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Discussion Starter #1
after researching and taking the suggestions of members at another forum, i decided to proceed with a 20x24x24 (WxLxH) slot port (20x22.6x1.5) tuned to 20Hz. i am going to power the sub with a dayton 500W plate amp given i have no eq. i will be documenting my build once i get it up and running. need to order everything first and waiting for nicer weather...hopefully in the next few weeks.

do these dimensions sound about right? i modeled them in WinISD and just want to be sure before i begin. what type, if any, internal bracing would be needed for this sub? as stated, this will be my very first build and am hoping for good results.

any thoughts for a first time builder or other potential issues i should be made aware of? thanks in advance....
 

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Discussion Starter #3
yes those are the outer dimensions. was considering 3/4" MDF. trying to keep the cost down per WAF.
 

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Discussion Starter #5
looking at pdf, i see i could realistically tune the box to 18Hz. What would be the benefit or would this tuning be better considering the dayton 500W amp i am going to use? thanks for the input!
 

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I'm not so familiar with that amp, I'd wait for someone else to make a comment ;)

How big is the room that you are placing the sub in? Any big openings to other rooms?
 

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Discussion Starter #8
room is 19x10.5x9. no openings to any other areas. this sub will only be used as an HT sub.
 

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20x24x24 external is 18.5 x 22.5 x22.5 internal. That gives you 5.4 cu.ft. To tune it to 20 hz with a slot port the full width of the box and 1.5 inches high means the port has to be 41 inches long. The port would take up one cu.ft. so the box is now 4.4 cu.ft. The port air speed with the amp your considering (3rd order HPF at 18hz) would be 14 m/s. The same performance can be had with a slot port 9 x 2 by 21.5 inches long. The port airspeed would increase to 25 m/s which is under 26 m/s where port compression starts.
 

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Discussion Starter #10
ok, maybe i am understanding this incorrectly. i modeled the box in WinISD, but perhaps my understanding of that program is not a great as i thought!! would i be better off increasing all lengths of the enclosures by 1.5"; making the external dimensions 21.5x25.5x25.5? this would allow me to keep the slot port the full length of the box at 25.5 and still be 1.25" high correct?

and HERE is the link to the amp.
 

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This one is a little larger but easier to build because it uses the stock 4" Precision Sound Ports. What drove the choice of size, is the parameters of the driver, and the fact that this uses two full-length stock ports so it is easy to build.

I have the Google Sketchup file for anyone who wants it. Just email.



Kevin Haskins
Exodus Audio
 

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Discussion Starter #12 (Edited)
i agree that design looks a lot easier to build, but i am looking to build a slot port design. just like the look of slot ports! that and the round ports add an additional $40 to cost and keeping cost down is a priority. do you have a slot port design??

i ordered the shiva today and it will be here wednesday....now that is fast!!
 

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You know I don't and unfortunately I'm tied up for the next week where I couldn't pop them out. It isn't difficult.... I could do the napkin drawing fairly easily. I just don't have the time to CAD it.

If you do a cabinet 20" wide OD and use 0.75" material, you have a 18.5" width for the port. The other dimension to get you close to the right port area would need to be about 1.5". That gives you almost 28 inches square of port area (18.5" x 1.5" slot port). The dual 4" flared is about 25 inches sq. but has the advantage of nice flared terminations. I'd use a round over on the slot port termination and that should help and the extra area should make it roughly equivalent. It would need to be about 25-26" long assuming your inside volume is 5.5 cubic feet and your using 50% fill (5lb. box from WalMart). That gives you a 20Hz tune and if you use a subsonic filter around 18Hz you get awesome in-room output with a 500W amp.

With OD of 20" wide, 26" deep, 27" tall you should be able to hit that and have room for a cross brace internally. That will be a HEAVY box but it will be a beast.

Kevin Haskins
Exodus Audio
 

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external dimensions 21.5x25.5x25.5
Then the slot port would be 20" x 1.25" x 25.75" long to tune the cabinet to 20 hz. The port takes up .8 cu.ft and allow of .2 cu.ft for the sub and bracing. The net volume of the box is 5.6 cu.ft. Maximum port air speed would be 21 m/s. You would have to round over all edges and bends in the port to maximize air flow.
 

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Discussion Starter #15
is the port speed too high? i thought i had read that 17 m/s was the acceptable speed, but perhaps that was only with round ports? also, is this enough internal volume? thanks.
 

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Your fine.... you are modeling it at the limits. The models don't take into account any of the driver compression (BL, CMS & power) and in reality, you just don't use a sub at it's limits continuously unless you are playing test tones.

Kevin Haskins
Exodus Audio
 

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Discussion Starter #17
i know you said at "it's limits", but is this a bad thing? would i be better off building a smaller enclosure? sorry for the many questions, but i like to have all questions answered before i begin anything. saves for less headaches later. thanks again.
 

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i know you said at "it's limits", but is this a bad thing? would i be better off building a smaller enclosure? sorry for the many questions, but i like to have all questions answered before i begin anything. saves for less headaches later. thanks again.
No... you are building it right. By at "it's limits" I'm referring to the port noise. You don't get problems until you are at the limits of the amplifier. That means that under normal use you won't be getting into noise problems from the port.

Drive on.

Kevin Haskins
Exodus Audio
 

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Discussion Starter #19
thanks for your help kevin! will the dayton 500W plate amp be sufficient (too much or too little power) for the box i am proposing? i am sure there will be additional questions, but these are the ones at the top of my head at the moment.
 

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thanks for your help kevin! will the dayton 500W plate amp be sufficient (too much or too little power) for the box i am proposing? i am sure there will be additional questions, but these are the ones at the top of my head at the moment.
No...it is about perfect. You want the system to be power limited because if you have enough power on tap to mechanically damage the sub, you may eventually do so. The 500W amp works well because it gives you plenty of headroom & output and it will clip before you smoke the driver. The clipping sounds bad and you will turn it down.

Kevin Haskins
Exodus Audio
 
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