[Pylaczynski]

I’ll certainly ask the engineers for a more detailed explanation, but I’ll be quite honest, they are working extra-hard these days as we keep developing a number of new products coming out later this year and early next year. I’ll see if they can sit down with me and explain this out in writing. I’ve asked them before, and usually they say “anyone can measure anything, it’s not worth comparing numbers to numbers, the only important thing is how the device works when you use it yourself.”

At the end of the day, they are right, numbers are just numbers. The real determining factor is how it sounds when you use it. So far, with almost any headphone we pair it with (and that our customers have paired it with), the M15 shines. I’m hoping that you’ll have the chance to audition one soon! And I’ll let you know if I can get some more details out of the engineers.

Thank you for the answer, you don't need to bother the engineers if they are extra busy, but I know engineers always seem to be extra busy, so...

And I have mine M15, but I am using it only for IEMs, so cannot test powering of the more demanding stuff. With IEMs the volume on windows I have at 12/100 so, I guess headroom is there.

Just to clarify: the idea of my question is coming from the fact that there is a common perception in the audio that you need tons of power to juice stuff like Sundara (commonly people say 1W) etc, whereas if you calculate it from the sensitivity and impedance it looks like for 105dB SPL (ear blowing level) for Sundara you need 27mW and 30mA RMS. And I just think people don't test it in real life. For example I was able to drive my HE-400i with Qudelix with volume level killing my ears at -13dB.

Then there is driving and "driving propely" stuff and that is why I am wondering wether your M15 CMA has something to do with that by being able to deliver higher constant current level

BTW you are probably the best customer service guy of any hi-fi companies I know - very professional, responsive and down to earth - huge props!

 

[Questyle]

@Pylaczynski

I did find some time to sit down with one of the engineers today, and he laid it out for me in layman's terms (keep in mind this was all in Chinese, so I'm translating here, and as always some things might have been lost in translation. Also @Pylaczynski , it seems clear to me that you know a lot of what I'm about to say already, but I'll write it out anyway, just in case any others in the thread have questions.)

He assessed it from different perspectives:

Most headphone users do not need their headphones pushed more than ~100 dB. Any higher and, as we all know, you risk hearing damage. Devices with very large output power can of course push some headphones much above that. Frankly speaking, this isn’t necessary, nor for most applications is it useful. More than just that, large output power also means more power consumption, which is a major concern in mobile applications. And even further, in this case, amplifying the audio signal to that high level also entails amplifying the noise higher as well.

He went on to frame this using two metaphors. First, take premium cigars. Highly premium, luxury cigars are difficult to light. Does this mean you need a flamethrower or riot torch to light one? No, you just need a well-made, specifically-designed-for-premium-cigars lighter. As long as this lighter can light the cigar, then you’re good to go. The size of the flame doesn’t matter.

To use another metaphor, car engines. Take the engine of a pristine sports car: very powerful, very well designed, and perfectly powers the vehicle it is designed for. But that same engine probably wouldn't do well if put inside a 18-wheeler. Is that to say that an 18-wheeler's engine is better than a sports car engine?

(As with any metaphor, there are of course some potential logical fallacies. I’m simply repeating what one of our dear engineers told me today, so take it for what you will ）

The point with these two metaphors is that, in Questyle’s opinion, the pure output power by itself is not a specification that should be blindly compared between products. A large output power doesn’t by any means indicate that any one product is more capable than another one of lower output power.

And then the question, how does Current Mode Amplification play into it? I’ll be honest, I’ve had it explained to me many times, and I still sometimes struggle to wrap my head around it. Perhaps this article states it best, in layman’s terms. It refers to our previous product the CMA400i, but the logic remains the same:

