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New DIY Mid High (90deg) - AKA PM90
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<blockquote data-quote="Peter Morris" data-source="post: 138990" data-attributes="member: 652"><p>Re: New DIY Mid High</p><p></p><p></p><p></p><p><span style="font-family: 'Calibri'"><span style="font-size: 12px"><span style="color: #000000">Sound from the back of the box in simple terms is mainly caused by the defection of the box walls under pressure and exacerbated by resonate issues.</span></span></span></p><p></p><p><span style="font-family: 'Calibri'"><span style="font-size: 12px"><span style="color: #000000">For its weigh this is a very ridge box, and I have not noticed any issues with sound from the rear of the box. </span></span></span></p><p></p><p><span style="font-family: 'Calibri'"><span style="font-size: 12px"><span style="color: #000000">By the way of simple example to demonstrate where you need to concentrate your box design efforts … and because the sums for supported round plates are simpler than supported square plates; the defection at the centre of a circular plate under pressure supported on the edges like this box = 0.696pr^4/Et^3</span></span></span></p><p></p><p><span style="font-family: 'Calibri'"><span style="font-size: 12px"><span style="color: #000000">Where:</span></span></span></p><p><span style="font-family: 'Calibri'"><span style="font-size: 12px"><span style="color: #000000">t =the thickness of the plate</span></span></span></p><p><span style="font-family: 'Calibri'"><span style="font-size: 12px"><span style="color: #000000">r = the radius of the plate</span></span></span></p><p><span style="font-family: 'Calibri'"><span style="font-size: 12px"><span style="color: #000000">p= the pressure</span></span></span></p><p><span style="font-family: 'Calibri'"><span style="font-size: 12px"><span style="color: #000000">E = Young’s modulus – a constant for the material</span></span></span></p><p></p><p>Even though we are not using round plates the principle is the same - <span style="font-family: 'Calibri'"><span style="font-size: 12px"><span style="color: #000000">If you look at this equation what you see is defection is proportional to the radius of the plate to the power of 4 and the thickness of the material to the power of 3. </span></span></span></p><p></p><p><span style="font-family: 'Calibri'"><span style="font-size: 12px"><span style="color: #000000">Sooo if you reduce the unsupported width of the panels and increase the thickness of the material there is a dramatic effect on the wall deflection and sound being transmitted through the box walls. </span></span></span></p><p></p><p><span style="font-family: 'Calibri'"><span style="font-size: 12px"><span style="color: #000000">The other things you need to do is minimize resonances and standing waves. Parallel walls can cause issues, and once again this box has a lot of angles and not many parallel walls.</span></span></span></p><p><span style="font-family: 'Calibri'"><span style="font-size: 12px"><span style="color: #000000"></span></span></span></p><p><span style="font-family: 'Calibri'"><span style="font-size: 12px"><span style="color: #000000">In terms of resonance the trick with a wooden box is to try and keep any resonant modes out of the operating frequency range of the box, in this case between 100 and 700Hz.</span></span></span></p><p></p><p>You need <span style="font-size: 12px"><span style="color: #000000"><span style="font-family: 'Calibri'">to make the box as strong as possible so that it does not flex, but not use so much wood and bracing that it becomes too heavy .... I'm not sure you need the rear centre brace as shown but its defiantly not doing any harm. There also needs to be some bracing on the side panels. It would be best if you used a cross brace from side to side, but then you would not be able to get the 12” speakers in and out.</span></span></span></p><p><span style="font-size: 12px"><span style="color: #000000"><span style="font-family: 'Calibri'"></span></span></span></p><p><span style="font-size: 12px"><span style="color: #000000"><span style="font-family: 'Calibri'">I gave all of this quite a bit of thought even custom making the pole mount to join the bottom of the box to the 12" enclosure, making it as strong and ridge as possible without adding weight.</span></span></span></p></blockquote><p></p>
[QUOTE="Peter Morris, post: 138990, member: 652"] Re: New DIY Mid High [FONT=Calibri][SIZE=3][COLOR=#000000]Sound from the back of the box in simple terms is mainly caused by the defection of the box walls under pressure and exacerbated by resonate issues.[/COLOR][/SIZE][/FONT] [FONT=Calibri][SIZE=3][COLOR=#000000]For its weigh this is a very ridge box, and I have not noticed any issues with sound from the rear of the box. [/COLOR][/SIZE][/FONT] [FONT=Calibri][SIZE=3][COLOR=#000000]By the way of simple example to demonstrate where you need to concentrate your box design efforts … and because the sums for supported round plates are simpler than supported square plates; the defection at the centre of a circular plate under pressure supported on the edges like this box = 0.696pr^4/Et^3[/COLOR][/SIZE][/FONT] [FONT=Calibri][SIZE=3][COLOR=#000000]Where:[/COLOR][/SIZE][/FONT] [FONT=Calibri][SIZE=3][COLOR=#000000]t =the thickness of the plate[/COLOR][/SIZE][/FONT] [FONT=Calibri][SIZE=3][COLOR=#000000]r = the radius of the plate[/COLOR][/SIZE][/FONT] [FONT=Calibri][SIZE=3][COLOR=#000000]p= the pressure[/COLOR][/SIZE][/FONT] [FONT=Calibri][SIZE=3][COLOR=#000000]E = Young’s modulus – a constant for the material[/COLOR][/SIZE][/FONT] Even though we are not using round plates the principle is the same - [FONT=Calibri][SIZE=3][COLOR=#000000]If you look at this equation what you see is defection is proportional to the radius of the plate to the power of 4 and the thickness of the material to the power of 3. [/COLOR][/SIZE][/FONT] [FONT=Calibri][SIZE=3][COLOR=#000000]Sooo if you reduce the unsupported width of the panels and increase the thickness of the material there is a dramatic effect on the wall deflection and sound being transmitted through the box walls. [/COLOR][/SIZE][/FONT] [FONT=Calibri][SIZE=3][COLOR=#000000]The other things you need to do is minimize resonances and standing waves. Parallel walls can cause issues, and once again this box has a lot of angles and not many parallel walls.[/COLOR][/SIZE][/FONT] [FONT=Calibri][SIZE=3][COLOR=#000000] In terms of resonance the trick with a wooden box is to try and keep any resonant modes out of the operating frequency range of the box, in this case between 100 and 700Hz.[/COLOR][/SIZE][/FONT] You need [SIZE=3][COLOR=#000000][FONT=Calibri]to make the box as strong as possible so that it does not flex, but not use so much wood and bracing that it becomes too heavy .... I'm not sure you need the rear centre brace as shown but its defiantly not doing any harm. There also needs to be some bracing on the side panels. It would be best if you used a cross brace from side to side, but then you would not be able to get the 12” speakers in and out. I gave all of this quite a bit of thought even custom making the pole mount to join the bottom of the box to the 12" enclosure, making it as strong and ridge as possible without adding weight.[/FONT][/COLOR][/SIZE] [/QUOTE]
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