damonrpayne Posted April 7, 2005 Share Posted April 7, 2005 I'm picking up some supplies tonight and I have a question about the excellent drawings produced by forum members. The "ports" shown here, does anyone have a pic of what this looks like on a real cornwall? I'm having trouble visualizing this. Will the position of these ports be OK for a Vert cornwall? Many thanks! Quote Link to comment Share on other sites More sharing options...
Budman Posted April 7, 2005 Share Posted April 7, 2005 the vertical cornwall has the ports in the same position as the regular cornwall. the verticals that i have have 2 ports and my 76 decorators have 2 ports. most regular corns have 3 ports. Quote Link to comment Share on other sites More sharing options...
colterphoto1 Posted April 7, 2005 Share Posted April 7, 2005 Damon, the number of cutouts is not critical. What is critical is the total volume of the port, which includes the depth of the 'shelf' board. If you add up the sizes of the two or three 'hole' versions you'll see that they are exactly the same. I think the three hole model (mine are four) would be better than the two as it gives a little more strength to the motor board. Michael Quote Link to comment Share on other sites More sharing options...
3dzapper Posted April 7, 2005 Share Posted April 7, 2005 Michael, You got it right!!! Quote Link to comment Share on other sites More sharing options...
j-malotky Posted April 7, 2005 Share Posted April 7, 2005 Out of curiosity, as I no nothing about porting, does the position matter in the cabinet? Could it be in the middle of the cabinet insted of the botom? Reason I ask is I see tube ports placed any which way in speaker cabinets. If you would build the CornW cabinet say skinier and taller for example, if you kept the internal cabinet air mass identicle to the CornW, and the port air space dimentions exactly the same, would it work the same? On the same note, could you put in 4 or 5 tube ports that equaled the same air mass of the CornW port? Just wondering??? JM Quote Link to comment Share on other sites More sharing options...
Marvel Posted April 7, 2005 Share Posted April 7, 2005 You sound like an architect when you start talking about 'two holers' and 'three holers'. Marvel Quote Link to comment Share on other sites More sharing options...
boom3 Posted April 7, 2005 Share Posted April 7, 2005 ---------------- On 4/7/2005 7:03:12 PM j-malotky wrote: Out of curiosity, as I no nothing about porting, does the position matter in the cabinet? Could it be in the middle of the cabinet insted of the botom? Reason I ask is I see tube ports placed any which way in speaker cabinets. If you would build the CornW cabinet say skinier and taller for example, if you kept the internal cabinet air mass identicle to the CornW, and the port air space dimentions exactly the same, would it work the same? On the same note, could you put in 4 or 5 tube ports that equaled the same air mass of the CornW port? Just wondering??? JM ---------------- The volume of the air mass must be the same for the tuning to 'work', however, there is an minimum acceptable port diameter. Ports that are too small cause the air stream to increase in velocity and cause an audible 'chuffing' sound at high speaker excursions. Also, ports that are very small can actually whistle although this is also a factor at high excursions. The generally accepted minimum port diameter, for a tube-type port, is 2 inches and 3 inches or more is desirable. The ports must not be seperated far enough to be one-half wavelength apart at any frequency within the woofers range (this also includes an octave above nominal crossover) I once built a large vented enclsoure with two woofers and two ports equidistant from the woofer pair. I wondered why I had a very audible dip at 120 Hz. It was due to the interference betwen the widely spaced ports. I plugged one up and adjusted the tube length and the response flattend out. The port shelf of the Cornwall serves to brace the cabinet as well as port the back side of the woofer. Paul proved and refined this over many years. If you want to build a Corn-clone, stick to the master's design. Quote Link to comment Share on other sites More sharing options...
colterphoto1 Posted April 7, 2005 Share Posted April 7, 2005 There is much wisdom in Boom3's words. Although technically you could build a cabinet of identical volume with identical volume ports, the size and position of the ports, as well as the ratio of the cabinet dimensions (much like the ratio of listening room dimensions) play a huge part in the cabinets sound. PWK and associates played the R&D game when they designed the Cornwall. Recall that they did not have computer modeling and Thiele/Small parameters at the time. I have read that when compared to computer models, they were only off by like 3% or so. Stick to the original, accept no substititues for best results. Michael Quote Link to comment Share on other sites More sharing options...
3dzapper Posted April 7, 2005 Share Posted April 7, 2005 Too bad PWK didn't play around with the Heresy box size and port it at 40Hz. Rick Quote Link to comment Share on other sites More sharing options...
Olorin Posted April 8, 2005 Share Posted April 8, 2005 They call that a Tangent 400. Quote Link to comment Share on other sites More sharing options...