“At this point I would like to comment on the deceptiveness of power ratings. While the Questyle Audio CMA400i has a fairly respectable power output of almost 1 Watt at 32Ω, due the Current Mode Amplifier, it is actually equivalent to amplifiers of much higher outputs using other topologies. “How is that,” you ask? Well power is the product of Voltage and Current, essentially Voltage is pressure and Current is flow, and it is the Current that does the heavy lifting, since Current Mode Amplifiers operate in the Current domain, they tend to be Current heavy. To give an analogy that might be easier to understand, in an engine, Horsepower is the product of Torque (twisting force) and RPM (how fast the motor is turning). Torque is the equivalent of Current and RPM is the equivalent of Voltage. As any gear head can tell you, if you have two vehicles with all else being identical, it is the vehicle with more Torque that has the greater pulling power. Back in the world of audio, it is Current that determines how fast a speaker driver starts and stops, which determines how much detail you have and how accurate, especially in the low frequencies, which require much more Current to reproduce.”

https://headphone.guru/questyle-aud...mplifier-peer-into-the-black-depths-of-music/

Then, in terms of the multitone issue: it seems as if L7’s test was a 30-tone (perhaps 32-tone, but not clear), static multitone test. This test is of course useful to an extent — but it only shows the output at one amplitude level. L7 did this test twice, at 0 dbFS and -0.5 dbFS. But of course music signals and audio amplitudes are much more complicated than that. I’ll follow up with the engineers in the coming days on this in particular and see if they have anything to say.

To put it simply, we designed the M15 to drive virtually any headphone thrown at it. IEMs, over-the-ear, open back, closed back, and anything in between. We tested it in-house with HD 600, HD650, HD800S, HD820, HE6, DT990, and many, many others. We also tested it with a HUGE range of IEMs. We made sure this product would complement almost anything on the market, and so far it has.

At the end of the day, numbers really don’t mean much. Only one thing actually matters: the experience. Does a product give you the experience you want? Does it drive the headphones you want to use? Does it sound good? Does it make you feel good? Of course this is difficult to answer unless you’ve auditioned a product yourself. But by now, the number of at-length user reviews of the M15 is enough to give you a good picture of what its capable of.

A lot of our customers have brought up this exact L7 AudioLab review, asking for our response. Indeed, the review’s testing was done quite thoroughly and the numbers essentially cannot be argued. However, and with all due respect, the crucial fault of reviews on this site are that they omit the only thing that matters (in our opinion): the experience. Not many people buy mobile DAC/amps to measure the power output each day when they wake up; they buy them to listen to their music. I personally believe this review might have benefitted greatly from actually discussing the product in a practical way, not simply a statistical one; testing it on your ears, not only on top of a lab bench. Just as @LakeOfTheWyles said, we aren’t disputing L7 Lab’s numbers, they just aren’t the end all be all, not by a long shot. And just as you said as well @Pylaczynski … people don’t test these things enough in real life!!! So true. Kind of defeats the purpose, doesn’t it?

I hope that satisfied some of your curiosity. Let me know if there’s any more details or questions I can help you dive into And thanks as always for being a Questyle fan!

(I’ll also mention, if anybody wants to discuss any of the above points or point out an error, please let me know. Most of the above was translated from conversations I had in Chinese and perhaps I misunderstood something at some point. I’m always up for finding I was wrong, and learning what’s right!)

 

[Pylaczynski]

@Pylaczynski

I did find some time to sit down with one of the engineers today, and he laid it out for me in layman's terms (keep in mind this was all in Chinese, so I'm translating here, and as always some things might have been lost in translation. Also @Pylaczynski , it seems clear to me that you know a lot of what I'm about to say already, but I'll write it out anyway, just in case any others in the thread have questions.)

He assessed it from different perspectives:

Most headphone users do not need their headphones pushed more than ~100 dB. Any higher and, as we all know, you risk hearing damage. Devices with very large output power can of course push some headphones much above that. Frankly speaking, this isn’t necessary, nor for most applications is it useful. More than just that, large output power also means more power consumption, which is a major concern in mobile applications. And even further, in this case, amplifying the audio signal to that high level also entails amplifying the noise higher as well.

He went on to frame this using two metaphors. First, take premium cigars. Highly premium, luxury cigars are difficult to light. Does this mean you need a flamethrower or riot torch to light one? No, you just need a well-made, specifically-designed-for-premium-cigars lighter. As long as this lighter can light the cigar, then you’re good to go. The size of the flame doesn’t matter.

