Audio quality
 
My experience is very different from the other review for this earbuds. The reviewer says that these headphones have no bass at all, and I notice a very good amount of bass, not too extended but with very good impact probably due to the bass port.
 
However, to feel some bass, it needs to be EQd (I am not against EQing, on the contrary, I think it's OK to EQ headphones except when testing them), and they need to be adjusted to achieve at least a minimal seal. Due to the earhook, once adjusted they stay in place. Otherwise, indeed there is almost no bass, just as it happens with almost any earbud. One thing that can be done to improve sealing is use them with a foam.
 
Presentation is more forward than Sennheiser signature (tested against MX80, MX400, MX680 and OMX 90 VC Style). All Sennheiser earbuds have a somewhat dark and veiled sound signature (as in the PX 80, previously known as PX 100), and they differ in detail in mids and high, and rolloff quality. These Philips earbuds have a more forward presentation. Bass is less extended but with a little more impact.
 
While I'd say that Sennheiser signature is more leaned towards bass and gentle highs, Philips SHS3200 have a more V shaped signature. Highs can be a little harsh if not EQd. I find them superior to MX80, little better than MX400 and MX680, and almost on par with OMX 90 VC Style.
 
Compared against my AKG K311, the AKG is better with some kinds of music, but for the music I tend to listen when riding my bike or commuting, the SHS3200 do very well (I tend to listen to metal and EQ towards a strong bass since I need to listen environment and usually at low volumes bass is the first thing lost). 
 
 
Design and construction quality
 
Nothing to say here. I use them mountain biking (dirt/street/all mountain) and they havent failed. Although the cable is thin and simple, cable and connectors have been pushed beyond design limits and survived.
 
However, there is one thing that could be better: the cable does not follow the hook, but hangs directly from the earbuds. If the cable would be routed through the earhooks, the earhooks would be a much stronger stress relief. It's not difficult to fix it by simply hanging the cable over the ear, but that cuts some length of the cable. Depending on where you wear your audio rig (in my case, iPod Mini), cable could be a little shorter if weared this way.
 
They can be used for hours and hardly notice them. Very, very light and unobstrusive on the ear. Due to the extremely low weight and the earhook, is very difficult that they come out of place once adjusted.
 
 
Overall value
 
Excellent, for the price they are awesome. They compare very well to more expensive earbuds, and the added value of being extremely comfortable and not suffering from the usual issues with earbuds -that is, holding its position on the ear- make them an excellent value.

Preliminary words
 
As english is not my mother tongue, please pardon me for grammatical mistakes (I shouldn't have so many spelling mistakes, but... who knows   ).
 
 
Introduction
 
I bought this as a result of a search to replace my JVC HAS160. This are in a different league, but I didn't want to use my Sennheiser HD 25-1-II as a portable headphone. Though I love how the Senn sounds, its technical approach should not be used on, for example, the subway.
 
I was looking for a deeper sound of what could be provided by the JVCs, in a closed back format. My 1st gen PX100 certainly go deeper in bass terms than the JVCs, but everything is lost because of the open back format. At first I thought of the AKG K81DJ, which I tested before, but it was too much money for a beater that I was looking for, and I prefer all black headphones (I certainly love the looks of the HD25-1-II). As a cheap alternative I was between Sony MDR ZX100, Marshall Majors and this RP-DJS400. 
 
Build quality
 
I would give it a 6/10, but consider it as a preliminary qualification because I still haven't tested these on my day to day usage. Considering I managed to brake the JVC HAS160 at the joint between the headband and the speaker housing, I don't think this are going to endure a lot. The plastic seems a little cheap, and the swiveling articulation is composed of too many parts to last with the plastics it has been made. A better polymer (like the one used on the HD25-1-II) would have been a better choice. 
 
Comfort
 
As previously noted, it is not as comfortable as... well as any of my headphones. It is not unpleasantly uncomfortable, but certainly after a couple of hours ears become somewhat uncomfortably pressed against your skull. Nevertheless, it certainly can be used for a couple of hours without seriously feeling uncomfortable. However, my opinion is that it depends a lot on ear size. Given the size of the pads, my guess is that for small ears (significantly small) it could almost be circumaural, on the small size of circumaurals. For average size ears, it would be a somewhat big supraaural, while I think for above-average ears will be a common supraaural. The size is bigger than the size of the HD 25-1-II, which for me is a perfect supraaural. Hence, the RP-DJS400 excers some strange pressure on certain points of my ears. This doesn't mean it is uncomfortable, it's just that my ears are not used to feel anything on those places.
 
Performance
 
As it has been noted, it certainly doesn't need an amp and is much easily driven by my phone (Nokia E5 and Samsung Galaxy Y Pro B5510) than my HD 25-1-II. I would say that it is even easily driven than JVC HAS160. Haven't tested with my iPod since I'm rockboxing it, but I guess the same applies. These are easily driven
 
Sound quality
 
Much above but what I expected, but certainly need EQ. Out of the box and with flat EQ (on the setup given above, which is far from good but for testing purpose I tried the HD25-1-II and the RP-DJS400 on this setup), bass sounds deep but somewhat muddy, mids are present but not good and treble is deeply recessed. For comparison, the HD 25-1-II sounds very detailed but lacking bass. 
 
