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Old 9th May 2008, 07:14 AM   #1
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Default Jordan MLTL port question

Hi guys,

I am just finishing the boxes for the MLTL from the Jordan site and I realize that the tube I got for the board is 50 mm OUTSIDE diameter, inside it is 46,4 The specified size for the port is 50X127 mm. I spoke with a few shops, they say that this is the standard , everything here is metric and I am wondering what to do - should I use this one and change the length accordingly or should I delay the celebration and search the world for the right type? Please help, it's more that frustrating...
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Old 9th May 2008, 01:08 PM   #2
sreten is offline sreten  United Kingdom
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Hi,

TBH it will not make a lot of difference. It should be fine.

/sreten.
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Old 9th May 2008, 01:36 PM   #3
GM is offline GM  United States
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Greets!

Technically, it's 50.8 mm i.d., but then I imagine you already know this. Anyway, at 46.4 mm i.d., this is about as small as I would use and if you want to maintain tuning, shorten it to 4"/101.6 mm.

This has been asked enough that hopefully Colin will add this info to the Jordan website.

While we're on the subject, please post the standard metric inside diameters of tubes normally used for vents from ~1" - 8" since the chart I have lists varying thicknesses for a given outside diameter based on its material/application and none work out to 46.4 mm i.d..

GM
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Old 9th May 2008, 01:43 PM   #4
Colin is offline Colin  United Kingdom
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Hi GM - my hint-detectors were working overtime. Yes, I'll put that to Ted and post here when done.

If anyone would care to post standard internal tube diameters (metric or imperial, we swing both ways in the UK), I'll put a small chart on Ted's page. I'll add the ones I can find here in the UK at Wilmslow Audio and the like.

Whilst we're on the subject of ports, what's the largest diameter/shortest length you can use for the 31" port? I've asked on another thread but would appreciate your input as the designer. I'd like to use a forward-firing tube in a triangular enclosure without messing around with u-bends.
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Old 9th May 2008, 02:14 PM   #5
GM is offline GM  United States
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Greets!

Hmm, since a vent's CSA dictates its length and 'speed', normally we speak in terms of what's the SMALLEST acceptable CSA that doesn't audibly 'honk'/'wheeze' to keep it as SHORT as practical, so the largest I recommend is the one I spec'd, 2" i.d. x 5" long, though if you want the euphonic harmonic distortion of a Jensen Ultraflex/Onken, then use a 3-3.25" i.d. x 13.5" long vent.

GM
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Old 9th May 2008, 02:35 PM   #6
Colin is offline Colin  United Kingdom
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Hi - Back to basics for me, then, as I'd assumed you just had to keep the same cubic volume of air in the port and could trade length against CSA. Thanks for the info, as always.
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Old 9th May 2008, 02:39 PM   #7
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Ha, this is exactly what I was looking for, I am in the same situation !! And I would have made the same mistake - I would use a longer pipe to compensate for the smaller diameter...
Thanks folks.
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Old 9th May 2008, 06:35 PM   #8
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Wow, so I should make the port shorter??! I thought I had to keep the volume the same... I am so happy that I posted this question... I will have a look at standard metric sizes and I will post them. Thanks a lot
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Old 9th May 2008, 07:15 PM   #9
GM is offline GM  United States
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Right, look at it this way, if you take this constant volume assumption to the extreme, then you wind up with an extremely long, solid rod, converting the cab to a sealed one, so intuitively this can't be correct........

GM
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Old 10th May 2008, 08:41 AM   #10
Colin is offline Colin  United Kingdom
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In my case, the misunderstanding comes from reading that the reflex or port system uses the mass of air in the port. I had assumed that to keep the mass constant, it was necessary to keep the volume the same. Glad I posed the question.

I'm not sure how Ted calculates his reflex ports, but he seems to favour the long, narrow approach.
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