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  • bracing question

    in a vertically oriented mtm cabinet, is it a) good, b) bad, or c) doesn't matter, to have a shelf brace which essentially divides the cabinet into two equal halves (starts at the rear of the cabinet and reaches almost all the way to the back of the tweeter)? i know volume-wise it shouldn't make any difference to the woofers whether theres one in (for instance) .5 ft^3, or two in 1 ft^3, but i'm wondering if there are other factors at play (backwave interactions, etc).

  • #2
    Re: bracing question

    I'm sure I'm going to be in the minority here, but all the bracing is designed to do is make the cabinet less resonant. As long as you have a piece that ties the front to the back, and the sides to each other, you need not do anything more elaborate than necessary.

    If it's a vented design, I'd leave them in "common airspace". If they are sealed, it probably won't make any difference if you add some stuffing to dampen the back wave.
    Lou's Speaker Site [speakers.lonesaguaro.com]
    "Different" is objective, "better" is subjective. Taste is not a provable fact.
    Where are you John Galt? I may not be worthy, but I'm ready.

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    • #3
      Re: bracing question

      Originally posted by LouC View Post
      I'm sure I'm going to be in the minority here, but all the bracing is designed to do is make the cabinet less resonant. As long as you have a piece that ties the front to the back, and the sides to each other, you need not do anything more elaborate than necessary.
      .
      +1.
      www.billfitzmaurice.com
      www.billfitzmaurice.info/forum

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      • #4
        Re: bracing question

        Some people go nuts with bracing some don't. I have yet to have the time and patience myself, or see someone else build two of the exact same speaker, one without bracing and one with insane extra bracing and see how audible the effects are.

        But yea what Lou says is pretty accurate, what you're doing when you brace is dividing each large panel into smaller sections that will each individually resonate at a much higher frequency (hopefully outside of the band of the mid range and bass drivers. (This may not be 100% correct per physics, but thats pretty much whats going on.)

        By that logic a piece of plywood or a dowel rod connecting side to side and front to back is more than good enough. On the other hand some people enjoy bracing stuff, it gives you a warm fuzzy feeling inside to know that if Godzilla attacks tomorrow and happens to stomp on your house that your speakers will probably still be ok. So its really up to your personal taste and discretion, a little bracing never hurts, but if it'll make you feel better, go nuts. Just leave plenty of room for air and sound waves to move about inside the cabinet in an unrestricted manner.

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        • #5
          Re: bracing question

          Originally posted by evilskillit View Post
          what you're doing when you brace is dividing each large panel into smaller sections that will each individually resonate at a much higher frequency (hopefully outside of the band of the mid range and bass drivers.
          That's the accepted theory, but IMO more of a result of than the reason for bracing effectiveness. The smaller the free panel area the more resistance it has to being vibrated by the air pressure exerted against it by the driver. With sufficiently small area/adequate stiffness it won't be able to vibrate enough to add audible coloration. Making the panel stiffer also raises its resonant frequency, but it's the resistance to vibration that gives the desired result, not the higher resonance that results when you do so.
          www.billfitzmaurice.com
          www.billfitzmaurice.info/forum

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          • #6
            Re: bracing question

            thanks for the responses so far, but i think maybe i wasn't clear enough in my question and thats caused everyone to misunderstand. i wasn't asking if i needed bracing, or what it was for, etc. in other words, i wasn't asking if it's good, bad, or doesn't matter to have the kind of brace i described, as opposed to no brace at all. the jist of the question was meant to be whether or not it would be good, bad, or didn't matter to have something nearly dividing an mtm cabinet in half. in this particular situation that "something" just happens to be a brace. but the effects of a brace as a brace (or lack thereof) are not meant to be the issue here.

            to put it visually, would the situation shown in picture 1 have any positive or negative effects as compared with the situation shown in picture 2 and/or picture 3, not related to the piece in question's effectiveness as a brace.

            i feel like i'm rambling, but hopefully someone out there can make sense of my ramblings. oh, and yea, i should have mentioned that this is in regards to a sealed cabinet, so impeding airflow in or around a port isn't a factor here.


            picture 1


            picture 2


            picture 3

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            • #7
              Re: bracing question

              It makes sense to me that you'd not want to divide the cabinet exactly in half--that a slightly off center brace would produce two different resonances of lower amplitude. Better still your second illustration where ther is even less ability to resonate.

