Concrete Speakers Are Attractive And Functional

In a lot of fields – motorsport, space exploration, wearables – lighter is better. But it’s not always the case. When you want to damp vibration, stop things moving around, and give things a nice weighty feel, heavier is the way to go. This is the case for things like machine tools, anvils, and yes – speakers. Using this philosophy, [SoundBlab] built a set of concrete speakers. (Youtube link, embedded below)

The concrete speaker enclsosures are sized for 3″ drivers, and were cast using two measuring jugs as the mold. This gave the final product a smooth and glossy surface finish, thanks to the surface of the plastic used. The concrete was also agitated during the casting process to minimise the presence of air bubbles in the mixture.

Once cast, the enclosures are fitted with plywood end caps which mount the Fountek FE85 speaker drivers. These are a full-range driver, meaning no cross-overs or other drivers are required. The speakers are then mounted on stands constructed from wood edging, which are stained in a contrasting colour for a nice aesthetic touch. Felt pads are placed on the base, and polyfill inside the enclosure to further minimise any unwanted vibrations.

The sound test confirms the speakers perform well, and they look great as a part of a lounge audio setup. We think they make an excellent pair of bookshelf speakers, which would be ideal for comfortable listening at moderate volume levels.

We’ve seen many speaker builds at Hackaday, from 3D-printed omnidirectional builds to the more classical designs. Video after the break.

24 thoughts on “Concrete Speakers Are Attractive And Functional

  1. Very concrete results…

    But isn’t concrete heavy as all hell, I’ve seen USB hubs too, and all I keep thinking of are pavers…
    Not something I’d put on a desk.

    1. Why put it on a desk? Make a large speaker with a big cone, put it on the floor. Better, buy a concrete or tile pipe cheap, design a bass reflex port to fit, put on the floor, annoy the neighbors with your new sub. Use those little speakers from 100 Hz up.

  2. 3″ isn’t a size that can’t be packed in anything. I’d say 6″ is where enclosures start to matter. (It’s not the size but the bandwidth below ~100 Hz at significant levels)

    1. Agreed, but it is a novel, attractive and economical way to make a good small enclosure. All the same, I don’t think I’ll be making concrete cabinets for my 15″ Altec coaxial drivers any time soon.

  3. Has anyone tried epoxy-granite for speaker enclosures? It’s used for some shop machinery such as lathes and milling-machines as it supposedly has superior vibration-dampening characteristics to cast-iron.

    1. (ex-audiophool here) Most probably almost anything you can think of has been tried. If the builder has a clue, vs just a hobby horse, at some point he figures out that vibrations of the cabinet matter a heck of a lot less than things like standing waves in the air inside the cabinet – which affect the speaker diaphragm directly, the even-harmonic distortion of the air itself (long before air “clips” on the vacuum side of the sound wave), the execrable linearity of any driver vs how good the electronics are these days and so on – I could easily write more scientifically backed words about all this than would cover this entire site for a day.
      In the end, I became a musician and learned the differences between “perfect”, sound production, and sound _re_production. They’re vast…

      Example on reproduction – if you can record dropping say, a quarter on the floor, and play it back in the same room over your reproductive system and everyone instinctively looks at the exact right spot – you’re onto something good.
      If you mix a recording of thunder into the background of the music, will people go and roll up their car windows on a sunny day? This “you need a trained ear” BS is just that. You only need training to tell between terrible and less terrible, and maybe have a clue why each is so bad. When it’s good, it’s so obvious everyone knows.

      Being a real EE, I never fell for much of the audiophool stuff. Instantly figured out that TIM was slew rate limiting and not caused by too much negative feedback, though too much used in the attempt to correct a bad design was correlative. Ditto super speaker wires and so on. I actually made a decent living making good stuff, but the BS level of all of it offended me and I went on to other things.

      FWIW, back in the days when horns were popular, Altec-Lansing used lead, which is really good for this kind of thing. Harry F Olson (RCA), who worked more with lower frequencies, is the guy who pointed out the distortion of the air itself for the first time as far as I know. Beranek’s “Acoustics” has much, much more.

