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post #1 of 697
Thread Starter 
The last few weeks I have been spending a lot of time listening to the Equation Audio line of headphones, or as Equation calls their line “EarTools”. I was intrigued by the no nonsense straight forward style and statements on their web site. The Engineer’s and Musician’s experience with Equation microphones and headphones I read seemed genuine and compelling.

I decided to get 3 pair of Equation headphones. I chose the RP-21, RP- 22X and the portable RP -15 MC. These are Equation’s number one, two and three models in their Professional line respectively. All three models are a closed circum-aural style.

For specifics on each model and more information go to: http://equationaudio.com/index.htm

Some of what attracted me to Equation Audio, a relative unknown in the Head-Fi market: #1) affordability #2) what I perceived to be a very honest approach and presentation to their products #3) the RP21 and RP 22X have 50mm transducers, these are big, I was curious #4) detachable cable, available on the portable RP 15 MC as well ( tweakable) #5) 32 ohm impedance which I have always liked


These are well made headphones, comfortable. The detachable cable is robust. The cable is terminated on one end with a right angle mini plug and on the other end, which plugs into the headphone, there is a straight mini plug that snaps securely into the headphone socket. A quarter inch screw-on adapter is supplied for the amp end of the cable if needed.
The ear-cup is made of synthetic leather like material found on many headphones, they are well padded. The sound is detailed, crystal clear and quite neutral. The soundstage is intimate, placing me in the front row center. The depth and width of the soundstage is remarkable. The nuance is incredible. I wrote in my listening notes “you can hear the brass in the horn”. Time and time again I was jolted by the entrance of another player into the soundstage. I would be totally absorbed in listening to a beautiful section of a recording and then another instrument would join in and just surprise me with the clear, clean and crisp added dynamics. The smoothness and seamlessness with which this happens with the RP-21 is just fantastic. The fade in and out of the musician’s microphones is captured, the attack and decay, the timber of the musical wave form and the loudness and pitch is extremely well articulated. The RP-21 fully engaged me in my listening experience; there was no wandering off on other thoughts. During a complex passage each instrument retains its own integrity with a very clean mixing of the multiple sound wave forms. The RP-21 lets me hear everything as clearly and cleanly as it is put down on the recording. The harmonic resonance is beautiful, realistic and true to the recording. The low frequency detail and resolution is intriguing. It took a good 20 to 30 hours of run time on the RP-21’s to really clarify the bass response and each day it becomes more revealing. A remarkable quality in the RP-21 is the sound from an upright bass, or kick drum. There is a resonance, a quality of vibration I had not appreciated in 10 years of listening to headphones. Listening is similar to hearing/experiencing a loudspeaker or live performance.

The headphones disappear into the music very easily. Very often the encumbrance of the RP-21 transcends the listening experience and I am left in a big wide space with just the music and acoustics of the venue, be it the studio or concert hall.


The RP-22X has the same strong build quality. The detachable cable feature is also standard. The RP-22X comes with a coiled style cable. The RP-22X has a unique inner ring of padded synthetic leather material inside the ear cup. So you have the padded ring surrounding the ear then another ring inside this one. In their product information Equation Audio states this design feature allows for extended response, more bass and gain. This proves true to my experience.

The RP-22X has a different sound signature than the RP-21. Again it took a minimum of 20 to 30 hours run time for the sound to begin to blossom. The RP-22X has a more rounded, creamy quality yet the uppers and mids shine through. It’s a sweet listen. There is also this beautiful loudspeaker quality to the sound. The bass is accurate and doesn’t cover or cross over the other frequencies of the recording. Highs and mids are clean and clear. I think the listen is a bit further back. For me it’s as if the music is filtered through distance/space before it reaches my ear mellowing and warming the sound somewhat, still a very intimate and clear sound.

I admit to it taking me a little while to appreciate the RP-22X’s. I couldn’t get a feel for the bass. I really had to think about what it was I was hearing. I concluded that Equation Audio has designed a headphone that is able to present a full spectrum of sound without compromising any one area for another. The bass frequency is really accurate and sounds true and placed on equal footing with the other instruments. There is no veil over one frequency to compensate for another. These are very synergistic headphones.

Portable model

This is a great little headphone, a giant killer perhaps? The RP-15 MC folds into a nice compact size and shape. They have the same rock solid build quality of the 21’s and 22X’s and also sport the detachable cable. The straight cable on the RP-15’s is smaller in diameter (still robust) than the full-sized versions and is terminated on each end with a straight mini plug. The RP-15 MC is billed as the “baby pro” and does a great job, performing much like the RP-21. As with the other Equation headphones the transducer in this portable headphone is big at 38mm. The sound signature is much like the RP-21 offering balanced accurate sound presentation and startling dynamics. I have been revisiting my music collection, both on my computer and CD, with the RP 15’s. It does well with many genres and provides a nice big sound. The bass is amazingly full, deep and rich for a relatively small portable headphone.


I really like these headphones. If Equation built their current line with the professional Audio Engineer and Musician in mind, in the process, I believe, they hit upon a very good all around musical headphone design. I go for the feeling I get from music. I was not sure how a closed headphone designed for professional and technical application might sound. These headphones have all the right stuff for my listening ear and my tapping toes! The presentation on each model is dynamic and engaging, warm and musical with a loudspeaker like sound quality which I have not heard, quite like this, on other headphones.

