DIY Flat Panel Speaker Love

[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]

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 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]

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]

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.

[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]

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.

[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]

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]

I'll start experimenting with the 9 1/2 x 14 and see where it starts rolling off on the low end and will try slightly larger if needed.

Something I've been considering instead of the weather strip pressed in between the frame and edge of the panel as in the bertagni, is to use a custom milled wooden frame with a channel that is lined in felt. The frame would be made of two complete halves to where I can line the two halves of a 1/4" x 5/8" channel with 1/16" felt and when the two faces are screwed together, it could be shimmed to where there is just enough pressure to allow the panel to be slid around with moderate force but hopefully allow the perimeter edge to not be so forcefully captive. Hopefully allow a slight increase in low frequency extension. A lot of work but I've got the time and the wood shop facilities to fabricate them for experimentation. I'm sure it's like most neat ideas, a lot of work and sounds good on paper but produces no real advantage.

[Unbiasedsound]

No, thats the only problem is that they dont list the density but it seems to be of higher grade then the standard densities found if local hardware stores. I use to buy all my EPS from Mr.Polystyrene on ebay but he is in the UK and seems to no longer ship to USA.

[Unbiasedsound]

It would be safer to go with the 9-1/2 for 150hz. If you look at most DML panels they are rectangle in shape including Bertagni speakers. It seems to increase the high frequency response. Also the longer the height from the width the more the panel will flex bend which in theory should produce more bass but there is a limit to how tall you can make it which is why I say at max double the width. I prefer 4-6inches taller then the width.

[allenb]

Have you been able to find the density of the eps from these ebay sources?

[allenb]

I'll be experimenting with variations of the smaller panel but have a couple of questions related to the frequency range I'm shooting for. I'm looking for a crossover point of 150 hz. In your estimation, will the 6" width allow going that low? Or, would the 9 1/2" you posted have a better chance making it down that low? I'm also ok shooting for 200 hz if neither panel is large enough.

Second question is what benefit is it to make the panel taller than it's width?

Thanks,
Allen

[Unbiasedsound]

Also I am not saying that you cant make your panel 12X12 as larger panels will sound fuller and play lower but some highs will suffer the larger the panel becomes.

This EPS is 9-1/2inch width X 14inch height X 1/2 thick.

https://www.ebay.com/itm/293551185538?_trkparms=amclksrc%3DITM%26aid%3D1110010%26algo%3DHOMESPLICE.DISCCARDS%26ao%3D1%26asc%3D20200818141627%26meid%3D4d9a8b2d49ba4d4c82d5036009777b27%26pid%3D101110%26rk%3D1%26rkt%3D1%26sd%3D313071588553%26itm%3D293551185538%26pmt%3D1%26noa%3D0%26pg%3D2563228%26algv%3Ddefault%26brand%3DUnbranded&_trksid=p2563228.c101110.m1982&amdata=cksum%3A2935511855384d9a8b2d49ba4d4c82d5036009777b27%7Cenc%3AAQAGAAAB4BcY%252BPGj0%252Fw3tw%252FEqsmVcHQZEcNlKURXf1JOEXJTljA9E6rktOIkhfPgryltpc%252BhdYeRdjm0Tu3mxmTAomIy%252BAVSMtW2IUBlJkoM8jS%252BeetWZsJlyIO6IueaBhUMg6k9%252BblD6th3OVJcwwWOrlbg3M8z57R88SSN3zALyRZleLetrKzayumnG3tHAGyHxH5MfcRM4dmMljlrZWto1bVWwcnI23v%252FMef1jg%252FKlt7ecM4VQDT%252Bs%252FdJjWtqAkV%252BlJL%252BKlR0hZKLexdyofVxOdorr95U5FJVe4HSmAwfOTjhgT6ldL%252BygZrOZ58DJyGAHy4EP73METtDvGQgCJFk6IjcHJaZBscoLQ2sHHVfBTW7GghQ8B0UWiZ7egNUm3S4DEjALGyY0KIvzQBSr3l7%252Be2l63JSHxW%252FtpyxaLM8CQpYn2kbMIGsNvEhe8BmZ9nHLQjHSyGphAJ%252B0eGVQvbE%252FX8vaSMhsdd5QLlJ%252Fu74P%252FZ23u7PO%252FvIy8Zis4iE1rFxognSVXnhSGD06WBtNzkChL9r87QFJBBhQAi2OUYwlDdkX1Im3yssfGvy%252FBWpPL9aiT%252BFAA0SBmTieBBrBSVMtGr1zK6aoRlJGFev9dZ6bvDRz3hLeDBbNIGUilGO9x%252FAXs5ikA%253D%253D%7Campid%3APL_CLK%7Cclp%3A2563228