Headphone Reviews

Sound Quality
The overall sound quality of the Porta Pro is warm and laid-back. The bass is weighty and reasonably executed for a headphone of this type and price, but it lacks tight slam and extension you can get with better, and more expensive, headphones. The mid-range is very well balanced, and though slightly overshadowed by the bass, integrates quite well to deliver a satisfying heft and truthful impression of the body of the recording. The highs are somewhat inarticulate and slow in addition to being somewhat withdrawn in level relative to the bass and mids, which gives these cans a somewhat muffled presentation. The good news is that the highs aren't strident in the least. The dynamic punch and imaging of these little headphones suffer from both the poor punch in the bass and withdrawn highs.

If budget allows, moving up to the similar Sennheiser PX 100-II ($89), or somewhat larger Grado SR60 ($79), will reward you with significantly better sound quality on all fronts.

Measurements

Frequency response raw measurements show these cans are fairly insensitive to positional changes. Corrected frequency response shows bass at maximum at about 100Hz. Bass roll-off below 100Hz is remarkably gradual for a headphone of this size/type. This is an okay bass headphone, and certainly remarkable in it's class.

From 100Hz to 2kHz the frequency response is remarkably smooth, however it begins a herky-jerky downward ride thereafter. I think I heard this in listening as a good general portrayal of the music and vocals, but a general lack of definition, image, or sparkle from the treble.

30Hz square wave response shows limited bass response, but otherwise no troublesome artifacts. 300Hz square wave has good shape, but indicates a lack of articulation, as does the Impulse response which is a bit stunted. On the other hand a lack of ringing and noise in these measurements show that the cans are nicely damped and produce little in the way of extraneous noise.

THD+noise with the 100dB trace mostly at or below the 90dB trace shows the cans have good power handling characteristics except in the bass where the small open pads are not containing the pressure of the low frequency excursions, which is not surprising in the least.

These open earpad cans, of course, have poor isolation.

Impedance and phase response chart shows a 60 Ohm headphone with a 100Hz primary driver resonance. With 47mVrms needed to achieve 90dBSPL, these are an appropriate can for use with portable players.

Summary
Simply put, the Koss Porta Pro has been one of the best sub-$50 convenience headphones for a quarter century and remains so to this day. They sound terrific (at this price), transport and store easily, and come with Koss' excellent lifetime warranty. The Porta Pro is an excellent student headphone or kids beater can, and I'm very happy to give it a strong recommendation. My desire for great headphones in the world has me hoping that 25 years from now these cans will no longer be such a strong recommendation ... but it wouldn't surprise me if they remained a benchmark performer in this category. Great stuff, nice and cheap!

A big thanks to HeadRoom for lending me the Porta Pro and 25th anniversary edition for this review.

Resourses after the video!

Resources
Koss' history of the Porta Pro and company history.
Independent company history from Funding Universe.
Koss page for the Porta Pro and now discontinued 25th Anniversary Edition.
Koss pages for the similar Sporta Pro and KSC75.
Head-Fi Porta Pro reviews and 25th Anniversary Edition thread.