I wan't really looking to buy the Yamaha Pro 500s. But I saw them on an Amazon lightning deal for $150 and decided what the heck.

Overall, this headphone competes well in the $200 to $250 price range, and would be good for those looking for bassy signature. Here are some random thoughts about them.

Comfort, Fit, & Isolation

I can understand the complaints by some people that these headphones are too heavy and uncomfortable. In fact, I really wonder whether Yamaha designed these headphones and did extensive testing, or whether they contracted out and this is what they got because they seem like they were designed for the big and tall crowd. As if some big headphone designer male made them to fit his head without considering others. I wear a 2XL hat size, and with these headphones, I've only needed to add a click or two of extension on each side. Given the weight of the cups and drivers, I would imagine that they would be uncomfortable for any extended use for anyone with average head size or less who wouldn't be able to position the headband to distribute the weight onto the head.

As for the pads, after about five days of use, they are starting to soften up (not high comfort, but OK), which has reduced the feel of the clamping pressure just a bit. However, as other reviewers have noted, the smaller round size of these circular pads make them rest partially on on my ears. Nothing I can't live with, but just not optimal.

So on the one hand, the cup/pad size seems designed for a small to medium head/ears, while the overall size of the headphone band with weight distribution otherwise seems designed for XL or larger hat/head size. Really does make you wonder who tested the prototype of these headphones.Just a bit smaller length to the size of the headband and slightly larger cups, and they'd be a better fit for a larger range of people.

Volume & Sensitivity

Yamaha rates these as 106 dB ±3 dB (1 kHz, 1 mW). They seem a lot more sensitive to me than that. My Sansa Clip Zip can drive them to very loud volume. Innerfidelity's measurements show that they need 0.013 Vrms to reach 90db. Compare this to the ATH-M50s (0.073 Vrms) and you can see how very loud they can get.

Yamaha also rates them with a maximum power of 1000mw. Assuming that's correct, the Pro 500s should be screaming into someone's ear at near deafening volumes before they reach their limits (don't test this--lol).

Sounds similar to UE6000 and K550?
When I was researching these after buying them in the lightning sale (still had time to cancel my order), I saw a couple of comparisons to the AKG K550s and UE6000s in the discussion thread for the Yamaha Pro series. Of these two, I feel the Pro 500s are much more similar to the UE6000. The Pro 500s have a warm, bassy signature with a decent spacious enveloping sound for a closed headphone. Perhaps a little less dark than the UE6000. Bass seems a bit more controlled over the UE600, and overall clarity a bit better.

Now I do prefer the K550 over the UE600. I just like a sound that is more neutral than warm. Using Rockbox on my DX50 and Clip Zip, I am able to use the tone controls (~ -3db bass, +4 treble) to bring them into the balance I want. Some experimenting with PEQ instead of tone controls should help to make them better suit my taste.

I feel like they are an upgrade in SQ over the UE6000, although not enough to justify a $399 price tag. Around $200 would be better pricing for them given their sound quality. At $150, they were a great buy.

A few months ago, I got my 13 year old son the AKG K518 DJ LE, based on the listing of the K81 DJ on Innerfidelity's Wall of Fame.

The sound was disappointing. Very heavy muddy bass that overwhelmed the mids. While OK for the price I got them at, this was not what I expected.

Then yesterday, we decided to mod the headphones. The blue tack mod is a popular mod for the AKG K518 DJs. Because I was afraid of over dampening the phones, we used blue tack sparingly and put duct tape on some of the rest of the inside cup to curb the resonance (see pic in this post).

The results? Absolutely a world of difference. Here is what I was expecting from a headphone whose design had made it on Innerfidelity's Wall of Fame. Bass impact was reduced slightly because the muddiness was gone. No longer a thumper, but a headphone with highly textured bass with very good transient response, and yet still significant bass emphasis. As a results, mids are much clearer as well.

So if you can do the mod (and it's not hard), this is an excellent headphone for those looking for some portable headphones with some strong, but good SQ bass emphasis. Considering these can often be picked up for less than $50, they are a bargain

I've had Sony MDR-V6s for about 12 years, and I was looking for an upgrade. The Sony MDR-V900HD seemed to fit the bill, and I wanted to love these.
 
In many ways, I was not disappointed. Good comfort, isolation. The clarity of the mids and highs is exceptional. I can see why people that buy the V900s love them (or the MDR-7509HD, same headphone, different styling). Their highs and mids have a precision and accuracy that is alluring.
 
However, the bass response is lackluster. While I knew from seeing frequency response charts of the 7509HD that this might be a problem, I had high hopes that the bass response might be enough for me. Unfortunately, it's audibly obvious that the bass starts to roll off rather steeply below 100hz. And when I EQd the lower frequencies up to flatten the response, I didn't feel that the texture/detail of the bass response was up to that of the mids and highs. The bass detail was very good, but not great. 
 
So while the phones are otherwise excellent, it doesn't make sense to me that Sony would design a monitor headphone for the digital age with the "HD" moniker that doesn't have a fairly flat--or at least more gradual sloping--low end response. There is simply more music than ever using the lower bass frequencies (e.g., compare modern/alternative rock with classic rock). And let's not even talk about movie watching on a pair of cans. The MDR-V6s can handle it. Why not a more expensive, revised model in their monitor series?  
 
My final recommendation is an analogy: if you are the kind of person that is satisfied with the bass response from a great pair of 6.5" driver bookshelf/monitor speakers, than these could be an excellent choice for you. But if you are looking for the low end reaching bass response of a pair of floorstanding speakers, look somewhere else.