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Old 2nd October 2005, 12:53 AM   #101
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A thought about the fat Thor, I think a deep Thor might be better because it wouldn't make you revise the crossover. As shown by Bjorn's measurements, the design is perfectly flat through the baffle-step region but making the baffle wider would change that. Another bonus, making the cabinet deeper wouldn't make it look any bigger from the front.
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Old 2nd October 2005, 02:40 AM   #102
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Quote:
Originally posted by catapult
Another bonus, making the cabinet deeper wouldn't make it look any bigger from the front.
It would have to be a bit taller to accomodate the large cross-section thru the bend -- you might be able to compensate somewhat by exiting the terminus out the top.

Making it deeper was my 1st thot, just for the reason you gave -- no mucking with the XO... it would be almost 2/3 of a metre deep...

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Old 2nd October 2005, 03:59 AM   #103
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It would have to be a bit taller to accomodate the large cross-section thru the bend
Good point, Dave. That might actually work quite well because the tweeter in the stock version is only about 31" above the floor. That's a bit low for an MTM and most listener/chair combos. Moving it up another 5.5" (doubling the cross-section) would be about right for me and my chair.
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Old 2nd October 2005, 08:55 AM   #104
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There are also some advantages to having a top-mounted vent (although I'd restrict the area a bit for some mass-loading. Probably). At present, the vent only works on the horizontal room-modes to any great extent, and also, I'm with Lynn Olson on this: if you're going to drive the room's horizontal mode, the vent is best near the floor to get some additional gain there. Placing the vent on the top might increase a bit of ripple, but it would also drive the room's vertical mode very well too, which is very useful - the vertical room mode[s], tend to sound faster, and cleaner than the horizontal modes.
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Old 2nd October 2005, 09:19 AM   #105
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I wonder if some appropriate offset could be added, flip the box over (allowing a floor exit) and still get the drivers at an appropriate height?

quick & nasty -- 0.336 offset from Martin's tables... about 2.05 metre line ... ~690 mm from the bottom of (upside down) box, add 140 for the FatThor, and say another 50 for a stand to allow bottom exit -- 880 mm ~ 35" tweeter height.

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Old 13th October 2005, 09:48 PM   #106
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1st pass plans for the "Fat Thor" inspired by this thread. There may be some room for further optimization (ie can it be a bit smaller?)

Twice the cross-section, drivers offset as per MJK tables for a 3:1 taper ratio, terminus out the bottom.

dave
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Old 14th October 2005, 11:26 AM   #107
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MathCad predicted response of FatThor:

Much better. As a bonus, the vent's on the floor too. Good job, Dave!
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Old 14th October 2005, 12:28 PM   #108
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Okay, after playing around with the dimensions, here's my final offering for these drivers, based on Dave's FatThor:

Line length, geometry and driver positions remain as per the FatThor CAD drawing above.

So = 2.5 Sd (just under actually: 13.5"x7.5"). This will make for a cabinet that's around 3.25" shallower than the FatThor overall, which is useful, though it's never going to be a small cab!

Keep Sm as per Dave's diagram, which is an area of 1Sd. Now, mass-load the cabinet a la Martin's proceedure by installing a 3"x4" (WxL) port near the base of the rear panel (my choice), or on the base itself. Stuffing remains the same as the original Thor at 0.78 lbs to the cubic foot -these drivers in a TL of any type appear to need it, though you can reduce to taste if you don't mind sacrificing an increased level of ripple. As per usual, remember to add 6 db for the paralleled drivers, and remember to take baffle step loss into consideration.

These are big cabinets, but as they're built from MDF (potentially), they should be cheap enough to construct -there's nothing fancy about them, so I'd encourage any existing Thor owners to spend 30 on some more MDF and a couple of ports and rough up a pair of these, or the FatThor cabs I based them on that Dave has drawn. Either would be worth it, of that I'm sure, and both will do justice to these drivers.

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Old 14th October 2005, 01:51 PM   #109
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1. Scott - I am not sure I undertand - do you mean an additional port?

2. Scott - Here 30 Pounds will get you a 16mm sheet of MDF. A 22mm Sheet is double the price. This is 1/4 of the average monthly salary in SA so maybe not all that cheap.

3. Planet - Why do you prefer having cabinet open to the floor?
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Old 14th October 2005, 02:47 PM   #110
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Quote:
Originally posted by Byrd
1. Scott - I am not sure I undertand - do you mean an additional port?

2. Scott - Here 30 Pounds will get you a 16mm sheet of MDF. A 22mm Sheet is double the price. This is 1/4 of the average monthly salary in SA so maybe not all that cheap.

3. Planet - Why do you prefer having cabinet open to the floor?
Sorry if I wasn't clear. No, it means that the end furthest from the drivers is sealed, not open, but has a 3"x4" port in it, or just above. This is the mass-loading technique suggested by Martin -the constricted area and air-mass in the port provides additional loading to the quarter-waves in the cabinet. It's unusual to employ it with a traditional TL geometry, I admit, but not unknown.

Ouch. I didn't know MDF was so expensive over there an 8'x4' 3/4" sheet is circa 10 - 12 in the UK. My apologies. Then again, as these are hardly cheap drivers etc, I assume that few people on the average monthly wage would be able to build Thors? I know I can't afford them (at present...;-)!

I'm with Dave on the low-mounted port / vent. They couple better with the floor and room boundaries than high-mounted vents. It's quite an interesting effect I find: speakers with a vent high up often sound more strained than an otherwise identical design with it mounted lower down. Every little helps. And mounting it as Dave has done in his FatThor means it will drive the rooms vertical resonant mode too, which can give quite a clean and fast boost with fewer of the drawbacks to driving the horizontal mode -there's less in the way for example.

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