[Lohil]

Back in college I did a little undergrad researching into various elements of audio design centered around headphones. Primarily this focused on opamp and filter designs.
But when it comes the production of the sound itself by an acoustic driver not so much, so my question is:
What makes for good Bass reproduction in a driver? Specifically sub and mid bass as opposed to its other frequency ranges.

What got me thinking this was I was looking for new drivers for studying just the production of these frequencies ~ 20 – 150hz, I asked ai and it recommended these https://www.amazon.com/OneOdio-Head...YRR&utm_source=Perplexity&utm_medium=referral
My only guess is that because they have large 50mm drivers and rare earth magnets w/e but I had to kinda laugh because I’m thinking well these are probably absolute garbage.
But now here the question, why are they garbage? (probably) obvious answer is well they’re cheap, but what exactly happens to the drivers by being cheap that effects their sound quality - I realized I don't ult. know.

Currently I’d been listening to Bass reproduction on some DT770 80ohms but sadly one of drivers wiring has always been about to go and I just permanently broke it in my attempt to fix.
So a recommendation on alternatives (they theoretically only need to work well from 20-150hz) would also be appreciated.

 

[castleofargh]

If you want very flat FR very low, then dynamic drivers aren't the best answer. But if you're looking for the speaker like bass, then it's more complicated because even dynamic drivers tends to already extend more than a typical speaker(with no woofer!). And obviously a significant portion of the low end feeling is provided in a tactile feeling(how it shakes our body).
The easy answer is to use a woofer with a headphone, but most people using headphones are already doing it to avoid making too much noise. Another option is to get a shaker(some stuff that vibrates and is tied to the chair or straight on your body). It's not the same, but it's been shown to increase the perception of low freqs somehow(the vibration doesn't even need to be at the frequency of the signal for some impact to exist). It's not magical, just one variable that could be added to help convince the brain.

Personally, my best friend for headphone and IEM bass tends to be EQ. I happen to not mind very low end distortions most of the time, so I can usually find some tuning I will enjoy even on something that's pathetically rolled off by default. Then again, I don't listen to music loudly so I need more bass, but at the same time, because I don't have a high SPL, most drivers aren't getting pushed to their mechanical limits.

 

[bigshot]

For the best bass get speakers and an acoustically sympathetic room. I have a Sunfire subwoofer that does a good job.

Headphones present mid bass and above listenably with a proper response curve.

 

[Lohil]

If you want very flat FR very low, then dynamic drivers aren't the best answer. But if you're looking for the speaker like bass, then it's more complicated because even dynamic drivers tends to already extend more than a typical speaker(with no woofer!). And obviously a significant portion of the low end feeling is provided in a tactile feeling(how it shakes our body).
The easy answer is to use a woofer with a headphone, but most people using headphones are already doing it to avoid making too much noise. Another option is to get a shaker(some stuff that vibrates and is tied to the chair or straight on your body). It's not the same, but it's been shown to increase the perception of low freqs somehow(the vibration doesn't even need to be at the frequency of the signal for some impact to exist). It's not magical, just one variable that could be added to help convince the brain.

Personally, my best friend for headphone and IEM bass tends to be EQ. I happen to not mind very low end distortions most of the time, so I can usually find some tuning I will enjoy even on something that's pathetically rolled off by default. Then again, I don't listen to music loudly so I need more bass, but at the same time, because I don't have a high SPL, most drivers aren't getting pushed to their mechanical limits.

Well for my purposes I am looking at what is done / can be done with a driver element contained within a typical over the ear headset. What is the effect of impedance, driver size, rigidity of diaphragm etc. on the production of sound specifically at these low frequencies.

 

[XTF1]

Well for my purposes I am looking at what is done / can be done with a driver element contained within a typical over the ear headset. What is the effect of impedance, driver size, rigidity of diaphragm etc. on the production of sound specifically at these low frequencies.

These are questions only a headphones (your defined scope) manufacturer or designer can answer. The responses will be technical in nature with insights about headphones design constraints and tradeoffs.
I don’t think there is much science involved here, but could be wrong !!!

 

[bigshot]

As castle explained, sub bass is felt more than heard. A headphone just can’t do what speakers can do. If you like bass the best way to handle it is to apply a little EQ bump in the mid bass.

 

[Lohil]

As castle explained, sub bass is felt more than heard. A headphone just can’t do what speakers can do. If you like bass the best way to handle it is to apply a little EQ bump in the mid bass.

