Ultra compact ported 15" Dayton Ref HO - Page 4

col · 4th October 2012, 12:30 AM

To calculate triangle ports do you just calculate a square one and chop it in half?

turbodawg · 5th October 2012, 12:18 PM

Quote:

Originally Posted by col

To calculate triangle ports do you just calculate a square one and chop it in half?

That seems to be it, but due to shape, they will actually tune lower. It seems to be the case with any non-round/square ports that they tune lower than predicted.

turbodawg · 5th October 2012, 12:37 PM

I sketched out some plans last night, and just wasn't able to come up with a compelling design with two triangle ports. It seemed like adding complexity for very marginal gains. If I was going to go with a harder to build port setup, I'd go 3x 4" with bends or one large square port with a rounded bend.

I can do the slot port box much more quickly and easily, and will nicely flare the in and out of the slot per some designs I've seen. I haven't built a box in several years and my woodworking skills are pretty basic. We'll see how this works out, and maybe I'll do a box with a large square flared vent at some point if the slot port box falls short at high output.

bjorno · 5th October 2012, 01:09 PM

Quote:

Originally Posted by turbodawg

That seems to be it, but due to shape, they will actually tune lower. It seems to be the case with any non-round/square ports that they tune lower than predicted.

Hi,

They don’t tune lower it seems you’ve only used the wrong end correction factor(s) as the triangular ports are not 'one end open and one end 'IB' terminating at the baffle .

b

turbodawg · 5th October 2012, 01:26 PM

Quote:

Originally Posted by bjorno

Hi,

They don’t tune lower it seems you’ve only used the wrong end correction factor(s) as the triangular ports are not 'one end open and one end 'IB' terminating at the baffle .

b

Everything thing that I've seen says that as you move away from a round port, you end up with a lower tune than the equivalent round port. Regardless of end correction. Probably because the sound propagation isn't quite as linear. This also explains why if you model a folded horn in hornresp, with round sections, if you then build it with rectangular sections, you get a lower response than modeled.

bjorno · 02:03 PM

Quote:

Originally Posted by turbodawg

Everything thing that I've seen says that as you move away from a round port, you end up with a lower tune than the equivalent round port. Regardless of end correction. Probably because the sound propagation isn't quite as linear. This also explains why if you model a folded horn in hornresp, with round sections, if you then build it with rectangular sections, you get a lower response than modeled.

Youre partly right on your observation but the valid end correction factor depends on Port diam. to lenght, wavelenght to diam., sound pressure and air velocity... baffle placement..speaker placement to room boundaries...and so on.

Dont know if this picture(my notes) can be of any help:

b

PS: For PA I use the notes under 'End corrections' for a conventional simple port with aspect ratio <= 3:1 L/Diam. placed away from the corners and the sides.

dstmbgh · 5th October 2012, 06:20 PM

Quote:

Originally Posted by bjorno

the valid end correction factor depends on...

Dont know if...my notes...can be of any help

Bjorno, regarding end correction factors, I'm hoping your notes and expertise might be of some help to me regarding a slot port for an enclosure not flat on the floor, but placed on a stand.

In the interest of getting some clarification from you without distracting from the topic of this thread, I have sent you a PM. Please check your PMs, and thanks in advance for any help.

David

turbodawg · 5th October 2012, 11:46 PM

Bought wood and misc stuff today, will start building and post some pics soon.

col · 6th October 2012, 01:41 AM

Perhaps the old Fane sub plan is the way to go to keep it KISS. It would give good venting without "touching the sides" making the tuning difficult to predict?

http://www.fane-acoustics.com/downlo...nch200Lres.pdf

col.

turbodawg · 9th October 2012, 02:59 PM

So I did get to work on this a bit over the weekend...

Got some 1/2" birch ply. This has 3 main plys and inner and outer veneer. It's just shy of 1/2" thick, more like 7/16-15/32. In a big sheet it seems pretty flexy, but it's plenty stiff in small panels. I will brace it pretty well.

I managed to get 4 sides of the box done. Cutting with a small 5-1/2" circular saw, battery powered. I've got a larger saw too, but the small one cuts well enough and is easier to handle. With a guide and carefull measuring the cuts are accurate to about 1/32". Using 90 clamps and 3 or 4 small sheetrock screws per side, pre drilled holes, titebond 3 woodglue. Next step is getting the port mounted, then the bracing, then last side, then the baffle. Will post some pics when there is something interesting to show.

Outer dims are 20x16x22, with the sub and slot port on the 20x16 side. Port should be about 15x2.5x21 actual, 23" effective length, for a tune in the mid-high 30's. Will put a 1" radius flare on one side of the exit, and there will be a proper bend on the inside.

Checked the fit in the car, with some creative moving around, I can actually fit 2 of these in the trunk. So I could run them as a car sub......lol.

4th October 2012, 12:30 AM	#31
col diyAudio Member Join Date: Feb 2008 Location: Melbourne, Victoria, Australia	To calculate triangle ports do you just calculate a square one and chop it in half? __________________ http://www.minirig.org.au

6th October 2012, 01:41 AM	#39
col diyAudio Member Join Date: Feb 2008 Location: Melbourne, Victoria, Australia	Perhaps the old Fane sub plan is the way to go to keep it KISS. It would give good venting without "touching the sides" making the tuning difficult to predict? http://www.fane-acoustics.com/downlo...nch200Lres.pdf col. __________________ http://www.minirig.org.au

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5th October 2012, 12:37 PM	#33
turbodawg diyAudio Member Join Date: Feb 2004	I sketched out some plans last night, and just wasn't able to come up with a compelling design with two triangle ports. It seemed like adding complexity for very marginal gains. If I was going to go with a harder to build port setup, I'd go 3x 4" with bends or one large square port with a rounded bend. I can do the slot port box much more quickly and easily, and will nicely flare the in and out of the slot per some designs I've seen. I haven't built a box in several years and my woodworking skills are pretty basic. We'll see how this works out, and maybe I'll do a box with a large square flared vent at some point if the slot port box falls short at high output.

5th October 2012, 11:46 PM	#38
turbodawg diyAudio Member Join Date: Feb 2004	Bought wood and misc stuff today, will start building and post some pics soon.

9th October 2012, 02:59 PM	#40
turbodawg diyAudio Member Join Date: Feb 2004	So I did get to work on this a bit over the weekend... Got some 1/2" birch ply. This has 3 main plys and inner and outer veneer. It's just shy of 1/2" thick, more like 7/16-15/32. In a big sheet it seems pretty flexy, but it's plenty stiff in small panels. I will brace it pretty well. I managed to get 4 sides of the box done. Cutting with a small 5-1/2" circular saw, battery powered. I've got a larger saw too, but the small one cuts well enough and is easier to handle. With a guide and carefull measuring the cuts are accurate to about 1/32". Using 90 clamps and 3 or 4 small sheetrock screws per side, pre drilled holes, titebond 3 woodglue. Next step is getting the port mounted, then the bracing, then last side, then the baffle. Will post some pics when there is something interesting to show. Outer dims are 20x16x22, with the sub and slot port on the 20x16 side. Port should be about 15x2.5x21 actual, 23" effective length, for a tune in the mid-high 30's. Will put a 1" radius flare on one side of the exit, and there will be a proper bend on the inside. Checked the fit in the car, with some creative moving around, I can actually fit 2 of these in the trunk. So I could run them as a car sub......lol.