DIY Flat Panel Speaker Love

[Unbiasedsound]

Since you are only using your panels at 150hz then your method would be ok. If using it at full range the more low end frequency and at high volume levels the more the panels "VIBRATE" and the stronger the vibrations the more securely (tighter) you need to adhere the panels to the frame so it does not move.

The foam basically acts like the surround on a conventional cone speaker which is to hold the diaphragm in place and add some dampening to the edges just like a BMR driver. You can use different types of surrounds like foam, rubber, and cloth. This is why I stress that the physics are very similar to conventional cone drivers.

[allenb]

We'll, for sure, stuffing a foam strip around the channel perimeter that is oversized would be much simpler and if there is a need for a good, secure edge then this is the way I will go. The felt method would have been a lot of additional work.
One thing I worry about is even with the foam pressed in on the 1/2" edge of the perimeter, since there will be at least a 1/4" of panel within the channel groove, could this vibrate in the groove at certain frequencies? Or, with sufficient pressure pushed in against the panel perimeter by the foam strip, would that pretty much eliminate that possibility?

[Unbiasedsound]

It will still vibrate within the groove as the pressure of the foam is not sufficient enough to completely stop all the vibrations. The foam combined with pressure acts like damping or crossover where it reduces the vibrations (example like 12db) but it wont completely stop it.

If you want some of the frequencies to reach the edge all you have to do is cut the foam into 1 inch strips and leave 1/4-1inch gaps inbetween. This technique will let some of the higher frequencies reach the edge.

[Unbiasedsound]

Bertagni uses a similar technique but instead of cutting the foam into strips they shape the edge of the EPS panel leaving 1 inch gaps in between.

[Unbiasedsound]

This pic shows the gaps in between so only 1 inch is in contact with the foam behind it. You can do it this way or you can cut the foam into 1 inch strips. For me its easier to cut the foam then it is to shape the edges of the panel like in the pic.

[allenb]

Interesting technique. A couple of observations. The foam in the cutout voids does not come up to full depth of the panel.

Also, the frame looks like it doesn't sandwich the perimeter edge of the panel at all and the only retaining force is the foam to keep the panel from sliding in or out which makes sense.

So, when using the frost king foam. Use the type without adhesive? I can't envision trying to stuff foam into the smaller space without adhesive sticking to the one side.

[Unbiasedsound]

Yes that is how the technique works as the foam is used as damping as well as surround support. Anything thing that is not touching the foam will have less damping properties so that some of the high frequency vibrations are able to pass easier to the edges.

Bertagni does not use sandwich technique on the perimeter edge and you dont have to use it as there are many ways to adhere the eps panel to the frame. There are 3 ways to do it. One is sandwich which is the most secure but has the most damping, second is like Bertagni in which only one side (the back side) uses the foam. 3rd. Is to attach frost king foam to the "SIDES" around the whole panel.

Technically the proper way to use Frost king is to adhere both sides of the frost king foam using one side to adhere to the eps panel and the other side to the frame, the same way a conventional cone drivers surround is adhered to the driver cone and to the frame with some type of adhesive.

[allenb]

So, the Bertagni in the photo you posted, the foam surround is adhered to the frame and to the back side edge at a width as wide as the cutouts and is not protruding into the cutouts?
How thick do you think this band of adhesive backed foam surround is?

[Unbiasedsound]

Yes......not sure exactly how thick the foam but my guess is around 3/4-1inch. thick. Also thicker the foam equals more damping while thinner the foam less damping. For my (1/2inch thick) panels i use the 3/16inch thick by3/8 wide Frost King rubber foam as they come in different sizes for you to choose. If you need more damping just go one size larger. Also the larger the panels the larger the foam surrounds need to be to support the heavier panels.

[allenb]

Ok, I'm having a complete block and not able to envision how the foam surround is existing in relation to the frame and the panel. Let me give you a verbal visual example of what I thought was the layout.

Suppose we have a 9" x 14" x 1/2" panel laying on a table. Next to one edge of it we have a 1/2" thick x 2" wide by 9" long board laying adjacent to the 9" wide end of the panel. Now, we lay our adhesive backed foam surround down on top of the two pieces with half of the width of the adhesive foam surround laying down one edge of the panel and the other half laying down the length of the board. The board being one member of the frame. In this layout, the foam bridges the frame and the panel with a small gap in between the two.

Is this how you are intending the foam surround to be used?

[Unbiasedsound]

No, but I am not saying you cant use it that way as like I said before in my other post that there are many ways you can mount the eps panel to the frame with the frostking foam as there is no really right or wrong way just personal preference.

The way I do it is the foam goes inbetween the gap between the frame and the panel sides (thickness).

[allenb]

The way I do it is the foam goes inbetween the gap between the frame and the panel sides (thickness).

Ok after much thought on this, this will be the method I experiment with. A question on how you do your frame with this in mind. Does your frame sandwich the area where the foam resides in the gap and a little of the first bit of panel or is the foam surround and all of the panel free floating with the only locating force keeping the panel centered on the surround being the pressure of the surround exerted on the edge of the panel?

[Unbiasedsound]

Its hard to explain but its similar to this pic >

[Unbiasedsound]

Found a better pic. This new version of Bertagni speakers use the foam surround all around the sides of the panel the same way I do it.

[allenb]

Ok, understood. The foam pressed into the gap is the only force keeping the panel centered within the frame and must have enough force to prevent the panel from eventually relocating itself in or out of center in relation to the foam surround due to vibration.

So, with that said, with the 3/16" foam thickness you use for your surround, how much less is the gap you utilize (less than 3/16") so I can get an idea of how much the foam will compress to ensure I have enough holding force to prevent the panel from moving in or out of the frame due to normal vibration? Would a 1/8" gap between frame and EPS panel allow enough compression when inserting the 3/16" foam in the gap?

[Unbiasedsound]

The compression does not need to be that high it just has to fit smug enough so that the panel does not fall out of the frame when placed upside down. Plus you have to glue both ends of the foam one to the panel and the other side to the frame.