Sure but there are headphones that do better job at recreating bass frequencies than others (even if it is just mostly thump), the question is why

 

[bigshot]

Tranducers are subject to the laws of physics. It isn’t possible to make a perfect transducer because it’s mechanical. So manufacturers make compromises and trade offs to come up with a happy medium. Maybe they focus on getting distortion right, or they focus on flat response or they focus on forward bass or sparkling treble. It’s all a trade off. All headphones are different and what sounds perfect to your ears may not sound perfect to mine. So headphone designs are all different. You listen and choose the one you want.

 

[old tech]

Tranducers are subject to the laws of physics. It isn’t possible to make a perfect transducer because it’s mechanical. So manufacturers make compromises and trade offs to come up with a happy medium. Maybe they focus on getting distortion right, or they focus on flat response or they focus on forward bass or sparkling treble. It’s all a trade off. All headphones are different and what sounds perfect to your ears may not sound perfect to mine. So headphone designs are all different. You listen and choose the one you want.

It is not only that it is mechanical, a transducer changes the state of energy, e.g. from an electrical signal to mechanical movement or vice versa. As in the first law of thermodynamics, any change in energy state results in some inefficiency or energy loss.

 

[bagwell359]

It is easier for me to start this with bass WRT speakers/rooms. Pretty much everyone gets FR as a key factor. But once that's dealt with (and in rooms that 20-30 Hz and other discrete frequencies often presents lots of problems with loose boundaries, vibrating objects (including the drivers, boxes, ports,) bric a brac... Then there is the inescapable issue of peaks and nulls in the room itself, and the speakers relative to boundaries just add to the complexity/unevenness one can face. Assuming those issues are dealt with (to some extent) then you have to face driver/box/port Q. In acoustic suspension (no port) the goal for best overall performance is a Q of .707 - which gives you both fairly quick response and also fairly good sustain. Higher Q can get you more volume at the expense of reaction to the initial pulse. Low Q can get you the quick response to a signal, but, then can lack sustain - which can make it seem lacking/over damped. Port(s)/slots if properly tuned get you more lower bass than the closed box, but also will give you less flat bass and multiple places of fundamental resonance.

The ideal room would be along the lines of 1, 1.67, 2.5 ratio of distances - with non parallel walls, and apatures (window/door ways) to help mitigate standing waves and snooth response. Then there is the whole balance of absorption, reflection, diffusion., and how much you can/want to tune given living space/WAF issues.

And then in the solid majority of cases where the bass is flatest is not where the speakers image/soundstage best - seemingly always true with panel speakers.

Have new speakers that get me the 30-70 Hz area my prior bookshelfs did not have, but the room dims with unfortunate dims of my speakers to boundaries added in is forcing play at low volumes, or dealing with some real peaks and valleys that only PEQ, and some more well placed padded furniture will be able to mitigate. I mourn my last 3 rooms covering 40 years that were a lot better (built one to spec, tuned all 3)

Are we having fun yet? Headphones seem easier, but very early reflections, vibrations, the issues of tuning closed backs (which is why its always open back for me), and the constant distances in the front and rear flanges of the cup gives uneven FR also (that pesky upper mid dip in so many cans is a symptom). Even the HE-6 6 screw with a mega amp cannot give the visceral bass that I'm getting with my speakers - which is why IMO bass cannons seem more popular among audio fans than those focused on room speakers.

I'm tired, it's late. I'm sure I left out a lot, and misstated other things - but yes, its a large topic area.

 

[castleofargh]

Well for my purposes I am looking at what is done / can be done with a driver element contained within a typical over the ear headset. What is the effect of impedance, driver size, rigidity of diaphragm etc. on the production of sound specifically at these low frequencies.

For the obvious, in a somewhat vented design, you just want a bigger diaphragm. Of course with that comes a long list of problems because you also wish to keep it lightweight and as stiff as possible while it's moving a lot more air from being bigger. And unless you ignore high frequencies, you still want that driver to move fairly fast. It's almost more of a dilemma than an engineering challenge because there is no ideal solution to properties pulling away from each other.
But if we disregard distortions in the bass and everywhere else, then a bigger driver should usually do the trick.

Another option could be to get the deadliest seal possible and hope for something similar to the piston effect of non-vented in ears.
What is sure is that you want to mitigate the sort of high pass filter effect we see on most headphones when the pads don't seal well(SR80 style!). That too is less obvious with bigger drivers, but I couldn't tell if it's a direct relation or if it's because the bigger drivers require bigger airflow to begin with, so there already is plenty of venting with or without good pad seal.

The Sennheiser guys talk about trying bigger drivers and finding that the HD800 driver size is about their optimal result globally, they were not talking just about getting more bass! And again, their drivers are dynamic types, which is not what gives the lowest extensions on headphones anyway.