To use another metaphor, car engines. Take the engine of a pristine sports car: very powerful, very well designed, and perfectly powers the vehicle it is designed for. But that same engine probably wouldn't do well if put inside a 18-wheeler. Is that to say that an 18-wheeler's engine is better than a sports car engine?

(As with any metaphor, there are of course some potential logical fallacies. I’m simply repeating what one of our dear engineers told me today, so take it for what you will ）

The point with these two metaphors is that, in Questyle’s opinion, the pure output power by itself is not a specification that should be blindly compared between products. A large output power doesn’t by any means indicate that any one product is more capable than another one of lower output power.

And then the question, how does Current Mode Amplification play into it? I’ll be honest, I’ve had it explained to me many times, and I still sometimes struggle to wrap my head around it. Perhaps this article states it best, in layman’s terms. It refers to our previous product the CMA400i, but the logic remains the same:

“At this point I would like to comment on the deceptiveness of power ratings. While the Questyle Audio CMA400i has a fairly respectable power output of almost 1 Watt at 32Ω, due the Current Mode Amplifier, it is actually equivalent to amplifiers of much higher outputs using other topologies. “How is that,” you ask? Well power is the product of Voltage and Current, essentially Voltage is pressure and Current is flow, and it is the Current that does the heavy lifting, since Current Mode Amplifiers operate in the Current domain, they tend to be Current heavy. To give an analogy that might be easier to understand, in an engine, Horsepower is the product of Torque (twisting force) and RPM (how fast the motor is turning). Torque is the equivalent of Current and RPM is the equivalent of Voltage. As any gear head can tell you, if you have two vehicles with all else being identical, it is the vehicle with more Torque that has the greater pulling power. Back in the world of audio, it is Current that determines how fast a speaker driver starts and stops, which determines how much detail you have and how accurate, especially in the low frequencies, which require much more Current to reproduce.”

https://headphone.guru/questyle-aud...mplifier-peer-into-the-black-depths-of-music/

Then, in terms of the multitone issue: it seems as if L7’s test was a 30-tone (perhaps 32-tone, but not clear), static multitone test. This test is of course useful to an extent — but it only shows the output at one amplitude level. L7 did this test twice, at 0 dbFS and -0.5 dbFS. But of course music signals and audio amplitudes are much more complicated than that. I’ll follow up with the engineers in the coming days on this in particular and see if they have anything to say.

To put it simply, we designed the M15 to drive virtually any headphone thrown at it. IEMs, over-the-ear, open back, closed back, and anything in between. We tested it in-house with HD 600, HD650, HD800S, HD820, HE6, DT990, and many, many others. We also tested it with a HUGE range of IEMs. We made sure this product would complement almost anything on the market, and so far it has.

At the end of the day, numbers really don’t mean much. Only one thing actually matters: the experience. Does a product give you the experience you want? Does it drive the headphones you want to use? Does it sound good? Does it make you feel good? Of course this is difficult to answer unless you’ve auditioned a product yourself. But by now, the number of at-length user reviews of the M15 is enough to give you a good picture of what its capable of.

A lot of our customers have brought up this exact L7 AudioLab review, asking for our response. Indeed, the review’s testing was done quite thoroughly and the numbers essentially cannot be argued. However, and with all due respect, the crucial fault of reviews on this site are that they omit the only thing that matters (in our opinion): the experience. Not many people buy mobile DAC/amps to measure the power output each day when they wake up; they buy them to listen to their music. I personally believe this review might have benefitted greatly from actually discussing the product in a practical way, not simply a statistical one; testing it on your ears, not only on top of a lab bench. Just as @LakeOfTheWyles said, we aren’t disputing L7 Lab’s numbers, they just aren’t the end all be all, not by a long shot. And just as you said as well @Pylaczynski … people don’t test these things enough in real life!!! So true. Kind of defeats the purpose, doesn’t it?

I hope that satisfied some of your curiosity. Let me know if there’s any more details or questions I can help you dive into And thanks as always for being a Questyle fan!

