Fostex BK-12m Folded Horn Kit - Pair

Fostex BK-12m Folded Horn Kit - Pair
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Price: $359.00


Manufacturer: Fostex
Product ID : BK12-Kit
Weight: 83.00 lbs
Manufacturer: Fostex
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Fostex BK12m – 4.5” Full-Range High Efficiency Folded Horn Kit
Price shown is for a PAIR

Madisound is pleased to bring you the BK12m, a high efficiency single driver speaker kit. The Fostex FE126En 4.5” Full-Range driver is combined with a custom designed folded horn enclosure. The driver is run full range without a crossover, with a very lifelike and engaging overall presentation. These speakers can be driven with very low powered amplifiers and effortlessly produce satisfying sound levels for all but the largest rooms.

The FE126En is one of, if not the most, popular full range drivers from the long running Fostex FE line. This reasonably priced driver strikes a favorable balance of physical size, high sensitivity, satisfying low end extension, sweet midrange and extended high frequency reproduction.  The F3 is about 65Hz and the roll off is gradual.

We would like extend a big thank you to David Dlugos of Planet_10 Hi-Fi for his time and effort in this project. The first-rate enclosure design and cabinet drawings make this a very special kit offering for the full range enthusiast. Please visit the Planet_10 Hi-Fi website to explore another world of drivers and cabinet plans.

The cabinets are locally cut by CNC machine from high quality multi-layer 11/16” Baltic Birch and delivered flat packed. The through hole for the driver is chamfered to promote optimal air flow. Wood glue, clamps and a little sand paper are all that is required for assembly. Detailed assembly instructions are also included.

Completed cabinets measure 31 5/8” tall x 7 1/4” wide x 14 1/2” deep. The unfinished/unstained wood is ready for your choice of finish. You may also choose to round over the edges if you prefer that style of appearance. High quality internal hookup wire (Supra Classic 1.6) and damping material (Acousta-Stuf) and are included with the kit purchase. The rear of the cabinet is already cut with two holes for binding posts. We recommend the Propeller Posts. Please select your preference from the drop down menu. You may also choose to cut a hole for an input cup if you prefer a flush rear of the cabinet as opposed to binding posts.

Nominal impedance ~ 8 ohms

F3 ~ 65 Hz

Download BK-12m Cabinet Plans


BK-12m Kit Includes:

  • 2x Fostex FE126En 4.5” Full Range Drivers
  • 2x Unassembled and Unfinished Baltic Birch Cabinets (Assembled measurements 31 5/8” tall x 7 1/4” wide, 14 1/2” deep)
  • 3 oz. Acousta-Stuf internal damping material (Dampen each driver chamber with this. We prefer using about 1/2 the quantity provided. Adjust to taste.)
  • 5 ft. Supra Classic 1.6 15 AWG Internal speaker wire
  • 4x QC187 Quick Connects (2 red, 2 black)
  • 8x 8X1 Socket Head Wood Screws (8x Philips Head wood screws also included)
  • Assembly Instructions

Tools Required for Assembly:

  • Elmer’s Wood Glue
  • Sand Paper
  • Bar Clamps (3x 24", 2x 36" - the more the better. Available at your local hardware store, or online at
Optional Parts:

Internal Side View of BK-12m Folded Horn Enclosure

Front Angle View of BK-12m Enclosure Partially Assembled

Rear Angle View of BK-12m Enclosure Partially Assembled

Assembled Pair of BK-12m Speakers
Fostex FE126En 4.5" Full Range Driver

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Product Reviews

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Reviewed by OQZN
08/24/2019 - 02:33:28 PM
A Worthy Product follow up
The speakers have found their way into a more appropriate system. I am running them with an NAD 7050 digital integrated amplifier using Tidal HiFi running from an iPad. The wires are AudioQuest; Carbon digital and Rocket speaker wire. I have now added a sub; a Mirage Prestige S8 that I had. Using a crossover of 100 Hz, in phase.

This is a very satisfying system and a cost-conscious quality answer for computer audio. I set this up next to the big system for casual listening and I find myself spending more and more time with it. Of course the the big system is better, but this is quite satisfying, even in direct comparison.

Of course everything has changed in HiFi over the last few decades, but this system shows that streaming audio and a modest system can compete with spinning discs and vacuum tubes for musical satisfaction.
Reviewed by OQZN
03/22/2018 - 12:23:36 AM
A worthy project
It has been a long time since I have built speakers, but these came together exactly as stated. The cabinet is cut very accurately. The only change that I made was to add sound deadening foam to the back, sides and top wall of the primary chamber. This with the specified stuffing.