      1. “If you mix a recording of thunder into the background of the music…”

        There is a song I have, and in the background near the intro, is a faint beeping sound.
        I don’t know how many times I pulled my headphones off while listening to that song to answer my phone!
        B^)

        1. I have an album with a song on it that has a couple of seconds mixed in that sounds exactly like the ringtone on my parents landline handset, makes me jump every single time.

  4. Someone left out the port/vent for this speaker!?

    https://en.wikipedia.org/wiki/Bass_reflex
    A bass reflex system (also known as a ported, vented box or reflex port) is a type of loudspeaker enclosure that uses a port (hole) or vent cut into the cabinet and a section of tubing or pipe affixed to the port. This port enables the sound from the rear side of the diaphragm to increase the efficiency of the system at low frequencies as compared to a typical sealed- or closed-box loudspeaker or an infinite baffle mounting.

    A reflex port is the distinctive feature of this popular enclosure type. The design approach enhances the reproduction of the lowest frequencies generated by the woofer or subwoofer. The port generally consists of one or more tubes or pipes mounted in the front (baffle) or rear face of the enclosure. Depending on the exact relationship between driver parameters, the enclosure volume (and filling if any), and the tube cross-section and length, the efficiency can be substantially improved over the performance of a similarly sized sealed-box enclosure.

    1. Bass reflex speakers cut a sharper deal with the physics, but there’s no free. They fall off 6dB/octave faster than acoustic suspension below the port resonance, and while not a detriment, do require a different driver design to be optimal. You generally need a larger cabinet, but all that depends on the Thiele-Small parameters of the driver.
      (I was partners in an outfit, C&S Audio, that designed and sold “the woofer tester” for measuring things like that, our customer list included some big driver manufacturers)

      I’ve seen designs where closing up the port improved the extreme low end, because acoustic suspension falls off slower at the bottom. Also, when driving near their limits, a reflex needs a high-pass filter to limit cone excursion below its nominal cut-off. It’s easy to get outside the limits of linear magnetic field interaction even long before you run out of suspension travel (linearity suffers either way).

      The thing is, even the T-S parameters change with level – try Fs at very low level (the usual signal generator and big series R) and high level – surprise! Now what loudness are you designing for, and at what limits of dynamic range do you want it to sound good? Heh, there’s a lot going on….

    2. A reflex cuts a sharper deal with the physics, but there’s no free. They fall off 6 dB/octave quicker than an acoustic suspension below Fs(net). Below the box resonance, it’s easier to drive the speaker into generating harmonics as there’s much less control of excursion. You design for what you like…

      For fun, measure say, the Fs of a speaker at both low and high levels. Surprise – your design was based on error if the playback doesn’t have every bass note at the exact same level (no chance in real music).

  5. Once again, that appears to be cement that was used for this build, not concrete. Concrete is a mixture of cement, sand and gravel and I do not see any signs of anything but the cement. Don’t get me wrong, for a project like this Portland cement is just fine and you can make it very smooth as you can see. I just think the terms concrete and cement should not be used synchronously as they are totally different materials.

  6. The reflection coefficient for sound and vibration is based on the density and speed of sound of the materials. http://www.physics.mcgill.ca/~guymoore/ph224/notes/lecture18.pdf

    Concrete is a good example of a material that has much higher impedance than air, and would reflect a lot of sound. Overall, the impedance would make this enclosure have sound that only comes out of the front and nowhere else. It’s true that wood is another commonly used enclosure material, but its impedance is not as large as concrete/cement. You’ve probably witnessed this type of thing with concrete walls vs Sheetrock walls.

    I like the idea, but the weight can be prohibitive if scaled larger. Nice implementation though. Good work.

  7. The round and symmetrical shapes are not the best shapes to use. They promote standing waves lumped together. A fat leaf-pod shape with constantly changing curves would be better and doable by molding in cement. If not clay slip pour-off would give the hollow shape. Could this be done with cement? Balloon inside, pop later?

    1. Just chip the enclosure back with a chisel and you’d remove most of the standing waves. Reverberation chambers use this technique on the walls/ceilings of rectangular rooms.

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