(I’ll also mention, if anybody wants to discuss any of the above points or point out an error, please let me know. Most of the above was translated from conversations I had in Chinese and perhaps I misunderstood something at some point. I’m always up for finding I was wrong, and learning what’s right!)

Amazing answer, thank you a lot! <3

And I have to admit you got me at this HE6. I was just about to refer to your analogy of motor engines and ask what do you consider 18wheeler in audio world (adding "... probably something more like Sundara already, because HE6 would be heavily armorded tank right?"). I guess though that while HE6 would be driven to desired loudness (it just need 10mW RMS by specs for 85dB!, but also 15mA RMS current which may be bottleneck for some sources) it may lack some headroom for transients in the very dynamic recordings. But it is also one of the heaviest hitters of all potential headroom in the world, so nothing to be unexpected!

Wish I could use headphones longer than 30mins before my ear tissue start to dissolve due to heat, so I would really put it to test with some heavy stuff I always wanted to be able to use comfortably. And in fact the case is that this device is not doing something unexpected "scientifically". In fact it is just the opposite the real life is aligned with calculations. It kind of his at "scaling with power" idea which I don't really understand.

 

[jmwant]

@Pylaczynski

I did find some time to sit down with one of the engineers today, and he laid it out for me in layman's terms (keep in mind this was all in Chinese, so I'm translating here, and as always some things might have been lost in translation. Also @Pylaczynski , it seems clear to me that you know a lot of what I'm about to say already, but I'll write it out anyway, just in case any others in the thread have questions.)

He assessed it from different perspectives:

Most headphone users do not need their headphones pushed more than ~100 dB. Any higher and, as we all know, you risk hearing damage. Devices with very large output power can of course push some headphones much above that. Frankly speaking, this isn’t necessary, nor for most applications is it useful. More than just that, large output power also means more power consumption, which is a major concern in mobile applications. And even further, in this case, amplifying the audio signal to that high level also entails amplifying the noise higher as well.

He went on to frame this using two metaphors. First, take premium cigars. Highly premium, luxury cigars are difficult to light. Does this mean you need a flamethrower or riot torch to light one? No, you just need a well-made, specifically-designed-for-premium-cigars lighter. As long as this lighter can light the cigar, then you’re good to go. The size of the flame doesn’t matter.

To use another metaphor, car engines. Take the engine of a pristine sports car: very powerful, very well designed, and perfectly powers the vehicle it is designed for. But that same engine probably wouldn't do well if put inside a 18-wheeler. Is that to say that an 18-wheeler's engine is better than a sports car engine?

(As with any metaphor, there are of course some potential logical fallacies. I’m simply repeating what one of our dear engineers told me today, so take it for what you will ）

The point with these two metaphors is that, in Questyle’s opinion, the pure output power by itself is not a specification that should be blindly compared between products. A large output power doesn’t by any means indicate that any one product is more capable than another one of lower output power.

And then the question, how does Current Mode Amplification play into it? I’ll be honest, I’ve had it explained to me many times, and I still sometimes struggle to wrap my head around it. Perhaps this article states it best, in layman’s terms. It refers to our previous product the CMA400i, but the logic remains the same:

“At this point I would like to comment on the deceptiveness of power ratings. While the Questyle Audio CMA400i has a fairly respectable power output of almost 1 Watt at 32Ω, due the Current Mode Amplifier, it is actually equivalent to amplifiers of much higher outputs using other topologies. “How is that,” you ask? Well power is the product of Voltage and Current, essentially Voltage is pressure and Current is flow, and it is the Current that does the heavy lifting, since Current Mode Amplifiers operate in the Current domain, they tend to be Current heavy. To give an analogy that might be easier to understand, in an engine, Horsepower is the product of Torque (twisting force) and RPM (how fast the motor is turning). Torque is the equivalent of Current and RPM is the equivalent of Voltage. As any gear head can tell you, if you have two vehicles with all else being identical, it is the vehicle with more Torque that has the greater pulling power. Back in the world of audio, it is Current that determines how fast a speaker driver starts and stops, which determines how much detail you have and how accurate, especially in the low frequencies, which require much more Current to reproduce.”

