DIYNewbie said:
Now you're playing the game!
I see what you are doing but the 1 inch port was for the inner diameter and not radius. If it was radius you would have been on the right track, volume wise. Unfortunately, calculating equivalent vent volumes does *NOT* give you equivalent tunings. Lazy begger that I am, I let my software calculate my vents for me. If anyone wants to insert a tutorial here, please do. I would be the first to benefit.
For a rectangular port of 7.75" width WinISD give me a reasonable length or depth of 4.94 for a height of .3 ( assuming we are still gunning for the 12.5 liter box tuned to 42 hz (an unproven but reasonable sounding approach))
That feels very narrow to me but WinISD doesn't have a problem with the vent mach. In other words the dread "chuffing" is not predicted. YMMV.
Remember that you will have to take the volume of the vent and vent materials into account when you calculate the volume of your enclosure and increase the inner dimensions of your enclosure accordingly.
Dave Jones said:
And I wish I really intuited why! Anyone who has a pointer to a good explanation of the dynamics of vents and box tunings, please send us that way.
tgorham3 said:
It's kind of complicated. When the distance between the driver and the port is short compared to the wavelength of the tuning, the box behaves as a Hemholtz radiator, like the jug in a jug band.
http://www.diysubwoofers.org/portcal.htm
When the distance between the driver and the port is a significant fraction of the tuning wavelength -- (a quarter wavelength is particularly important) -- even more interesting things happen. Our own Martin King is a foremost authority when it comes to analyzing such systems. I think getting around the wave equations would be a daunting undertaking for someone who does not have much of a background in physics (like me). But Martin has magnanimously put software up on his web site.
http://www.quarter-wave.com/
There's a new thread on this BB also.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=36424
http://www.diyaudio.com/forums/showthread.php?s=&threadid=36424
What woudl be a "proven and reasonable" approach. I picked the 12.5 liter box from the Jordan website. I'm not wed to that size...
If you intend to use the speaker close to a wall then put the port on the front. You need an accurate volume to work out the dimensions. There used to be an on-line port calculator at www.loudspeakers101.com but the site has expired (anyone know where it's gone?)
If you are close to the wall you can try doing without any xover. I found that the Jordan recommended baffle step correction improved bass at the expense of the higher frequencies and dispensed with it.
If you are close to the wall you can try doing without any xover. I found that the Jordan recommended baffle step correction improved bass at the expense of the higher frequencies and dispensed with it.
DIYNewbie said:
Jordan's 12.5 liter design has a 7 X 7 cm port that is 36 cm long. That would tune a 12.5 liter box to 53 hz giving it a bit of a boost from 70 to 100 hz. IF you want a proven volume and tuning, give it a try. Understand that because it was designed as a free standing speaker rather than a book shelf the bass boost may or may not be a good thing. I would be reluctent to call it a proven design because the cabinet shape is would be very different when realized as a bookshelf design.
A truly proven design is Jim Griffin's 7 liter box tuned to 55 hz. This is what CSS's kit is based upon as well. It too has a bass hump.
3db on the Jordan design is around 50. 3db on the Jim Griffin design s about 62.
Parts Express has a cabinet that just about meets your size criteria. The 0.25 cu ft cabinet measures 12" x 7.5" x 10". The exterior finish is top notch for a budget cabinet. It's well braced and has a 1" thick front panel. I've used these cabinets in several of my projects and highly recommend them.
Since you don't have any DIY experience, I suggest one of their kits that use this cabinet:
http://www.partsexpress.com/webpage.cfm?&DID=7&WebPage_ID=209
You get a choice of piano black, cherry, or beech finish. The only drawback is the rear-mounted port. If you're willing to use a subwoofer, then you could just insert some foam to block the port, which will give you a nice 12dB/octave roll-off to integrate with your sub.
I would also highly recommend their 10" subwoofer kit. They're currently running a special of free shipping, well worth it since it weighs in at 64 lbs. It has a 250W plate amp with high and low level inputs. For $360 it will compare favorably with $800-$1000 subs.
http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=300-760
Since you don't have any DIY experience, I suggest one of their kits that use this cabinet:
http://www.partsexpress.com/webpage.cfm?&DID=7&WebPage_ID=209
You get a choice of piano black, cherry, or beech finish. The only drawback is the rear-mounted port. If you're willing to use a subwoofer, then you could just insert some foam to block the port, which will give you a nice 12dB/octave roll-off to integrate with your sub.
I would also highly recommend their 10" subwoofer kit. They're currently running a special of free shipping, well worth it since it weighs in at 64 lbs. It has a 250W plate amp with high and low level inputs. For $360 it will compare favorably with $800-$1000 subs.
http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=300-760
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