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Superlux HD668B Review (headphone)

amirm

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#1
This is a review, detailed measurements and equalization of Superlux HD668B semi-open headphone. It was kindly purchased by a member new and drop shipped to me. It costs as little as $40 including free shipping on Amazon.

Needless to say, you are looking at all plastic headphone here:

Superlux HD668B Review cheap Semi-open Headphones.jpg


It looks like you can adjust the headband but you can't. Trust me, I tried at first. :) the little pads on top are supposed to be a self-adjusting mechanism. They kind of work but then put pressure on two small spots on your head.

The cable terminates in a male connector which is unusual:
Superlux HD668B Review cheap Semi-open Headphones removable cable.jpg


The cups are on the larger side which helps a lot with comfort given the stiff spring action. I would give it an 80 to 90% comfort after you wear them a few minutes.

Superlux HD668B Measurements
Here is the HD668B frequency response:
Superlux HD668B Measurements Semi-open Headphones.png


We see good adherence to our target curve from 70 Hz to 2.5 kHz which is good. But then we have a trough and two peaks. We also have our usual bass drop off. Subtracting the frequency response from our target we get this kind of deviation:

Superlux HD668B Measurements Relative Frequency Response Semi-open Headphones.png


As you see, we have huge variation in span of just a few Kilohertz as noted on the graph. That first peak interestingly enough, correlates precisely with distortion at that frequency:
Superlux HD668B Measurements Distortion Semi-open Headphones.png


That's good news in that we need to take down that peak anyway and with it, we will be also reducing distortion as a bonus.

Unfortunately we are not helped with the high distortion in bass. Boosting that may be a compromise between enough sub-bass response and more distortion. More on this later in the equalization section.

Here is our log display of distortion showing what we already know:

Superlux HD668B Measurements Absolute distortion Semi-open Headphones.png


Group delay is not very informative:
Superlux HD668B Measurements Group Delay Semi-open Headphones.png


By now you should know not to try to fix any large dips in the high frequencies as they are results of two waves cancelling each other. Any EQ will change both resulting in the same cancellation. This shows up as large group delay as indicated by the spike I have marked.

Impedance vs frequency graph is a constant so no worry about the amplifier impedance being high (although you should avoid such amps anyway):
Superlux HD668B impedance measurement.png


Let me know if you like this kind of non-zoomed display better. I think it is obscuring some info of interest in the graph but can be confusing to see it highly zoomed at first glance.

Sensitivity is good (lower, better):
Most sensitive headphone review.png



Superlux HD668B Headphone Listening Test and Equalization
Quick listen showed somewhat exaggerated highs with grittiness added for good measure. At the same time, there was a bit of dullness which I know is an oxymoron in that context. Overall it was not a pleasant experience. So let's try to fix the issues:

Superlux HD668B Equalization Semi-open Headphones.png


Wow, what a transformation. If blindfolded you and put these on your ears, you would swear you were listening to very expensive headphones. The large drivers provide good bit of spatial information (separation of instruments), creating a soundstage that dangles from your ears down and to the back with the mono content behind your forehead. This added effect combined with now good tonality and much deeper bass provided a very enjoyable experience. Love the collaboration of Nick Cave and Nicholas Noorenbergh on this track for example:


Let me indicate though that the sound can get a bit boomy (likely due to harmonic distortion of sub-pass) and the highs persisted to be a bit bright at times especially on female vocals. A high frequency shelving filter would fix the latter but I wanted to stick to my philosophy of not piling on too many filters. As I indicated, what is there already provides excellent performance.

OK, I lied a bit. There was something bugging me still. When I played the track, Sever The Ego by Jewel:


I kept hearing her voice to the left of center. At first I ignored but then I realized same was happening in other tracks. I looked back at the frequency response and realized that one channel is lower level across the board. So I pulled up the Roon level controls and boosted the weak channel using pink noise:

Superlux HD668B Channel Balance Semi-open Headphones.png


This nicely anchored the mono aspects of the track in the center, removing the hanging nail effect of channels not being balanced.

Conclusions
We have yet another example of an out of box objective and subjective performance that is disappointing. You could try to forgive it given the cost but why? With equalization this headphone (as with most) can outperform speakers costing thousands of dollars in tonality! Fit and comfort is good enough and spatial effects very satisfying. Wonderful experience is being had for $40 and a bit of software and signal processing.

You can predict my summary then: no good as is but recommended with equalization. And a bargain.

Measurement data included, this time as .csv file. Let me know if you like it better.
 

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sweetchaos

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#2
For Equalizer APO users:
Preamp: -8.5 dB
Filter 1: ON LS Fc 30 Hz Gain 4.0 dB Q 1.0
Filter 2: ON LS Fc 50 Hz Gain 4.0 dB Q 1.0
Filter 3: ON PK Fc 4000 Hz Gain 5.0 dB Q 2.0
Filter 4: ON PK Fc 5380 Hz Gain -7.0 dB Q 6.0
Filter 5: ON PK Fc 8582 Hz Gain -7.0 dB Q 5.0
For more info, see List of Amir's Headphone PEQ filters.
 

abdo123

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#3
Quite an interesting review and headphones!

I don't typically use headphones (except for zoom meetings), and i have been waiting for an affordable piece to be reviewed.

Is this a headphone you would recommend in this case? or should i wait for more products and reviews?