https://headphone.guru/questyle-aud...mplifier-peer-into-the-black-depths-of-music/

Then, in terms of the multitone issue: it seems as if L7’s test was a 30-tone (perhaps 32-tone, but not clear), static multitone test. This test is of course useful to an extent — but it only shows the output at one amplitude level. L7 did this test twice, at 0 dbFS and -0.5 dbFS. But of course music signals and audio amplitudes are much more complicated than that. I’ll follow up with the engineers in the coming days on this in particular and see if they have anything to say.

To put it simply, we designed the M15 to drive virtually any headphone thrown at it. IEMs, over-the-ear, open back, closed back, and anything in between. We tested it in-house with HD 600, HD650, HD800S, HD820, HE6, DT990, and many, many others. We also tested it with a HUGE range of IEMs. We made sure this product would complement almost anything on the market, and so far it has.

At the end of the day, numbers really don’t mean much. Only one thing actually matters: the experience. Does a product give you the experience you want? Does it drive the headphones you want to use? Does it sound good? Does it make you feel good? Of course this is difficult to answer unless you’ve auditioned a product yourself. But by now, the number of at-length user reviews of the M15 is enough to give you a good picture of what its capable of.

A lot of our customers have brought up this exact L7 AudioLab review, asking for our response. Indeed, the review’s testing was done quite thoroughly and the numbers essentially cannot be argued. However, and with all due respect, the crucial fault of reviews on this site are that they omit the only thing that matters (in our opinion): the experience. Not many people buy mobile DAC/amps to measure the power output each day when they wake up; they buy them to listen to their music. I personally believe this review might have benefitted greatly from actually discussing the product in a practical way, not simply a statistical one; testing it on your ears, not only on top of a lab bench. Just as @LakeOfTheWyles said, we aren’t disputing L7 Lab’s numbers, they just aren’t the end all be all, not by a long shot. And just as you said as well @Pylaczynski … people don’t test these things enough in real life!!! So true. Kind of defeats the purpose, doesn’t it?

I hope that satisfied some of your curiosity. Let me know if there’s any more details or questions I can help you dive into And thanks as always for being a Questyle fan!

(I’ll also mention, if anybody wants to discuss any of the above points or point out an error, please let me know. Most of the above was translated from conversations I had in Chinese and perhaps I misunderstood something at some point. I’m always up for finding I was wrong, and learning what’s right!)

Realized I had some misconceptions.

 

[manueljenkin]

The numbers don't show anything audibly concerning to be honest. And resistors are not a 1:1 replacement of headphone for analysis purposes. Resistors have no mechanical load or movement, while a headphone does. While I am yet to buy a questyle m15, I do have an apogee groove, which uses current drive amplifier (or something similar, specifics are not known), and it sounds more powerful than its numbers suggest.

 

[Questyle]

@Pylaczynski

Sounds like you need to invest in a good near-field air conditioner if you can't keep cans on for more than 30 minutes!! haha just kidding

Funny enough, we are actually quite similar — I myself am also a mechanical engineer by training, so I have a good grasp on physics and am also very curious about why certain things act the way they do. I suppose at the end of the day, the typical measurements and specs given for hi-res audio devices and equipment are built upon a "voltage amplification" foundation. Questyle's products, since they are tested by the same metrics, give weird or sometimes even "bad" results. But this isn't to signify our little babies aren't up for the task, but rather that they are assessed by tests that don't perfect apply to them, tests that don't give a complete picture of what's happening.

So, one choice would be to dig into the rabbit hole of physics and measurements and understand it perfectly and thoroughly (which I honestly hope to do one day, time allowing)... and, then, the other choice is to just sit back, relax, and enjoy the music for what it is, forget about the measurements and numbers for a while, and maybe switch to the right brain for a hot second and allow yourself to believe that maybe, just maybe, current mode amplification and the M15 are magic in the very same way that music itself is magic.

