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New DIY Mid High (90deg) - AKA PM90
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<blockquote data-quote="Max Warasila" data-source="post: 215791" data-attributes="member: 3845"><p>I suppose I may have just gotten used to the error and correction factors for the port styles that I often use.</p><p></p><p>I don't know where you're calculating those numbers but my point is that you certainly can't build a row with KS28 and SL-Sub horizontally across the truck. It's just less options and a 50" + wide cabinet is starting to get uncomfortably wide. I agree that the stacked carts are the way to go at the size of event that they are designed for, but with the added cart lip width it just means they'll fit horizontally even less often in a truck.</p><p></p><p>I've done a lot of experimentation with how much port you actually <em>need</em> relative to Sd, and I was surprised to find it was often less than 0.5 Sd. It's certainly nice to have that if you can, and with the face area of 22.5" x 48" that would be friendlier to truck pack, I <s>think </s>know you can definitely get the requisite port area to even satisfy the 0.5 Sd crowd.</p><p></p><p>There's a lot of misconceptions about how the physics behind that shape of port work. There are two things in particular that I find relevant. </p><p></p><p>First, the shape that L'acoustics is using is based off of the JBL paper. That shape showed the best results experimentally for port distortion and performance before becoming a noisy hole - but not really by all that much where it matters. Sure, at lower excursions, it shows better distortion performance, but near the limits just a straight walled port with flanges on both sides is already extremely close to the performance of the sculpted port. People seem to think the take away is that you need some crazy flared port geometry to deal with vortex shedding and such. However, I think the real takeaway is that symmetrical port flanging has extremely large benefits, as well as that clearly the primary cause of problems in ports at their extremes is the vortex shedding. One of the reasons that ports adjacent to a cabinet wall isn't just that it functions as an extension of the wall port, but more importantly that there is no vortex shedding happening to cause losses. </p><p></p><p>The second point to make is that at their core ported cabinets are still Helmholtz resonators. That means the critical parameters are the volume of air in the cabinet (C), the mass in the port (L), and the surface area between the two. "Necked" ports, shall we call them, mess are nice because they present a larger apparent surface area for the same mass in the port. The problem is that as the "slug" moves in and out, the impedance matched cross sectional area moves along the flare. It's also possible to have a sudden pressure spike blow out the slug in most necked area of the port, though I have not simulated this explicitly. (Getting more familiar with CFD is somewhere on the stack of TODOs.) I think this, combined with the low tuning, is why SB28 and KS28 seem chuffy despite their fancy "L-Vents" claiming to have laminar flow - I think they actually cause more problems during transients where they help during steady state operation.</p><p></p><p>I think KS28's internal cabinet volume is yea around 350L from what I have been able find and the measurements available. The issue isn't that the volume is too much per driver. I agree that it's almost on the small side per 18" driver - heck I've even seen some questionable cabinets that use nearly 300L per 18" driver (which is is too much, I think). The issue is that it's a single volume which can resonate as one volume because of the appropriate volume behind the vent that connects the two halves of the cabinet. It's not the primary issue I have with the cabinet but I just don't like to design a volume much larger than 300L.</p><p></p><p>I totally agree that getting down low to 30 Hz can really make a difference. However, you don't have to tune a port that low to get that output, and sometimes I think cabinets get tuned lower than ideal in pursuit of that extension. That's usually what I take issue with - I just don't think it's a good design compromise unless you're explicitly trying to make an infra-sub.</p><p></p><p>Personally I've worked a fair bit with B2 and B22. While B2 is definitely a bit of a one-note wonder, I actually find B22 plays quite nicely throughout it's bandpass. The newer motor technology combined with the improvement D80 brought from D12 really helps the driver overcome some of the difficult acoustic impedances presented by the design. I like it way more than I expected to after B2. It's footprint is also smaller than 48" across. <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite6" alt=":cool:" title="Cool :cool:" loading="lazy" data-shortname=":cool:" /></p><p></p><p>SL-Sub is just so much displacement in a single cabinet. It's truly a behemoth.</p><p></p><p>I mean, as far as I can tell SCP is an iPAL implementation. It should be <em>louder</em> that most any other 18" as a result of the increased linear excursion that comes with the platform. I think my all time favorite front loaded double 18" is the Clair CP218, but not everyone can afford the cost that comes with the descendant of the bow-tie.</p></blockquote><p></p>
