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| Revisiting Koss "The Plug" Headphones | |||
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by Chu Moy
[The original modification for the Koss Plugs was a substitution of the cushions only. This revision of the article describes a second modification to mitigate the "tinny" sound quality that manifests itself even after the cushions are replaced. The latest production of The Plugs comes with cylindrical cushions in addition to the conical type. Recent reports indicate that while the cylindrical may be a better fit, the soft foam may still not provide an adequate seal for some ears.] When I purchased Koss' "The Plug" canal-type headphones, I was filled with great expectations. Its cousin, the famous Etymotic Canalphones, retailed for over $300 and were prized by many headphone devotees for their acoustic isolation and clarity of reproduction. Here, for less than $20, the Koss Plugs promised many of the same advantages of the illustrious Etymotic headphones. The Koss packaging loudly proclaimed "isolation to the max," "custom fit," "deep bass" and "sounds great." I could not wait to try them.
Unfortunately, from the moment I first put them on, the disappointment began building. The Plugs fit so loosely that they fell out of my ears with the slightest tug. I tried reversing the funnel-shaped cushions as the instructions suggested, but then they were uncomfortable, and I could feel the hard plastic acoustic tubes pressing against my ear canals. Nor was the acoustic isolation anything to marvel at. I could hear noises around me as clearly as when I had nothing in my ears. And to top it all off, the sound was tinny and there was no deep bass to speak of. I put them away and did not think about them again, until a posting in the HeadWize forums complaining about the poor design of The Plugs led me to think about how to improve their performance. The poor bass response was at least partially due to the inadequate seal provided by the ear cushions. The original Plugs had only the conical cushions, which were supposed to help "focus" sound directly into the ear. The size of the cushions was too small and the density of the foam too low to be a good match with my ears. The tinniness, though, was most likely a reflection of the irregularities in the treble response of the transducers. The first modification is to create new cushions for The Plugs that have superior sealing characteristics. To smooth out irregularities in the treble response, the second mod adds acoustic damping to the Plug enclosures. Neither of these mods is permanent. If you don't like the sound of a particular mod, you can remove it. Each mod can be installed independently of the other. If the Koss cushions fit your ears, then try mod #2 by itself. Although the mods can be done in any order, I recommend that mod #1 is done first, so that the effects of the second mod can be judged with the new cushions installed. These mods may also work for other canal-type headphones that suffer from similar fit and frequency response characteristics. The cushions will work best on canal-type phones that have an acoustic tube about the same length as The Plugs. With shorter length tubes, the cushions will have trouble maintaining the seal. Modification #1 I based the new cushions on foam ear plugs, and cylindrical-shaped plugs generally have a more effective seal than the conical types when the foam expands after insertion. The shape and the material composition of the ear plugs could affect the sound. It is a good idea to test several brands of ear plugs for the best sound quality, as well as the best individual fit and noise reduction. For example, if The Plugs with ear cushions made from the Flent's turn out to be bass-heavy, another set of ear plugs with a different shape or composition might result in a more balanced frequency response. I have not tried the cotton-wax and silicone putty-type ear plugs. Since these types are moldable, they might serve as replacement cushions by wrapping the material around the transducer tubes. Putty-type plugs may last longer than the foam ear plugs, which will lose their ability to recover their shape after about a week or two of constant wear. However, they usually do not attenuate noise as well as foam ear plugs. Pre-molded ear plugs (the rubbery kind) may require additional preparation (such as drilling or shaping) to work in this application.