I put them up in the big system and right away they sounded good. There was dynamic constrain that slowly went away. By 30 or 40 hours, they were in good form. Moving them against the back wall improves bass response, but also induced midrange resonances. About 42 inches out seems best. The bass is like a nice stand mount, enough for most music, but not enough to do justice to hip hop or EDM.

There is enough treble for my taste. Only in direct comparison with 10x more expensive speakers did I notice the difference.

These speakers are about the midrange, and it is both glorious and flawed. Which depends on the program material. The tonal balance is tilted up, with increased upper midrange energy. They sound more like professional monitors than hi fi. This is hard on thin recordings but adds life to female vocals and recorded applause. They have a unique, lively and dynamic presentation which makes them interesting. On excellent acoustic recordings like Herbie Hancock's River they are extraordinary, easily competing with speakers 10x their cost. On female vocals with acoustic instruments you could be completely happy. The Cowboys Junkies Triniry Sessions is spectacular.

What I did not understand is that a lot of sound comes from the horn; it is not like a bass reflex port. The horn output extends from the lower midrange to probably 60Hz and it is out of phase with the driver. In some cases the color from this is pleasant- it adds a woodyness to cellos, for instance. But for other sounds it destroys the image focus, like male vocals. Piano is treated quite well, I am still thinking about that one.

The soundstage is not particularly large. I was hoping that the single driver with high sensitivity would pay dividends here, but no. It can be very precise though, Piano trios on Dorian were gorgeous, both in tonality and imaging.

In summary, these do many things well and are certainly worth having. The flaws are they do not have enough bass for hip hop or EDM and they have a particular color in the lower midrange due to the horn output that does not work with certain music. That aside though, if you like jazz, acoustic recordings, female vocals and small scale classical works you could be happy with these forever.
Reviewed by bought "Fostex BK-12m Folded Horn Kit - Pair" on our website
04/11/2017 - 12:35:06 AM
BK-12m First Impressions
My build of the BK-12m speaker kit was completed with the Fostex FE108SOL drivers as a substitute. I chose the FE108SOL for three reasons:

A)I thought that the flatter response curve, as well as the purported lower range might make for a better sound than the standard FE126ENs

B)I like the idea of having a “limited edition” driver. It makes the speaker a bit more of a conversation piece.

C)I think the circle on rectangle shape is more aesthetically pleasing than the square on square, but that’s strictly picking nits.

The FE108 Sigma is the new upgrade driver, it would seem, since the FE108SOL is no longer available. I suspect it would be similar to the drivers I selected in many ways.


The provided instructions were mostly accurate and complete. Building the kit was relatively easy, following the instructions precisely. I did run into a couple of build issues:

A)The instructions call for 5 clamps, of two lengths, 24 and 36 inches. After a small gap on the first speaker, I realized a sixth clamp was needed, although it need only be 12 inches. In at least one step, the instructions called for clamping one edge with a single clamp, when clamping two corners of the edge were really necessary for a sure fit.

B)The circular edge of the FE108SOL drivers meant that the holes drilled passed through the beveled edge the driver is installed in. Although I don’t believe there is reason to suspect this will have either sonic or structural effect, the shape of the FE126EN drivers would not have this issue. Were I to purchase this kit again, I would probably choose the standard drivers.

Otherwise, the fit and finish of the flat-pack pieces was impeccable. I went with a simple urethane gloss finish, since I very much enjoy the organic patina that birch gets as it ages. Even though it’s plywood, it’s worth showing off in its natural form.


I am driving these speakers with the Musical Paradise MP-301 Mk3 integrated amplifier. The drive tubes are old stock RCA 6SJ7, while the power tubes are PSVANE KT88-T Mark II. The sound source is a Shiit Modi Multibit DAC, with FLAC input.

Previously, I had used my old Energy 22.1 reference class speakers. These are outstanding two-way bookshelf speakers, but were built for a time when high powered solid state amplifiers were the status quo. The MP-301 struggled to drive these speakers, which is why I had swapped in the KT88s. I did a quick A/B speaker comparison with one of my favorite Mazzy Star tracks, and right away, I realized there was no point in the comparison. The two speakers were apples and oranges.

I am very pleased with the result so far, but I’ll need to do a lot more listening, burning in, and tube rolling before I can offer an objective review. My first impression was that this type of speaker is made for low-power tube amps. My second impression was delight, that such a small driver could be coaxed into producing so much sound.

Thanks, Madisound!
Reviewed by jyungk
03/25/2017 - 04:21:34 PM
Very Pleased!
I needed a second set of speakers for the upstairs office for listening and mixing down live recordings. They're mated to a H. H. Scott LK-30 that was recently recapped and refitted with NOS Telefunken's tubes. The sound is sweet and they're not yet broken in!

