Blog Forums DIY Speakers and Subwoofers Cinema 6 speakers MDF does not come in three quarter-inch thicknesses in Europe.

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    • #26202
      Sarah Staar
      Participant

      I just purchased your plans for the Cinema 6 speakers.

      I plan on constructing 3 of these from my front soundstage….

      However I’m based in Europe and we use the metric system…

      MDF does not come in three quarter-inch thicknesses in Europe.

      The closest thickness is 18mm or 22mm

      I’m having a MDF company cut everything to size for me and I’m worried that the pieces won’t fit together properly because the thickness of the MDF will be different to your plans…

      Just wondered if you could do a version of your plans or at least a cutting list in metric for people in Europe.

      I would be happy to purchase the plans again with metric dimensions.

    • #26208
      tvor-ceasar
      Moderator

      The critical thing that you have to keep in mind is that the inside dimensions stay the same and how the pieces are put together. And knowing that helps with the conversion. I use whatever calculator comes with either my computer or my phone, or the online conversions from websites such as Google, etc., to change back and forth from metric and imperial in decimal form.

      3/4″ is a hair over 19 mm, so choose accordingly.

      Next, figure your inside dimensions in metric, then using the assembly guide / drawing (not sure what is included) to see what pieces extend past the inner boundaries so you can add the appropriate extra for the cuts.

      For the cut outs on the face plate, if you are going with the 18 mm, converted dimensions should be close enough. Just make sure that anything that is flush with the inside is measured as such.

      BTW, there’s a thread somewhere in a past iteration of the forum talking about various “cut list” programs, and if you go up to the search bar and put in cut list, you’ll find a write up out on the main page of one that Nick (Toid) recommends. I believe the program can be set for either metric or imperial.

      **Addendum – I looked at that program and it is in imperial measure. The good thing is that once you figure out the sizes in metric, you can then convert back to imperial and use the decimal form to set up the cut list in the program, converting back to metric one last time. With enough decimal digits, there should be little to no error in converting so many times.

       


    • #26211
      Josh Evans
      Participant

      3/4″ is 19.05mm

      18mm is only 1.05mm under whereas 22mm would be 2.95mm over

      as we are not dealing with precision engineering here TBH you might get away with just converting all the dimmention straight to metric and letting the slight differences in final internal volume be as it it. Most people using hand tools will have some varience in their cut dimmentions anyway so CNC cut direct conversion to metric might not be much worse. This isnt a suggestion just a thought aloud!

      Alternatively you could get any parts with critical dimmentions cut over size so you can sand down to fit perfectly upon assembly if that is something your comfortable doing


      Josh Evans, Professional Live Sound Engineer, High End Commercial AV Install Technician
      • #26213
        Sarah Staar
        Participant

        Thanks for the clarification….

        I didn’t realise that the boxes didn’t need to be that accurate….

        I was worried that if the wood was a slightly different thickness and the boxes ended up a slightly different size it might affect the sound quality?

        But from the sounds of it, it doesn’t need to be that exact.

      • #26214
        Josh Evans
        Participant

        Im sure if measured with calibrated mic setup we’d be able to find a difference but in terms of an audible difference to the vast majority of the public a couple of mm shouldnt make much difference, as long as all the edges meet for an air tight seal, thats what matter more

        For a woofer with port tuning anything below around 240/250hz the wavelengths are much bigger than the overall speaker so a mm or 2 wont matter, 240hz has a wavelength 1.43m and they get longer as frequencies get lower

        If you were building a more complex multi way speaker with a mid range driver (for example 600hz-2500hz) that needed its own smaller enclosure within the main cabinet or for some reason a tweeter that isnt already enclosed (if they exist) it would probably matter as you start dealing with frequencies having wavelengths shorter than the dimentions of their drivers respective chamber(s)

        For more context, even if you were batch building speakers to sell the dimmentions still dont have to be exactly precise after conversion they would just have to be consistent unit to unit

        EDIT- Also it’s occured to me that most people dont even think abbout the internal volume they lose when they add bracing and that its usually much more volume change than conversion accuracy losses in this instance


        Josh Evans, Professional Live Sound Engineer, High End Commercial AV Install Technician
      • #26216
        tvor-ceasar
        Moderator

        All I can add is: “What he said. ^”

        There is quite a bit of minutiae that should be considered, but is mostly overlooked. Why? Because up to a certain percentage of volume can be added or subtracted before it really affects the sound quality. So when you are dealing with such minimal differences, that percentage is tiny. That’s why I put that qualifier at the end of my last reply. You should be fine using the 18mm and going more or less straight conversion.


      • #26290
        tvor-ceasar
        Moderator

        Oh, one last thing to mention:
        The thickness of the material affects unwanted resonances in the box. The thinner the material, the more the box can have undesired resonances, which would necessitate more inner bracing to get rid of them. That, in turn, would reduce your interior volume and the vicious cycle would continue – enlarge the box, a little more bracing, a bit more box size… until you balance and by then you’ve strayed away from the original dimensions more than you’d like.

        When using the 18 mm instead of 3/4″, that’s only ~ 1/25″ less, which is actually well within tolerance of the 3/4, which can vary by quite a bit more. So yes, go ahead and use the 18 mm knowing that it is a very compatible size exchange.

        Also, here’s a hint for others when building boxes: the smaller the panel, the more rigid it is for it’s thickness. And if it won’t be subjected to massive pressures, it won’t have the same resonance issues. For example, using a 4″ driver with 2 mm XMAX in a 0.25 CuFt (~7 Ltr) box would be ~9.5″x7.5″x6″ inside, so 3/8″ ply could be used quite sturdily, while using a 10″ driver with 12 mm XMAX in a 2.5 CuFt (~70.8 Ltr) box would be ~20.5″x16.3″x10″ inside and would need at least 3/4″ plywood/MDF with bracing. It’s all a matter of scale and pressures.

        /tangent off

         


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