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Old 7th July 2008, 12:36 PM   #1
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Question bd pipes port material?

Hi all-
First post in this forum, I usually post in the Tube Amp forum.
Now I'm working on the parts that my tube amp plugs into

I'm just finishing a pair of the BD pipes, found here:
BD pipes

My question is in regards to the port diameter and material.
Is the 68mm the inside diameter of the port tube?
If anyone has built these, I'd like to know what they used for material for the port? I've used PVC tubing before on other speakers, but I can only get 2" (50.8mm) ID PVC tubing. If I was to use this, would the length get shorter? I can't find anywhere in the article what the port is tuned for. From using a few port calculators on the web, it looks like the enclosure is tuned for around 48Hz.

Any suggestions would be appreciated from anyone who has built a pair of these speakers.

Thanks
Glenn
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Old 8th July 2008, 02:10 AM   #2
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I interpreted the drawing as 68 mm OD. Assuming 2mm thick walls, that works out to ~2.5".

I used a 2.5" ID and kept the same length.

BTW - what drivers are you planning on using?
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Old 8th July 2008, 11:33 AM   #3
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Hi Giovanni, thanks for the reply.
Yes, I assumed the ID to be 2.5"also, I was more interested in what people were using for the actual tube material. PVC tubing comes in even sizes around here. I know 2.5" is manufactured, it's just not readily available.
I actually wound up using 2" ID, and adjusted the length accordingly. I just hope the port isn't too noisy as the velocity of the air moving through it will be higher. I did epoxy the tube to the inside of the cabinet and routed a nice radius to smooth the airflow. We'll see how it works.
I'm planning on using a Tang Band W4-616SA driver as a start.
http://www.partsexpress.com/pe/showd...number=264-818
I really can't afford four Fostex drivers right now, so we'll see how these work.
How do you like these cabinets? What drivers are you using?
I'm looking for more efficient speakers for my SE KT88 amp, that's what started me on this project.

Glenn
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Old 9th July 2008, 04:07 AM   #4
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ABS pipe might be available in more size choices. I don't imagine 2" diam will cause port noise with these small drivers.

Those TB drivers params seems close enough. IMO, they look better than the fostex drivers. Trying a 4" woofer on the rear might be fun.

I used the RS 40-1197. This was my first FR speaker and I was immediately impressed. The box tuning is low, so you can't get much SPL, but they sound nice at low volume.

Post some pictures when you are done.

Cheers
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Old 9th July 2008, 11:40 AM   #5
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After I posted, I ran across a web site that gives some calculations for max velocity to avoid port noise. I ran the numbers, and as you said, the velocity was well below the recommended max. value to avoid port noise.

I did wind-up using the 2"ID PVC with the length suggested by the software. http://www.linearteam.dk/default.asp...ventcalculator

I'm actually thinking of upgrading at some point to the Tang Band with the coaxial tweeter for the front, and a woofer as you mentioned for the back.
Tang Band coaxial 4"
Tang Band 4" woofer

I've got to remember to take some pictures before I glue the sides on

Glenn
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Old 9th July 2008, 12:19 PM   #6
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Quote:
Originally posted by porkchop61

I was more interested in what people were using for the actual tube material.
Most folks use whatever~rigid plastic or cardboard pipe/tube is the 'close enough' diameter.

GM
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Old 9th July 2008, 02:43 PM   #7
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Yeah, that's what I figured. My real issue was finding something the right diameter locally. I saw that cardboard shipping tubes were available in 2.5"ID, but everyone around here (Staples, etc.) only carried even sizes, 2", 3", etc.

I think the 2" PVC I used will work fine with the length re-calculated accordingly.

I'll keep everyone posted.

Thanks
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Old 9th July 2008, 04:38 PM   #8
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FYI you can make a square tube with the same cross sectional area (CSA) and length from scrap for oddball sizes or just use Ron E's math to scale it up to the next readily available diameter:

GM

square inch is a measurement of area
a circle with an area of 25 square inches is :
Area = pi*diameter^2/4
rearrange:
sqrt(4*Area/pi) = diameter
For your area of 25 square inches, the diameter is 5.64 inches, or 14.3 cm.

It is hard to make a round port a specific size, so you can scale your length, based on available port diameters.
L1/L2 = A1/A2, where L1, A1 are the original length and area, and L2,A2 are the new length and area...
rearranging again, and Realizing that area is proportional to diameter squared:

L2 = L1*(D2^2/D1^2), where D2 is new diameter and D1 is the original diameter.

You input the diameter of the ports you can get, and from that you can get the new length.....
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Old 9th July 2008, 06:14 PM   #9
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Okay, now we're talking my language!

Using the formula L2 = L1*(D2^2/D1^2), and the following port dimensions:
L1=131mm (old port length)
D1=68mm (old port diameter)
D2=50.8mm (2") (new port diameter)

I get a new port length of 73.11mm (2.878").
That's a good check, because using the online port calculators I got a new port length of 2.86", pretty close.

Thanks very much for the ratio formula!

Glenn
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Old 10th July 2008, 01:16 AM   #10
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Quote:
Originally posted by porkchop61
Tang Band coaxial 4"
Tang Band 4" woofer
I thought you couldn't afford the FE103E!

BTW - Peter Millet employed a woofer on the rear.
http://www.pmillett.com/tqwp.htm
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