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Will
8326
Chief Product Officer
Jan 9, 2015
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Hi Everyone,
It’s been an exciting few weeks watching the community react to the K7XX. All the reviews, videos, and discussion posts are more than we could have asked for. You’ve got everyone involved with this project (and several other players in the audio industry) looking at the Massdrop community as more than consumers. They’re starting to understand you’re industrial designers, electrical engineers, people who purchase based on quality first and hype second.
It’ll take some time, but this the type of change we wanted to make by starting Massdrop and I can’t tell you how much we appreciate your support.
In that same vein, we put as much weight on your feedback as we do your support. Over the last few days we’ve been testing K7XXs, looking to replicate and determine the cause of the rattling sound some users have reported. Looking at all the posts it was clear that some members received defective units (pictures of wires where they shouldn’t be, etc), but it’s important to remember, any headphone driver will emit a rattling sound if you drive it hard enough at low frequencies (like the ~20hz figures being referenced in several posts). As we saw people posting rattle related experiences like this one: https://www.massdrop.com/buy/akg-k7xx-massdrop-first-edition-headphones/talk#!124009
It became clear some folks were in danger of overdriving and possibly damaging their headphones in an effort to test for a rattle. One member was running the K7XX (impedance of 62ohms with a maximum input power of 200mW) out of his motherboard equipped with a TI TPA6120A2 headphone amp circuit capable of output up to 1.5W, with the volume set to 80% playing frequencies from 10hz (human hearing doesn’t pick up until 20hz, 10hz is feeling air movement) up to 50hz. Pushing that much power through the K7XX driver at those frequencies will cause the driver to fold on itself and produce some kind of rattling/flapping sound (this is the driver membrane being collapsed and expanded rapidly, doing this damages the driver). If you were to play a song at that setting while wearing the headphones, the volume would be well over 85db and in the realm of volume induced hearing loss. After seeing a few posts like this, I decided to run a quick test today.
Using five different units we had in the office (mixed serials representing different parts of the batch) this is the process I followed. A quick caveat before we continue, I’m not an Audio engineer, I’m just an audiophile, feel free to post suggestions on how I can make these tests more exhaustive.
1. Open a new Audacity project and generate a sine wave at 20hz with an amplitude of 1. Set the time to 1 second, set the tone to repeat, hit play. Now you’ve got a perpetual pure 20hz sine wave. Pause the sine wave. 2. Power on Grace Design m920 (http://www.gracedesign.com/products/m920/m920.htm) and set the headphone offset to 0 3. Set the m920 volume to 0.0 and plug in the K7XX 4. Setup a new repeating one second sine wave at 440hz with an amplitude of 1. Let this sine wave run. 5. Turn up the volume until the volume reaches 85 decibels (the CDC’s threshold for sustained volume induced hearing loss, measured with a Tascam DR-44WL). 6. Turn off 440hz tone, turn on 20hz tone at the same volume and note any audible rattle. 7. Repeat step six, increasing the 20hz tone by 1hz until 50hz is reached.
Doing this, I experienced no rattle or flapping sound on any of the sets tested. It’s easy to play a test tone below 50hz on headphones and crank the volume because we don’t so much hear those frequencies as much as we feel them. There’s nothing obvious to stop you from listening at damaging levels when you’re in the 20hz to 50hz range but play a higher frequency (like 440hz) at the same volume level and you’ll quickly find the test your running is well beyond any volume you’d want to experience.
Hopefully that clears things up for all the folks running tone tests without an audible rattle at normal listening levels.
Now, for the people experiencing issues at normal listening volumes, there’s something wrong with your headphones and we’ve got an update from AKG on the repair process:
Domestic orders:
1. We have been assigned a specific AKG representative, Hector Hernandez, from the AKG USA California office who will handle all issues related to K7xx headphones. Contact him by emailing your request to service.us@akg.com with a full description of the problem. NOTE: Currently only issues relating to physical defects (XLR port, physical driver damage, etc.) are being handled. AKG is still reviewing the data (and sample units) on the sub-50hz “flapping” - we’ll have an update on that process in the next 2 weeks. For now if you email about that the request will likely be ignored/filed for future reference. 2. Hector will review the service request and will follow AKG service procedures to evaluate and correct any manufacturing defects. Units that are deemed defective will be repaired, not replaced.
