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Old 23rd March 2004, 04:10 AM   #1
nrgy is offline nrgy  United States
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Default Vented Enclosures - What type is this?

I'm looking around at some different style vented enclosures, trying to get ideas, and I came across Boston Acoustics BT1100 subwoofer, and was wondering if anyone could provide a little more detail on this type of enclosure. Here is the product page for the sub: http://www.bostonacoustics.com/hs_pr...1&CategoryID=6

Basically, how is this type of enclosure constructed, and what are the pros and cons over a typical vented box? Thanks.
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Old 23rd March 2004, 03:01 PM   #2
kan3 is offline kan3  United States
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its a slot port that uses sides of the walls as part of the port - generally when people say "slot port" they are refering to this

advantages = saves internal space because of end correction factor and not having to use seperate material for the port because your using the walls

all ported boxes I build are slot ported...saves space and time
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Old 23rd March 2004, 03:05 PM   #3
sreten is offline sreten  United Kingdom
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The enclosure appears to be a bandpass with a slot port.

Search on bandpass subwoofers for more info.

sreten.
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Old 23rd March 2004, 04:40 PM   #4
markp is offline markp  United States
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LIke kan3 said it is 'slot loaded'. It is the same as a bassreflex port, just use the area of the slot as the area of the port and calculate length as you usually would. It has the benifit of a large opening to reduce port noise but is also usually long due to the area and sometimes must be bent inside the box.
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Old 24th March 2004, 04:37 AM   #5
nrgy is offline nrgy  United States
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Thanks for the info. I had a few more questions however. I would like to build an enclosure for a Shiva, and would like to make a clone of the Boston enclosure I linked to above. The bandpass design using the slot port seems somewhat difficult figuring out all the dimensions, and wondered if anyone had any ideas how to determine the length.

The Boston slot is 16" wide x 3" high, and when I plug this into WinISD it suggests a length of 46", obviously too long. I read somewhere, however, that the length of a slot port does not need to be as long. How do I determine this length?

Also, I did a quick drawing of another idea, and wondered what the enclosure labeled Box 1 would be referred to as. Would this simply be a ported enclosure, or a 6th order bandpass? If Box 1 is simply a ported enclosure, would there be any downsides to doing it this way?
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Old 24th March 2004, 06:36 AM   #6
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The box #1 might be a little difficult to accurately design. The slot will add mass to the driver, lowering it's fs and raising it's Q. The way it is placed will also help to couple it to the adjacent boundary. In other words: it will show some effects of a downfiring sub but offer good mechanical protection.
All additionall effects might be difficult to model accurately (it will also show resonances).
But it has been done already with success. Some P.A. cabinets by EV use it with reflex enclosures. An older compact P.A. by Peavey used it as well with a closed box. And I have once read a review on an Australian sub for HT that uses such a slot with a reflex tunnel which is also coupled into the slot (close to it's mouth). The review was quite good.

Regards

Charles
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Old 24th March 2004, 03:22 PM   #7
kan3 is offline kan3  United States
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curious as to why your going for the bandpass box? also what kind of FR are you trying to get out of it?


model :

2cuft sealed chamber / 2 cuft ported chamber - 40hz tuning

that look good or where you going for something else? it looks like a nice response and just add to the ported chamber for gain adjustments
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Old 29th March 2004, 07:55 AM   #8
nrgy is offline nrgy  United States
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Well, I'm not really sure why I'm going bandpass. I'm new to this hobby, so I'm basing most of my decisions right now on design and asthetics, and I thought I could make a nice looking bandpass box. Whether it's the correct decision I don't know. As far as frequency, I'm a little embarrased to ask, but how do you determine what type of frequency you want out of a particular driver? And how do you achieve this frequcency using a program like WinISD? Just enter the tuning frequency you wish to have?

Since I can't get the length I need using the 4th order bandpass design because of the depth, would it be ok to extend the slotted port length by adding a solid brace type structure above the first slotted port, as shown in the picture below, or is this typically not done?
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Old 29th March 2004, 08:21 AM   #9
Alcaid is offline Alcaid  Norway
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What end correction factor do you use when you use a slot port? Do you use the normal 0,732 that is used for a normal port with one flanged end?
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