[scuttle]

Quote:

The frequency response of headphones isn't supposed to be flat.

 I've been wondering about that - what is the ideal fr for headphones?

 

[jaddie]

Quote:

The frequency response of headphones isn't supposed to be flat. But the graphs here measure the frequency response of the device, not the headphones, and that's supposed to be flat no matter what.
Here and here, and here's the Clip+ (all with the same IEMs).

Ok, so this is another measurement of response of a device with a complex load Z.  
 
Like I said before, it's the total system including the transducer output that tells the real story, though the voltage drop across the transducer probably bears some relation to it.  Perhaps a lot, depends on the transducer efficiency plot, etc.  Hard stuff to simplify this way.

 

[xnor]

As skamp wrote, what's measured as FR here is the voltage across the load. The FR of the headphone (driven by a Zs=0 ohm amp) can look completely different. The sum of both FRs is what you hear.

 

[scuttle]

Quote:

Do we know this [that the 801 dac is non-oversampling]  for a fact?  Non-oversampling with a gentle filter is pretty old-school.  I'm mean like 25 years old-school or better. Hard to imagine that would ever be better than oversampling with an out of band filter.  Where would you even buy such a DAC these days?

I confirmed this with a google search for the 601, but the 801 uses a different dac chip, which is oversampling:
 
Quote:

 
For rhttp://www.stereophile.com/news/10221/
 

Burr-Brown Breaks New DAC Ground with PCM1704

By Barry Willis • Posted: Jul 25, 1998

The DAC performance envelope has been pushed further by Burr-Brown Corporation. The Tucson semiconductor company has just announced the commercial release of its new PCM-1704, an ultra-high-quality digital/analog converter chip boasting a 120dB signal/noise ratio. The new chip supersedes the company's PCM-1702, a DAC found in many high-end products and widely considered the state of the art. The 1704---priced at $12.95 each in OEM quantities of 1000 or more---is a small 20-pin SOIC requiring a ±5V supply. It will accept input data words of 20- and 24-bit lengths at sampling frequencies up to 96kHz, and will support 8x oversampling at the highest sampling rate. Its SNR is near the theoretical maximum for all electronic devices, and enables a 112dB dynamic range---a 6dB improvement over the highly regarded PCM-1728 (see previous story). Unlike delta-sigma converters, Burr-Brown's BiCMOS device is "not sensitive to clock jitter," according to audio product marketing manager Mike Centorino. "Sign-magnitude designs are inherently better than delta-sigma types at handling jitter," he said. "It's a different architecture, specifically designed for high-end performance."

 
So - state of the art 15 years ago...

 

[jaddie]

Quote:

As skamp wrote, what's measured as FR here is the voltage across the load. The FR of the headphone (driven by a Zs=0 ohm amp) can look completely different. The sum of both FRs is what you hear.

Not exactly, but I'm not gonna be your nit picker...

 

[scuttle]

This might explain some of the other weirdnesses of the design:
 
Quote:

http://www.inearmatters.net/2010/12/review-hifiman-hm602-and-hm801.html
 
After HifiMan released, it has been met with a lot of doubts and criticisms. Some of the more noticeable one is the treble roll off (attenuation) between 10 kHz to 20 kHz. It is about -2.5dB on 15 kHz and roll down to about -5dB at 20 kHz. While some consider it as a defect in design, it is actually being done intentionally. There is always a low pass filter after the DAC stage (or integrated internally) to remove the high frequency component (> 20 kHz) in order to remove noise as well as the inaudible frequency. Human hearing is generally recognized as 20 Hz to 20 kHz, but in real life the full range is between  16 kHz for most adult and down to 80 Hz in bass (*anything below increasingly tends to be felt more by skin rather than heard by ears, which we often refer as  ‘chest pounding sound’). What HifiMan employed is called a Butterwoth filter (a.k.a. Maximally Flat filter). AS I have read, the characteristic of this filter is that the passband (the desired range) has a maximally flat response (no ripple in frequency response) as well as a more linear phase response (no uneven phase shift in individual frequency). The downside is that it doesn't roll-off quite as fast as other types of filters (which create the slope or ‘roll off’ in HifiMan’s upper treble). I think the consensus is that there is no such thing as one perfect filter for everything. Each type of filters has its own pros and cons and it is up to the implementation as well as what goal the designer wants to achieve to determine what is best for a certain design. In fact, quite a few well regarded high-end DAC and CD player also employs Butterwoth filter because it is considered more analog, musical sounding than other filters.  I think the problem of Butterwoth filter on HifiMan has less to do with actual performance, but whether some can accept that you don’t need absolute perfect flat line to create a player that sounds good. If you can’t, then you know what you won’t be buying. I am not an electronic or audio engineer that can tell you what should have been done that could yield a better result or whether a Butterwoth filter is indeed the right choice – but rather trying to interpret whether the end result sounds good to me or not

 
Perhaps it is the (I think rather nutty and bs-filled) reviewer's bias, but it sounds like the Hifiman players were engineered to try to sound analog - or at least how certain people think analog sounds.