For maximum acoustic isolation, it is important to get foam ear plugs that fit snuggly and have a high noise reduction rating. The noise reduction figure is usually prominently displayed on package. I chose Flents ear plugs (figure 1) that reduce ambient noise by 29dB. A Flent's box containing 10 pairs of ear plugs costs about $4.00 and is sold in drugstores. The ear plugs should be long enough to cover the length of the acoustic tube, although they may have to be shortened later during testing. A note to the style conscious: most ear plugs are white or beige. There are colorful alternatives, although flashy foam ear plugs are not easy to find. In addition to colored foam plugs, pre-molded ear plugs that are sold in a variety of colors and shapes. However, non-cylindrical ear plugs may not be physically suitable as ear cushions for the Koss Plugs, and the sound quality, fit and noise reduction of the ear plugs should not take a back seat to style. My original method for making the holes in the foam ear plugs was to use a large sewing needle to pierce the length of the ear plugs and ream a hole. However, this method was both tedious and messy, and resulted in a rough finish. Some DIYers have reported that an electric hobbyist drill (such as the Dremel) does the job nicely. I don't have a hobbyist drill, and my Fiskar's hand-drill would compress and get stuck in the foam material. Trevor Walton emailed me with the idea of using a hot nail (held with pliers and heated with a torch) to melt a hole in the ear plugs (see the addendum). Mark Calder followed up with an email saying that the hot-nail method worked beautifully. The nail does not need to be red hot. He held the nail with pliers and heated it with a match instead of a torch. I didn't have any nails handy (at least none that were thin enough for this application), so I adapted this idea for use with a soldering iron as a heating element. I call it the "heated needle" method.
First, make a "needle" from a 4-inch length of 22 ga. solid wire. A 20 gauge wire may be preferable as it will create a larger hole, and will not need further enlargement. However, there is also less room for mistakes. Strip off the insulation from about 2 inches and wrap the insulated length around one jaw of a mini needlenose plier. Bend the exposed wire so that it is straight and perpendicular to the pliers (figure 2).
A book cover can serve as a work surface for positioning the ear plug. Center a piece of double sided tape on the book cover, and gently put the ear plug on tape. Apply only enough pressure to anchor the ear plug on the tape - or the plug may become permanently attached to the tape. Choose ear plugs that are as close to perfect cylinders as possible. Squished or mis-shaped plugs may be corrected by tugging and pulling at them.
The goal is to make a single hole for the Plug's acoustic tube that is centered all the way through the ear plug. The same hole is formed twice to ensure that the opening has not closed back up and to correct any mistakes. Make the hole by holding the needle perpendicular on top of the earplug, and centering it. Apply a hot soldering iron to the needle and slowly push the needle through the earplug until the it hits bottom, keeping the needle straight and perpendicular all the way down. The soldering iron must NOT touch the foam. Pull the needle out. Carefully lift the ear plug off the tape, turn it over and put it back on the tape. If the first hole is correctly centered, then repeat the process by inserting the needle through the same hole. If the first hole is not centered correctly, form the second hole to compensate.
With a 22 ga. needle, the hole will still be too small. Enlarge it with a 3/16" drill bit, gently pushing it through the ear plug while twisting it forwards and backwards between your fingers. As a safety precaution, it is a good idea to put the heated needle back into the hole one more time to "cauterize" any loose bits of foam. The hole should be just large enough for the acoustic tube to go through, but not allow the cushion to fall off. Adjusting the New Cushions
When installing the new cushions, the shiny end should face out and be flat with the opening of the acoustic tube, but not extend beyond it. Examine each end of the ear plug - one side is shinier than the other. Stephen Lafferty says that the shinier side inserts into the ear canal more easily. Apply a utility knife to the other side of the ear plug and cut off about 1/8" so that the cushion installs flush with the acoustic tube.
Put on The Plugs one at a time. First, squeeze the cushion all around the acoustic tube to flatten it. Then insert The Plug into the ear canal and hold it there for a few seconds until the foam expands. Test the new ear cushions by listening to a variety of music. Be prepared for the near lack of ambient noise and the "dead quiet" background of these headphones. If The Plugs sound muffled, it may be because the expanded foam is partially covering the transducer tube inside the ears. First, try pushing the cushions back until the transducer tubes protrude slightly. If the sound is still muffled, bevel cushions by trimming a small amount of foam off the top along the outer perimeter of the cushions. If the sound is still wanting, then trim back the length of the cushions by a millimeter or so. Do not to trim too much.