International Orders:
1. AKG is not providing international service (we weren’t supposed to sell internationally in the first place). If you are an international customer, you will need to contact support@massdrop.com and arrange to have your unit shipped to our offices in San Francisco. We’ll then coordinate the RMA procedure with AKG USA, and when the unit is repaired and returned to us, we’ll ship it back to you at your international destination. NOTE: Currently only issues relating to physical defects (XLR port, physical driver damage, etc.) are being handled. AKG is still reviewing the data (and sample units) on the sub-50hz “flapping” - we’ll have an update on that process in the next 2 weeks. For now if you email about that the request will likely be ignored/filed for future reference. 2. Hector will review the service request that Massdrop submits on your behalf and will follow AKG service procedures to evaluate and correct any manufacturing defects. Units that are deemed defective will be repaired, not replaced.
For all repairs that involve swapping out drivers, AKG has guaranteed your drivers will be swapped with matched drivers. Turnaround time for repairs from AKG is 7-10 business days. AKG is shipping in K7XX replacement parts now and repairs will be able to start as soon as the necessary parts arrive. We’ll have a concrete ETA on the parts arrival early next week but we’ve been told their arrival time will have minimal, if any effect on turnaround time for the initial repair requests.
At this point, whatever your circumstances, you should know the correct next steps. If you’re still not sure, respond to this post and I’ll do my best to help you as quickly as possible.
Thanks for supporting this drop,
- Will
Jan 9, 2015
tommydadog
177
Jan 10, 2015
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Hey Will, thanks for the update.
Who pays for the return shipping cost?
Jan 10, 2015
nicdub
55
Jan 10, 2015
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Thanks for the update, Will. Just did your test, and it definitely confirmed a defective driver on the right side, with lots of flapping/rattling at normal volumes. Defective driver for sure. Happy to know you guys are taking care of it. Thanks again for the drop!
Jan 10, 2015
Will
8326
Chief Product Officer
Jan 10, 2015
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Hey Tommydadog,
AKG cover shipping cost to and from he customers having their headphones repaired for domestic customers. If you're an international customer then Massdrop covers shipping both ways.
Customers aren't paying any shipping costs in either situation.
Jan 10, 2015
tommydadog
177
Jan 10, 2015
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Thats good to hear.
Some of the people were able to fix the rattling issue by poking the diaphragm with a qtip. Guess there's that option for those who don't want the hassle of shipping it and waiting for it.
Jan 10, 2015
zondaf
8
Jan 10, 2015
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AKG might be greatly over exaggerating their maximum input power with the 200mW figure. I tested my pair with the uDAC-2 (max power of 80mW at 16ohm) because I wanted to make sure I stayed well under the 200mW limit. The right diaphragm starts to break up and creates the flapping noise just past 1 o'clock and the left side starts at 2 o'clock. The power at that setting into a 60ohm load is well under 40mW. The flapping noise occurs up to 50Hz. How can AKG claim a rating of a max handling power of 200mW when the diaphragm starts to breakup and causing the flapping noise at under 40mW?
Someone else made a video of the diaphragm breakup and flapping noise:
Jan 10, 2015
shadowarrior
27
Jan 10, 2015
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Hi Will,
Thanks for your update.
The Texas chipset TI TPA6120A2 and the onboard Wolfson WM8741 DAC is equipped on the MSI Z97 Gaming 9 AC, not the Z97 Gaming 7 which I have. The Gaming 7 looks like it only has a pair of TI OPA1652, one for the front audio out port and the other for the rear. I have still submitted a support ticket with MSI to confirm the specifications.
Every other headphone/speakers I have used, the Windows volume has stayed constant at 100%. Reducing the volume to say 60% on my motherboard makes the headphone volume really low. If the headphone outs were amped, then 60% Windows volume should not give me really low volumes that it needs another amp. If they are not amped, then 100% in windows should not be pushing the headphones to rattle. So bit confused there.
You are correct about the normal use though. The only song so far which has shown signs of rattle on the right is Hans Zimmer's Why So Serious around the 3:15 mark or so when the sub-bass sweeps kick in.
I will wait on MSI's reply and till then check on some other sources to find out about the safe amped volume to use.
Also could you comment on the pictures I posted about the wires near my right side drivers?
Cheers.
Jan 10, 2015
TianZi
37
Jan 10, 2015
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Thanks for the update.
Not sure what AKG is reviewing that takes 2 more weeks for another update, but it seems like they'd be able to find issues faster by getting people to send in the defective ones.
After testing a bunch of headphones including: 2x Q701 (1 China, one Austria), K701, k240s, HD600, HD650, HD800, M50s, Phillips X1s, and 2 pairs of K7XX, both of the K7XX were the only headphones that had obvious issues with one side (both left) rattling when running audio check test. Even disregarding other headphones, the K7XX should at least be able to play any frequency at the same volume level as Q701 and K701 headphones.
