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jack ruby commented on jack ruby's instructable Concrete Loudspeakers

Q1- the "standard" speaker box material is MDF (medium density fiberboard) which is not terribly stiff, but it's non-resonant. Some people use plywood, which is stiffer and stronger, but might resonant. Some companies use more esoteric materials like aluminum extrusions or carbon fiber. The goal is to stop the cabinet from releasing sound energy, which can introduce "colorations" or "smearing" of the sound. If you think of a sound wave being generated from a speaker, the cone has to move in and out to create the wave. That means there's an equal amount of energy on the back side of the speaker that must be dealt with (absorbed, usually). The box contains that energy, and if it doesn't completely contain it, the box will release that energy out of sync with th…

Q1- the "standard" speaker box material is MDF (medium density fiberboard) which is not terribly stiff, but it's non-resonant. Some people use plywood, which is stiffer and stronger, but might resonant. Some companies use more esoteric materials like aluminum extrusions or carbon fiber. The goal is to stop the cabinet from releasing sound energy, which can introduce "colorations" or "smearing" of the sound. If you think of a sound wave being generated from a speaker, the cone has to move in and out to create the wave. That means there's an equal amount of energy on the back side of the speaker that must be dealt with (absorbed, usually). The box contains that energy, and if it doesn't completely contain it, the box will release that energy out of sync with the wave from the speaker which will impact the tone of the sound or the ability to localize the sounds. So concrete is ideal (in my mind) because it is strong, stiff, and non-resonant (and looks cool). It _is_ heavy though :) This company makes commercial speakers out of concrete https://www.concrete-audio.com/en/ Q2: monitors just means reference speakers used by audio engineers to "monitor" the mix. Usually, it will refer to smaller "bookshelf" speakers when used in the hifi world. This design is based on a true monitor - the BBC Ls3/5a which is considered one of the most neutral designs ever made. Jeff Bagby used that design as the basis of his monitor design. Since this is for my friend who is a composer, it's a true monitor, being used for composition and audio engineering. Just a note on "neutrality" what we mean is a loudspeaker that reproduces the input signal as accurately as possible. Tonal neutrality means that the frequency response is as flat and accurate as possible. I hope that helps clear up some of that terminology. Here's a couple of audio glossaries if you want to learn more! http://www.enjoythemusic.com/audioterminology.htm https://www.moon-audio.com/audiophile-terms-guide

IDK that I'd call it "brute force"... maybe the cinder block would be brute force :D I like the idea of doing the rails in the cement. That would definitely save some time trying to cut all the bracing to the precise size/contour of the concrete. What you describe with troweling, letting it set up, then rotating is basically what I did, except I spray a skin coat, then hand-packed. Basically doing a concrete countertop all the way around the mold. The VOH cement sets up _very_ quickly, so by the time the bottom was done on both speakers, I could move to the left side, then the top, then the right side, so by the time the cement had to be upside down, it was already firmed up. The challenge comes because it sets so quickly, I had to work really fast to keep the stuff in the bucke…

IDK that I'd call it "brute force"... maybe the cinder block would be brute force :D I like the idea of doing the rails in the cement. That would definitely save some time trying to cut all the bracing to the precise size/contour of the concrete. What you describe with troweling, letting it set up, then rotating is basically what I did, except I spray a skin coat, then hand-packed. Basically doing a concrete countertop all the way around the mold. The VOH cement sets up _very_ quickly, so by the time the bottom was done on both speakers, I could move to the left side, then the top, then the right side, so by the time the cement had to be upside down, it was already firmed up. The challenge comes because it sets so quickly, I had to work really fast to keep the stuff in the bucket from setting into a brick!

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