Modification #2 The Koss Plugs with and without the new cushions have been the subject of some discussion in the HeadWize forums. One frequently raised complaint about the sound quality was a peak in the lower treble that made listening to The Plugs for long periods very fatiguing. I wondered if I could change that as well. My first thought was to replace the original Koss Plug transducers with better sounding ones (as suggested by "Strap" in the forums). Unfortunately, the transducers have to be 13mm or they will not fit the Plug enclosure. Strap used transducers from Sony E837 earbuds, which at 13.5mm are too large. He somehow managed to cram them in. In general, earbuds with 13mm transducers are not common except in the budget models. The only ones I could find were in the EarHugger A1000; the A1000 sounded terrible. Even if I could find earbuds with 13mm transducers, I did not want to spend too much money on replacement transducers. Since I would not be able to substitute transducers, I thought about altering the frequency response of The Plugs themselves. One common cause of frequency response irregularities in headphones is underdamped transducers and/or a resonant enclosure. Several mods had been posted in the forum to address this issue. For example, Bob Horn suggested adding mass to the enclosure by drilling a hole in a penny coin and putting the coin on the acoustic tube before installing the cushions. Since The Plugs have a vented enclosure, I could dampen the transducer's response by acoustically loading the vent holes with some earbud cushion foam. This method has the advantage of not increasing the weight of the Koss Plugs and dampens both the Plug housing and transducer.
The acoustic foam for my mod came from the EarHugger A1000 cushions. Other foam cushions should work equally well. Select a thin cushion material - it is not necessary or advisable to spend money on thick, "high quality" cushions. To disassemble a Koss Plug enclosure, gently slide the edge of a pocket knife along the enclosure's blue/yellow seam line where the front and back parts meet until it "slips" in. Then rock the knife edge slightly to open the enclosure. Be careful not to damage the transducers!
Cut a 3/8-inch foam square from an A1000 or other earbud cushion. Insert the foam square behind the transducer over the enclosure's vent holes. Reassemble The Plug enclosure by snapping the front and back parts together. Leave the other Plug enclosure unmodified for now and audition The Plug headphones with a music source. The size of the foam square will affect the degree of damping. It will smooth out the upper frequency response, but it will also augment the bass response. If the foam square is too large, The Plugs will sound muffled. If necessary, reduce the size of the foam square to achieve the best balance between the bass response and treble damping. Once the sound of the modified Plug is optimized, apply the same mod to the other Plug enclosure.
Even when optimized, the bass response of The Plugs will be very strong and will have a slightly loose or "tubby" character. If you like the sound of The Plugs at this point, then you need not go further. The next step of this mod is to restore some balance and control to the bass frequencies and is based on a mod for the Sony MDR-EX70 headphones described by "Neruda" in the forums. Cut a strip of the foam 1/8-inch wide by 1-inch long. Cover the opening of the acoustic tube with it and secure the foam against the acoustic tube with a piece of adhesive tape. Do not use too much tape or it will be difficult to re-install the cushions. Add this modification to the other Koss Plug and audition the headphones. If the treble is too muted, try pulling the foam tighter over the acoustic tube or reduce the width of the foam strip so that a small bit of the acoustic tube's opening is exposed. The Results
The final assessment: quite listenable! These mods together demonstrate the great potential of the Koss Plugs. I don't claim that the modded Plugs will trounce the Etymotic canalphones, but they do a very credible job. I imagine that they are an unbeatable value for travel headphones and for listening in any environment where acoustic isolation is important. Because of cord noise (a problem with all canal-type headphones), I do not recommend The Plugs for jogging or other activity which causes the cord to thrash about, unless it can be immobilized (such as by pinning it to clothing). The modded Plugs are slightly less efficient than the stock version, and seem to be missing the highest octave of treble and transparency. Nevertheless, I think that the modded Koss Plugs will please very much - especially when compared to the originals. Where