Jan 10, 2015
shadowarrior
27
Jan 10, 2015
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That is exactly my point. If my volume output is too high, why doesn't my ~$50 headset Plantronics Gamecom 377 with specs: Dyn Range 20-20,000Hz, Impedance 32 Ohm ( https://www.inet.se/files/pdf/6303317_0.pdf ) have any rattle at exact same volume level using the same test file for Headphone Bass Shaker connected to the same port? And I have been using this headset since 2010 and retired it with the K7XX for PC use.
Jan 10, 2015
FractalPie
74
Jan 10, 2015
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Yeah, that update wasn't very helpful for those with the rattle. I mean seriously my cheap headphones don't even rattle which doesn't make any sense. The way they talked about switching the drivers for ones that have been matched gave me the impression that maybe they didn't do a great job matching the rattling headphones in the first place. I honestly feel bad for Massdrop as none of this is really their fault yet they are dealing with most of it.
Jan 10, 2015
shadowarrior
27
Jan 10, 2015
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Agreed, they are trying to manage it the best they can, and they did mention this was if not the, but one of the biggest drops.
AKG's decision to not support International Orders half way through the drop was one big blunder. But what worries me most is this line: "1. AKG is not providing international service (we weren’t supposed to sell internationally in the first place)." So MassDrop has to honour the 2 year warranty for international buyers by being the middle man between the customer and AKG. But if worst case scenario, Massdrop does not exist through the warranty term, yet AKG does, then the international buyer's 2 year warranty is null and void.
But at least to start with Massdrop has to issue a statement which clearly in writing mentions that the international buyers warranty will be honoured through MassDrop for the complete warranty period.
Jan 10, 2015
zondaf
8
Jan 10, 2015
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I just took some measurements of the uDAC-2 with a 60ohm load with volume dial at 1 o'clock and 2 o'clock. The voltages are 1.1V and 1.2V respectively. That comes out to 20mW and 24mW, which is far lower than the 200mW max stated in the AKG specs. I also remember my sound meter showing a severe drop off after 50Hz. I took wrote down the measurements and got 30Hz=40dB, 40Hz=45dB, 50Hz=55dB, 100Hz=75dB.
Jan 10, 2015
Tiktak1
6
Jan 10, 2015
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I don't like the handling of the international orders, shipping back and forth will take about 2 months for european customers. The international customers weren't aware of trouble like this when they joined the drop. My Beyerdynamic and Sennheiser headphones don't rattle when I drive them loud.
Jan 10, 2015
BeHik
28
Jan 10, 2015
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Yep, that is my video :) Left driver on the K7XX in the video starts to rattle at about 3 o'clock on JDS o2 amp with default gain, which is way below 85db and 200mw limit. In the same condition Q701 do not have even a slightest hint of a rattle. Q701 do not rattle even at 3.5 gain at 3 o clock, which is much higher volume level. Also, there is no rattle from the right driver and it works fine on even much louder levels (starts to rattle on 3.5 gain at 2 o'clock). My source is Asus Xonar D1 with the 2 Vrms maximum output voltage the power into a 100 Ω headphone load is limited to 9-10 mW
Jan 10, 2015
zondaf
8
Jan 10, 2015
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I measured the uDAC-2 and it was only putting out 20mW and 24mW with a 60ohm load at 1 o'clock and 2 o'clock. The K7xx driver seems to only be able to handle 1/10 of the 200mW power listed in the AKG specs. I can't do any more testing with the K7xx since I already sent them to my sister. Did you also notice a steep fall off of the sub bass, below 40-50Hz? I can't hear anything below 35Hz at my normal listening level. I had to turn the volume up another 20-25dB to hear tones 20-30Hz, even then they were well below 50dB according to my sound meter.
Jan 10, 2015
Tacoboy
35
Jan 11, 2015
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BeHik, ever though of getting an external headphone amplifier, to use with the Xonar D1, the FiiO E11K amplifier is only $60 or a Schiit Magni, $99. Should help with the detail in the audio signal.
Jan 11, 2015
theupandcomingcorey
Jan 11, 2015
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Can we simply return defective headsets for a refund?
Jan 11, 2015
tommydadog
177
Jan 11, 2015
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You want to try fix it first? if so check the side that is rattling and see if you can see the wire like this one
search

(thanks @shadowarrior for the pic)
If so you can give it a gentle poke with a qtip at point A and hopefully that will fix the rattle.
Jan 11, 2015
BeHik
28
Jan 11, 2015
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Ah, i actually have one, and i mentioned about it power specs and rattle :) JDS Labs O2 amp.
Jan 11, 2015
theupandcomingcorey
Jan 12, 2015
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That seems to have fixed the issue for now.
Jan 12, 2015
tommydadog
177
Jan 12, 2015
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yay! another one fixed (for now) :D
Jan 12, 2015
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