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Fostex BK-12m Folded Horn Kit - Pair

Fostex BK-12m Folded Horn Kit - Pair
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Price: $329.00
Product ID : BK12-Kit
Manufacturer: Fostex
Weight: 83.00 lbs
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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

Tool 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:
  • Select binding posts from the drop down menu above

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

Product Reviews

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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: