Hello folks! First time posting here. I love the podcast and have been tuning in for quite a few. Here are some topics I’d like to see in future episodes (I ramble for quite a bit so just read the bold text 
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The Value of “Quick & Dirty” Measurements
There are 2 review sites I can think of: Audio Science Review (ASR) and Reference Audio Analyzer (RAI). I know you guys have pushed back on these kinds of reviews, for valid reasons, of course. However, I see a lot of valuable elements in them which can’t be easily found anywhere else. I hope I can see these elements in your future tools, reviews, or videos.
1. For Headphones:
1.1. The Misconception of “Dynamics”:
When I first started in this hobby, I thought “dynamics” literally meant how the loudness changes in relation with input signal, like gamma curve in imaging. A few minutes on RAI showed me that an increase of 10, 20, 30, etc. dBV equals an increase of 10, 20, 30, etc. dB SPL, regardless whether it’s a DCA or a Focal. I can’t find information anywhere else. I know you guys keep preaching that “dynamics” is just an effect, but I think there’s a value in showing, not just telling, that any passive headphones (so not Apple) are perfectly linear devices.
1.2. Impedance Curve:
Common wisdom is that you have to be careful with low impedance headphones and high impedance source, since it can change the FR. If you’re deep in the weeds, you’d know that it doesn’t apply to most planars, since they have flat impedance curves. If you’re deeper in the weeds, you’d find out that some dynamics like K371 or IEMs like 64 Audio also have flat impedance curves. It’d be nice if you guys have a database of impedance curves like ASR and RAI for all headphones/IEMs headphones.com carries.
1.3. Distortion vs Frequency Graph:
Having watched enough episodes, I think I get a sense of where you guys’ stances on distortion on headphones. For @Mad_Economist , I think he’s of the opinion that you can EQ the HD 800 to high heaven without any meaningful distortion at appropriate listening levels. Whilst for @Resolve , I think he’s more cautious about recommending certain headphones for folks who EQ and/or listen at high levels, such as the obvious Focal Clear, but also the HD 650 and HD 800 S to some extent. For me personally, I can do +20 dB sub-bass on the Focal Clear just fine. (I don’t, but I tried once as a stress test.) Other users such as Amir didn’t share my experience, and his unit measured fine.
All of that to say, I don’t think a Pass/Fail is enough for distortion, according to that one episode you discussed. Let’s say some headphones have a 10% distortion in the bass at 94 dB SPL, but also have a colossal +30 dB bass to begin with, you can’t just put a blanket statement like “If you’re someone who EQ, this headphones isn’t for you.” Because most likely, people would want to EQ that bass down, not up. In another instance, like for Abyss headphones, the distortion is massive in the upper treble to the point where it’d actually considered “Fail”, but that’s irrelevant for those who just want to know whether they can EQ the bass.
So, what’s the solution here? For most consumers, I’d say don’t even bother with distortion. Even Pass/Fail is misleading IMO. But we’re an edge case of a community with some listening at concert-level and beyond, some sniffing so many graphs that do +30 dB with Q=10, some turning on XBass on the Eris, and some are a combination of everything. Then there’s Abyss with distortion indistinguishable from EEG during seizure but still sounds remarkably fine. I’m interested to hear your thoughts on what kind of data representation that (a) isn’t misleading and (b) shows the complete picture on the degree of EQ/SPL a user can expect from a given product.
For now, since we’re in the “Dark Ages”, I have no other choice but to look up ASR for distortion vs frequency graph. Let’s take the notorious Focal Clear for example: maximum 3% THD at 30 Hz at 104 dB SPL. For me, that means I can crank the bass to high heaven without a problem. For others, clipping at 114 dB SPL is a deal-breaker. For the HD 650, which doesn’t clip at 114 dB SPL (I don’t know what level of distortion that is, and that’s the flaw of ASR), but has maximum 5% THD at 30 Hz at 104 dB SPL. FR matters as well, since the HD 650 has worse bass extension compared to the Focal Clear, you have to EQ crank the bass considerably more to get the same bass level (i.e. more distortion for HD 650). So, at lower bass levels, the Focal Clear is better; at higher bass levels, the HD 650 is better (?) (hard for me to say since if it’s like 50% THD at that levels then it’s a moot point, but you guys have that data so you should know).
Having sniffed enough graphs, I’ve concluded that at my listening levels, I can EQ however the hell I want for any of my headphones, and I don’t own any planar or estat. I’m curious why @Resolve is quite reluctant to crank up the bass on dynamic headphones, since I don’t think you listen that loud anyway.