The build was pretty straight forward. As others have mentioned, I read through the instructions to make sure I was clear on each step and took my time to make sure every thing was lined up correctly. My only problem was as others have mentioned were connectors to the driver; they're a very tight fit and was concerned I would snap the clips offs, so in the end I simply soldered the wires to the drivers. For finishing, I used a pre-stain due to baltic birch's tendency to come out blotchy. I then used a natural stain and some wipe on poly.

I also purchased the Fostex driver covers. The generic covers didn't really fit the FE126En's well at all.

Reviewed by EastofMars
03/07/2016 - 10:27:31 PM
My Dad was wanting some speakers for the new house. It was close to Christmas and I had the wild hair to build him a pair rather than buying some crappy sound bar or a standard transmission line. I decided to go with the Fe126en. ( My friend was rather impressed by the 93db to 1w spec. ) Since I work in a wood shop and have access to CNC routers and 16mm Finland Birch Plywood I naturally followed the blueprints instead of getting the kit.

The box went together pretty well. I used wool stuffing instead of acousta stuff. I stained the plywood rather dark and it went real well with the cream colored speakers. When I brought the Cabinets home to my house to test out, I was completely blown away. I didn't want them to leave my house. But I did take them to my Parents on Christmas. The first track I played was Todd Terje's "Leisure Suit Preben" from his album "It's Album Time". The sound was awesome and it actually brought the old man to TEARS. Everyone was saying Holy S*** those little speakers are doing that!!

They sound good! Not just loud or bassey or whatever else. These are a real clean speaker and cabinet. You will want to just sit in front of your speakers close your eyes and listen to music.

You will not be mad that you spent $330 on this project.
Reviewed by mrcolson
02/10/2014 - 11:19:04 AM
Great Speaker!
I purchased and built this kit about a year ago - my goal was to build a full-range studio monitor for a record I was mixing ("Use Your Weapons" by Valley Lodge). I mixed the entire record on the BK-12ms, and was very pleased with the experience, and with the results. The speakers have a focused and nicely balanced sound. Wonderful midrange. Voices sound amazing.

A couple of points I would bring up. The enclosures fit together nicely, but I highly recommend taking your time when you build them. You don't need expensive clamps, but it is very helpful to have quite a few of them.

I found that the speakers sounded best in my room and system when I listened to them somewhat off axis. They do have a peak in their response just under 7kHz, but when I set them up pointing straight ahead, or toed in very slightly, the peak was a non-issue.

All in all, these speakers are an amazing value. I am very happy with them!
Reviewed by bernie
05/20/2013 - 07:12:07 PM
She's in your living room
A number of years ago, I purchased two FE126E speakers from Madisound, built bass-reflex enclosures, and used them as computer speakers. After reading about horn enclosures, I thought these little drivers and their accompanying horn plans might be suitable for our living room. Ultimately, I decided to purchase the enclosure kit vs. building from scratch. Iâ
Reviewed by bernie
05/20/2013 - 07:12:07 PM
She's in your living room
A number of years ago, I purchased two FE126E speakers from Madisound, built bass-reflex enclosures, and used them as computer speakers.  After reading about horn enclosures, I thought these little drivers and their accompanying horn plans might be suitable for our living room.  Ultimately, I decided to purchase the enclosure kit vs. building from scratch.  I'm glad I did; the CNC work is very precise and the kit went together without any difficulty.<br />
The plywood is far superior to anything I see in a home-improvement store.<br />
Nine (!) plies plus two Aye grade skins.  No cut surface on any panel exhibited voids.  Each enclosure weighs 25 lbs.<br />
<a href="">Image One</a><br />
I would suggest reversing the orientation of the final panel.  Place the side on the work surface, apply lots of glue, then lower the assembly onto it, rather than v.v. per the plans.  Prevents large quantities of glue running down interior passageways (that cannot be corrected).  I used Gorilla brand wood glue and do not recommend it; the work time is too short.<br />
In an e-mail exchange with Brian at Madisound, he stated that they prefer no fiber fill in the enclosure.  I experimented with several densities, and ultimately decided on 0.75 oz. vs. the 1.5 oz. specified in the plans.<br />
YMMV.  I did fill the three small sealed corners with fiberfill, just for luck.<br />
The sound:  In a word . wonderful.  +1 with Sheepracer re: Dusty, transients, and revelations of poor recordings.  I'm running these with a 2 x 55w SONOS Class D amp and 11 ga. Supra interconnects. Library is (mostly) Apple Lossless encoding.  Because I already had these drivers in existing enclosures, I had the opportunity to A/B them.  The sound difference is astonishing; it's hard to believe they are the same driver.  HiFi pioneers were really on to something with horn enclosures and a single full-range driver.  What you give up at the frequency response extremes is insignificant when measured against the smooth and crisp sound of this combination.<br />
<a href="">Image Two</a><br />
Enclosures were finished in rosewood veneer and sprayed with automotive clear.  The finish was knocked down with 000 steel wool and paste wax.  The grille frame is 3/8" quarter-round, fabric from Madisound.<br />
<a href="">Image Three</a>, <a href="">Image Four</a>, <a href="">Image Five</a><br />
Best regards,<br />
Bernie Seneway
Reviewed by bought "Fostex BK-12m Folded Horn Kit - Pair" on our website
04/01/2013 - 11:01:40 PM
Musical Great Sound-Amazing Value
The kit arrived in 3 Boxes, 2 large flat ones with the cabinets and stuffing and another smaller square box with the drivers, connectors, wire and more stuffing. The instructions are on 2 sides of an 8X11.5 sheet. It is worth reading through this until you can visualize the assembly. The instructions are very good and will take you through the process, but reading through will help you prep the steps. I've been building furniture for ~15 years and combined a few steps, but if you are new to this it is worthwhile to pace yourself to the instructions. The only challenge was the spade connectors and the spades they attached to. Industry standards are poor on tolerancing so it is likely to have the "right" size not fit. You never want to be forcing the spades. They are fragile and a tear jerker to repair. I fettled on one speaker and punted to straight soldering w/o spades on the other.

