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Dayton BR-1 foam density

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  • Dayton BR-1 foam density

    Hello, I would like to know which is the correct density of the foam used in the kit Dayton BR-1 since I can only find information about its thickness which is 1-1/2" but not about its density which I understood is equally important.

    Can somebody help me (also in understanding how much using a foam with "wrong" density can affect the sound)?

  • #2
    Did you not buy the kit (use what they gave you)? Line internal surfaces w/it.

    Density (like lbs. or oz./cu.ft.) applies to stuffing (like polyfill or fiberglass), not lining, really.
    Mostly what matters is that you use open-cell (as opposed to closed-cell) foam. That means you can breathe through it.

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    • #3
      Originally posted by Chris Roemer View Post
      Did you not buy the kit (use what they gave you)? Line internal surfaces w/it.

      Density (like lbs. or oz./cu.ft.) applies to stuffing (like polyfill or fiberglass), not lining, really.
      Mostly what matters is that you use open-cell (as opposed to closed-cell) foam. That means you can breathe through it.
      Sorry, I didn't specify, I bought these speakers built whit Dayton BR-1 kit used, and I wanted to replace the internal foam since it is ruined in a sort of DIY restoration attempt. That is why I was asking this. So you assure me that different densities of the foam used will not change the frequency absorbed by it? Or maybe even if it changes, it will be just negligible on the final result?

      Edit: can it be safe to assume the one used with this kit (and thus in this video https://www.youtube.com/watch?v=c-N_vx6oOVE&t=612s) is this one https://www.parts-express.com/acoust...ul-94--260-516

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      • #4
        The foam is pretty non-critical, as long as it's open cell. It's just there to absorb some of the internal standing waves. 1.5" or 2" thick open-cell eggcrate foam is the usual.
        Francis

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        • #5
          Can I ask what changes increasing the foam tickhness? More bass frequencies are absorbed?

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          • #6
            Originally posted by mt196 View Post
            Can I ask what changes increasing the foam tickhness? More bass frequencies are absorbed?
            Yes, the foam is absorbtive, so making it real thick will impact the bass. Specifically, the port output will decrease.
            Francis

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            • #7
              Originally posted by mt196 View Post
              Can I ask what changes increasing the foam tickhness? More bass frequencies are absorbed?
              No bass frequencies are absorbed, it would take a foot or more of foam to do that. Too much damping extends absorption to the lower midrange, with the result being a very dead sounding speaker.
              Specifically, the port output will decrease
              That usually requires completely filling the box, if not compressing it as well. In WinISD you can model the effect by changing Qa. The default value of 100 is a bare box, 50 is lined, 10 is filled, 5 is filled and compressed. How it does what it does in the lows is less about absorption, more about the alteration of Q, which is the result of how the damping affects the impedance.
              www.billfitzmaurice.com
              www.billfitzmaurice.info/forum

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              • #8
                Just to educate me since you seem very expert, which frequencies reflections is absorbing a 3cm thick foam (more or less)?

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                • #9
                  Try to resist this ad copy. Actually, I got some of this in some PE subwoofer kits. I like it. Very sticky, one chance to get it on right. Various thicknesses available to mystify and confuse you. I would say it's "fairly dense".

                  https://www.parts-express.com/sonic-...-x-24--260-520

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                  • #10
                    Originally posted by mt196 View Post
                    Just to educate me since you seem very expert, which frequencies reflections is absorbing a 3cm thick foam (more or less)?
                    All of them, at different levels, with more absorption as frequency is increased. At 3cm you might be reducing 15kHz by 30dB, but 500Hz at only 3dB. As you make the damping thicker you don't lower the frequency at which it's effective, you increase the absorption across the board. Below roughly 500Hz it takes a lot of damping to have any effect, That's why when you see pictures of anechoic rooms the damping material can be three feet or more thick. It's also why bass traps are more properly referred to as midbass traps, because they're too small to have much effect below 80Hz.
                    www.billfitzmaurice.com
                    www.billfitzmaurice.info/forum

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                    • #11
                      Originally posted by billfitzmaurice View Post

                      All of them, at different levels, with more absorption as frequency is increased. At 3cm you might be reducing 15kHz by 30dB, but 500Hz at only 3dB. As you make the damping thicker you don't lower the frequency at which it's effective, you increase the absorption across the board. Below roughly 500Hz it takes a lot of damping to have any effect, That's why when you see pictures of anechoic rooms the damping material can be three feet or more thick. It's also why bass traps are more properly referred to as midbass traps, because they're too small to have much effect below 80Hz.
                      For the record, Dayton answered that the foam used in the kit is 14Kg/m3 , and it is 3,8cm(1-1/2 inch) thick. I bought a 3cm (standard measure, otherwise it would have been 4cm) thick that has a density of 30Kg/m3 (I cannot find anything lower than 25Kg/m3 on ebay). Can I know, roughly, how does that change the absorbed internal reflections? Thanks

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                      • #12
                        Higher density increases damping. I haven't run into a problem with it, even when using mattress topper foam, which is my preferred foam because it works well and is very inexpensive. The only foam I've found to be so dense that it causes over-damping is memory foam.
                        www.billfitzmaurice.com
                        www.billfitzmaurice.info/forum

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                        • #13
                          Originally posted by billfitzmaurice View Post
                          Higher density increases damping. I haven't run into a problem with it, even when using mattress topper foam, which is my preferred foam because it works well and is very inexpensive. The only foam I've found to be so dense that it causes over-damping is memory foam.
                          Just for my knowledge, since you seem expert, I read in the foam I bought that it dampens 0,06(125hz) 0,18(250hz) 0,33 (500hz) 0,49(1000hz) 0,68(2000hz) on a scale of 0-1. How can I espect this behaviour to change? Since the one used by Dayton is more or less half dense, will it be like 0,03 0,9 etc or it is someway a exponentia/logaritmic proportion?

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