It's been more than a year since I modified my Creative Aurvana Live! (CAL!), you can read the thread here.
 
This time I will use a similar approach to make the already quite neutral HM5 even flatter and better.
 
I am not the first person to modify the HM5 headphone; several people have done mods to their FA-003/HM5. In this thread, not only will I describe to you what particular mods I intend to use, I will also explain the rationale behind my approach as well as provide you with some objective results by way of measurements.
 
I measured my stock HM5 soon after I received it in the mail. The measurements were rough as I have stated there, because I measured both ears at the same time and the seal wasn't ideal. There was no "rig" to speak of.
 
For a long time (not really, only 5 months), I have been very satisfied with my stock HM5. That's why I have been reluctant to make any changes to it, but my audiophile side got the better of me. So, it's time to make some upgrades of my own. After I gave it some thoughts, I made up my mind in terms of what mods I would use on the HM5.
 
This a measuring rig made out of a shipping box. It's simple.
 

 
The mic used is a Panasonic WM-61A. It's a electret/condenser capsule that's used in many entry-level measurment mics. It's flat enough for my purpose even without proper filtering and amplification (or calibration).
 
DAC/amp is FiiO E10. NwAvGuy has measured it thoroughly, and it's truly high fidelity. Frequency response is within [size=x-small]+/- 0.1 dB. Go to his blog if you want more details.[/size]
 
My laptop's mic-in has hum issues. ADC (Analog to Digital Converter) is Music Fairy USB card, cheap and low quality. Here's the FR and impulse response of the ADC. All the measurements are adjusted for ADC's FR variation (esp. the bass roll-off), unless specified otherwise. The impulse response, on the other hand, might not be too meaningful...
 

 
Here's the FR graph for stock HM5.
 

 
Explanation of how to use Dynamat
 


 
I originally wanted to put a big chunk of Dynamat on the cups, but it could be too heavy for HM5s. The felt on the earcup already acts like DynaXorb, so I don't believe replacing it with other sound absorbing materials will make a difference.  Not to mention, the felt is kind of glued onto the cups. Unlike the mods I did for CAL!, I only put Dynamat behind the drivers as shown below. The weight increase is noticeable. I imagine the wooden cups would still be quite a bit heavier.
 

 
Based on information about DIY speakers or speaker modding, people would put materials inside wooden enclosure to get rid of reflection/resonance, etc. Perhaps, wooden cups (without sound absorption such as using felt) aren't a good idea for headphones after all. Another thing people in the DIY community do is stuff polyfill (e.g. from pillows) in their speakers or headphones. For speakers, the polyfill is supposed to confuse the drivers into thinking that the enclosure/box is bigger than it actually is. Although cup size is not usually discussed among headphone enthusiasts, I suspect something similar is in action here. Enclosure size is far more important in speakers than headphones, but because of limited room area people usually stuff their speakers rather than make their speakers infinitely larger.
 
The trick is not to stuff too much and tease out the polyfill to make it nice and loose. The photo is not doing a great job to show you the little amount I have used. In reality, it's not that much. It must be the lighting and the white filter behind the phlyfill, which gives the illusion of a lot.
 

 
The next thing I wanted to modify is the vents of the HM5s. There are two vents on each cup. They are very small and hard to locate at first; they are located at the rears of the cups - the place where the headband is holding the earcups. I believe those are the headphone equivalent of speaker bass reflex ports, which are installed in speakers to enhance bass response and allow more air to move. Some have had success with covering partially the vents of HM5. From the measurements I made back in January, I also stated that covering the vents completely would eliminate the 300Hz dip. Due to the lack of a rig, the previous measurement was't too reliable in showing changes in the lower frequency.  The following graph illustrates much better than before effects of the vents on the FR of HM5. (this is the only graph without compensating for ADC variations, ADC is responsible for most of the bass roll-off)
 

 
The red line is stock whereas the blue line is when both vents are fully covered (with sticky tape). The green line is what happens when you only cover half of each vent. Based on this experiment, I decided to cover only the front vent for each earcup, which turned out to achieve pretty much the same results as covering half (green line). The next photo shows you how the front vent is covered with a little Dyanamat. But you can use anything you have available for that.
 

 
Here is the measurements of the fully-modded HM5 and stock HM5, side by side.
 

 
The most obvious difference is that the upper bass/lower midrange is now more linear as a result of the vent mod. However, it's not immediately obvious what the two other modifications have done to SQ. I'd probably need a cumulative spectral decay plot, square wave and distortion graphs to see more clearly and quantitatively the improvements brought about by the Dyanamat mod and polyfill mod. I feel the modded HM5 sounds fantastic and better than stock, but YMMV. I think bass is tighter and slightly deeper; the soundstage is as big as before if not bigger, yet more realistic; the flatter response lets more details and treble to come out, etc.
 
