Oh wow, I was totally unaware of the ER-3 models. To be honest I've thought about just using cheap earbuds until I can get ER-4XR, just didn't want to be obnoxiously vague on my budget haha. Thank you for bringing another interesting option to my attention.
I upgraded to the ER3XR from the HF5. The HF5 has been my daily go to headphone to throw in my pocket and take on the go and to the office for the past year. I started looking into etymotic for passive noise isolation after listing to the "best" active noise canceling headphones out there and realizing ANC is garbage at best.
If you are familiar with the HF5, the ER3 is a step up in the detail and separation in the sound. Maybe not a huge improvement for some, but it is very noticable to me on first listening. This is especially true in the treble detail. The biggest improvement however is in the bass region. The ER3XR clearly have a much needed bass boost in the low bass/sub bass frequency response compared to the HF5. It is very clean, separated and detailed bass and not overly bass heavy. Just gives a nice bit of increased support in the low end which was the main limiting factor with the HF5.
The build quality is also significantly improved. The HF models have a plastic body and durable but thin cable. The ER3s have aluminum bodies with detachable cables which can be replaced. From what i understand, Etymotics is planning to release a range of aftermarket cables for these and the ER4 models. The cables on the ER3 are still quite thin but feel a bit more premium overall. This is nice as the cable seems to usually be the place where the HF models fail.
In short, the HF5 are a durable but ultimately a "disposable" ....albeit costly, consumer product by build quality standards. The ER3s are approaching more of the professional build quality with replaceable parts so they should last longer. That should be enough of a reason to buy them over slightly cheaper monitors.
If you are on a tight budget, go with the HF5 while they are on sale. If you can justify the additional $50-80 it is definitely worth it to go with the ER3.
Based on the general impression so far, it recommend strongly that most people will really enjoy the ER3xr for listening to music. The flatter response of the ER3sr may be better suited for studio monitors or musicians monitoring live performances. Again, the slightly emphasized bass boost on the XR is far from what I'd call bass heavy. Definitely still very balanced sounding in my opinion.
One general comment/observation I've had on etymotic earphones is that they seem a little treble heavy and bass light with almost a very "digital" sound straight out of the box. They really open up and smooth out significantly after several hours of playback. I usually run them overnight with white, pink or brown noise playing through them to break the drivers in a bit.