The Plugs before were loose-fitting, they are now molded to the ear canals for a true custom fit. Where The Plugs before had poor acoustic isolation, external noise is now substantially attenuated. Where The Plugs before had a bright fatiguing sound with no low end, they now sound balanced with a clear and strong bass response. And despite the slight drop in efficiency, they still run plenty loud from portables. I particularly recommend these mods for current Plug owners. Anyone who is dissatified with the sound of The Plugs should try these modifications. Since the investment in materials and effort is so minimal, modding the Koss Plugs is like getting a new pair of quality headphones for the price of a bus ride. Addendum 12/13/99: Added figure 4 and section on adjusting the new ear cushions. 12/15/99: From Sebast on the MiniDiscussion board:
12/20/99: From John B on the MiniDiscussion board:
1/7/00: From Jerry Johnson:
1/14/00: JKaiser in the HeadWize DIY forum recommends using a round toothpick to make the hole in the ear plugs and then use a drill bit (not a drill) to enlarge the hole. Complete instructions are in his forum posting. 5/1/00: JonR in the HeadWize DIY forum suggested this idea for making the ear plug holes:
7/7/00: Trevor Walton writes:
10/9/00: Leon Werenka had these suggestions for punching holes in the ear plugs:
- hardware stores sell the two pieces needed for putting snaps in clothing (like the front snap on blue jeans). Before they are compressed with a tool, one piece looks like a little funnel with a tiny hole. The edge is actually needed to punch through the cloth in the installation process. One of these could be purchased for a few cents and easily be pushed through the ear plug against a hard surface. 5/24/01: Mark Calder suggests that DIYers who have constructed the Koss Plug replacement cushions with a drill bit may want to "cauterize" the interior wall of the hole to prevent any foam bits from coming loose and lodging in the ear canal. Since the acoustic tube of the Plug presses against the interior wall of the cushions, I don't think it is easy for foam bits to come loose, but cauterizing the hole is a good safety precaution. The cauterization can be done with a hot nail (see Trevor Walton's suggestion) or with the simple heated needle method described above. 5/27/01: Major revision of article. Added description of heated needle method for making holes in the ear plugs. Also, added section on damping the Koss Plug transducers (modification #2). 5/27/01: "Duncan" in the forums reports on the latest mod (which was posted in the forums prior to this article update):
8/7/01: Richard Petrilla made replacement cushions for the Koss Plugs from Smith & Wesson "Quick-Fit" ear plugs, which cost about $5.00 per set at Walmart. He writes: The plastic cord between the two sides easily slides off and this leaves a guide for you to bore a hole. You can use a drill, but I would suggest using a hot piece of straight coat hanger. My holes ended being very straight with this method. There is very little melted plastic mess if you do it quickly. I also cut the base just a tad to get the plug at its fatest part. My plugs have a removable acoustic tube and no mute button. It took me a while at first but now I could do a pair of replacement cushions in five minutes. The cushions are installed on the acoustic tubes up through the middle. Now for the sound. I like the isolation that the plugs provide. I used mine a few times on the plane and it blocks out a good portion of the outside noise. As typical with other in-ear plugs, the sound can change quite a bit by the way they are worn. If you leave them out a bit, they sound lean. If you push them in farther, they get bass heavy. I did eventually find a good balance and they sound respectable for the $20 that they ended up costing me. I find these to be more comfortable than the foam cushion pads but others may not.
8/7/01: Forum member Mail4U tried the mods on the new version of the Koss Plugs (removable acoustic tube, no mute switch) with these comments: "I did the complete cmoy mod - this needs to be done or it sounds very tinny. With the cmoy modification the treble smooths right out, though accurate bass is still a problem with the foam ear plugs. The midrange and treble to me are very liquid and non-fatiguing with the mod. I replaced the foam mod with the Etymotic ER20 ear pieces ($10 + $5 shipping). Bass much clearer and isolation is excellent. Generally very smooth non-fatiguing sound. For total $30 cost can't be beat. Think it gives a lot of the under $100 phones a run for the money - the cheapskates Etymotic ER4P!"
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© Chu Moy, 2001