Folded-horn High Accuracy Full-range Speaker System




Introduction: Folded-horn High Accuracy Full-range Speaker System

Had been browsing the web for good speaker designs and was intrigued by the concept of horn speakers. Thought I would go ahead and make one just to see if the claims on the web were true or not (very high efficiency, no cross over distortion, great sound in th mid range, and bass up to 30-50 Hz without woofers) . The designs on seemed well thought out and the Spawn family seemed to be good performers especially after the glowing reviews on equivalent speakers. I was planning on recycling drivers (3 inch or 4 inch speakers) that I already had so therefore selected the least wide Spawn speakers.

The picture shows how the speakers turned out. Wife likes em! Will post a video later on.

Printed the plans out. I needed 18 inch wide panels for the sides and 5 1/8th inch wides for the baffles and dividers etc. Closest were 16 inch wide and 5.5 inch wide. So decided to get enough of the 5.5 inch white MDF panels to make one speaker. Also bought some nice plywood and Lowes cut it for me to 18 inches wide. Was simpler to stick to the original 18 inch dimensions otherwise I would have to recalculate the internal baffle dimensions.

Step 1: Cutting the Wooden Pieces for the Speaker

I cut the 18 inch wide panels to a height of 6 feet from it's original height of 8 feet. I then drew the locations of the internal baffles onto the plywood panel. Then drilled 1 mm dia. holes though the panel so that I could attach nails to hold the baffles.
Got busy with the glue bottle and clamps and screws to assemble the the back, top, bottom and front panels (baffled) onto one 18 inch by 72 inch side panel. Used biscuits to hook the panels together which makes the final assembly quite a bit easier. You can see the biscuit slots in the left most speaker. Even with biscuits is is important that the panels are perpendicular otherwise the final large panel will not fit on top.
While the glue was curing, I cut the 5.5 inch wide panels into 38 pieces based on the handy table included in the plans. This was a bit of a work as only had a handheld circular saw.
Glued the internal labyrinth of baffles in. And painted exposed surfaces with black paint. Let everything dry and cure overnight.

Step 2: Connecting the Speaker Driver

Could not wait to see if these speakers actually performed as stated so wired an RCA socket on one end and a 3 inch speaker that I removed from a Creative Labs D80 bluetooth speaker box. The original speaker output on the amplified Creative bluetooth D80 unit was extended with a longer wire to which I soldered an RCA plug. Know this is not the ideal speaker driver but it was good enough for a test.

Without the second side panel, the sound was not too bad! And not that different from the second speaker still in the creative box. This got me a bit worried. Anyway clamped the other panel on temporarily to see if the sound was different, and yes, it was, there was more bass and more 'presence", more gravitas! So even with mediocre speaker drivers there was a bit of an improvement. Ok, this might be worth putting more effort into.

Based on the above informal test, I decided to use speakers that I had removed from a Fostex SPA11 powered speaker unit. Expanded the hole in the front panel to fit the speaker (used a jigsaw to cut the hole). Stuffed the speaker chamber only with polyester stuffing to minimize sound reflections. And permanently attached the side panel with expanding polyurethane glue and tons of clamps, weights etc. to really push the side panel onto the baffles. Also applied a few strategic screws to hold and clamp the side panel in place.

I did something stupid, directly attached the speaker to the iPhone head phone output. Yes, without an amplifier, and the sound was nice and loud. Did a bit of testing using an oscillator app on the iPhone. Could hear from about 40Hz to about 16KHz.

The picture shows my crude cutting set up. The baffles with the trial speaker attached. Close ups of the stuffing behind the speaker. Temporarily placing the side panel for testing!

Step 3: Finishing the Speaker ...

After the speaker bodies were assembled I attached black velvet across the fronts of the speakers covering up the horn openings. As was using scrap velvet left from a previous project that was not big enough had to use two pieces for each speaker, one piece covering the top half of the speaker and the other piece covering the bottom half, with the seam in the middle. Attached the velvet with glue and staples.

I then attached standard-of-the-shelf 0.75 in x 1.5 inch wooden strips to the top, to the sides (to hide the velvet edge), and the bottom of the box for additional support. I used standard 6 feet long strips from Lowes. These projected out below the bottom of the speaker box forming support feet.

The diagram will make a bit more sense. The left three boxes show how I added the velvet fabric. The right three boxes, how the wooden strips were added.

Finally, added molding on the top and bottom, stained, soldered the speaker clips to one end of lamp wire and an RCA jack to the other after confirming continuity with a multimeter. Added the driver.

Step 4: Conclusion ...

They do sound pretty good. Was it the worth the effort of constructing these? Am not sure. Am glad that I did make them but most likely would not make these again.

Do now like listening to music again (the sound is different and somehow more connected) but the speakers are pretty massive (6 feet tall and nearly 2 feet deep).

Will add a bit more info later on once I get used to them.



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36 Discussions

Haven't seen a folded horn like this in years, was very popular in the 50s. You can find old magazines where people built them into the house walls as I recall. That over priced Bose folded waveguide ad always reminds of these old folded horns.

4 replies

Bose reminds you of the old folded horns only for one reason. Because it is the old folded horns! ??