In the meantime, still waiting for an engineer to get back to me about the multitone, please have patience with this one, all of the engineers are floored out at the moment... we have a bunch of new products in the pipeline that we're developing simultaneously and they are working around the clock these days.

---

@jmwant

Yep, me too. I understand Current Mode Amplification to a point, but I still don't know it well enough to, say, teach it in a classroom... and so every time I get the opportunity to sit down with an engineer, I also realize new misconceptions that I had as well.

---

@manueljenkin

Completely agree. In my personal opinion, it's a shame how much this field has become obsessed with numbers. To an extent, of course I understand... a lot of new devices on the market aren't available for personal testing or auditioning, and as such, some customers have no other choice to rely on numbers. But indeed, numbers are a very lousy way of accurately describing what a given product is capable of. Stuck between a rock and a hard place...

 

[gadgetgod]

Just received a mail from @Questyle , Got their flagship M15 USB DAC/AMP. Just unboxed and I am literally awestruck with its outstanding build. I instantly connected it to my iPad Air and Senn IE600. This little baby sounds super clean, the background has no signs of hiss or noise. Bass feels tighter especially in the sub-bass section(which is actually the tuning of IE600), so I guess the M15 has a highly transparent sound presentation.

More impressions with time See how beautiful this baby looks <3

 

[hongky]

... we have a bunch of new products in the pipeline that we're developing simultaneously and they are working around the clock these days.

Any plan to make DAC/AMP with bluetooth & battery ?
Maybe bigger than M15

 

[Questyle]

@hongky
At the moment, we don't have a product like that in the pipeline, to be very honest with you (other than a possible DAP we have in the works). But this sounds like an interesting idea, one that I could certainly forward to the engineers. By bluetooth, do you mean able to receive bluetooth signals as an input? Or able to send bluetooth signals as an output? Or both?

---

@gadgetgod
So glad to hear that you like it! Yes, that black and red combination is rather sexy, isn't it? Especially when you get the glass to reflect light just right (you nailed it in your second photo!!)

---

@Pylaczynski
More updates for you! Got one of our senior engineers to quickly talk to me about the multitone testing.

His response (again, translating from Chinese):
"It's true, when you put the M15 at full 100% power, there is a small amount of distortion (around the -85dB mark), as seen in L7's graphs. We know this actually, we did this precise multitone test and many others as well during designing the M15, but in our opinion this isn't an actual issue at all. Why? The problem with this test from L7 is that almost no professional audio recordings are recorded up to 0dB. As seen in L7's testing, once the audio signal hits -0.5dB the distortion virtually vanishes. We actually specifically designed the system in a very intentional way, and this 0dbFS "issue" is one of the manifestations of this intentional design: we wanted the M15 to be as least power-consuming as possible (aka optimize power efficiency), and to be able to drive almost any headphone adequately without needing to reach 0dbFS... and as such this distortion at 0dbFS is a phenomenon that almost no user of the M15 will ever experience themselves when listening to music."

Again... the problem is that numbers and graphs really don't tell a complete story when it comes to music or music playback equipment.

Our engineer also remarked that he tried to leave a comment on that precise thread before, but L7 blocked his comment... unfortunately.

 

[hongky]

At the moment, we don't have a product like that in the pipeline, to be very honest with you (other than a possible DAP we have in the works). But this sounds like an interesting idea, one that I could certainly forward to the engineers. By bluetooth, do you mean able to receive bluetooth signals as an input? Or able to send bluetooth signals as an output? Or both?

Bluetooth receiver, something like FIIO BTR series

 

[Questyle]

@hongky Gotcha, yes that's a pretty good idea indeed! I'll forward that to the engineering team and see what they think of it. Thanks for the tip!

 

[rocketron]

Questyle please make something like the Go Blu.
Absolutely loving the M15.
Well done

 

[rocketron]

Please tell us more about the dap you have in development?

 

[Questyle]

@rocketron Well, we have a house policy of never leaking our products before they hit the market So please be patient with us, you'll know everything when the right time comes!

 

[gadgetgod]

Especially when you get the glass to reflect light just right (you nailed it in your second photo!!)

So true!!!