Thank you!
 
OP
amirm

amirm

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Thread Starter #4
Is this a headphone you would recommend in this case? or should i wait for more products and reviews?
I would. I am actually continuing to listen to it as I type this!

Note that it is semi closed meaning it picks up some sounds from outside and transmits some. If these are not issues, then yes, it makes a very good starter headphone.
 

sweetchaos

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#6
I've been an AKG fanboy since the early 90s when I got AKG K240Ms (the original 600ohm version.) I upgraded to 240DF at some point and used those for 15 years or so until they broke.

I bought these Superlux-headphones because there was good reviews online. I was very disappointed with the sound. Harsh and gritty. Nice too see that the measurements confirm what I heard. I quickly gave these to my friend as I couldn't stand listening to them.

I currently have AKG K712s and I'm very happy with the sound.
 

wje

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#8
Quite an interesting review and headphones!

I don't typically use headphones (except for zoom meetings), and i have been waiting for an affordable piece to be reviewed.

Is this a headphone you would recommend in this case? or should i wait for more products and reviews?

Thank you!
Wouldn't you be looking for a pair of headphones with an included microphone for those Zoom meetings?
 

L5730

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#9
From what I've read around, this seems to be the conclusion. A good budget starter headphone in terms of sound after modding and/or EQing. However, I also read that the build, for even the low price that it is, is pretty bad. The argument being that yes it is cheap and not bad after EQ, but just won't last a couple of years.

Interesting review, none-the-less. Thank you.
 

Robbo99999

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#11
Not bad, it's not far off the Harman Curve to start and you can tell from the frequency response that it's gonna be quite nice to EQ to the Harman Curve without any big problems, not really any glaring unfixable dips and quite a smooth response overall. Distortion in bass wasn't a great quality, but if you don't listen loud probably not a big deal, just don't boost up the bass by too much when you EQ it. +5dB on the bass is often a safe figure for bass boosts based on what I've seen from Oratory and interpreting distortion measurements from other sources. Well, a great value headphone!

EDIT: Channel matching not good, but can fix that in Equaliser APO & doing listening tests......I'd turn the windows volume down as low as I could detect sound from each channel independently to see if it was equal (making note of the lowest detectable Windows Volume for each channel), if it wasn't I'd use the Left & Right Channel function in Equaliser APO to apply a negative preamp to the stronger channel until they were equal.
 
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amirm

amirm

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Thread Starter #12
It's a little confusing whether this is HD688B or HD668B. I'm seeing both mentioned. Please confirm.
Sorry about that. It is 668B. I will correct the graphs later. Changed the text now.
 

Maki

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#14
I think a linear scale instead of a log scale for impedance would work better.
 

Francis Vaughan

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#15
It seems that the use case for adding EQ to, minimally dedicated DAC/Amp units, but even DACs in general, is growing. Perhaps this is the must
have feature for the next generation of devices.
The implementation of EQ isn't hard, but adding a useful UI that makes it easy to use is another matter. Considering the woeful quality of UIs in audio gear, I won't hold my breath on anyone getting this right easily. Auto downloading of EQ settings would be the right answer.

It would be interesting to get a feel for what the requirements for a useful EQ would be. Half a dozen PEQ stages would be a start, but I don't have much of a feel for what would actually be useful.

My impression is that there is room in the XMOS U208 often used (unless someone insists of listening to DSD.) It may not be all that difficult to get the ball rolling here. Moving to a 200 series with even more cores would make things much more easy. It should not add much to the BOM.
 

TulseLuper

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#16
It seems that the use case for adding EQ to, minimally dedicated DAC/Amp units, but even DACs in general, is growing. Perhaps this is the must
have feature for the next generation of devices.
Necessity of EQ is the common thread in Amir's headphone reviews. More hardware options to do this would be welcome.
 

Maki

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#17
It seems that the use case for adding EQ to, minimally dedicated DAC/Amp units, but even DACs in general, is growing. Perhaps this is the must
have feature for the next generation of devices.
The implementation of EQ isn't hard, but adding a useful UI that makes it easy to use is another matter. Considering the woeful quality of UIs in audio gear, I won't hold my breath on anyone getting this right easily. Auto downloading of EQ settings would be the right answer.

It would be interesting to get a feel for what the requirements for a useful EQ would be. Half a dozen PEQ stages would be a start, but I don't have much of a feel for what would actually be useful.

My impression is that there is room in the XMOS U208 often used (unless someone insists of listening to DSD.) It may not be all that difficult to get the ball rolling here. Moving to a 200 series with even more cores would make things much more easy. It should not add much to the BOM.
My dream is to have impedance sensing on the output of the amplifier which automatically sets an EQ preset for the transducer you're listening to, which can be loaded in via USB from a computer or bluetooth with a phone app. The app could take care of auto downloading, or the unit could ship with the most popular models matched to their impedances and allow additional presets to be added by the user. I think that would cover most people, since usually people have a phone or at the very least a computer.
 

bobbooo

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#19
It seems that the use case for adding EQ to, minimally dedicated DAC/Amp units, but even DACs in general, is growing. Perhaps this is the must
have feature for the next generation of devices.
The implementation of EQ isn't hard, but adding a useful UI that makes it easy to use is another matter. Considering the woeful quality of UIs in audio gear, I won't hold my breath on anyone getting this right easily.
Qudelix have already.
 
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