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Superlux HD668B Review (headphone)

L5730

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I noticed the effect of the packaging on the HD681b, and a much lesser extent on the HD688b. Due to just being a sheet of cardboard with a shaped hole in it to fit the headphones in, any pressure during shipping/storage means that the dust cover foam gets a ridge in it too.
I did consider the bass cloud on the HD668b causing the treble to feel less than the HD681, however, I did EQ that down and still feel the HD681 delivers a brighter treble.

That said, with both having the 2 ply tissue, I did listen exclusively to the HD681 last night and found it seemed to be getting less extreme, or I was getting more used to it.

I wonder, when they are EQed, is it worth to get HD681 over HD668b?
This was something I wondered before. However, I do not have a measurement rig to remotely accurately measure the differences.

As @solderdude says, comfort, build/design and price might be factors. To be honest though build and cost are so similar that I'd say they are moot and that one should mentally prepare to replace the cables/re-solder connections at some point anyway. The HD681 has much less clamping force and a more comfortable headband comparatively and I'd assume it suits more people. I don't find the HD668b all that uncomfortable, but I think I am in a minority.
 

L5730

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According to the measurements, the HD668b has a wider dip ~4k than the HD681, so I cut a narrow -6 dB @ 4700 Hz from the HD681 it softens the upper mid enough to make them tolerable. I can even scoop out 2 dB ~5 Hz somewhat doing a very dirty simulation of what adding foam would do to the FR. This is all with 2-ply tissue paper installed. I maybe just extra sensitive to that frequency.

I do think the treble is for want of better words, more nimble sounding on the 681. Should I succeed in getting these two really close, I think the mid-high area quality is better on the 681. For me, it takes less work to make the 668b useable - tissue paper and done. No complaints, just observations.
 

L5730

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Forgive me for continuing a Hd668b vs. HD681 discussion. I'd be happy to split it to another thread should that be preferred.

I did a recording comparison test for my own sanity.
Playing pink noise (from AudioCheck.net) from Foobar2000, ASIO driver, Tempotec Sonata HDPro.
Same volume, same everything, just switch headphones.
Using Behringer XM8500 dynamic mic and RME BabyfacePro FS (+65dB max pre-amp gain!).
Single microphone placed equidistant between ear cups just touching bottom inside edge of earpad. Laid upon a soft duvet.

So, the test is not comparable to others. I've done zero offsetting for mic characteristics (nor proximity effect). Also no seal effect, so the bass characteristics are way off as are any resonances and standing waves.
However, it should give a reasonable idea of a comparison between the two and allow spotting of areas to tweak to make one sound more/less like the other.

There is a difference in levels between the two (32ohm vs 56ohm drivers), although mic position could account for some error here, so have applied 2 dB gain correction in post to best match plots.
1678132311411.png

Green is HD681 (+2 ply tissue paper over drivers)
Blue HD668B (+2 ply tissue paper over drivers)

Some similarities to Solderdude's measurement make me feel good - eg ~3dB @ 150 Hz, and HD681 showing greater extension overall.
I am wondering what I am hearing in terms of brightness and shoutyness, as that graph is telling me that the 668b (blue) is the brighter of the two (+bass cloud)!
If I EQ out the lower frequency boost that the HD668b has, the HD681 still sounds brighter/sharper.

Perhaps there is some of that tonal tilt still in play with perception as well as being coupled with a volume difference in some areas making for a change in actual playback level, and thus increased problematic ~4 kHz distortion.

Using Foobar2000's Graphic Equalizer, +2 dB @ 4kHz and -6 dB @ 5kHz sounds pretty smooth and takes the edge off for me, whilst also adding some vocal clarity.
 

L5730

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For those who favour EqAPO, this is what that looks like:

1678230157780.png

Code:
Filter: ON LSC 12 dB Fc 10 Hz Gain 3 dB
Filter: ON PK Fc 4000 Hz Gain 4 dB Q 5
Filter: ON PK Fc 5000 Hz Gain -7 dB Q 4
Filter: ON PK Fc 6300 Hz Gain 1 dB Q 3.5

Makes these cheap headphones very listenable too.

A quick google search for "HD681 filter" comes up with someone's 4800 Hz circuit diagram. So maybe it's not just me?
 
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