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<blockquote data-quote="Loren Jones" data-source="post: 59770" data-attributes="member: 829">Re: B&amp;C Sub designsKip,The&nbsp; baltic birch plywood grades refer to the presentability of the surface veneer layer.&nbsp; It does not reflect upon the structural integrity of the product.&nbsp; The grade should be essentially irrelevant for building pro sound subwoofers that will presumably be coated with something thick and black.As far as trying that design to get away from port choking that you see in your current cabinets loaded with SW115 drivers, I would be a little circumspect.&nbsp; The port area in that design is around 265 sq cm.&nbsp; The Sd of an 18&quot; driver is around 1200 sq cm.&nbsp; Additionally the port is not flared in any way.&nbsp; Finally the SW115 is a monster of a driver capable of a real serious amount of excursion (xvar is 16mm).&nbsp; I know only a little about this subject (having learned some from being around the forums here) but would bet that an 18SW115 driven hard in a cabinet with a port area around 21% of the driver Sd will suffer from significant port compression to the extent that if you were driving a great driver like that with enough power to approach its limits you will have enough port compression that your performance will be closer to that of a sealed box.&nbsp; With a lesser driver it would be less of an issue but with a top notch driver like that I think you will find you are wasting a fair bit of it&#039;s performance advantage due to port compression.Port area up to 80% of driver Sd has been recommended and you might be in decent shape at 40% to 50% of Sd especially if the port is flared.&nbsp; But a straight profile port with only 21% of the area of Sd using that driver isn&#039;t going to give you the results you are looking for.&nbsp; I would refer you to Phil Graham&#039;s article on subwoofer port behavior here <a href="http://www.passbandllc.com/articles/" target="_blank">PASSBAND, llc | Articles</a> which is essentially my only source of knowledge on this subject (along with getting some help from Phil in the past on designing a reflex enclosure to help minimize port compression problems).&nbsp; Phil or others please chime in and correct me where I might be wrong since I am certainly no expert.Best luck,Loren Jones</blockquote>

[QUOTE="Loren Jones, post: 59770, member: 829"] Re: B&C Sub designs Kip, The baltic birch plywood grades refer to the presentability of the surface veneer layer. It does not reflect upon the structural integrity of the product. The grade should be essentially irrelevant for building pro sound subwoofers that will presumably be coated with something thick and black. As far as trying that design to get away from port choking that you see in your current cabinets loaded with SW115 drivers, I would be a little circumspect. The port area in that design is around 265 sq cm. The Sd of an 18" driver is around 1200 sq cm. Additionally the port is not flared in any way. Finally the SW115 is a monster of a driver capable of a real serious amount of excursion (xvar is 16mm). I know only a little about this subject (having learned some from being around the forums here) but would bet that an 18SW115 driven hard in a cabinet with a port area around 21% of the driver Sd will suffer from significant port compression to the extent that if you were driving a great driver like that with enough power to approach its limits you will have enough port compression that your performance will be closer to that of a sealed box. With a lesser driver it would be less of an issue but with a top notch driver like that I think you will find you are wasting a fair bit of it's performance advantage due to port compression. Port area up to 80% of driver Sd has been recommended and you might be in decent shape at 40% to 50% of Sd especially if the port is flared. But a straight profile port with only 21% of the area of Sd using that driver isn't going to give you the results you are looking for. I would refer you to Phil Graham's article on subwoofer port behavior here [url=http://www.passbandllc.com/articles/]PASSBAND, llc | Articles[/url] which is essentially my only source of knowledge on this subject (along with getting some help from Phil in the past on designing a reflex enclosure to help minimize port compression problems). Phil or others please chime in and correct me where I might be wrong since I am certainly no expert. Best luck, Loren Jones [/QUOTE]

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