[b0ck3n]

I have searched the interwebz for the answer to this question but failed to satisfy my curiosity: what is the reasoning behind using 5-10 drivers per earpiece, as we see in flagship IEMs?

I'm going to start off by making a few assumptions, just to let you know that I'm not that lazy. Firstly, you use different types of drivers for different frequency ranges because they handle the different ranges with varying levels of distortion, i.e. 1 woofer/1 midrange/1 high freq driver in a 3-driver IEM. Since these three will be manufactured to handle their respective ends of the frequency range I kinda get why you want them all: to produce loud, distortion free sound. Am I also right to assume that it's easier to manipulate the frequency response of a 3-driver and crossover setup than it is to manipulate a single driver?

When you go to extremes, and we humans always do, I start wondering why because admittedly I find it fascinating and it's liable to cause me financial harm. Is the purpose of a 12-driver IEM to play extremely loud, or to be extremely customizable? Am I oversimplifying or missing something?

 

[castleofargh]

there are several IEM manufacturers on headfi so it would certainly be better if they came to give their own reason why they do what they do. sadly I doubt many of them are avidly reading new posts in the sound science section.
it obviously provides one more tool for the tuning of the frequency response, having only one BA IEM(as that's what we're talking about here), can indeed show limitations. guys like Etymotic still do that and they kind of rock at making the right acoustic chamber for the signature they want, but admittedly the distortion levels aren't all that amazing and before the latest generation, people used to complain about the low end being too weak. it's obvious that adding one or a big BA driver dedicated to the low end can really help, even more when you can pick within a vast catalog of drivers with clearly defined specs. for the treble the idea is supposedly the same, but in practice I've seen a great many multidriver suck in the high frequencies, so I'm guessing there is some acoustic issue there and not everybody figures out how to overcome it.

about why they use like 4 drivers for the same frequency range in each ears, I can imagine 3 possibilities, but I am only guessing:
- marketing "wow! much drivers, many stronk! worth more money!", or even "I have the most drivers, the best drivers, the other guy only uses 12 per ears, SAD!".
- lower impedance. I don't get why but somewhere it must be interesting because they all go lower and lower despite how it makes the amp section of our gears live a nightmare and perform way worst than they could into a 60ohm load. but obviously I've never made IEMs so I only see one side of the story, the fairly ignorant consumer side ^_^.
- stability. with 4 times the same model set the same way you statistically improve the stability of the frequency response compared to the tolerance offered by the manufacturer.

maybe you'll get more luck if you go in a few sponsor topics and ask them why they do it.

 

[bigshot]

Do they stack up the drivers concentrically? I imagine they would have to or alignment would cause problems.

 

[b0ck3n]

- stability. with 4 times the same model set the same way you statistically improve the stability of the frequency response compared to the tolerance offered by the manufacturer.

Thanks for your reply! Could you clarify the above for me please? As I understand it the common practice is to use several drivers of the same make/model to handle the same range of frequency (the high range isn't divided among the 4 tweeters, they all do the same job).

 

[castleofargh]

Do they stack up the drivers concentrically? I imagine they would have to or alignment would cause problems.

in most cases, multi BA have a little plastic tube stuck directly at the output of the driver and going all the way to the nozzle of the IEM, so they really just have to work out the length of the tubes and they can arrange them however they like in the shell.

Thanks for your reply! Could you clarify the above for me please? As I understand it the common practice is to use several drivers of the same make/model to handle the same range of frequency (the high range isn't divided among the 4 tweeters, they all do the same job).

sure what I had in mind is that it's very typical to get a few dB of variation from one driver to the next(same model), be it overall or in a specific area of the audible range. it is rather obvious when measuring single driver IEMs even the left and right ear of the same pair show variations, and getting a few pairs of the same IEM show just as much or often even more variations in the frequency response. the pairs I own often have around 3db difference somewhere in the 100hz 10khz range. Etymotic certifies +/-1dB on the er4 series (so still up to 2dB over the all frequency range), and they're almost an exception in the business.
by having 4 times the same driver in each side, I would assume the chances to get a more even overall response is increased. but as I said I have no practical experience playing with many identical drivers and testing what happens when you put then all together. this is just my guess.

 

[b0ck3n]

in most cases, multi BA have a little plastic tube stuck directly at the output of the driver and going all the way to the nozzle of the IEM, so they really just have to work out the length of the tubes and they can arrange them however they like in the shell.


sure what I had in mind is that it's very typical to get a few dB of variation from one driver to the next(same model), be it overall or in a specific area of the audible range. it is rather obvious when measuring single driver IEMs even the left and right ear of the same pair show variations, and getting a few pairs of the same IEM show just as much or often even more variations in the frequency response. the pairs I own often have around 3db difference somewhere in the 100hz 10khz range. Etymotic certifies +/-1dB on the er4 series (so still up to 2dB over the all frequency range), and they're almost an exception in the business.
by having 4 times the same driver in each side, I would assume the chances to get a more even overall response is increased. but as I said I have no practical experience playing with many identical drivers and testing what happens when you put then all together. this is just my guess.