Sound? After a little more than 100hrs; amazing. Their efficiency makes them "fast", revealing the overtones that defines and differentiates instrument and vocalist voices. Is there some coloration? I haven't heard a speaker without some. These are musical. I attended AXPONA shortly after finishing these and I don't think you could touch anything better for less than twice the price and they play better than some at 3 & 4X. I can listen for hours and hours w/o fatigue. I am rediscovering my vinyl collection all over again. These speakers flatter female voices. (Dusty Springfield/Julia Migenes Johnson/Niko Case) Fair warning though, they are revealing. Full recordings with broad dynamics are incredibly exciting, filthy records and ho-hum recordings will have you stop the program early. Debbie Harry and Blondie were great, but "Parallel Lines" was a ho hum recording and Debbie's voices is stuffed as a result through these. G.I.G.O

Summary-Easy to build, great musical sound, great value (Note: these are heavy packages and you should realistically calibrate your expectations for the shipping cost)
Reviewed by sprigmore
sprigmore bought "Fostex BK-12m Folded Horn Kit - Pair" on our website
07/30/2012 - 02:19:35 AM
Love these speakers! I am driving these with a 2.5 watt SET, they will perform well beyond listening level with little or no loss of clarity or control. Of course you won't have the bass extension of a multi-driver speaker with an actual woofer. However, the bass extension, with the horn design is surprising. Imaging is fantastic. One thing, Fostex drivers require an extended break in period, (100 hrs. Or more), so you might be underwhelmed with the sound at first. Your patience will be well rewarded though.
Reviewed by jmuth
jmuth bought "Fostex BK-12m Folded Horn Kit - Pair" on our website
06/18/2012 - 11:00:14 PM
Very Nice!
After 20 years without a stereo system, I decided to build a DIY system. I chose the Madisound BK12m speaker kit and paired it with a S5 K12m amplifier I also built from a kit. The results are excellent.

It sounds so good that a few days after I got it all working my wife said "that sounds really good. What would it take to get this kind of sound on other rooms?" This from a woman who 20 years ago fooled me with the old "since the receiver is broken, why don't we move the stereo into the garage until after the holidays" ploy (what can I say, I was young and in love).

Bottom line: great sound, great value, works well with low powered amps. Not only passes the spouse test, but makes her actually *like* the idea of a stereo in the house.
Reviewed by bought "Fostex BK-12m Folded Horn Kit - Pair" on our website
04/23/2012 - 03:26:17 PM
These are amazing.
I've constructed all three sizes of the Fostex cabinet kits that Madisound sells and I must say that in many ways these small ones are my favorites. Most full-range speakers have a rising response but these are amazingly well balanced over the frequency range. They also are highly efficient and sound good when driven hard, lacking the harshness caused by cone break-up that larger speakers have. The horn-loaded bass is quite satisfying: the ideal way to extend the bass of a small speaker, in my view. I have been experimenting will full-range speakers for years, and I think these are the best design overall.
Reviewed by emdobbs
01/09/2012 - 07:36:44 PM
Outstanding Value!
Detail, clarity and sensitivity.

This was my first DIY speaker project, and I couldn't be happier with the result.

However, I will have to replace much of my music collection as these speakers really uncover shortcomings in source material.

See the finished result here: