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Headphones, Impressions

Modded Koss PortaPros

The Koss PortaPros has been lauded in Head-Fi as one of the best truly bang-for-buck headphones you could get. And I agree. Even though that my highest priced audio gear is my FXT90 at $108, and second goes to my T50RP (final impression write up pending) at $78, I still think that the PortaPro really delivered more than it should at it’s price of $35. You can read what I thought about them and what mods I already did with them before here. But I added some new changes since then.

First off, the use of the HD414 ear pads. While this is nothing new in the PortaPro’s history of modding, this is something I wanted to do. Once changed though, I’m not quite happy with the sound at all. The HD414 pads are still stock and without any mods yet. So I proceeded to quarter mod it. Still unsatisfactory, and more to the point, the bass volume lessens by a quite a lot. Now I’m not a basshead but the amount lost is just detrimental to some songs that need at least some semblance of bass.

But that’s not all though. What intrigues me by a lot since I read the PortaPro appreciation thread is that the quarter-modded pads are mounted in reverse, so that the thicker part is towards the ear and distanced the drivers quite some ways away from my ears.

This ended up with quite some width to the soundstage at the expense of more bass loss and recessed mids and vocals. Treble got quite aggressive and bright, but spiky. I thought “maybe I really do need to apply the other, more permanent mods done by earlier modders.” Seeing that I am too much of a cheapskate, and quite unskilled at drilling, I quickly abandoned that idea. Also note that I wish I could write some more sound impressions of what I did there, but it became too painful for me to give more listening time for them.

But inspiration comes from the unlikeliest places. Reading the MA900 discussion thread, I remembered that the MDR-F1, and the recent MA900 have this so called “acoustic bass lens”. I’ve looked around the Internet, but either my Googling skills are pathetic or there’s just not much talked about acoustic bass lens, but there are quite a few said about acoustic lens though. So basing on that picture and this concept, I fashioned a felt ring the size of the opening of the pads.

The bass lens concept used in the MDR-F1 explained simply.

Additional info came in from a Head-Fi called Nevod. S/He said :

 The idea is simple – layer of dampening material with an opening. Reduces high frequency content coming from driver’s edges while passing lows through and at the same time not interfering with the high frequency content coming from under the opening, thus not mudding the sound. May be used in various shapes…

I should also give credit to LarsHP and his picture of a bass lens.

With all of these info coming in post-mod, it validates my train of thoughts and what I am hearing. I guess I should show my (almost non-existent) readers how I did my lens.

I removed the adhesive from the 38mm-wide felt disc and cut a coin-sized hole. In other words, it’s just a felt disc furniture feet lining I got from Ikea. I don’t know what coin to use in other currency, but I used a 10 Ruble coin; that’s around 21mm in diameter.

After that, I just plopped in the ring into the middle of the ear pads and voila! It’s not too secure though; it kept moving around and that made me somewhat apprehensive that it might affect the sound in the long run. So in an effort to make it stay put I did this:

A holder template made out of cereal box cardboard. The inner diameter is the same as the outer diameter of the felt ring, while the outer diameter of the card is a further 5 mm. I also did this because the HD414 pads won’t keep itself centred; in doing this I’ve made a way to secure the felt ring and the pads forever centre.

The spokes are used to secure the felt ring using double-sided tape. I don’t know if this will affect the overall acoustic lens, but I kept it to a minimum as possible. Also I suspect that the outer lip of the card ring may also affect the acoustic. The spokes side are adhered to the driver baffle on the PortaPro and it will look like this:

I’m sure that it would be less hassle to use a bigger stiff felt to fashion a bass lens, but currently I’m quite busy, so I just use anything I can get a hold of at arms length. So what do they sound like?

In a sense, the bass did come back and the treble is reared back. So goal accomplished. Bass is quite forward, and IMO has an accentuated midbass. It’s not very punchy, but from a non-basshead, the quantity is more than enough. I don’t know about the quality though, as I’ve never focused too much on bass, but from what I listened to, it’s not a one-note bass. It is also IMO not flabby or loose, but not quite tight too. Drums are quite satisfying for me, but still wishing for a little bit more punch and impact. The bass does not bleed into mid-range.

Mids on this setup is enjoyable for me, but not great. More like more than good. Male vocals though sounds quite good, but female vocals is not as sweet as I’d like, but still quite enjoyable.

The highs though really took a hit. Whereas before I got quite annoyed and painful with the piercing highs, now it’s overshadowed by the other sections. Not too much that the highs are too laid back, but just enough to make cymbals sound papery. It’s there and I can hear it, but it takes a back seat now.

Soundstage is fairly wide left and right, but still quite shallow front and back. It’s not an in-the-head experience, but somewhere like in front of my face.

Guitar sounds amazing, but not ZOMGmazing. Works quite well with the handful of metal songs I have. But what stands out the most for me is how violins are presented. It sounds so full, warm and clear. Truly sublime of the few songs that I have that featured violins quite prominently.

For some reason though, I get quite fatigued quickly when using my PortaPro in this setup. In my understanding, usually the cause of ear fatigue in most is because of strident or aggressive treble. But in this setup, as I noted the treble isn’t all that aggressive, more like laid back. I might be dead wrong with what’s causing ear fatigue though.

But all in all, I am quite satisfied and proud with what I achieved. Of course this is not the end of the modification. I aim to use a larger single piece of stiff felt, and in light of more information, will want to try and raise the felt ring above the driver baffle itself and make a sort of  felt enclosure, much like the MDR-F1 and the MA900. They have the advantage of size and a true baffle that is enclosed above and around their massive drivers though, but I think if I use the “well” from what the HD414 pads provided, I could achieve teh same effect, hopefully. This also shows that I need to read the MDR-F1 documentation/picture as it explained what the Sony engineers did before I go asking around in the MA900 thread. Silly me.

A look at the MA900’s bass lens.


About fEast91

A foreign student who happens to like manga/anime and headphones.


8 thoughts on “Modded Koss PortaPros

  1. try the stock portapro or sportapro or ksc35 drivers, with the stock pads attached to the clips that the ksc75 uses.. After doing all the mods in the book, I found this setup the best to my ears.

    Posted by Chris Langley | June 23, 2012, 5:50 AM


  1. Pingback: Initial impressions: Fostex T50RP « Kuusou Rumba and Headphones - May 8, 2012

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