I'm chiefly interested in CIEMs, and while I know they're all individually tuned and tested, I have no idea what variations they're willing to accept. But to sum up, not only does 12 drivers per ear allow for distortion-free loudness but also enables more precise manipulation of frequency response. Thanks for your input!

 

[castleofargh]

hold on, what I proposed were my guesses as to why they may do what they do. please don't make your decisions based on stuff I said.
personally I'm not a big fan of multidriver IEMs. I've always considered IEMs a clear compromise of sound for size and possibly isolation. so as soon as the size starts becoming significant, I stop being interested and tend to give my vote for a headphone(for sound), or a small single driver IEM(well, for size) instead. but now that is my opinion, which is even less of a technical fact than my previous guesses.

 

[bigshot]

Better yet, good speakers and a decent room

 

[Niouke]

Better yet, good speakers and a decent room

I wonder how good the speakers and the room have to be to obtain the level of detail provided by multi driver IEM's. WIth my mid-fi setup I'm clearly not there, while it is still an enjoyable listen.

 

[Jazmanaut]

In my understanding, they put more drivers for freq band to gain more output, without distortion.
In pro live IEM:s, you sometimes want to go louder, than in "normal" use.

 

[Oscar-HiFi]

@64Audio @piotrus-g @Clear Tune Monitors @FullCircle amongst many others may be able to tune in and help...

 

[FullCircle]

I wonder how good the speakers and the room have to be to obtain the level of detail provided by multi driver IEM's. WIth my mid-fi setup I'm clearly not there, while it is still an enjoyable listen.

The room acoustic properties makes an impact as well

One of my professors would say, "If you change one thing, you change everything."

 

[piotrus-g]

I have searched the interwebz for the answer to this question but failed to satisfy my curiosity: what is the reasoning behind using 5-10 drivers per earpiece, as we see in flagship IEMs?

I'm going to start off by making a few assumptions, just to let you know that I'm not that lazy. Firstly, you use different types of drivers for different frequency ranges because they handle the different ranges with varying levels of distortion, i.e. 1 woofer/1 midrange/1 high freq driver in a 3-driver IEM. Since these three will be manufactured to handle their respective ends of the frequency range I kinda get why you want them all: to produce loud, distortion free sound. Am I also right to assume that it's easier to manipulate the frequency response of a 3-driver and crossover setup than it is to manipulate a single driver?

When you go to extremes, and we humans always do, I start wondering why because admittedly I find it fascinating and it's liable to cause me financial harm. Is the purpose of a 12-driver IEM to play extremely loud, or to be extremely customizable? Am I oversimplifying or missing something?

Your assumption is generally correct.

There are few different approaches you might consider.
The most common is multiplying the same type of driver - often times seen as dual CI (lows), dual Sonion 3300/3800/DTEC (lows) or dual/triple TWFK (highs)
2x CI will decrease THD - as both drivers are typically stack up together so their vertical vibrations from motors will cancel each other out. You can have two configurations parallel or series - each will impact impedance and SPL output differently - depends on what designer wants to achieve.
Sonion 33-37-3800 or KA DTECs are already duals so there's no extra advantage on mechanical THD reduction, but if you divide power between say two 3300 then you decrease load on each of those drivers and you get reduction in THD as well. Still you can wire both in series or parallel adjusting SPL and impedance as well as other factors which impact how driver behaves in whole design.
n X TWFK - same concepts as above (SPL, THD) but since those are used as tweeters typically the point is to reduce overall HF impedance (metioned by @castleofargh ) as with standard BA driver impedance increases dramatically with frequency so in order to match output of the tweeters to LF drivers you need to multiply HF drivers.
Generally speaking multiplying same drivers gives you increase in headroom (volume before distortions) so the IEM sounds overall louder and "bigger"

There's also another way you can go - by adding different types of drivers for the same fr range - for example combining CI and 3300 for lows only - this gives you all above benefits but with changes to sound signature as CI and 3300 have completely two different sounds and definitions of low frequency - with CI being "slow" with long decay and 3300 (considering non-vented option) being fast and precise. So it's kind of like mixing flavors to achieve desired texture or sound signature or definition etc.

about why they use like 4 drivers for the same frequency range in each ears, I can imagine 3 possibilities, but I am only guessing:
- marketing "wow! much drivers, many stronk! worth more money!", or even "I have the most drivers, the best drivers, the other guy only uses 12 per ears, SAD!".
- lower impedance. I don't get why but somewhere it must be interesting because they all go lower and lower despite how it makes the amp section of our gears live a nightmare and perform way worst than they could into a 60ohm load. but obviously I've never made IEMs so I only see one side of the story, the fairly ignorant consumer side ^_^.
- stability. with 4 times the same model set the same way you statistically improve the stability of the frequency response compared to the tolerance offered by the manufacturer.

maybe you'll get more luck if you go in a few sponsor topics and ask them why they do it.

Marketing is sort of factor too. But I think also depends on philosophy of company, there are those who don't even bother with selling 1 or 2 BA IEMs.
Impedance - as for the purpose mentioned above.
I don't think I would agree fully with the last point. Drivers coming from factory have typically very tight matching, adding drivers typically can make the circuit very prone to acoustic phase problems meaning it's actually harder to match L/R channel with higher driver count.