2. For Amplifiers:
2.1. Output Impedance:
This is fairly straightforward. It doesn’t require the fancy APx555 or a lot of time to measure. Yet, this is perhaps the most significant specification, especially for tube amps, that many manufacturers don’t specify. It’d be great for consumers if you guys can measure output impedance on every amplifiers headphones.com carries. I don’t see it for Feliks Audio amplifiers for example.
2.2. THD+N vs Power/Voltage Graphs for Various Loads:
I don’t care about SINAD, not one bit. I only care at which point does the amplifier clip or distort so bad that it’s unlistenable. ASR usually only does 300 Ohms and 33 Ohms for SE, and 50 Ohms for BAL, which is good enough for me. L7Audiolab does it a lot better. RME is the gold standard for manufacturer IMO; their datasheet and measurements are extremely detailed. Having cross-referenced RAI and ASR measurements, I’ve concluded that the Qudelix-5K can power the Susvara to at least 102 dB just fine. And according to specs of the Tungsten, the Qudelix-5K can also power the DS version to 98 dB just fine. By just fine I mean -87 dB THD+N. I couldn’t care less if it’s higher. From that aspect, I really appreciate the shear quantity of measurements pumped out on ASR. @GoldenSound mentioned this as well. As someone who understands which metric to pay attention to and which to ignore, ASR is valuable in helping me understand the capabilities and limitations of products I want to purchase, as well as just for my curiosity. For those who just look at the big numbers and rankings, well, I’m not too sure it’s quite as productive.
“Low-End Amplifiers Can’t Never Do High-End Headphones Justice”
I live in a place where Hi-Fi physical stores are everywhere. I’ve tried pretty much every high-end headphones at length under the sun, including the HE 1. I’m also a graph sniffer who EQ everything I own and try (aside from the HE 1 since I’m not gonna buy it anyway lol). The main thing I look for in headphones aside from ergonomics is the treble response, since I gave up EQing that a long time ago. (It changes every time I put on slightly differently so what’s the point?) The one thing I always carry with me is the Qudelix-5K, since I can adjust PEQ on my phone on the fly instead of a laptop.
Most sale reps thought I was insane when I said I wanted to use my Qudelix-5K to power the Focal Utopia. For reference, it can do 123 dB SPL (-87 dB THD+N), way beyond the clipping point of the Utopia. And those sale reps were audiophiles way in the weeds already. Their response was “Well, it might tell you that on the spec sheet, but it doesn’t sound like that.” If it was a decade ago, they might be right. Even high-end DAPs like Astell&Kern struggled with high current. So, even if it could technically provide enough power on the spec sheet, the distortion would be so high that you could hear it. That’d show up on the APx555; it’s just that no one did the measurements back then. On the other hand, for most decent modern amplifiers including the one in Qudelix-5K, the performance actually goes up the higher power it provides. Consumer DACs and amplifiers have evolved, but the stigma is still present.
I’m curious to know if what’s your experience with people’s resistance of using low-end amplifiers with high-end headphones.
Source Gear For People Who Aren’t Into Source Gear
I’m in the camp of “Even if I can ABX between two amplifiers or DACs, at no point do I care.” I think @Resolve said something along those lines if I remember correctly. Even if I don’t care about it’s sonic performance, I still need to buy a DAC and amplifier of some sort. Here are my criteria:
- Not broken. Surprisingly not a given for many HiFi gears.
- Enough gain. There was one film I watched that even gunshots were probably around -40 dB. Sure, I could increase the preamp in EQ APO but it felt so good turning that JDS Element knob all the way to the right.
- Big knob. Because of that macro contrast.
- Aesthetic. All Denafrips are ugly. Fight me.
- Features. PEQ is the main one.
What’s your source gear recommendation for those who aren’t into source gear?
Here are my desktop picks:
- Topping D50 III (PEQ, cheap)
- JDS Element IV (PEQ, big knob)
- RME Fireface UCX II (8 analog channels + 2 SPDIF channels 9-band PEQ, mic preamp)
- RME ADI-2 DAC FS (2 channels 5-band PEQ, higher performance but again I don’t care)
- Feliks Audio Euforia EVO (big knob, absolute stunning)
- Ferrum WANDLA GSE (that HM1-like DSP is pretty cool, but I want it in software)
My end-game DAC is the Fireface UCX II ever since RME updated it with Room EQ.
My background is in Mechanical Design. I love @Mad_Economist 's take on headphones mechanical design. Sadly, many designs you see everyday started with the silhouette before functionality, even in the aerospace industry. I don’t think it’s a stretch to think many headphones manufacturers took the approach. Keep up the good work! Love the podcast!