DrWho Posted April 8, 2005 Share Posted April 8, 2005 ---------------- On 4/7/2005 7:03:12 PM j-malotky wrote: Out of curiosity, as I no nothing about porting, does the position matter in the cabinet? Could it be in the middle of the cabinet insted of the botom? Reason I ask is I see tube ports placed any which way in speaker cabinets. If you would build the CornW cabinet say skinier and taller for example, if you kept the internal cabinet air mass identicle to the CornW, and the port air space dimentions exactly the same, would it work the same? On the same note, could you put in 4 or 5 tube ports that equaled the same air mass of the CornW port? Just wondering??? JM ---------------- The port can be anywhere on the cabinet. As mentioned though, the ports should be close to each other and all that shnazz. The reason ports can go wherever is based on a pressure inside versus pressure outside type of scenario. The whole reason we even put speakers in cabinets is to keep the out of phase signal from the rear of the diaphragm from cancelling out the front. A port is a device that actually reverses the phase of the rear wave (over a narrow band), thus preventing the cancellation from happening. An alternative to using a port is to use just a baffle that is 1/4 wavelength in diameter of the "tuning frequency." By the time the air pressure from the front and back get to the edge of the baffle, they both end up being in phase. As long as the volume of air behind the woofer trapped inside the cabinet is the same, you will maintain the same "acoustic spring" and therefore you will get the same driver behavior. It's the "springy" action that makes ports work (it's not good to think that when the driver moves out, that it sucks air in through the port and vice versa...when the woofer moves out, it creates a wave behind it...it's totally possible for air to rush out of the port when the woofer is moving out at the same time.) The Chorus I is probably the closest thing to a skinny cornwall, using different ports. Quote Link to comment Share on other sites More sharing options...
damonrpayne Posted April 8, 2005 Author Share Posted April 8, 2005 OK, but does anyone have pictures that can help me visualize to build this? My own .02 on Johns question regarding dimensions: I would think it would have to affect it in some ways. Look at the move towards curved cabinetry... Quote Link to comment Share on other sites More sharing options...
colterphoto1 Posted April 8, 2005 Share Posted April 8, 2005 Damon, what exactly is your construction question? The diagrams should be pretty self-explanatory. There are rectangular cutouts with rounded corners in the motor board, the shelf extends back the given distance. Review the 'ok, lets build a Cornwall " a couple months ago. Call me if more quesitons, Michael Quote Link to comment Share on other sites More sharing options...
damonrpayne Posted April 8, 2005 Author Share Posted April 8, 2005 I have all the pics from that thread. From how they look, I can see the shelf but now how the ports look in/under the shelf. Does that make sense? Quote Link to comment Share on other sites More sharing options...
Klewless Posted April 8, 2005 Share Posted April 8, 2005 damon, That shelf is the port, there is only one. The rectangular openings could just as well be viewed as "windows" into the port. Klipsch could have designed it differently by stopping the front panel at the top of the port shelf. Then he would have had to put in something around the edge to attach the grill onto. Quote Link to comment Share on other sites More sharing options...
Marvel Posted April 8, 2005 Share Posted April 8, 2005 Damon, Look at the slot across the bottom of these Yamaha cabinets. That whole slot is the port, and has a shelf going back just like the Cornwall does. These just have the entire width open. btw, I got a set of these for free. They sound pretty nice, but don't go very low. Marvel Quote Link to comment Share on other sites More sharing options...
jwc Posted April 8, 2005 Share Posted April 8, 2005 Ok Damon, The picture is of a cabinet with motor board on and motor board off. Here you can visualize the shelf. If this doesn't clear it up...well...you'll just have to come on over an see em'. jc Quote Link to comment Share on other sites More sharing options...
j-malotky Posted April 8, 2005 Share Posted April 8, 2005 Damon, sounds like a nice project. I know you were planning on using Khorns in your new HT. Are you going to use the K400 horn to match the Khorn, or the standard K600 Cwall midrange? Let me know how it goes, I would like to see it.... And hear it too JM Quote Link to comment Share on other sites More sharing options...
damonrpayne Posted April 9, 2005 Author Share Posted April 9, 2005 K-601. I'm hoping to bring it to the labs in June. Quote Link to comment Share on other sites More sharing options...
Thumpelstiltskin Posted April 16, 2005 Share Posted April 16, 2005 Are you just wanting a picture of a Cornwall's ports? Here's a two-holer (CDBR) decorator and a three-holer (CBR). I hope this helps. Quote Link to comment Share on other sites More sharing options...
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