Update: Replaced blurry photos with new ones in this post. There's been some minor adjustments to the mods I did. Here's the post that describes those mod changes, and it also includes the frequency response measurements of HD 25-1 II and Beats Solo for comparison. Below is HM5's final version mod results vs first version mod results.
 

subbed

Woah! Fantastic post kingpage. FR graph definitely looks like a huge improvement.

It now isolates better too since there's less noise that can get in through the vents.
 
One of my housemates has a HD-25 Adidas Original (HD 25-1 II), and another has Beats Solo (I think) who is a basshead. I'll ask them to lend them to me to see how they measure up against the modified HM5. Not really a fair fight, IMO.

I added black electrical tape to cover one vent on each cup.  I need more time to evaluate it though.

Update: Replaced blurry photos in the first post with new ones. Included side by side comparisons. The photos now reflect the newest mods instead.
 

 
I have managed to open up the HM5 one last time, for measuring it without the back cover (i.e. fully open back). The above FR is like a "exaggerated" FA-002.
 

 
The FR of HD-25 Adidas Original (HD 25-1 II) is flatter than I expected. It measures very well for a portable, even better than the many HD-25 graphs from innerfidelity. HD 25-1 II is flat from 60Hz to 2.5kHz, but bass is down by 10dB at 20Hz. There's a sharp increase in treble at around 12750Hz, rather than a 8-10kHz peak in innerfidelity's charts. Like my HM5, the left and right channels are matched in sound level, and they hardly deviate from each other
 

 
Beats Solo's is quite bassy as expected. Although the graph shows that the green line and the red line are similar in sound level, the truth is another story. The drivers are not well matched in levels, which meant I had to turn down the volume on one side so that it didn't clip. The drivers also deviate from each other quite a lot. All these are consistent with head-fiers' common belief that Beats headphones aren't made for audiophiles. The results are extremely similar to innerfidelity's first sample. Beats Solo's FR will be used as a low anchor for comparison.
 

 
During this last time of opening up HM5, I moved the tiny Dynamat pieces from behind the drivers to around the drivers. I figured the black foam is already absorbing waves/vibrations from the back, and the sides are closer to the actual drivers. In addition, I also evened out the amount of polyfill in each earcup. I also redid the part where I covered vents. The new photos in the original post were taken after I made these new changes. The above chart is the results of measuring the modified HM5 again. The new FR is ever so slightly flatter than the first after-mod measurement, especially the sub-bass hump. The new FR is essentially flat from 20Hz to 2.5kHz, and the impulse response is a lot nicer than HD 25-1 II's. I wish you guys could hear my modded HM5. It sounds so natural and immersive!
 

 
I have combined the left and right FR for each headphone. While HD 25-1 II's FR looks close to HM5's, the HD 25-1 II's soundstage is much smaller and it's more intimate and darker than the HM5. HM5's treble is a lot smoother than HD 25-1 II, both subjectively and objectively. There's hardly any sub-bass roll-off with the HM5, as the chart indicates. Of course, in terms of portability, HM5 is the worst out of the three. But then, who really cares about portability in this sub-forum?

Quote:

manveru said:

Woah! Fantastic post kingpage. FR graph definitely looks like a huge improvement.

Click to expand...

 
The latest mod version is even better.

Hi.

Long time lurker, first time poster here. This is a great accomplishment! Would you please describe how you open the back cup covers for newbies like me?

I covered the 2 front vents with tape and didn't like the sound after ~ 15 minutes. It sounded more closed in and songs with deep bass were missing the rumbling/rattling in comparison . It didn't feel right, so I reverted to stock.

You can turn the earpads to the left by 90 degrees, and they will easily come off. You'll then see four small holes in the four corners, where you'll find the screws.
 
For me, this is more than just covering the vents. All the mods I have done are full reversible, but they do take a bit of an effort. I have no idea what it would sound like with just one of the vents covered because I never bothered to try something half-done. The final result is more open, better detail, higher quality bass more or less coming in same quantity. It's a good enough upgrade that will satisfy me for a long time. But like I said, your mileage may vary. It just sounds a lot more natural.
 
If you want more bass, this is definitely not a mod you'd want to attempt. The modding will make the headphone more revealing, so I tried to use the best recordings and uncompressed (e.g. flac) songs to do the assessment. I also understand not everyone has Dynamat or other sound dampening materials around, but I'd recommend the polyfill and the vent mods instead, or at least the polyfill mod if you don't want flatter response.

