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  • Unbiasedsound
    replied
    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.
    Last edited by Unbiasedsound; 10-21-2021, 10:34 PM.

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  • allenb
    replied
    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.

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  • Unbiasedsound
    replied
    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.

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  • Unbiasedsound
    commented on 's reply
    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
    replied
    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.

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  • allenb
    replied
    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?

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  • Unbiasedsound
    replied
    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.

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  • allenb
    replied
    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.

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  • Unbiasedsound
    commented on 's reply
    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
    commented on 's reply
    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
    replied
    Have you been able to find the density of the eps from these ebay sources?

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  • allenb
    replied
    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

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  • Unbiasedsound
    commented on 's reply
    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/29355118553...Cclp%3A2563228

  • Unbiasedsound
    replied
    Originally posted by allenb View Post

    Thanks so much for the quick replies. The reason I had settled on the 12 x 12 in the 1/4" thickness is from advice you had given Listencarefully a few pages back when he had built a pair. So, it appears you have done additional testing and found the 1/2" thickness in a narrower width is advantageous over a 12 x 12? One would think such a small panel in that thickness would have zero flex and would instead act as a solid piston up until wavelength became shorter than it's width but maybe that provides an improved acoustic performance.

    Have you built a few of these and is definitely your preference for a mid that can reach down to 150 hz up through the normal upper mid frequencies?

    It will be so much easier to access the 1/2" EPS compared to the 1/4!

    Are you still advising the 2lb density with a thicker, smaller panel? Or will a lesser density suffice?

    Last question. Are you still suggesting the TEAX19C01-8 exciter for these small panels?

    My apology for the multiple questions but want to get this right!

    Thanks,
    Allen
    I explained on post #1392 and 1394 in more detail of why I changed my panels design. Its because you cant defy physics as DML's are very similar to conventional cone drivers. Less flex (stiffer)=better highs while more flex= better bass so you have to find a balance.

    3 major factors that effect the frequency response of DML panels.

    1. Type and size of exciter used as larger exciters have more bass while smaller exciters have better highs but less bass. This is physics and was explained in earlier post.

    2. Density of panel as the higher the density the better the high frequencies while lower densities will produce more bass but less highs.

    3. Size of panel as larger panels will produce more bass but the higher frequencies will suffer while smaller panels will produce less bass but better high frequency response.

    There are usually compromises when using a full range driver and you have to find the right balance for your application.

    2-3lbs of density with 1/2 thickness. Higher (4-5lbs) the density the better the high frequencies BUT the higher the density the less efficient they become due to being to dense. Again you have to make compromises. What works for my design might not work for your design.

    Oh yes most def. the TEAX19C01-8 is the best when it comes to balance of highs, mids and bass as this is my go to exciter for all my designs. I dont like to mention this because P.E will raise the price. LOL

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  • allenb
    replied
    Originally posted by Unbiasedsound View Post
    There are 1/4 thickness on ebay but I prefer the 1/2 over 1/4 as the 1/2 sounds more full while the 1/4 sounds more thin. As for the width of the panel 12 inches is too wide/large..... A small panels ideal width should be around 5-8 inches give or take a few inches, while the height can be the same and or at max double the width. This is the reason I recommended the 6X10X1/2 EPS.

    Also ideal DML panel height placement when you are sitting down is below ear level. DML's have very wide dispersion patterns so if the panel is to tall the high frequencies tend to go over your head.

    To many people watch Tech Ingredients vids and think that there panels should be placed higher up above ear level which is not the ideal height placement.
    Thanks so much for the quick replies. The reason I had settled on the 12 x 12 in the 1/4" thickness is from advice you had given Listencarefully a few pages back when he had built a pair. So, it appears you have done additional testing and found the 1/2" thickness in a narrower width is advantageous over a 12 x 12? One would think such a small panel in that thickness would have zero flex and would instead act as a solid piston up until wavelength became shorter than it's width but maybe that provides an improved acoustic performance.

    Have you built a few of these and is definitely your preference for a mid that can reach down to 150 hz up through the normal upper mid frequencies?

    It will be so much easier to access the 1/2" EPS compared to the 1/4!

    Are you still advising the 2lb density with a thicker, smaller panel? Or will a lesser density suffice?

    Last question. Are you still suggesting the TEAX19C01-8 exciter for these small panels?

    My apology for the multiple questions but want to get this right!

    Thanks,
    Allen

    Leave a comment:

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