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Speaker baffle interface and cabinet resonance questions - Getting that last 10%

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  • Speaker baffle interface and cabinet resonance questions - Getting that last 10%

    Hello,
    I am about to built a pair of DIYSG HTM-12 speakers was wondering if there were potential ways I could maximize the quality of the speaker build. Reading around it does appear there are some potential things that could help but I am just wanting to make sure they are correct and ask for feedback.

    1) I was wondering about the speaker driver / baffle interface. I have read that having some dampening material (such as weather stripping or neoprene etc) can help reduce the transmission of vibrations to the speaker cabinet. I could not get it to be a fully floating driver but I was wondering if instead of the driver being simply screwed into the MDF if this design would be beneficial:
    Speaker driver -->
    Dampening material -->
    MDF baffle (drilled through, so no direct contact with the bolts)-->
    Dampening material -->
    1” plywood with T nuts for bolting the speaker to (the plywood could either be cut around the whole speaker cut out, or could be in smaller pieces for each individual bolt hole)

    Do you think that would help isolate the driver from the baffle and be worth doing? Any room for improvement?

    2) I was looking to minimize cabinet resonances and so I have read that the main way to do this is through adding more mass to the walls, adding more bracing to the walls, adding dampening material, absorption.

    Mass: I have looked into constrained layer dampening and using green glue, and so I could potentially put another layer of MDF on the back wall. Would this be beneficial? Any other options / thoughts?

    Bracing: I certainly can add more MDF bracing to the cabinet. Are window braces most effective? Any places that I should avoid putting bracing (i.e. right behind the main driver)?

    Dampening: This is where I haven seen lots of opinions yet have not figured out what truly would be best. I have heard of people using dynamat, roofing felt, industrial floor tiling, rubber gym mats, memory foam, bubble wrap, etc. Would all of these be options? Any personal preferences people have? Also how does this affect the effective volume of the cabinet, like can one go too overboard with this stuff?

    Absorption: The speaker design is a ported design and calls for ~3inches of absorption on the back wall and 1.5inches on the side and to keep the ports clear. I have read that the maximum velocity of standing waves is in the middle of the cabinet, so then hanging the absorption material ½ way through the cabinet would be most effective would it not? But are their down sides to this? Also if it was in the way of the direct path from the speaker to the ports would that change the port tuning, or is that all about the internal volume and should not be a problem? Also, more absorption would change the effective volume and thus change the port tuning so maybe not changing the absorption would be ideal? I have also heard that there are significant downsides with over stuffing a speaker yet I have not personally made any speakers so what should I be looking for if that occurs?

    Ok, I think those were the main things that I was looking into to try and squeeze that final 10% of performance out of this DIY build. I would appreciate any feedback on the proposed alterations and also let me know if there are any glaring ways I could further improve on the cabinet making.

    Thanks!

  • #2
    IME isolating the driver doesn't do anything. Vibration isn't sourced from the driver frame, it's sourced by sound waves. You do want to eliminate any vibration between the frame and baffle, which is best accomplished by making that connection as rigid as possible. As for cabinet panel vibrations, those are best controlled by panel to panel bracing. That's what I use, and it allows me to build concert grade subwoofers from 1/2" plywood that don't vibrate at all. WIndow bracing is less effective, and it puts too much material where it doesn't do anything useful. Standing waves were a concern when speakers were four cubic feet or more, sometimes much more. Today's compact speakers don't have standing waves to deal with. Damping in cabs is used to prevent midrange reflections inside the cabinet that if left undamped cause uneven midrange response. One to two inches of cabinet lining is sufficient. Damping material has no effect on the cabinet volume, although using too much lowers Q to the point that it can affect response.
    www.billfitzmaurice.com
    www.billfitzmaurice.info/forum

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    • #3
      Originally posted by billfitzmaurice View Post
      IME isolating the driver doesn't do anything......
      Thanks for the input. So I guess focus more on panel to panel bracing and then use some yet not excessive dampening.

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      • #4
        I did some testing using a phono cartridge as a panel vibration pickup. I found it is more hype than real. My "best" sealed subs are 3/4 MDF with 1/8 ply skin. My current HT sub is 3/4 Baltic Birch ply. Off-center cross braces. As I prefer sealed systems, my boxes are stuffed to a measured .5 Q. I also measured my "monitor" size boxes. 5/8 MDF. No problem. Notice the double box sand filled games have gone from the market. I am sure you can still buy any sort of miracle treatments for inside boxes invented on Madison Ave. rather than in engineering labs. I pay more attention to diffraction as it matters more.

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        • #5
          Originally posted by johnp98 View Post
          So I guess focus more on panel to panel bracing and then use some yet not excessive dampening.
          For sure. A single brace connecting the middle of two opposing panels has the same effect as doubling their thickness, and more is even better. Where the drivers are concerned one way to insure the most rigid possible connection to the baffle, while bracing both the baffle and back, is to use 1x1 braces that span from one or more of the driver mounting holes to the back.

          www.billfitzmaurice.com
          www.billfitzmaurice.info/forum

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          • #6
            Originally posted by billfitzmaurice View Post
            For sure. A single brace connecting the middle of two opposing panels has the same effect as doubling their thickness, and more is even better. Where the drivers are concerned one way to insure the most rigid possible connection to the baffle, while bracing both the baffle and back, is to use 1x1 braces that span from one or more of the driver mounting holes to the back.
            Yeah that seems like a great idea, I had not thought of that. But then it would be attached with screws eh? As it would go though the front baffle and then into the cross beam that goes to the back panel. For whatever reason in my mind using bolts into tnuts seems more secure, but maybe right into the cross beam would be better. Also, should there be no braces directly behind the woofer for a certain amount of distance?