Yes, but Bose pretends it is something new, innovative. It's what you can use when you want to use cheaper speaker, can't or don't want to build a quality cabinet, and if you are a manufacturer and you want to make a cheap to make but high profits speaker that "can fill a room" with sound, well, slap on some hyperbole, you are in business. My point was "it reminds me" was, I don't think you are getting your money's worth, I know why people used to build long folded horns. But that's just me.

Good Gosh i remember these wow they sounded Amazing and were SUPER expensive in the 70's used !

Great Ible i'm gonna build me some of these ...

Thanks for sending the link. Yes, does look similar except the volumes on the Bose are substantially lower. Confession - currently I have Bose Acoustimass 5 speakers, but the ones I made sound much more better. I just hooked up a cheap Tripath chip based amp from Leipai (less than $20) and the speakers suddenly came alive! Quite unexpected. Am tempted to try a version of these speakers which can handle larger 8 inch drivers.

95% of the cost of commercial box speaker manufacturing is in the box. 5% is in the drivers.

An exponential folded horn is probably the most efficient design and the most difficult to manufacture.There are a number of reports that state stepping the sides to replicate a folded exponential horn makes no perceivable difference to the bass frequencies.

The horn design you used is a proven design and will provide more bass drive for a lower power than a standard sub-woofer box.

What will improve the sound is the box material. Regardless of the price, commercial manufacturer's will not use plywood because the material is too resonant and too difficult to quality control the bass. The best material is HDF. If you cannot find HDF; use MDF or particle board. Instead of using stepped corner pieces, an easier method is cut the corner pieces so one piece fits at a 45 degree angle and it cuts down on the overall weight of the box.

A sub-woofer box will not improve the bass response, but it may give you a honky bass that a lot of people perceive as lower bass. You could use the same box and use a better quality driver, try Parts Express, that would give you a far superior sound than any sub-woofer design. You can also try inserting anti-resonant material at the mouth of the horn.

2 replies

I was wondering about the choice of materials while reading this. Very curious about this design and just got started playing with pro audio again. Could be good or bad timing, depending on how you look at it. But I was always told the same, that MDF was the way to go because hardwoods are too resonant.

One of the two speakers has the internal baffles, speaker bottom, top, back and speaker front panels of MDF. Had a pile of ready-to-use 5.5 inch wide primed MDF 6 feet long panels from Lowes (typically used in shelving). The left and right side of this speaker is plywood.
The second speaker is all plywood.
So would be a good way to test if MDF has an impact on sound quality by comparing the two.
On the stepped corner, guess it attentuates high frequency more effectively than a smooth panel so you get more bass reflected out.
I hooked up a cheap T amplifier ( and the sound quality us stunning and loud (from 10 W RMS)! Do not see a need for a sub-woofer. Honestly, am really loving these speakers.
Am toying with the idea of making another pair with 8 inch drivers that I had bought a while back from guess what - Parts Express! These are not Fostex but some other full ranges with a wheezer cone that I was going to use for in wall speakers.

Really cool! This is the first I've seen the design - And I'd love to hear them.

As a recovering audiophile, I can attest to the deep psychological impact of spending a day or two building something to improve the sound. I bet it's just as strong as spending very large amounts of money.

They are very cool looking though, and if I were to build them I'd have to figure out a way to make the baffles visible.

2 replies

Neat idea! Acrylic side panels would be phenomenal but the cost would be astronomical.

I have seen some well done acrylic cabinets, including at least one folded horn design previously. The "true audiophile" will not stand for the use of such material for dozens of reasons. Mainly, rigidity and unwanted coloration from resonance. But, speakers are kind of a personal thing. As far as I'm concerned, if you want them, make but. Just always remember that there is time proven reason for component selection, materials, and construction methods for those who take such things in esoteric doses.

Since your speaker is quite narrow, it could be used as a starting point for designing a woofer which can be placed under the sofa - a design with a high WAF (wife-acceptance-factor).

1 reply

Folded horn woofers are quite common. But a full range of a single driver is where the magic is. Unfortunately, my wife is in the process of rediscovering her Anya and Clannad collection on the new speakers! And she has been dropping hints that another pair for the living room might be ok (the ones I made are in our finished basement).

Nice looking job. One minor observation regarding the folded horn section is that from the photographs it does not look like the cross-sectional area of the horn is gradually increasing (ie the walls look to be parallel). Did you use a mathematical formula to calculate the horn size or was this by eye and ear trial and error (nothing wrong with that of course as it will also produce the right result).

2 replies

Yes they are parallel. I coped the design from and as these based on MathCad analyses. A gradually increasing cross-section might help but again I was experimenting to see if the original design worked or not. Maybe a brave soul would like to try your suggestion!

Ah, that link is very informative, thank you. Now I've scanned through the patent I can see how this (manifold solution) reduces the high-frequencies acoustically without an electronic filter - a cunning solution that I may employ on my next speaker build.

this is a nice project, adding a small piezo tweeter would help for the high notes of the spectrum.

1 reply

Yes, quite a few commercial versions of these type of speakers do include a tweeter. Example, and But then I will need a capacitor as a crossover to pass high frequencies to the tweeter.