Equation Audio has some magic going on with their headphones to be sure. Their design efforts have really created something unique. Equation Audio’s presentation at their web site has proven honest and accurate in every way. Of course the audio presentation is created by more than just one element. The source, amp, speaker/headphone and cable all contribute. What I want to emphasize is that Equation headphones take the information they are given and create the end product, music, extremely well.

The last few weeks of listening have been exciting for me. I can think of only one other time I was as absorbed in listening to and thoroughly enjoying the music. This being when I got my first pair of great headphones 10 years ago.

RE: Prices for Equation products.
Equation Audio has a fresh and commendable approach to marketing their product. It's independent, it is grass roots, it is old school and it is great value to performance pricing. Please help keep independence alive by allowing your local Equation Audio dealer to deal directly with each customer. DON'T POST PRICES ON THIS THREAD (check out the posts by Sybrsound )
post #2 of 697
Golly, thanks for doing that! I've been feeling bad about putting off writing up a review of my friend's RP-21 for weeks now. I've just started a new job, and been under a lot of pressure to paint my house, and a few other things.

One of the things that most impressed me about the RP-21 was my inability to feed it a signal that would cause it to misbehave.

Wil Oldham (aka Bonnie Prince Billy) has an album called "Master and Everyone" where apparently the concept was to get a really loud open-air-gig style acoustic guitar, stick a piezo pickup on it, and have an electric bass play backup as well.

It's good stuff, but the resonance from the guitar can be deafening. If a headphone has the ability to make the midbass go HOOOONK, just about any track from this CD will make it do it. Even my DT-770 Pro/80 does it just a little bit.

But the RP-21 gracefully reproduced it without any distortion. I was floored.

Oh, about the coiled cord on the RP-22X - any authorized dealer can order you a straight cord (the RP-21 cord) for about $8. I don't have the item number here, but i can get it from my dealer friend.
post #3 of 697
I've got a pair of the RP-21s and man, I LOVE 'em I'm glad to see I'm not the only one to find them so sweet to listen to.

I've got a bunch of pictures of my RP-21s:
post #4 of 697
Yeah, Eric got me intrigued the other day when mentioning the RP-21 (what?). So, I did a little research. They look promising, but even more so after reading a review like this from another Head-Fier.

What about availability? I was running through the dealer list, but it looks mostly like high-end audio/musician stores. Not that that's bad, per se - but a possible discount source would be a nice option.
post #5 of 697
FullCompass carries them, also proaudiosolutions.com, whoever they are.

I can personally vouch for House of Hindenach in Findlay OH, since the proprietor is a friend of mine.
post #6 of 697
Thanks for your time and efforts to write down your impressions.
I've just visited the website and couldn't find the MSRPs so it's not exactly clear what you mean by "affordability".
Another question:How well do they block out noise?
And I've just checked your profile, but it's not filled out.What's your frame of reference as far as headphones related gear is concerned?
post #7 of 697
Street price (brick and mortar) for the RP-21 floats between $120 and $150. Minimum advertised price is $99, the price you see at most online vendors.

The RP-22X costs more, the RP-15MC costs less.
post #8 of 697
Thread Starter 
All three headphones block out noise very well. They are studio quality closed headphones. In the studio environment it is a must.

Reference CD player, portable headphone amp and a borrowed Grado amp
post #9 of 697
Originally Posted by ericj View Post
FullCompass carries them, also proaudiosolutions.com, whoever they are.

I can personally vouch for House of Hindenach in Findlay OH, since the proprietor is a friend of mine.
Don Hindenach (proprietor) is a great guy he can be contacted at don@audiosys.com http://www.audiosys.com He doesn't have the Equation stuff listed on his web page yet, but he does carry 'em.
post #10 of 697
Originally Posted by ericj View Post
Street price (brick and mortar) for the RP-21 floats between $120 and $150. Minimum advertised price is $99, the price you see at most online vendors.

The RP-22X costs more, the RP-15MC costs less.
Wait, is the RP-22X or the RP-21 their flagship?

EDIT: After reading the specs, the RP-21 seems to be the clear flagship model. . . .
post #11 of 697
yeah, the RP-22X is the "More Bass" version of the RP-21. I've never heard it because, well, the RP-21 has plenty of bass.
post #12 of 697
Thread Starter 
The RP-22X has a great sound, for my music preference I find I go to them most often. I listen to a lot of 50's (1950's) Jazz and live performance. The 22X is a "sweet" listen. I think it would be better to say the 22X has an extended frequency response. The 21 may be the better all around headphone, for all types of listening. It's subjective for sure. They are two different headphones to be sure.
post #13 of 697
Thread Starter 
NICE PICTURES REDBEARD! Do the ear pads come off and on?
post #14 of 697
I noticed them before. They seem to me in a lot of respects awfully similar to Ultrasones.
Can anybody make this comparison?
post #15 of 697
You just read my mind

Originally Posted by Kees View Post
I noticed them before. They seem to me in a lot of respects awfully similar to Ultrasones.
Can anybody make this comparison?
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