Instructables
Picture of Conspeakuous: Concrete Speakers
It takes a lot of science and a lot of magic to make a good pair of speakers. From hard calculations with Thiele/Small parameters to ideas like 'transparency' and 'presence,' a lot of decisions make up a good speaker design.

One important factor is the material that you use for your enclosures; concrete has some distinct advantages structurally, acoustically, and aesthetically. It is very stiff and heavy--great for supporting the speaker drivers without changing their vibrational dynamics. It also damps out vibrations well, so it doesn't contribute unwanted rings and unpredictable tones to your sound reproduction. Equally important for something that sits in plain view all the time, it has a unique and interesting visual appeal.

So dust up on your concrete mixing skills and lets get to work!
 
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Step 1: Find the Molds

Picture of Find the Molds
08.JPG
Choose some outer molds that are the right size and will let your speakers balance as you want them. Shiny plastic molds release the concrete well. The ones in the photos are affordable but nicely designed melamine bowls from a department store.

For the inner molds, a kids' rubber play ball works great. This one is especially good because the nubs prevent it from touching the outer mold in a large area. You can adjust the internal volume by adjusting how far the inner mold sits down into the outer mold. Put sand in the ball so that they don't float in the concrete.

Also, don't forget that the molds are about to get very heavy, and will be difficult to move when they're full. Think ahead about where you set up your work. The surface should be as level as possible because the top of the wet concrete will level itself, and you want it to match to the height of the mold all around.
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mark.coop.334 months ago

Looking everywhere for these bowls or something similar, does anyone have any ideas at all? Thanks!!

jgonza449 months ago
as the molds you used are no longer available, do you know of any comparable alternatives? I've hit a wall!!
Henkie1 year ago
What speaker did you use, or what are the specs so Ik can find one myself
Hey would these be good drivers for this design?
http://www.seismicaudiospeakers.com/Titanium-Horn-Tweeter-p/sahg207b.htm?utm_source=googlepla&utm_medium=CSE&utm_campaign=CA&utm_content=productAdSAHG207B&CAWELAID=1912445395&catargetid=1911682958&cadevice=c&cagpspn=pla&gclid=CMi6kf6Dz7kCFRDl7AodplcA9w
themakerage (author)  Karl0thomas1 year ago
That driver is only designed for high frequencies and would probably not be what you are looking for (unless you are looking for only high frequencies). The driver we selected has a range from below 100hz (we are talking 3db down here, they have a fair punch and response below 60) to above 20Khz.
Ah ok, so something like the 4" full range drivers that Dayton Audio has?
abdulah941 year ago
Me gusta!! Hagan más instructables de esto!
Eh Lie Us!1 year ago
This is great, man. Amazing.
poofrabbit1 year ago
Just wanted to say congratulations on being a finalists in the Concrete & Casting Contest! This was a fantastic instructable! Good luck!
lynn07591 year ago
Found the link for the bowls. I just ordered them in black.....

http://www.target.com/p/room-essentials-melamine-geo-serve-bowl/-/A-14511968#prodSlot=medium_1_2

I also thought I might try this one in the future but I don't know if it is deep enough:

http://www.webstaurantstore.com/red-get-b-790-rsp-1-9-qt-angled-red-sensation-catering-bowl/375B790RD.html
The 9-quart angled red catering bowl looks boring. It will produce a shape that looks like a slice off an egg. It also has the disadvantage of being angled, so it would have to be supported on an inclined plane during the concrete pour.
I like the shape of the bowl, but that's my personal opinion. If it will affect the sound though, I will take that into consideration. Thanks!
pcooper21 year ago
The best speakers would be to mount the drivers in a rigid, soundproof wall with an infinitely large space behind the wall. Good in theory, but not always practical.
Can you tell me where you were able to find the bowls you used for the molds?
looks like maybe the bowl is from this set: http://jennskistudio.blogspot.com/2012/07/geometric-dinnerware-at-target.html which is no longer available at Target.
It looks like they have a picture of a blck version here:
http://www.target.com/c/dinnerware-kitchen-dining-home/-/N-5xtrv
But when you click it they don't have it listed anywhere...
*black
I found the black ones, they are smaller dipping bowls:
DSC06712.JPG
themakerage (author)  godzillalaughs1 year ago
You got the source for the bowls right, picked them up a few weeks ago so they might still be on the shelf even if they show "no longer available." We would encourage you to always keep an eye out for cool looking molds, you could do something very similar with almost any container.
No resonating I say ! Should sound very neutral without dips or peaks
great idea!!!, So, could you comments any idea to use them in gardens or external places? Many thanks.
joshme1 year ago
This is a really great instructable. Thank you! Can you share some cost estimates for how much this project cost you?
themakerage (author)  joshme1 year ago
Mainly depends on your budget for the speakers, you can spend as much ($200+) or as little ($30 for a decent pair probably) as you want.
Thanks! I was hoping you could shed some light on the cost of the other pieces (i.e. what did you spend on the cement, molds, release spray, etc.).
Rimwulf1 year ago
I don't see any use of concrete, cement yes- did you mix anything in the cement?
red7media1 year ago
It would be nice to see some grills on these - no protection = $$ down the drain!
I built a set of sub enclosures back in 1990 for car sound offs made of concrete.
I would have made a fiberglass enclosure for that type of driver used.
The terminal cups are also exposed, they should be recessed in the enclosure!
I do like the angles of the enclosure itself.

