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Driver/port direction a factor?
Driver/port direction a factor?
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Old 8th May 2008, 06:05 PM   #1
asiquis is offline asiquis  Canada
diyAudio Member
Join Date: Jul 2007
Default Driver/port direction a factor?

I now have the driver (Tempest X) it's bigger than the whole 8" BIC subwoofer that now resides in the corner!

Looks like I will go with the sub placement underneath and hidden by a new "false front" on the existing entertainment unit.
400 liter box stuffed with about 80 oz of polyfill
500 wpc BASH with 13.9 Hz highpass
tuned to around 16-17Hz.
8" port around 30"
The box will be centred on the front wall under the TV (the TV will be attached to the wall -not sitting on the subwoofer ) dimensions of the box 49" wide 26" deep 24" high and the sides of the box will be 48" from each side wall.

With the room size (50' x 12.5' x 7.5' basement)I do not get much if any room gain so I guess it is best to keep the tuning frequency up a little (this will be for home theater and a little music)

My question:
What is your opinion on which direction to face the driver and the port and why?

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Old 8th May 2008, 06:12 PM   #2
AndrewT is offline AndrewT  Scotland
Join Date: Jul 2004
Location: Scottish Borders
more importantly, why stuff a vented box?
How does the sound wave couple with the resonant box and resonant vent to create the "tuned" effect?

Another thread asked a similar question. I said it does not matter. The others disagreed with me. Go read.
regards Andrew T.
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Old 8th May 2008, 06:44 PM   #3
asiquis is offline asiquis  Canada
diyAudio Member
Join Date: Jul 2007
I am going by what the manufacturer suggested with respect to
the stuffing (polyfill).
I beleive this driver likes lots of volume and the stuffing helps in this regard?....

I sent an email to Tom Nusaine citing his article on stuffing that one can find on the net--his reply:
What a great question. I'd have to sat that stuffing in a very large cabinet would have little, if any, advantage except to help higher range harmonics from "bleeding" through the final output.I would ask myself the question "if want subwoofer performance why would I consider a ported enclosure?" The main problems with bass reflex cabinets is that they 'enforce' a 24 dB/octave roll-off below port tuning. If you want 15 Hz output just use a large sealed or Infinite Baffle cabinet.

The 'stuffing' stuff I published some 12-15 years ago didn't directly address the effects of stuffing a large ported ecnlosure. But I would also say that the effects of 'stuffing' are progressively reduced as the size of the enclosures are increased.

One of my earlier Subwoofer projects was a 25 ft3 enclosure stuffed with 1# per ft3. The box was originally tuned to 16 Hz and the one-pound filling perfectly matched the T/S expected tune. This means that there was probably NO effect of cabinet filling at 25 ft3. But, again this was a bass reflex enclosure. And I was, at that time, just like you and enthusiastic DIY.

So I would recommend that you use a one-pound filling (primarily becuz it'll keep 2nd and high harmonics from burping out the port) and just go about making the project you are considering. Just remember there are a couple rules about DIY:

1. It's easier to fill an enclosure with old books and magazines if it turns out to be "too Big" than it is to rebuild the whole damn thing when it turns out to be too small.

2. Always make your enclosure compatible with changing it from sealed, IB or ported if you decide to check things out later. Over time I've gone from the ported stuff and would up in IB territory. But if you do all the design math why not just think aout "what if I did this .... and then decided that I should have gone the other way" why not just have a box that .... "could go both ways"....?
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