 

[b0ck3n]

Better yet, good speakers and a decent room

I got into CIEMs for two reasons: stage duty and mobility. Nowadays only the latter applies but it really is quite amazing the quality of sound you can get anytime, anywhere.

Your assumption is generally correct.

There are few different approaches you might consider.
The most common is multiplying the same type of driver - often times seen as dual CI (lows), dual Sonion 3300/3800/DTEC (lows) or dual/triple TWFK (highs)
2x CI will decrease THD - as both drivers are typically stack up together so their vertical vibrations from motors will cancel each other out. You can have two configurations parallel or series - each will impact impedance and SPL output differently - depends on what designer wants to achieve.
Sonion 33-37-3800 or KA DTECs are already duals so there's no extra advantage on mechanical THD reduction, but if you divide power between say two 3300 then you decrease load on each of those drivers and you get reduction in THD as well. Still you can wire both in series or parallel adjusting SPL and impedance as well as other factors which impact how driver behaves in whole design.
n X TWFK - same concepts as above (SPL, THD) but since those are used as tweeters typically the point is to reduce overall HF impedance (metioned by @castleofargh ) as with standard BA driver impedance increases dramatically with frequency so in order to match output of the tweeters to LF drivers you need to multiply HF drivers.
Generally speaking multiplying same drivers gives you increase in headroom (volume before distortions) so the IEM sounds overall louder and "bigger"

There's also another way you can go - by adding different types of drivers for the same fr range - for example combining CI and 3300 for lows only - this gives you all above benefits but with changes to sound signature as CI and 3300 have completely two different sounds and definitions of low frequency - with CI being "slow" with long decay and 3300 (considering non-vented option) being fast and precise. So it's kind of like mixing flavors to achieve desired texture or sound signature or definition etc.


Marketing is sort of factor too. But I think also depends on philosophy of company, there are those who don't even bother with selling 1 or 2 BA IEMs.
Impedance - as for the purpose mentioned above.
I don't think I would agree fully with the last point. Drivers coming from factory have typically very tight matching, adding drivers typically can make the circuit very prone to acoustic phase problems meaning it's actually harder to match L/R channel with higher driver count.

Thank you for providing some insight into the decision process when designing multi-driver IEMs! These things are usually so easy to drive it's enough to run them at the lowest volume setting possible on an iPhone, but covering all your bases with several types of drivers to handle the entire FR is interesting.

 

[castleofargh]

@64Audio @piotrus-g @Clear Tune Monitors @FullCircle amongst many others may be able to tune in and help...

nice call. you've gathered a few dragons on the thread. I should have done that from the start ^_^.

Your assumption is generally correct.

There are few different approaches you might consider.
The most common is multiplying the same type of driver - often times seen as dual CI (lows), dual Sonion 3300/3800/DTEC (lows) or dual/triple TWFK (highs)
2x CI will decrease THD - as both drivers are typically stack up together so their vertical vibrations from motors will cancel each other out. You can have two configurations parallel or series - each will impact impedance and SPL output differently - depends on what designer wants to achieve.
Sonion 33-37-3800 or KA DTECs are already duals so there's no extra advantage on mechanical THD reduction, but if you divide power between say two 3300 then you decrease load on each of those drivers and you get reduction in THD as well. Still you can wire both in series or parallel adjusting SPL and impedance as well as other factors which impact how driver behaves in whole design.
n X TWFK - same concepts as above (SPL, THD) but since those are used as tweeters typically the point is to reduce overall HF impedance (metioned by @castleofargh ) as with standard BA driver impedance increases dramatically with frequency so in order to match output of the tweeters to LF drivers you need to multiply HF drivers.
Generally speaking multiplying same drivers gives you increase in headroom (volume before distortions) so the IEM sounds overall louder and "bigger"

There's also another way you can go - by adding different types of drivers for the same fr range - for example combining CI and 3300 for lows only - this gives you all above benefits but with changes to sound signature as CI and 3300 have completely two different sounds and definitions of low frequency - with CI being "slow" with long decay and 3300 (considering non-vented option) being fast and precise. So it's kind of like mixing flavors to achieve desired texture or sound signature or definition etc.


Marketing is sort of factor too. But I think also depends on philosophy of company, there are those who don't even bother with selling 1 or 2 BA IEMs.
Impedance - as for the purpose mentioned above.
I don't think I would agree fully with the last point. Drivers coming from factory have typically very tight matching, adding drivers typically can make the circuit very prone to acoustic phase problems meaning it's actually harder to match L/R channel with higher driver count.

for impedance I indeed didn't think about how it often rises like crazy in the high freqs, that indeed is something one might want/need to mitigate. thanks for pointing this out.
and thanks too for your last sentence. so my guess was plain wrong and now I know from someone who actually works with those things. I'll go to bed a little less wrong which is always a good way to end the day.

@b0ck3n . see, I told you not take my guesses as facts. I have a lot of ideas, but I'm also very well informed about my own ignorance.