+1 for appearance
-2 for protection
themakerage (author)  red7media1 year ago
Could always be more cautious, but we are happy with the way they turned out. Might design some grills for the next set!
realguy1 year ago
You mentioned design criteria - where is your observance of T-S parameters here?

I love the cabinet - and I see a tightly sealed driver that I'm sure sounds quite nice, but I don't see any enhancement based on T-S, low end extension, efficiency gains, etc., etc.

Concrete used to be the suggested way to utilize the 30 inch woofers from ElectroVoice, that were available from ~1955 through 1985. But even they have very specific requirements for dimensions of the port and the depth into the concrete 'cabinet' in order to maximize low frequency response.

Have you made any with true T-S design parameters in mind as of yet?

Also, did you consider utilizing a driver that could withstand the rigors of outdoors, given the cabinet material?

Last, although obviously much more difficult, a reverse throw or a simpler downward firing addition (using a PP or other polymeric cone) and nubs for enough height to throw out the wave, would make for some impressive outdoor (really, only one is needed) subs that fit the parameters and are omnidirectional, at bass frequencies very difficult to obtain for the average mortal!!
themakerage (author)  realguy1 year ago
No attenuation circuits or anything fancy, just selecting a nice driver and sizing the volume to suit. We might try some 2-ways in the future and those would have a little more math involved.

Don't tempt me with comments about making subs, if we did they would be absolute monsters!
What kind of speakers are these? They look awesome. And hopefully sound awesome too.
themakerage (author)  Yerboogieman1 year ago
We got them from parts express, but they seem to be out of stock. There are a lot of great options, just depends on your budget and application.
eldiahlo1 year ago
You will save concrete using another bowl instead (they're stack-able, thus no ball is needed)
themakerage (author)  eldiahlo1 year ago
Stacking the bowls would leave the wall too thin, unless the "bottom" were very thick. The angle isn't right. If the sides were approx 45* to the bottom, stacking would be a good option. Even though the concrete is sturdy, it will resonate if it gets too thin. To be honest, saving concrete isn't much of a priority; once you are all set up to mix a little, you might as well mix a lot.
macrumpton1 year ago
Any reason to not make the front plate from concrete as well? You could color it for contrast.
themakerage (author)  macrumpton1 year ago
Front face out of concrete would be nice, but it is difficult to size it exactly right, and sanding/polishing the edges to size would affect the finish, but I'm sure it would still look good! It also complicates the speaker mounting a little bit, but nothing we can't figure out.
Nice! How do they sound? Also, I wonder how making these a vented enclosure would help too.
themakerage (author)  CreativeGeek1 year ago
Vented enclosure wasn't something we were looking for on these. They are desk or bookshelf speakers, have nice even response with very clear mid/lows. "Help" is a relative term, it depends what you are looking for in the sound, we didn't need super strong low end, looking more for clarity.
chuckyd1 year ago
So, how did you calculate for the volume inside the box?
themakerage (author)  chuckyd1 year ago
The interior volume was verified with a plastic bag full of water. There are many online calculators that can help you determine what interior volume you want, and many drivers are rated with a recommended enclosure volume. The full calculations and methodology for how to match a driver with an enclosure are beyond the scope of this instructable.
Really cool idea, So many people back in the day, thought solid wood enclosures would be a sign of quality. In fact, wood is the worst material for speakers due to resonance. Same reason musical instruments are made from wood. Most speakers that appear to be wood, are in fact particle board. Concrete is much better, and avoiding parallel surfaces in the enclosure is a big plus.
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