CHANGSTAR: Audiophile Headphone Reviews and Early 90s Style BBS
Lobby => Headphone Measurements => Topic started by: Solderdude on December 05, 2013, 01:37:06 PM
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Reveived a second hand K551 a few days ago for a very low price.
Didn't like it in stock condition very much, the highs are 'off', sometimes sibilant and although 'accurate' sounding was still a bit 'off' in the mids.
This is how it measured (stock):
(http://diyaudioheaven.files.wordpress.com/2013/12/l-r-k551-stock.png?w=659)
So I tinkered with it and now have it like this:
(http://diyaudioheaven.files.wordpress.com/2013/12/evo-felt-low-filter.png?w=1037)
No more sibilance / slight shrillness and lovely sounding....
Bass extension is excellent (when your head allows a good fit and by forcing the cups in the right position) and measures down to 5Hz !
Driver matching is not great but +/- 2dB is not extreme and cannot hear it either.
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What did you do to them?
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That was uber-awesome! Specially the treble tuning... What was used to restrain it?
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Wow, the modded ones look great! That's an AKG I could get behind.
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I used a piece of quite thick felt which I removed of modified a HD681-EVO.
Tried various felts and creatology felt types but that Superlux felt really did the trick.
The felt is 3mm thick and quite dense.
It even makes sense to buy a HD681-EVO for this and buy some Chinese pads to use on that one and you have 2 fine headphones. headbang
As the dip around 5kHz is actually a resonance, that dip is much smaller as well and the highs are now silky and behave quite well.. bye bye sibilance !
Trouble was... the bass became relatively lifted because of the highs were too tame and it became too dark for me.
From 200Hz to 3kHz there is a 5dB drop which needed to become smaller.
This was my 'first attempt' and will try to tweak it further.
That is done electronically with a very simple filter that consists of a resistor and capacitor in series.
When I am completely done with it I will make a pdf about it.
Wouldn't surprise me if the bad sounding K550's could benefit from the same mod as well.
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What about those nasty resonances that existed before? Still there at all, even with the improved FR?
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The resonance is much smaller now (dies out pretty quick) and is less 'sharply defined'' in the CSD.
Might upload the CSDs, they look quite clean and only showed some nasties around 5kHz and some up higher to begin with.
Didn't make a picture of the CSD's yet, but did have a look of course.
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hello,
looking forward to the pdf for a potential mod of my K550's. ;D
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Took me a few days but the article (in pdf format) is ready and can be downloaded here:
http://www.mediafire.com/view/pzbaqy8nuek1kkq/AKG%20K551%20modifications.pdf
It may very well be applicable to K550 as well (those that sound 'edgy' and a bit 'off' that is).
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:-0
That is a FANTASTIC paper...downloaded and need to study. Thank you for quite a contribution!!!
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In some ways, Solderdudes' approach is "revolutionary" because it's doing what speakers have been doing for a long time - having eq/compensation circuits built in. The only headphone which did this was the FA-011 (but with a rather interesting tuning.) Make you kind of wonder why others aren't doing this.
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Ultrasone does it, though to paradoxical ends based on herr Dr.'s ideas of how ears should work.
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In some ways, Solderdudes' approach is "revolutionary" because it's doing what speakers have been doing for a long time - having eq/compensation circuits built in. The only headphone which did this was the FA-011 (but with a rather interesting tuning.) Make you kind of wonder why others aren't doing this.
Yup. it just make so much sense.
Really good work, Solderdude. It's stuff like this that's putting a hell of a lot of pressure on manufacturers. They know we can see what they're doing and it's a bit embarrassing when we fix their shit. Fortunately, they've (the competent manufacturers) got good people and development gear, and I think things are beginning to turn around.
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This definitely takes modding to a whole new level. Do you think it's possible to add a subtle lowpass filter to the HE-400 to help lower the treble? Or even better, do you think it's possible to add something to remove the tizz? I don't have as much of a problem with the treble as much as the tizziness associated with it.
Anyway, great work, Solderdude. I'm constantly impressed by the work you put into evolving this hobby, even aside from headphone modding. Project Ember continues to blow my mind with every new piece of equipment I throw at it.
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This definitely takes modding to a whole new level. Do you think it's possible to add a subtle lowpass filter to the HE-400 to help lower the treble? Or even better, do you think it's possible to add something to remove the tizz? I don't have as much of a problem with the treble as much as the tizziness associated with it.
yes and yes. With HE-400's flat Z, it's easy.
There may be disadvantages though. Crazy SET guys, to varying extent, think crossovers / passive EQ circuits wreck the sound. Another option is digital PEQ
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No matter how much I tried, I couldn't ever get that tizz to go away, though I could lower its volume to make it less fatiguing. Meh, oh well. I'm an HE-4 fan boy now anyway.
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In some ways, Solderdudes' approach is "revolutionary" because it's doing what speakers have been doing for a long time - having eq/compensation circuits built in. The only headphone which did this was the FA-011 (but with a rather interesting tuning.) Make you kind of wonder why others aren't doing this.