 

[skamp]

 I've been wondering about that - what is the ideal fr for headphones?

Well, I meant that I don't think that headphones with a perfectly flat FR exist. Ideally, if "high fidelity" is what you're looking for, yeah, a flat FR would be desirable. But then there's everyone's preferences to take into account. Some might prefer headphones with emphasized bass, etc…

 

[scuttle]

Quote:

Well, I meant that I don't think that headphones with a perfectly flat FR exist. Ideally, if "high fidelity" is what you're looking for, yeah, a flat FR would be desirable. But then there's everyone's preferences to take into account. Some might prefer headphones with emphasized bass, etc…

 
Heretic! Preferences are what equalizers are for.
 
There are some very flat headphones at the high end:
 

 
 

 
And the author of the astonishing OP in this thread manages to get a $150 Fostex T50rp almost as flat - very scientifically, using successive tweaks and measuring gear:
 
http://www.head-fi.org/t/618659/fostex-t50rp-incremental-mods-and-measurements
 

 

[skamp]

Preferences are what equalizers are for.

Sure, and I do use them. But I don't think I can reproduce the mind blowing bass of my Sony MDR-XB700 headphones with an EQ.

 

[stv014]

Quote:

I confirmed this with a google search for the 601, but the 801 uses a different dac chip, which is oversampling:

 
Actually, from the datasheet it looks like the PCM1704 is not oversampling itself, it simply accepts oversampled digital input (i.e. it supports a maximum bit clock of 25 MHz). There is no digital filter in the DAC chip. The oversampling and digital filtering needs to be implemented externally, and it may or may not be present in the Hifiman player (but from the measurements I suspect it is not used, so it is indeed non-oversampling if that is the case).

 

[xnor]

Quote:

Sure, and I do use them. But I don't think I can reproduce the mind blowing bass of my Sony MDR-XB700 headphones with an EQ.

But you can reduce the XB's bass to acceptable levels.

 
No it's just that the headphone was designed to specifically resonate and be efficient at low frequencies. Any headphone with less seal will have troubles reproducing low frequencies with low distortion - obviously.

 

[EddieE]

Quote:

 
That is because it uses a non-oversampling DAC, which likely also has higher than usual amount of high frequency IMD and ultrasonic imaging, and not very good low level linearity. However, some may prefer it simply because of the "warmer" sound resulting from the treble roll-off.

 
Yes, that "lush warm" sound many report with the Hm 801 is likely down to this roll off, I detected it myself when A-Bing it with the Clip + at a meet. Must point out that this is a very subtle effect. Very little fundamental is going on beyond 16khz in music, so the dip is not critical, but it does add an overall subtle effect to the presentation that is audible.
 
Some say they like this, which is fair enough, but I would say stick with gear that works properly (i.e. is neutral) and chose warm headphones if you like it that way. Tastes change and you can change headphones when they do, but the player will remain a bottle neck. I'm just not a believer in audio gear (excluding speakers/headphones) having a "character" - these are devices with a specific function that should perform it, not add their own "twist" to it.
 
When you add its FR quirks to its high output impedance, its really not a device I would recommend. For balance, I would however recommend Hifiman headphones in an instant, don't want to come across as bashing the company as a whole.

 

[goodvibes]

What those graphs show is not tha actually measured output response from the headphone itself but how the amp responds to it's load. The deviation will still be there when measuring the IEM but it may also be less than it appears in those graphs. I say less because low impedance (dip) may increase efficiency and high impedance (bump) could decrease it. The graphs are generally accurate and telling enough but I think folks need to remember that we're not measuring the headphones actual deviation from linear but the amps behavior instead. When you want a very accurate result of a pairing it's best to measure at the end of the chain.
 
That said, the 801 measures poorly enough that I wouldn't fork that sort of coin for it.

 

[Satellite_6]

Bad is an understatement. 

 

[scuttle]

Quote:

Sure, and I do use them. But I don't think I can reproduce the mind blowing bass of my Sony MDR-XB700 headphones with an EQ.

 
Then the property of the bass you enjoy is not part of the FR. Which is why square wave graphs and CSDs are useful. But CSDs and square waves *are* better or worse, rather than preference.