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Discussion Starter #1
i have done a little with car audio builds but only with sealed boxes. i have just gotten into the ported boes. i am going to be using a MJ-18 because its price is just in my fairground. (college student living in mom's basement) lol. the box is going to be 10.8 cubic ft after displacements. its going to be tuned to 22hz with Four 4.3125in. by 7.31in, flared at outside end, aeroports. the graph in winISD shows this to have the most spl output for what i want. i am mainly going to be using this for watching movies and sometimes party or chill music. i am going to set the subsonic filter at around 18hz and highpass at 70hz. the air velocity peaks approx. 52miles/hour at 20.5hz. is this a low enough number for hometheater applications? the sub is going to be flush mounted. there is a .8mm over-excursion at 30hz but .8mm shouldnt be damaging right? with this tuned to 22hz i get between 119-118 dB until 22hz. between 22hz-20hz, i get 118-115 dBs. what do you guys think? and if theres something off or something i was mislead about please help a newbie out. sorry about going all over the place with my thoughts. thanks in advance for the help. ill post my whole set-up when i get home because i dont remember all of them exactly.
 

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Discussion Starter #3
Re: need some advice and guidance with my first hometheater build

newer, or watever specs are on the site now. i havent bought it yet.
 

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Re: need some advice and guidance with my first hometheater build

Then it's the MJ-18M. Tuning it to 22 hz instead of the recommeded 18 hz means you'll be giving up 4 db at 18 hz, which is noticeable during movies. On the other hand, tuning to 18 hz means you'll give up 2 db at 25 hz over a 22 hz tune. Tuning it to 20 hz would be a "happy medium" between the two. If you really want a 22 hz tune, let us know and we'll take it from there.
 

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Discussion Starter #5
Re: need some advice and guidance with my first hometheater build

this is the graph i got from the 20hz tuning compared with the 22hz tuning. its got a bigger spl output until down to 20hz and below but at those puts, i cant hear those frequencies anyways right?
http://i222.photobucket.com/albums/dd246/slim2fattycake/difference.jpg

this is the cone excursion graph. and i was going to use a subsonic filter around 18-19hz. is that right to do?
http://i222.photobucket.com/albums/dd246/slim2fattycake/cone.jpg
 

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Re: need some advice and guidance with my first hometheater build

its got a bigger spl output until down to 20hz and below but at those puts, i cant hear those frequencies anyways right?
But you can feel them. It's all part of the HT experience. It's depends on what you want. Here's the modeling of 20hz and 22 hz tuning. The 20 hz will take 50 more watts input power. Both models have a subsonic filter applied at 18 hz to keep cone excursion within Xmax limits. Both take three 4 inch flared ports to keep the air speed under 26 m/s.

mj18m spl.JPG

mj18m cone excursion.JPG

mj18m port speed.JPG
 

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Discussion Starter #8
Re: need some advice and guidance with my first hometheater build

i got the behringer 1500. so im guessing 800watts for the sub. i have a yamaha RX-V663 receiver. i use the eQ.2 for subsonic filter.
 

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Discussion Starter #9
Re: need some advice and guidance with my first hometheater build

well maybe im not understanding what a subsonic filter does because would it really matter what SPL difference im getting under 18hz if i apply a filter there? newb question i know. :) i mean, i want to be able to feel it, i guess. and this is a 80%movie,20% music set-up. should i have the subsonic filter at 18hz? i mean i dont want to damage the speaker. o and can you tell me what you input under the EQ/filter tab in WinISD for the subsonic filter at 18hz?
 

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Re: need some advice and guidance with my first hometheater build

The sub sonic filter blocks the frequencies below its set frequency. As shown in the cone excursion graph, at 18 hz it keeps the cone excursion below 15 mm, the Xmax of the sub, with 500 watts applied. in WinISD, click on the "EQ/Filter" tab, click on "Add", under "Filter Type" select Highpass and edit the Cutoff box from 20 to 18 and click on "Add". After it's applied you can select it, Click on "Modify" and change the frequency to see how different frequencies will affect the cone excursion and SPL.
 

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Discussion Starter #11
Re: need some advice and guidance with my first hometheater build

well, i am going to be facing the sub and box towards the audience so would i still be able to feel the lows?
 

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Discussion Starter #12
Re: need some advice and guidance with my first hometheater build


how about that? subsonic on 18hz. 3 ports.
 

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Discussion Starter #14
Re: need some advice and guidance with my first hometheater build

650watts and the excursion at 16hz is 15.56mm but i lose about 1 dB everywhere on the spl graph compared to 800watts. do i have to mind the excursion below the subsonic filter?

the room is large. its 41ft by 13.5ft. its the whole basement. the sub is going in a corner. two walls and a side of the entertainment center.
 

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Re: need some advice and guidance with my first hometheater build

do i have to mind the excursion below the subsonic filter?
If the Subsonic filter is properly applied then the sub won't exceed Xmax and you'll have nothing to worry about.

the room is large. its 41ft by 13.5ft. its the whole basement. the sub is going in a corner.
That is a big room! Corner loading the sub will help with maximum output. Depending on what your expectations are, you can see how one sub does in the room and add a second one in the future if you decide it's needed.
 

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Discussion Starter #16
Re: need some advice and guidance with my first hometheater build

I probably will not need it but i think when i get enough money ill still upgrade to two. :)
and i asked about the excursion below the subsonic filter because i was wondering why you wanted me to "lower the input power so the cone excursion is just above 15 mm at about 16 hz".
 

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Discussion Starter #18
Re: need some advice and guidance with my first hometheater build

but if i have the subsonic filter at 18hz, the sub will not reach xmax at 16hz right?
 

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Re: need some advice and guidance with my first hometheater build

Yes, as long as you don't apply to much power. In post #7 look at the "cone excursion" graph. The pink and green lines from the models do not go above the red line at 15mm, which is the Xmax of the sub. Now look at the input power in the same graph. One model took 500 watts and the other took 550 watts to reach the Xmax at 15 mm.
 

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Discussion Starter #20
Re: need some advice and guidance with my first hometheater build

but if i use the subsonic filter cutting off 18hz and below then why would it matter if i apply more power?
 
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