About impedance, at least for dynamic drivers there is always at least one sort of resonance the designers try to keep low freq, which could show as a little bump and depending on the amp's impedance, could EQ a little boost at that frequency. I don't know that it is an interesting tuning tool, though. When you go get a 130 ohm OTL amp just to add like 0.3dB at 80Hz, maybe it's time to just use EQ.

The other day someone brought up a headphone with a pad version that has a lateral vent to boost the bass, but my comment there was in relation to what's done on speakers and how below the resonance, we should be back to having to deal with bad seal and high pass filter effect. So it's a solution for sure(plenty of speakers do it), but doing it on the pads sure seems like a gamble to me.

The rest gets complicated fast, and too complicated for me almost as fast.

If all you want is flat forever(almost), then planar and electrostats are the way to do it. If you want an actual boost somewhere in the low end, then DD are the usual suspects, but be ready for the distos that come with that elevated low frequency.

 

[Lohil]

For the obvious, in a somewhat vented design, you just want a bigger diaphragm. Of course with that comes a long list of problems because you also wish to keep it lightweight and as stiff as possible while it's moving a lot more air from being bigger. And unless you ignore high frequencies, you still want that driver to move fairly fast. It's almost more of a dilemma than an engineering challenge because there is no ideal solution to properties pulling away from each other.
But if we disregard distortions in the bass and everywhere else, then a bigger driver should usually do the trick.

Another option could be to get the deadliest seal possible and hope for something similar to the piston effect of non-vented in ears.
What is sure is that you want to mitigate the sort of high pass filter effect we see on most headphones when the pads don't seal well(SR80 style!). That too is less obvious with bigger drivers, but I couldn't tell if it's a direct relation or if it's because the bigger drivers require bigger airflow to begin with, so there already is plenty of venting with or without good pad seal.

The Sennheiser guys talk about trying bigger drivers and finding that the HD800 driver size is about their optimal result globally, they were not talking just about getting more bass! And again, their drivers are dynamic types, which is not what gives the lowest extensions on headphones anyway.

About impedance, at least for dynamic drivers there is always at least one sort of resonance the designers try to keep low freq, which could show as a little bump and depending on the amp's impedance, could EQ a little boost at that frequency. I don't know that it is an interesting tuning tool, though. When you go get a 130 ohm OTL amp just to add like 0.3dB at 80Hz, maybe it's time to just use EQ.

The other day someone brought up a headphone with a pad version that has a lateral vent to boost the bass, but my comment there was in relation to what's done on speakers and how below the resonance, we should be back to having to deal with bad seal and high pass filter effect. So it's a solution for sure(plenty of speakers do it), but doing it on the pads sure seems like a gamble to me.

The rest gets complicated fast, and too complicated for me almost as fast.

If all you want is flat forever(almost), then planar and electrostats are the way to do it. If you want an actual boost somewhere in the low end, then DD are the usual suspects, but be ready for the distos that come with that elevated low frequency.

Thanks for the insight, I'm gonna try those $25 50mm driver amazon headphones and see how they fair on the low end sounds from the reviews it'd seem that while they're not so great for mids and highs (as one would expect) the actual lower end freq. come across well.

As for a flat response of planar and electrostatics it's beyond the scope of what I'm looking at right now (just interested in listening to 20-150hz sine waves) but I have always wanted to try them from a general audiophile standpoint.

 

[VNandor]

What makes for good Bass reproduction in a driver? Specifically sub and mid bass as opposed to its other frequency ranges.

A low enough resonance frequency is necessary for the driver to reach low frequencies. In an idealized "infinite baffle" situation, the driver will always roll off below that frequency by 12dB/octave. The Q factor decides how exactly the 12dB slope is reached.
https://www.diyaudio.com/community/attachments/guete_neu-gif.380323/
Note that all the slopes would be the same at low enough frequencies, the Q factor only changes the response around the resonance, it doesn't affect the order of the rolloff.

Real drivers have enclosures that are supposed to be tuned to the driver. They have their own Q and Fs and creates a system with the driver. The enclosure helps the driver to reach a lower cutoff frequency but then the speaker rolls of faster than 12dB/oct.

Ideally, the driver's suspension is linear as well as the magnetic field in the gap but that is never the case in the real world. The driver will have higher excursion at lower frequencies and the disproportionate increase in the suspension's force and the decrease of the Bl at the higher excursions will create a significant amount of harmonic distortion.

To get started, I would suggest looking at TS parameters:
https://en.wikipedia.org/wiki/Thiele/Small_parameters

There's this Klippel poster I've found that gives a very high level overview of driver fundamentals:
https://www.klippel.de/fileadmin/_migrated/content_uploads/KLIPPEL_Sound_Radiation_Poster_01.pdf