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              • #8
                Re: bracing question

                Non tecky answer - The more "something" you put inside the enclosure the more that the tuning of the enclosure is affected, which is one of the reasons that LouC suggested just simple dowels(about 1"dia) connecting baffle>back and side>side.

                ie minimum internal addition for maximum effect - corners of cabinets don't need bracing, it is the centers of the panels that can and often do resonate

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                • #9
                  Re: bracing question

                  Originally posted by CokewithLime View Post
                  Non tecky answer - The more "something" you put inside the enclosure the more that the tuning of the enclosure which is one of the resasons that LouC suggested just simple dowels(about 1"dia) connecting baffle>back and side>side.
                  true. i should have mentioned that subtracted volume issues are mostly immaterial in this particular situation too. with the speaker and crossover in question, anything +/- ~4L yields trivial response changes. sheesh, i'm really takin a ride on the failboat with this thead...

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                  • #10
                    Re: bracing question

                    I have found that Lou's guidance works pretty well with one addition - I believe that I notice a difference when I double up on a baffle more than I can few vs. lots of bracing. Below is a pic of a recent design and I use a shelf brace much like you have diagrammed above. You will also see that I have a number of dowels connecting front-back and side-side. Some of the side-side are to hold back stuffing as this is a ML-TL design, but they serve a dual purpose.

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                    • #11
                      Re: bracing question

                      Originally posted by absolootbs View Post
                      true. i should have mentioned that subtracted volume issues are mostly immaterial in this particular situation too. with the speaker and crossover in question, anything +/- ~4L yields trivial response changes. sheesh, i'm really takin a ride on the failboat with this thead...
                      Nah, I've got you. Its just basically everybody understood your initial question as "Is it cool if I put a big brace in the middle of the thing" to which we all replied "yeah bracing is cool".

                      Now you're asking specifically if any of those arrangements are better than any other ones. Without being able to see it in 3 dimensions its hard to say for sure. Chances are there will be little to no difference but from a purely mechanical standpoint the bottom picture is the best because it divides the panels into the smallest portions. I'm not sure whether you're talking about a window brace or just a rib going up the side or what. But the last one is the best as long as you ventilate the brace enough, or its free flowing enough in the first place so as not to break the cabinet up too badly.

                      Let me post a picture of the cabinet I built and how I braced it. Its a TMM instead of an MTM but the nature is similar.

                      In the following picture the cabinet is on it's side, with the front facing you. The top opening (left most opening) is the tweeter, the other two openings are the woofers and the right most opening (bottom) is the crossover housing. If you want to see the rest of the build (bracing) pics etc follow this link.

                      My Waveguide TMM Build



                      PS: I'm not suggesting by any means that my method is the best, but I like it and think it worked out well, plus at least it gives you some idea of what somebody else has done.

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                      • #12
                        Re: bracing question

                        Originally posted by absolootbs View Post

                        to put it visually, would the situation shown in picture 1 have any positive or negative effects as compared with the situation shown in picture 2 and/or picture 3, not related to the piece in question's effectiveness as a brace.
                        Unless the cab is very large, as in loaded with two twelves, there's no appreciable difference. There's also no advantage to shelf bracing, as most of their bracing effect occurs at the corners of the cab, where bracing is of the least, if any, benefit.
                        www.billfitzmaurice.com
                        www.billfitzmaurice.info/forum

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                        • #13
                          Re: bracing question

                          I'm all for bracing. I always do the "knuckle" test, before and after.
                          One brace in the middle all the way from the front to the back, just cut out a small recess for the tweeter magnet. I prefer a ventilated shelf when multiple identical drivers are used in one enclosure. That is, I prefer one common volume regardless if multiple woofers.
                          Last edited by ; 09-18-2010, 02:19 AM.

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                          • #14
                            Re: bracing question

                            I like to do way overkill bracing... that way if the speaker sounds like crud I can use the enclosure as another jack stand for the Mustang :D
                            Craig

                            I drive way too fast to worry about cholesterol.

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                            • #15
                              Re: bracing question

                              Originally posted by PWR RYD View Post
                              I like to do way overkill bracing... that way if the speaker sounds like crud I can use the enclosure as another jack stand for the Mustang :D
                              Like this?
                              Attached Files

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