Concrete Speakers

When I was young, I read lots about speakers.  One thing I read (and yes, I understand you don’t believe everything you read) was that concrete would make an ideal material for speaker cabinets due to its density, strength and acoustic ‘deadness’.  The only drawback is that it is quite heavy and moving a pair of concrete speakers from apartment to condo would be even less appealing than it already is with merely wooden speakers.  However, the though stuck in my mind that if I ever had a chance to build a house, I could build some concrete speakers right into the foundation.

Skip ahead 20+ years and we are embarking on an addition project on our house that includes – a new foundation and a room that will be a dedicated music room/theatre room/studio.  Hmmmm, maybe I can sneak in some concrete speaker cabinets….

 To make a long story only somewhat less long, we did it.  The foundation was designed to accommodate two rather large speaker systems, separated by a cavity that could include a large screen TV or amplifiers or an Isetta.  We even made the two outside walls a little longer so that the fronts of these speakers would angle in slightly toward the middle of the room.

 

Here you see the foundation before we poured the floor.  The middle cavity is for the TV.  The speakers are on each side of that.  The narrow cavities on the far outsides will possibly be used to make even more bass by means of exponential horns fed from the speaker cabinets.

In the following two photos you see the concrete cabinets after the rest of the house is basically finished.  The ceiling in this room is TJI joists with sprayed urethane foam on the underside of the floor above to help keep high frequencies from escaping.

   

 In the last photo, you can see the rack where I plan to install all of the audio-visual equipment such as DVD player, CD player, EQ, mixer, reverb processors, surround sound processors, flux generators, etc.  There will be a glass door in front of it and a regular 32″ door to the left of it.  If you look down the hall, you can see the new workbench that we are building for my amplifier work.

This is the latest photo that I have and it shows the baffle mounted with two Eminence Sigma Pro 18A drivers.  These are cast-frame 18″ drivers  with 3″ voice coils capable of withstanding over 650 watts of audio power.  They’ll take over 1200Watts peak!  They make larger ones that will take more power but the word from an Eminence engineer was that these were more linear speakers than the big dogs.  I’ll use two on each side for a total of four.

My plan is to use a Crown K2 to amplify these woofers.  The K2 is rated at 1250 watts per channel into 2 ohms!  I’ll be running 4 ohms on each side since I have two 8-ohm speakers in parallel on each side.  That will bring the output down to 800 watts per channel but I think that is still fairly potent and should provide for my needs. 😉  I’m trying to make a system here that will be “hifi”, not encumbered with brute force.  To that end, I am using a DCX2496 digital crossover by Behringer that allows me to send the various frequencies to any amplifier I wish at the push of a key on my PC.  It is extremely powerful and easy to reconfigure for any acoustic needs whatsoever.  I’ve found it easy to setup already.

I have some more work to do on the speaker baffles because they vibrate way too much already with only 120 watts on the woofers.  They will be liberally braced against the back walls and then I will do some testing of an exponential horn design to see if that works well.  Right now, these speakers are in a sealed cabinet.   Even in this sealed cabinet, the two woofers go down to 15Hz with some authority and they make lots of sound at 20 – 23 Hz.  Played along with my TransLam Alpha* speakers, the overall sound is quite amazing.  Adding that last octave to the TransLams is wonderful.

Later

-GDS

*The TransLam Alphas were built by Keith Kidder in NM and I bought them from him about 5 years ago.  They sound amazing and they look fantastic.  When the studio is finished, I’d like to build a matching subwoofer with the same technique and put that all back in my living room for strictly “two channel” listening. -GDS

Braced Baffles

This past weekend, we braced the baffle boards with some 2×6 boards and then we added a 2×4 brace back to the back wall to help prevent the baffle from moving.  I found that when those 18s were moving at 15 Hz, the baffle moved almost as much as the speaker cones.  Here is a photo of the brace as seen through the speaker hole in the right side where there are as of yet no drivers mounted.

I probably won’t get too much testing done now for at least a week, so hang tight for specs just a little longer.

Thanks for reading,

-GDS