Reversible Equation Audio RP-21 Mod (56K warning)

[BigAmish]

The Equation Audio RP-21s are a nice set of inexpensive closed cans. However, many experienced head-fiers have (justifiably) described the upper-mids and highs as areas where these cans could use some improvement.

Spurred by the success of mods on the K81DJ & KSC75, I was curious how removal of the foam pad covering the driver would affect RP-21 performance. Head-fi member Sulcata_geo had done this & reported positive results, so I decided to follow his advice & remove the foam that covers the drivers & give these cans another listen. Simply put, removing the driver foam opens up the upper-mids and highs, making them sound less artificial (some described cymbals as sounding like they came from a beat-box), more detailed, and more airy! This is a similar result to the K81DJ & KSC75 mods, and it really extends the bang-for-buck factor of these cans, IMO. I’m not saying it makes the upper mids & highs absolutely perfect, but IMO, it does improve them greatly.

Anyhow, I was real nervous doing this mod, so I thought I’d take pictures & walk you through the process step by step to minimize any critical screw-ups by anyone else who wants to try it out!

Start: My shiny “new” RP-21s…unmodded. FYI, they have about 300 hours pink noise burn-in.


Step 1a: Carefully pull back the earpad from the edge of the driver housing. Avoid overstretching the earpad as I envison the plastic tearing if you pull too hard.


Step 1b: Work around the driver housing, releasing the earpad as you go. After you release about ~50% of the earpad, the whole thing should come off of the driver housing with ease.


Step 1c: Pic of my headphone with the earpad completely removed. Notice the thick circular pad that covers the driver at the center. THAT is what we really want to remove.


Step 2a: Pinch the edge of the foam pad & pull back carefully. The tape adhesive that keeps it in place is pretty strong, but eventually it will release and start to peel back.


Step 2b: Work around the circumference of the foam pad pulling it away from the driver housing as you go. It should be much easier to pull back once you get it started (in Step 2a).


Step 2c: The thick foam pad has now been completely removed! Note the double sided tape that was used to keep the pad in place. Should you wish to reverse this mod, just (1) reaffix the foam pad (if the tape is still sticky), or (2) put 3 small drops of Elmer’s glue in a triangular pattern around the circumference of the driver where the tape residue is and put the foam pad back in place. The Elmer’s glue is more than strong enough to keep the pad affixed to the driver housing.


Step 3: Reinsert the earpad in the slot around the circumference of the driver housing, working around the pad until it is completely in place.


Step 4: Repeat steps 1-3 on the second driver housing.

DONE!

Again, this mod was done based on the encouragement and observations of Sulcata_geo…I am just corroborating his positive feedback about the mod results and am reporting detailed instructions on how to do it for those (like me) who are nervous about ripping apart $100 cans!

As you can see from my signature, I don’t exactly have a huge laundry-list of full-sized cans to compare sound qualities with, so I am really interested to know how experienced Head-fiers with RP-21s feel about the usefulness of this mod. All I know is that I no longer think about RP-21 issues with the upper-mids/highs like I used to. Again, I’m not saying this mod makes the upper-mids & highs perfect, but they are (to me) improved to the point where I focus on the music rather than any minor inadequacy in my RP-21s.

Enjoy!

[manhattanproj]

it'll be interesting to compare them "side by side" with the foam removed in one cup and not the other.

[BigAmish]

Originally Posted by manhattanproj

it'll be interesting to compare them "side by side" with the foam removed in one cup and not the other.

For me, it was similar to when I switched from the stock comfy pads (that cover the driver holes) on my MS-1s to bowl pads/reversed HD414 pads (that do not obstruct the driver holes). I seem to have a preference for cans that don't obstruct their drivers with foam as I am a bit of a clarity/detail junkie.

[sulcata_geo]

Good job,BigAmish.

I recommend this simple mod for many Head-Fier

[Skylab]

Nice! I'm going to try this, since the treble of the RP21 kind of bothers me.

[kamal007]

Originally Posted by Skylab

Nice! I'm going to try this, since the treble of the RP21 kind of bothers me.

let us know the result...will run to the guitar center tomorrow if the result is positive

[vorlon1]

Having read this I just tried the mod, and it sounds good. I didn't find the sound objectionable with the pad, but without it, everything seems better defined, including the bass. Nice sugestion, thanks.

[Psiga]

I wrote about my experiences with this (practically necessary) mod on the Equation super-thread:
http://www.head-fi.org/forums/showpo...&postcount=382

"Bottom line: Do this if you're looking for livelier vocals and treble. You won't think that you're listening to a next-step-up headphone, but you'll think that you're hearing an RP-21 that works the way it's supposed to."

[BigAmish]

I spent some time listening to my RP-21s with an alternative set of foam driver discs I cut out from a set of old, beat up ear pads from a no-name set of $5 headphones I bought a decade ago. I'd say that the alternative foam discs were about 30% thinner and more porous (i.e., less dense) than the stock discs that cover the RP-21 drivers.

My impressions (after spending some quality time with Norah Jones in A-B tests) are that foam disc thickness & porosity matter (duh?). As one would expect, details reveal themselves more as the foam pad gets thinner/more porous. Although the degree of treble 'sparkle' is nothing compared to foam-free drivers, those who find the uncovered drivers a little too bright for their tastes (but desire upper range improvements nonetheless) would do well to experiment with foam discs of different thicknesses/porosities to see if you can find a sound that works for your ears (similar in spirit to the Kramer JVC Marshmallow mod). I saw cheap headphones with pads ready to be cut up in a dollar store should anyone want to explore this option with a minimum of financial investment. Just make sure that the ear pad you want to use has a diameter > 2 inches/~5cm.

So far I still prefer the drivers foam-free, but I am an admitted Grado/Alessandro/KSC75 junkie and like my highs as unrestrained as my ears can stand. Not every head-fier prefers their highs like mine so your mileage may vary.

The best thing about this mod is that if you are sonically unsatisfied, you can just replace the stock foam driver discs & be no worse for wear.

Happy listening/modding!

[tbonner1]

I tried the foam free mod and it was slightly too bright for me. Just as with the Senn foam free mod, I believe the foam:
1-reduces the treble energy
2-absorbs some reflected energy and prevents energy from reflecting off the plastic

I tried cutting a quarter sized hole in a thinner replacement piece of foam that was a bit better than no foam.