[QUOTE="Max Warasila, post: 215791, member: 3845"] I suppose I may have just gotten used to the error and correction factors for the port styles that I often use. I don't know where you're calculating those numbers but my point is that you certainly can't build a row with KS28 and SL-Sub horizontally across the truck. It's just less options and a 50" + wide cabinet is starting to get uncomfortably wide. I agree that the stacked carts are the way to go at the size of event that they are designed for, but with the added cart lip width it just means they'll fit horizontally even less often in a truck. I've done a lot of experimentation with how much port you actually [I]need[/I] relative to Sd, and I was surprised to find it was often less than 0.5 Sd. It's certainly nice to have that if you can, and with the face area of 22.5" x 48" that would be friendlier to truck pack, I [S]think [/S]know you can definitely get the requisite port area to even satisfy the 0.5 Sd crowd. There's a lot of misconceptions about how the physics behind that shape of port work. There are two things in particular that I find relevant. First, the shape that L'acoustics is using is based off of the JBL paper. That shape showed the best results experimentally for port distortion and performance before becoming a noisy hole - but not really by all that much where it matters. Sure, at lower excursions, it shows better distortion performance, but near the limits just a straight walled port with flanges on both sides is already extremely close to the performance of the sculpted port. People seem to think the take away is that you need some crazy flared port geometry to deal with vortex shedding and such. However, I think the real takeaway is that symmetrical port flanging has extremely large benefits, as well as that clearly the primary cause of problems in ports at their extremes is the vortex shedding. One of the reasons that ports adjacent to a cabinet wall isn't just that it functions as an extension of the wall port, but more importantly that there is no vortex shedding happening to cause losses. The second point to make is that at their core ported cabinets are still Helmholtz resonators. That means the critical parameters are the volume of air in the cabinet (C), the mass in the port (L), and the surface area between the two. "Necked" ports, shall we call them, mess are nice because they present a larger apparent surface area for the same mass in the port. The problem is that as the "slug" moves in and out, the impedance matched cross sectional area moves along the flare. It's also possible to have a sudden pressure spike blow out the slug in most necked area of the port, though I have not simulated this explicitly. (Getting more familiar with CFD is somewhere on the stack of TODOs.) I think this, combined with the low tuning, is why SB28 and KS28 seem chuffy despite their fancy "L-Vents" claiming to have laminar flow - I think they actually cause more problems during transients where they help during steady state operation. I think KS28's internal cabinet volume is yea around 350L from what I have been able find and the measurements available. The issue isn't that the volume is too much per driver. I agree that it's almost on the small side per 18" driver - heck I've even seen some questionable cabinets that use nearly 300L per 18" driver (which is is too much, I think). The issue is that it's a single volume which can resonate as one volume because of the appropriate volume behind the vent that connects the two halves of the cabinet. It's not the primary issue I have with the cabinet but I just don't like to design a volume much larger than 300L. I totally agree that getting down low to 30 Hz can really make a difference. However, you don't have to tune a port that low to get that output, and sometimes I think cabinets get tuned lower than ideal in pursuit of that extension. That's usually what I take issue with - I just don't think it's a good design compromise unless you're explicitly trying to make an infra-sub. Personally I've worked a fair bit with B2 and B22. While B2 is definitely a bit of a one-note wonder, I actually find B22 plays quite nicely throughout it's bandpass. The newer motor technology combined with the improvement D80 brought from D12 really helps the driver overcome some of the difficult acoustic impedances presented by the design. I like it way more than I expected to after B2. It's footprint is also smaller than 48" across. :cool: SL-Sub is just so much displacement in a single cabinet. It's truly a behemoth. I mean, as far as I can tell SCP is an iPAL implementation. It should be [I]louder[/I] that most any other 18" as a result of the increased linear excursion that comes with the platform. I think my all time favorite front loaded double 18" is the Clair CP218, but not everyone can afford the cost that comes with the descendant of the bow-tie. [/QUOTE]
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