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rhalf t1_itr8fij wrote

Reply to comment by rhalf in Sincere question: does technicalities exist, or everything what matters is FR graph? by Then-Effective5434

The reason why peeps talk about frequency response and frequency response only is threefold:

First, headphones are tragically bad at it. Tuning a headphone is a nightmare as opposed to tuning a loudspeaker. They are often off by something like 10dB and it's not considered weird, that's how difficult it is to get that line flat. By comparison a reviewer's standard for a recommended loudspeaker is +/-1.5dB.

Secondly it's the only feature of sound that you, the user can affect. You can't change compression or ringing without comprehensive training in engineering. However you can push the sliders to make an EQ curve.

Lastly it has been shown that frequency response is very important. It's the most fundamental measurement that we have and our hearing agrees with the results of this measurement to the highest degree. Not 100% but still more than with anything else.

As a bonus I'll add that it's the easiest thing to measure. It doesn't require any special equipment or knowledge. The simple graph is also easy to understand. If I posted a waterfall graph instead, a common person reading it would be lost and had no idea what to make out of it.

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Technical_City t1_itrac83 wrote

>First, headphones are tragically bad at it. Tuning a headphone is a nightmare as opposed to tuning a loudspeaker. They are often off by something like 10dB and it's not considered weird, that's how difficult it is to get that line flat. By comparison a reviewer's standard for a recommended loudspeaker is +/-1.5dB.

This is really interesting. As a non-engineer, can you explain why it is that tuning headphones is so practically difficult? Intuitively I know it to be true (hence all the substandard headphones, etc.), but have no sense of why it's so difficult.

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rhalf t1_itrjv5j wrote

In order to understand the difference, you need to know how a loudspeaker is tuned. A hifi loudspeaker has bare drivers on a flat baffle. There is nothing affecting the sound between the diaphragm and a microphone. A loudspeaker designer than has a full arsenal of tools to affect it. It's like working in a chemical lab, where everything is in clear glass with no contamination and all the tools to precisely dose chemicals. If you want to alter a driver, you make a precise virtual model in software and the software spits out it's response. You know for sure that this response will be very close to the real thing. You can for example put the tweeter in a waveguide and an app will help you iterate the design 20 times before you can get all the lines parallel. You don't need to make the thing 20 times. You're done with the baffle and the thing is still not flat? That's OK, you can compensate any problems in the electric domain. You open another program that lets you make a filter out of electronic parts. It simulates a notch filter here and a shelf there and with 20 parts you have finally linearized the response. The whole thing weighs a ton and barely fits in the enclosure, but hey it sounds great. Oh did I mention that AI does that last part for you? Yup, there is an app that does just that. You give it a measurement and it spits out a circuit diagram.

Now headphones... Remember when I said that you can design a waveguide? So with headphones you are already forced to work with one. The ear cup is a waveguide, a terrible one and there's not much you can do about it. Headphone's ear cup is like room that cannot be detached from the loudspeaker. You can't take it to an anechoic chamber. You need to work with the mess that it creates. Sound is like light except everything is a mirror. A lightbulb in a torch illuminates the surroundings differently than a lightbulb in a chandelier. A headphone is a lightbulb in a crumpled tin can. The result is a mess.

Headphones are tuned by covering holes on the driver with lossy materials. You poke a hole and see what happens. Each time you change it, something drastic happens, but it's difficult to understand what. I have personally no idea what tools or software do the big guys like Sennheiser have to aid them with it. I guess a headphone designer would shed some light on it, not me. But even if you get the driver tuning right, you change the earpads and it sounds differently. More than that. You put it on someone with curly hair and glasses and that makes a difference as well :D That's because the enclosure is lossy. Very lossy. I personally don't understand why we can't add passive filters to headphones. It used to be problem of source output impedance, but now that everything is measured and reviewed, we can predict how a filter would sound. So it would be cool to see filter PCBs for headphones. It won't fix all issues because the most appalling resonances in headphones are destructive, meaning that they cannot be fixed without physical change. It can be used to attack broad valleys and bumps though.

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The_D0lph1n t1_itrurpc wrote

There's a site called DIYAudioHeaven that does provide schematics for analog filters for certain headphones. And I've seen speculation that the Dan Clark Audio Expanse uses a passive filter to produce its bass shelf that would normally be impossible on an open-back planar-magnetic headphone. So it's not unheard of to use passive filters, but certainly not commonplace. I suppose people who use high-output-impedance amps on headphones with highly variable impedance curves are doing some passive filtering too.

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rhalf t1_its457p wrote

Hey that's cool. I'll check it out.

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ThatsAlotOfBeanz t1_itswgfo wrote

Great response, just had to say your statement “a headphone is a lightbulb in a crumpled can” is perfect 😂 sincerely - a headphone designer after a long day.

To elaborate slightly about the tools the various “big guys” use, there are a handful of mathematical methods you can use to predict/understand what sorts of changes to make regarding the variables of headphones, but it is quite messy. And a lot of the more boutique headphone places follow the “pole a hole and see what happens” approach. - which isn’t a bad thing, just one of many design methodologies.

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Technical_City t1_itsf97l wrote

Thank you so much for writing this out. This is what reddit is great for. Very interesting.

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gr8john6 t1_iufeok1 wrote

This is why back in the 90's people tried to make a smallest well tuned loudspeakers to hang over ear. ;P Bypass all the problems with having to deal with human imperfections.

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knvngy t1_itrs83l wrote

> By comparison a reviewer's standard for a recommended loudspeaker is +/-1.5dB.

In real life you almost never get a loudspeaker that produces a flat frequency response within +/-1.5dB . That's fantasy unless you listen to very high end speakers in a perfect anechoic chamber which is not happening. So more like +/10dB in real life. In that sense both headphones and iems can produce a smoother frequency response than most loudspeakers.

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