Nice work, kingpage! Your findings have confirmed some thoughts I've had on my previous mod experiments. Taping up one of the vents and filling the cups with certain materials can alleviate the problems below 2KHz, namely the 300Hz dip and occasionally slightly bloated bass.
 
However, I find this makes the problems in the upper mids and treble more noticeable or exaggerated. Your measurements show some treble peaks as well, which may or may not be the same trouble spots for my ears. I would best describe it as occasionally "hot" sounding and a bit rough on my ears.
 
Either way, I've found a potential solution. Back when I was modding my D2000, I had problems with treble. So, I cut up the ear pads from my KSC75 into discs and placed them directly in front of the drivers. I also used a second, thin layer from a super cheap pair of headphones from Parts-Express. I simply took those out of my modded D2000 and placed them in front of the HM5 driver. I was able to attach the ear pads over them without issue. Here is the original thread where I got the idea (for D2000).
 
This is all on top of the previous work I'd done to my HM5 months ago. All in all, my mods are as follows:
 
1. Removed stock felt dampening from back of cups
2. Applied layer of Dynamat and Silverstone acoustic foam in back of cups
3. Applied Dynamat + Silverstone acoustic foam around driver and surrounding cup area
4. Lightly stuffed the cups, back side and around driver, with Acousta-Stuf (from Parts-Express)
5. Taped up one vent on each cup
6. Placed two layers of foam discs in front of the drivers (bottom layer from KSC75 ear pads, second layer from cheap Parts-Express headphones)
 
Placing the ear pad foam in front of the drivers really sealed the deal for me and helped smooth out most of the issues with these. Initial impressions are very positive. The HM5 no longer sounds weird to my ears. They're actually very enjoyable! I still think they could deal with smoother mids and treble, and some of the lower bass has been lost. 

Just ripped up an old pillow : )

I do not find HM5's treble to be problematic at all. It's tame to begin with and it is still smooth after the mods. The high frequencies change a bit depending on how the headphone is placed on the mic, so I wouldn't rely on the graphs for that. The peaks aren't much louder than the lower frequencies, while the the nulls/dips are the results of headphone-mic interactions.

Quote:

kingpage said:

I do not find HM5's treble to be problematic at all. It's tame to begin with and it is still smooth after the mods. The high frequencies change a bit depending on how the headphone is placed on the mic, so I wouldn't rely on the graphs for that. The peaks aren't much louder than the lower frequencies, while the the nulls/dips are the results of headphone-mic interactions.

Click to expand...

 
Could be a slight variance between our HM5s. Also, I do seem to be more sensitive to treble problems than some, so what I perceive as a rough spot to my ears may be no problem for others. Just doing what sounds good to me. 

Hey KingPage, you think you could test my idea here the same way you did your mod and post the results?  Important to note though, the mod idea only has merit where (or rather, I should say to who) it applies, then furthermore to the degree which it applies, AND if done properly (which isn't really hard I think XD).  With your method of testing, I guess you would have to do the idea of it backwards by pressing & holding the top part down and keeping the bottom part out somehow, although I don't think this would be taking everything into account like the actual human ear...  Still, it would be interesting to see.  You'll get what I mean if you check out even just the parts in bold from the last (5th) bullet point in my post.  This would really be appreciated and I mention it because I thought you might be interested
 
And by the way, this is great!  Thank you!  It's fairly simple too and I'm definitely going to try it!
 
 
EDIT: Reading even through some of the things here, my full post addresses these differences that many people seem to feel they have with their headphones.  I think when it comes to things like the Brainwavz HM5's in particular, it is very important to note.  TBH, I'm very curious about your input!

 
300Hz squarewave response of the ADC. It's not very good, but believe me the 30Hz one is much worse which is why it won't be included.
 

 
It looks fairly good, given the poor performance of the ADC.
 

 
Now, to see the effects of a tighter fit due to a bigger head (closer to an adult's head). Actually, previously I used the side of the box where the width was more akin to that of a child's head. As you can see below, tighter fit brings the dip up from 250Hz to 300Hz, which is basically what Innerfidelity's graph has indicated.
 

 
Next, it's to do what Typhoon859 suggested; lifting the bottom up just like how the area of the head above the ear touches the headphone more than the area below the ear.
 

 
The midrange is uniformly recessed and there's a bit less treble round 8Hz.
 

 
And finally, the bass boost of E10. Most of the boost occurs before 200Hz, while there's no more boost after 1kHz.  I rarely use it, since I do prefer a cleaner sound instead of a warmer sound.