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Old 26th June 2006, 08:44 AM   #1
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Default jX92 reflex design tips wanted

Hi, I am a bit new to speaker DIY and until now have only followed established designs. (I built the JUiliet design for the Jordan Watts about 25 years ago). I wish to design a dedicated reflex enclosure for a single JX92s. How do ensure the cabinet proportions and port dimensions are correct.

I am aiming for a single ported enclosure that will go down to about 45hz - probably a standard monitor size. Can I use any shape of cabinet - triangular or pentagon cross-section? Does the port have to be at the front if the cabinet is to be used against the wall? Any advice would be very welcome.
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Old 26th June 2006, 08:53 AM   #2
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I'm sure you're aware, but the Jordan site has recommended vented designs on it. If you want the cabinet to back right upto a wall or be close to it, then yes you need the vent on the front as it must not be obstructed.

Cabinet shape is not dramatically importance as long as the correct volume is there. Equal or direct whole multiples of sizes is to be avoided though or you will likely have resonance issues.

Recent evidence suggests that the position of the vent with regards to the height of the box can influence things if the box is tall enough. Check out Martin J King's spreadsheets.
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Old 26th June 2006, 09:11 AM   #3
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There are a couple of reflex designs out there - Ted's 8 litre box and Jim Griffin's original 7.4 litre enclosure. They probably sound similar, though I've only heard the one by Ted, which sounded pretty good. The Jordan design is here.

Regarding cabinet size - don't make any one dimension too large (a ratio once given in Speaker Builder magazine was 1.0 : 1.26 : 1.56). A triangular enclosure will help reduce the effects of the reflection from the back of the cabinet - especially worth doing in a reflex where ou can't damp the internal resonance by filling with wool or whatever. My own floorstanders have a triangular cross-section and it definitely works to tighten up the sound.

Keep the port at the front if using the cabinet against a wall The vent position probably doesn't matter too much as long as the cabinet isn't too tall.

There are some good constuction pics here of BrianGT's Griffin monitor.
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Old 26th June 2006, 09:31 AM   #4
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Thanks...

It it straightforward to re-calculate the port size if the dimensions change?
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Old 26th June 2006, 10:24 AM   #5
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Do you mean dimensions or volume? Change of dimensions but not affecting volume = no vent change.

If you change the volume then the response will be altered so the change in vent tuning and size becomes a whole new design.
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Old 26th June 2006, 11:29 AM   #6
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Richie,

Yes, I actually meant volume change - I appreciate the vent is the same for equal volumes. I wish to design a larger reflex box than 8l - possibly about 12l.

Thanks...
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Old 26th June 2006, 12:22 PM   #7
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Then you would need to model the response to see whether you prefer a longer of shorter vent, to suit your taste. Increasing box volume keeping the same vent will lower tuning frequency, which in turn with the larger box, will make the roll-off more gentle.
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Old 26th June 2006, 02:00 PM   #8
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Is it a matter of trial and error then, or can I predict changes in port dimensions for an increase in cabinet size, to make the best use of the increased volume.
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Old 26th June 2006, 02:05 PM   #9
Colin is offline Colin  United Kingdom
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The JX92 VTL enclosure was originally designed so it could be configured as a vented reflex enclosure. See diagram below. Ted also used to have a table of recommended reflex sizes on his site - again I've attached a pic.

The larger of his two reflexes was 12.5 litres - by the time you factor in the volume of the vent and the JX92, this comes to the tall, slim enclosure shown. You could also remodel this to a more traditional shape enclosure if you wanted.

I think the only reason the reflex version of the VTL was taken down was because the TL version was so popular that no one had built it.
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Old 26th June 2006, 02:07 PM   #10
Colin is offline Colin  United Kingdom
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And the original table of sizes
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