[Head Injury]

 
I'll see if I can pinpoint some frequencies from which the aspects of bass you asked about are derived.
 
Amount - This is just the whole thing, from about 20Hz to 160Hz, with the most effect from 50-120Hz or so.

Detail - Not directly related to frequency response graphs, so if the bass is boosted but well-controlled it will sound more detailed.

Bleeding - Mid-bass and low mid-range accounts for this, from about 100Hz to 200Hz. The length of decay here is also important, but not shown on most graphs.

Extension - How loud it is at 20Hz. An ideal headphone extension is either flat or slightly boosted to 20Hz (boosted due to the lack of physical vibration).

Impact - Mostly caused by a mid-bass hump peaking between 80 and 110Hz. Lots of sub-bass will, in almost all cases, soften impact. It's hard to have both.

Isolation - More bass will overwhelm quiet sounds at all frequencies, no matter what. Otherwise it's related to bleeding.

 


Reading frequency response graphs can be tricky. They are very useful, despite what some audiophiles think. The problem is they're centered at 1kHz (at least Headrooms are), so all headphones have +0dB at 1kHz. Even if a headphone has +10dB at 100Hz, it's not necessarily bassy if it has tall peaks past 1kHz. Probably the best way to determine the above aspects using a graph is to choose a frequency related to it, then draw a horizontal line (real or imagined) across the graph. Then compare how much of the graph is above or below that line.
 
When most people talk about bass quantity, they talk about mid-bass and impact. It's one of the possible explanations for why some find the LCD-2 (arguably the most bass-heavy flagship headphone) to be bass-light. It has no mid-bass hump but a lot of extension. Headphones with large bass humps and no sub-bass, like Grados, sound quicker and more impactful. Headphones with virtually no mid-bass hump compared to mid-range and rolled off extension, like the ATH-AD700, sound anemic to most.
 
Another important aspect of bass response is decay, which isn't shown on regular frequency response graphs. Waterfall graphs show it, but they're rare. If a headphone plays a bass note and the reverberations of that note stick around for a longer time than another headphone, it will sound louder overall. When the next bass note plays, you have a quieter first note still playing. In part because of this, closed cans sound bassier at the same relative level of bass. That's why closed headphone seal is so important to bass response. The sound waves are generally able to escape from open headphones (or poorly sealed closed cans) faster. Typically open headphones will have slightly less impact and a good bit less tactile feeling in the sub-bass, though they will often have better bass detail. There's obviously always exceptions. In other measurements, total harmonic distortion (THD) can play a role as well. If a headphone isn't able to produce deep bass notes but has a high THD, whenever it is fed a deep note it might play that note's harmonic louder than the note itself. As a result you might think you hear a 20Hz note from a headphone, but in reality it's a 40Hz note. This would be especially noticeable in a sine wave generator.
 
Driver size is also sometimes a consideration, though not as important. Larger drivers can push more air at a time, and increase the tactile feel of sub-bass. Planar headphones like the LCD-2 and top-tier Hifimans have large drivers with a flat surface area, and can push a lot of air at once. This allows them to extend scary low, and eliminate the mid-bass hump without sacrificing a whole lot of impact. They can rely on the piston-like drivers to push air a listener can feel, like a speaker. It doesn't work perfectly though, and on most modern recordings designed for mid-bass humps, sub-bass doesn't come into play and impact is lost.
 
I thought there was something else I wanted to say, but I forgot what 

 

[HairPhones]

Quote:

Reading frequency response graphs can be tricky. They are very useful, despite what some audiophiles think. The problem is they're centered at 1kHz (at least Headrooms are), so all headphones have +0dB at 1kHz. Even if a headphone has +10dB at 100Hz, it's not necessarily bassy if it has tall peaks past 1kHz. Probably the best way to determine the above aspects using a graph is to choose a frequency related to it, then draw a horizontal line (real or imagined) across the graph. Then compare how much of the graph is above or below that line.

 
So generally speaking, bassy headphones would have high amplitude on lower frequencies, and would slope down when approaching higher frequencies?
Could you explain the science as to why that is?
 