Ever since my first internal headphone mod (JVC HARX700), I've always wondered why headphones often seem to be so under-engineered relative to even fairly inexpensive speakers. I started with car and home audio. Crossovers and proper damping were a normal, expected thing. My first set of bookshelf speakers were the Dayton BR-1 DIY kit, and that was a good opportunity to learn about damping, controlling resonance, a little bit about how crossovers worked, etc. (also did some research on an alternative crossover and how it made the BR-1 better, so I was aware crossovers could directly affect the FR and other aspects of sound). Then you open up a headphone...I think it's pretty sad, but hopefully Tyll is right when he says things seem to be turning around.
Anyway, nice job, Solderdude!
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In some ways, Solderdudes' approach is "revolutionary" because it's doing what speakers have been doing for a long time - having eq/compensation circuits built in. *** Make you kind of wonder why others aren't doing this.
Agreed, and props to Solderdude!
I always wondered if the size of passive filters wasn't the stumbling block, but I never measured (drivers) and modeled (filters).
Also passive filters are nice because one can take them from source to source without worrying about EQ. K550's actually sound respectable when filtered through the Audyssey Amp iPhone app's curve, but then plug 'em into the MacBook and they're a tizzy mess.
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I have to print and do this soon, thanks so much in advance to solderdude and a happy new year to you guys.
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Because not everyone is willing to buy and sacrifice a set HD681-EVO to salvage the felt discs, I have been looking for some alternatives.
I found 2 mm thick acrylic felt and 3 mm thick wool-felt which both perform very similar (measurement- and sound-wise) to the EVO felt.
(http://i837.photobucket.com/albums/zz296/solderdude/filteredevovs3mmwoolfelt_zpsd8c1ceff.png) (http://s837.photobucket.com/user/solderdude/media/filteredevovs3mmwoolfelt_zpsd8c1ceff.png.html)
blue = EVO felt
orange = 3mm thick wool-felt (not acrylic which measures only slightly different)
The FR above is of a modified K551 so NOT just the felt discs but also internal damping and electronic filter components.
I suspect this to work equally well for the K550 which is the same headphone but with a longer cord and no remote/mic.
For Pirates I am offering a set of 2 handmade (so not nicely round !) felt discs for this mod.
price (included shipping) will be a whopping € 2.- when paid with IBAN/BIC and when paid with PayPal € 2.40.
Will be shipping to all countries.
Alas the biggest portion of this price are the shipping costs and PayPal fees O_o
€ 1.- = around $ 1.35
When you use these felt discs you MUST also do the filter-mod otherwise you end up with a dark sounding headphone.
(http://i837.photobucket.com/albums/zz296/solderdude/feltdiscs_zps6161e6a1.jpg) (http://s837.photobucket.com/user/solderdude/media/feltdiscs_zps6161e6a1.jpg.html)
I will only have a limited amount of material to make them
At this moment I have some black felt 3mm wool-felt and 2mm thick acrylic felt in dark blue.
PM me if interested.
Another option is to look for 3mm thick wool-felt in craft shops.
The material itself usually isn't very expensive and given the results I expect different felt not be perform that different.
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Excellent work. Seems about the same issue is hitting every damping approach - once you dampen, you lose treble and especially air - which is then hard to recover without a very strong boost. Said boost will then cause distortion to worsen...
Could you run THD and IMD on your setup?
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In this case there is no boost at all, only attenuation.
The efficiency drops by about 5dB.
The highs are attenuated by the felt and the rest by the filter.
The filter only works when driven from a low impedance amplifier but most pirates fear one >10 Ohm (supposedly damping factor fear).
Yes the amplifier must work a little harder to reach the same levels and yes that may increase distortion of the amp somewhat.
I can still play it sufficiently loud from Sansa Fuze so high power isn't needed at all.
Will be working on another mic pre-amp in due time.
The one I have no has the needed compensations and this increases the noise floor in the lows (did not use the optimal op-amps for pre-amp) and this higher noise floor (-40dB in the lows) obscures the THD measurements.
A K550 (and TH-02) are on their way to me...
Can compare/filter the K550 as well, I suppose they are more similar than different.
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Has anyone compared the modded K551 with the HD800? TIA.
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Dogears wanted to see measurements of the K550 with SRH-940 pads fitted.
see below:
(http://i837.photobucket.com/albums/zz296/solderdude/srh940pads_zps1f665b45.png) (http://s837.photobucket.com/user/solderdude/media/srh940pads_zps1f665b45.png.html)
blue line = K551 modified (left channel only)
purple line = K551 with filter + 3mm felt + SRH940 pads.
It should be noted that the pads are too small but with a little bit of stretching they might well stay on there.
For the test I taped them down.
At a first glance the bass levels would be too low but things aren't as they seem because the K551 here has a filter that lowers the amount of bass.
Fortunately the filter action is the same as the 940 pads do so...
Below the 'stock' K551 where you can see the 'warm' slant in the lows.
When you 'subtract' the purple line you will end up with a fairly flat FR.
(http://diyaudioheaven.files.wordpress.com/2013/12/l-r-k551-stock.png?w=659)
When you use a stock K550, use 3mm wool felt in front of the driver and fit SRH940 pads (very tight fit ?) you may well end up with a very linear FR without having to use the electronic filter.
good find dogears !
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Thanks much for the effort Solderdude!