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            • #7
              Screws are fine so long as there's at least an inch of penetration into wood. Braces behind the woofer are fine, they're too small in cross section to reflect the longer wavelengths that the woofer produces. I haven't used T-nuts for quite a few years, they strip too easily. When I have a baffle that's a half inch thick I put additional small blocks of 1/2" plywood behind the baffle for screw retention. You can see an example of that in this view of one of my cabs with the back not yet attached.
              Click image for larger version

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              www.billfitzmaurice.com
              www.billfitzmaurice.info/forum

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              • #8
                I use hurricane nuts. Never had an issue with them stripping. Maybe they are a bit better made than big box crappy T-nuts. They work a lot better in MDF. As I use smaller drivers, I don't want extra thickness around the back of the cone. Big honkers like above, not an issue at all and gluing in some scrap wood is free. Even making the front baffle double thickness if it can work out on the cut sheet.

                In the above picture, the braces not being in line reduce their effectiveness quite a bit. Getting around the back of the horn does require some creativity though. I would have brought down one off center all the way. Don't know what use those corner boards are for. If it is a PA for road use, I would have blocked the corners with 1 x 1. My goal would be to survive a 4 foot drop onto the floor.

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                • djg
                  djg commented
                  Editing a comment
                  The most important bracing in that cab is the 3 or 4 front to back braces. Supports the baffle around the heavy driver and braces the largest surface, the back panel.

                  The illustration was posted to show the extra blocks at the woofer attach points, not as an example of bracing.

              • #9
                Originally posted by tvrgeek View Post
                I use hurricane nuts. Never had an issue with them stripping. Maybe they are a bit better made than big box crappy T-nuts. They work a lot better in MDF. As I use smaller drivers, I don't want extra thickness around the back of the cone. Big honkers like above, not an issue at all and gluing in some scrap wood is free. Even making the front baffle double thickness if it can work out on the cut sheet.

                In the above picture, the braces not being in line reduce their effectiveness quite a bit. Getting around the back of the horn does require some creativity though. I would have brought down one off center all the way. Don't know what use those corner boards are for. If it is a PA for road use, I would have blocked the corners with 1 x 1. My goal would be to survive a 4 foot drop onto the floor.
                Dunno. True the stiffness isn't what it could be, but sometimes by not putting the braces right in line, you make a vibration absorber.
                Francis

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                • #10
                  Could you also make the cross bracing line up and support the driver magnet? Would that add extra support to the driver as then it would be anchored to the front but also resting on the cross bracing?

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                  • #11
                    Originally posted by johnp98 View Post
                    Could you also make the cross bracing line up and support the driver magnet? Would that add extra support to the driver as then it would be anchored to the front but also resting on the cross bracing?
                    You might, although most drivers don't need the extra support, and you might make a nice buzzing sound of the driver against the brace, unless you're careful.
                    Francis

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                    • #12
                      Originally posted by tvrgeek View Post
                      In the above picture, the braces not being in line reduce their effectiveness quite a bit.
                      Not in my experience. When I prototype a cab I make sure that the bracing is more than adequate.
                      Don't know what use those corner boards are for.
                      They're called 'ports', thought to be more accurate they're port ducts.
                      I would have blocked the corners with 1 x 1.
                      That's the last place that needs bracing, being the strongest point of the cabinet. It's a waste of wood, weight and time to use corner blocks.
                      My goal would be to survive a 4 foot drop onto the floor.
                      I've seen a reliable report of one of my cabs falling off the back of a pickup truck at 30MPH, suffering only road rash for the experience. I took their word for it, never bothered to try it for myself.
                      The illustration was posted to show the extra blocks at the woofer attach points, not as an example of bracing.
                      It's both. I didn't feel like scrolling through a few hundred pictures looking for one that only showed the blocks, so I posted the first one I came across that showed the blocks at all. That is a picture of the actual bracing scheme of a Simplexx 15.
                      www.billfitzmaurice.com
                      www.billfitzmaurice.info/forum

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                      • #13
                        Originally posted by fpitas View Post

                        You might, although most drivers don't need the extra support, and you might make a nice buzzing sound of the driver against the brace, unless you're careful.
                        Do you think that a liberal amount of dampening material would be sufficient? Or would that be potentially opening a can of worms?

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                        • #14
                          Originally posted by johnp98 View Post

                          Do you think that a liberal amount of dampening material would be sufficient? Or would that be potentially opening a can of worms?
                          I think you're trying to solve a problem that doesn't exist. But if you want to try it, yes, maybe a rubber hose around the brace would keep the arrangement quiet.
                          Francis

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                          • #15
                            I don't support the magnet on LAB 15 drivers that weigh 24 pounds, and that's in pro-sound cabs that get moved from gig to gig.
                            www.billfitzmaurice.com
                            www.billfitzmaurice.info/forum

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