 
 
Quote:

Originally Posted by Head Injury /img/forum/go_quote.gif
 
When most people talk about bass quantity, they talk about mid-bass and impact. It's one of the possible explanations for why some find the LCD-2 (arguably the most bass-heavy flagship headphone) to be bass-light. It has no mid-bass hump but a lot of extension. Headphones with large bass humps and no sub-bass, like Grados, sound quicker and more impactful. Headphones with virtually no mid-bass hump compared to mid-range and rolled off extension, like the ATH-AD700, sound anemic to most.

 
Is there a graph that tells and/or compares mid-bass & impact?

 

[Head Injury]

Quote:

So generally speaking, bassy headphones would have high amplitude on lower frequencies, and would slope down when approaching higher frequencies?
Could you explain the science as to why that is?

I'm not sure what I'm supposed to explain. A higher dB level at a frequency means more sound pressure and louder. A higher dB level at a frequency relative to another frequency means it's louder than that frequency. If bass is higher than everything else, bass will be louder. Well, in absolute levels, but you need a lot of bass to really hear and feel it with headphones.
 
Think of it like this. Treble's usually the most offensive region to our ears (especially around 8-10kHz where cymbals crash), yet it's also one of the most enjoyable because it imparts a sense of detail and air. So if you're not matching your volume to a specific average dB level (like I do), you're probably setting your volume knob to a place where the treble is loud enough to sound detailed but not harsh and piercing. If your headphone has more bass than treble, then at that volume level you're going to hear a lot of bass. If your headphone has less bass than treble, your treble will be at the same volume but bass will be quieter.
 
 

Is there a graph that tells and/or compares mid-bass & impact?

 
Not directly. Look at frequency response graphs to determine how loud the mid-bass is compare to the lower mid-range and sub-bass. It's all relative to other frequencies, and there are a lot of aspects like decay that come into play as well. It's hard (or even impossible) to say with absolute certainty which headphone hits harder using just a frequency response graph. It can leave clues, and tell about overall bass volume, but there are too many subtleties to say anything for sure.
 
Let's look at an example:
 

 
I own the LCD-2. It's nice and warm, with a rumbly low end and good impact on bass-heavy rap and electronic music, but not so much on loud rock. I haven't personally heard the Pro 900, but the consensus seems to be that it's a bass and bass impact monster.
 
When considering impact, the first place you look is the mid-bass, 80-110Hz approximately. It just so happens the Pro 900 has a big hump right there. Under 30Hz the LCD-2 actually has more bass relative to 1kHz, but this is the least important part of the bass. Few songs make use of it, and even when they do the sound is only perceptible at high volume because of headphone driver size. So as a result, relative to most of the mid-range the Pro 900 will have a lot more perceptible bass, and most of it's in the impact sweet spot. It drops quickly just above that from 200 to 300Hz and stays at or below the LCD-2's level until 2kHz, which prevents it from sounding as warm. That'll just make impact sound even faster and harder.
 
Compared to most of the mid-range, the Pro 900 has 10dB more mid-bass. In the same area, the LCD-2 has between 0-5dB more mid-bass. The Pro 900 is going to sound both bright and bassy. Its mid-range, arguably the most important area, is recessed. For bass impact, comparison to the lower mid-range and sub-bass is most important, because impact often relies on contrast between kick drum hits (around 80-110Hz) and the rest of the bass.
 
If any Pro 900 owners want to criticize my description, please do. And please list another headphone Headroom stocks that you've compared it to.  I want to see if I can fix my description using the graphs.

 

[HairPhones]

Thanks for all the good info.
Learning a lot about FRs & their uses.
Seems like if I want to know about some phones' bass w/o actually hearing them, I'd consult graphs done in labs ie. FRs?
 
Also, could someone explain to me how to read a waterfall graph & how you can tell about decay from them?
I came upon this thread but didn't know what the z-axis was, or how to interpret the shapes in the graph.
 
http://www.head-fi.org/t/566929/headphone-csd-waterfall-plots