My guess is that this headphones handle frequencies in a somewhat particular way. The EQ to achieve a good sound is +11dB on 60Hz, -3dB on 230Hz, +2dB on 900Hz, +6dB on 3KHz and +10dB on 12KHz. With this EQ the HD 25-1-II -and every other headphone I have- register a remarked bass, lose mid bass, and excessive treble. I'm not going to make a note on mids because I think mids presence is subject of personal tastes, but for the sake of this review with the EQ noted above voices are plenty.
 
The strong point of this headphones is bass. It is there, plenty of it, deep, controlled and with a good transition to mids. Certainly it is a goog headphone for bassheads, but I think it is more than acceptable for other kind of genders. I've listened to very different music (some MP3@256kbps and some audio CDs) and certainly amazes me how versatile are this headphones:
 

1. Jamiroquai: Live in Verona
2. Playing for Change album (directly from the original audio CD) 
3. Megadeth: Risk 
4. Marcelo D2: Acústico MTV     
5. Morcheeba: Fragments of Freedom
6. Audioslave: Revelations
7. Paul Tortelier: Bach Cello Suites
8. Prodigy: Greatest Hits (CD1)
9. Pendulum: Immersion
10. The Police: Outlando's d'Amour
11. Dave Grusin: Homage to Duke (specially Satin Doll, which is awesome)

 
Certainly RP-DJS400 do not excel with all those, but all in all is gentle enough to be good to listen to an ample range of genders. The bass, while clearly present, isn't bloated but precise -not at the level of, say, ATH-M50, but precise enough- and on the deepest notes of each song you can almost feel it on your ears. My believe is that this behavior with low frequencies is an important part of what make this headphones fun to listen to.
 
The transition from lows to mids is good, and since the treble is so recessed, the transition from mids to highs is gentle enough to not sound harsh (again, compared to HD 25-1-II, which sometimes it is too cold and harsh). EQed with this in mind the highs are all there, and detailed enough, but always kind of recessed. Without doubt I would characterize the RP-DJS400 is a warm headphone. EQed adequately is very gentle and easy to listen to.
 
Isolation
 
Isolation is good, but not excellent. It is better than JVC HAS160 because it is bigger and clamps stronger, but it is not as good as the HD 25-1-II. I would say nevertheless that it isolates a tad better than Senns HD 202 and similar. I used them at the subway and I didn't need to turn up the volume to ridiculous levels, in fact I used them lower than JVC HAS160, but as I said, RP-DJS400 are very easy to drive. 
 
Compared with
 
Compared with JVC HAS160 which they are meant to replace, sound signature is very different, but this is clearly given by the different format. While the JVC is a small supraaural headphone with 30mm drivers, the difference in size is clearly noted, with the RP-DJS400 having a much deeper bass signature and a more ample soundstage.
 
Compared with AKG K81DJ, to my ears the sound signature is kind of similar. The AKG K81DJ sounds very good out of the box, and doesn't need too much EQ to be easy to listen to. The Panasonic RP-DJS400 can also be very easy to listen to and can sound really fine, but needs to be EQed.
 
Compared with the Senns HD 25-1-II, they are on different leagues. While the HD 25-1-II is not an always easy headphone to listen to, the warm sound signature and very deep and clear bass of the Panasonic RP-DJS400 makes it for a fun and easy headphone to use, but nevertheless it is not able to perform any kind of monitoring task or such.
 
I know that equalizing for testing purposes is almost senseless, but I mentioned it and tested them as this because we're not talking about an audiophile's headphone but about a consumer headphone which can sound very good. Hence, EQ comes in play since it can be used to more or less adequate the way a given headphone sounds to listener's taste.
 
Conclusion
 
Comfort aside, I would give the Panasonic RP-DJS400 an 8,5/10 because as previously said, it is a very easy to listen to headphone. It's price/product ratio is very good, considering it costs 10% of what the HD25-1-II costs here in Argentina, but they are different headphones. 
 
The main issue with these headphones is comfort. I find myself moving them a little every 30 minutes or so because of those strange points where it presses my ears. After a couple of hours, I need to take them off for a minute or so. The second issue is build quality, and it really seems cheaply made, or at least, not at the level as the sound quality it has. Let's see what time says.
 
Anyway, given the very gentle and fine sound signature with almost any kind of music thrown at it, these headphones are a very good choice, specially for those who prefer warm sound signature, and deep and precise bass (certainly not a la Aiaiai TMA-1, which for me has a powerful bass but completeley uncontrolled, although for some it has a good bass). 
 
Please feel free to leave any comment, I hope this review helps.