers they add more bass drivers to affect the balance at most volumes plus minimize distortion - if you're already hearing a lot of bass at a certain setting, then you won't need to boost the volume, hence you don't get the bass drivers to use more excursion.
 

 
You don't see speakers designed this way, and it seems like drivers outputting the same thing would drastically increase distortion even if they were physically phase aligned.

 
You might not be looking far up enough price wise. Remember I mentioned Dynaudio and Focal?



 

In these cases they're designed precisely for phase alignment - the Dyns center the image closer to the center of the speakers, but that assumes your head is near that (rather than have the bass drivers pull the bass image down due to timing and reflections off the floor; the Contour Series doesn't use mirror image drivers but orients the high-mid-low drivers upwards). The Focals only mirror the midrange, in a way it might even be to balance out the efficiency/loudness of the midrange with the large bass driver (chosen since it can reach lower bass freqs), and then they have each driver in its own section of the enclosure that's angled and aimed towards the center (others just angle the bass driver at the bottom up and forward).

 

[DrGroove]

Thanks so much for the detailed responses guys.
 
Some takeaways I'm getting are that multiple phase aligned drivers will not increase distortion, and are used to increase volume of the of the driver's range while reducing stress on a single driver. This way the system can have lower distortion at a given volume, right?

 

[ProtegeManiac]

  Thanks so much for the detailed responses guys.
 
Some takeaways I'm getting are that multiple phase aligned drivers will not increase distortion, and are used to increase volume of the of the driver's range while reducing stress on a single driver. This way the system can have lower distortion at a given volume, right?

 

That or they're trying to fix the response balance, or deliberately making certain ranges louder. 

 

I think what you're referring to about multiple drivers and distortion might have more to with dynamic drivers, specifically with speakers, as since too many (low impedance) dynamic drivers on a single crossover network are mroe likely than any other design to present a complex load to the amplifier, even if that amp was designed for the nominal impedance of the speakers. Not too sure on that though, but again it might be that complex or badly designed crossovers might be enhancing the impedance swings.

 

In any case many of this isn't a problem with BA drivers, but proper crossover settings of course are still vital for maintaining a system response that won't be negatively affected by the overlaps.

 

[Raketen]

Good questions, enjoyed reading the answers so far... If I can add one- wondering if there are any TOTL CIEM that utilize a single transducer? There seem to be a fair number of non-custom TOTL in-ears that do- for instance Sony EX1000, Dita The Answer, Rhapsodio RTi1, the various Final Audio in-ears, Grado, JVC's woody series, etc...

 

[ProtegeManiac]

  Good questions, enjoyed reading the answers so far... If I can add one- wondering if there are any TOTL CIEM that utilize a single transducer? There seem to be a fair number of non-custom TOTL in-ears that do- for instance Sony EX1000, Dita The Answer, Rhapsodio RTi1, the various Final Audio in-ears, Grado, JVC's woody series, etc...

 
In addition to Post #3, one more factor is that a CIEM generally has a lot more interior volume than a universal shell. Think of that as having a spare room where you can use the tower speakers as in Post #3, and instead of trying to smoothen out the response of a single driver trying to do everything, they just use several drivers working in the range where each has a smoother (and stronger) response.
 
It's the same reason why huge dynamic drivers didn't catch on despite all that air volume. They did, but keeping the response wide and smooth has generally been an issue especially if they want a bigger driver to add more impact to the bass, so what they're doing instead are hybrids. Kind of like this bad boy here with a large bass driver, a midrange driver (notice how the surround isn't that large given its diameter, as it isn't expected to pump out low frequencies), and a really smooth ribbon tweeter: