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Discussion Starter #1 (Edited)
Help with Enclosure design (Update)

Hey guys,

This is my first attempt at building a sub. Original thread here http://www.hometheatershack.com/forums/diy-subwoofers/19981-help-noob-please.html

I finally got the Oaudio 300 and the Titanic MK-III and will now be building the enclosure. I tried to model WinISD but the final output is completely off.


Can you please tell me what i am doing wrong?

Thanks so much.
 

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You are putting it in a .2 cubic foot box. Bump that up to around 3 to 6 cubic feet and tune it to between 18 and 22 hz see if that helps.
 

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I'm coming up with about the same thing that Mike did. 3.5cubic feet (99liters) tuned to 21hz. You'll exceed excursion around 17 hz on the 300watts you said you have. Tuning lower would protect the woofer at lower frequencies but it would also REALLY compromise upper end extension. Here are the graphs I've come up with in Unibox.

 

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Discussion Starter #4
Thanks Derek. Here is what i got when I tried the other measurements.

and this is what I got.. Mike gave me this design in the Titan MK IIIprevious thread, and I am just trying to understand why I am not getting the same results..
 

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One thing that might be throwing off everything is becuase you are in "Transfer Function Magnitude" at the top of the WinISD Graph. Try clicking where it says that, and it should bring down a bar of multiple things that you can click on. Go down to where it says "SPL" and click on that. Don't go to Maximum SPL because it will show the driver's max SPL in that box size.

Also, try raising your tuning .5hz, and it should be spot on with Mike P.'s graph, but I don't know if anything else is different between your guy's graphs.
 

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Something is not right with your driver file from the looks of your modeling. Double check your parameters for the driver.
 

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Discussion Starter #10
Hey guys,

Finally found someone who will cut the wood for me. The final internal dimensions are 18x18x21 and
I plan on using ¾ MDF. Some questions on the design though. Should the port be a rear entry one or front? also how about downfiring vs front-firing?

My application will be about 60:40 HT and Music. I also have hard tiled floors, if that's relevant.

Thanks for your help!
 

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Discussion Starter #12 (Edited)
Thanks for your help Mike,

I checked the measurements and this is what I get

16.25" width
23.5" depth
24.75" height.

I am using .75" inch MDF, so the internal dimensions will be 1.5 inches less. The port would open at the back, I have just drawn the port on the front so that you can see the position. The box comes to a 4.366 cu.ft. after ignoring the port & the driver volume. You had suggested a volume of 3.8 cu.ft. I was forced to go with a bigger box, due to the port positioning within the enclosure. My understanding is that I have to leave a 4" gap from the end of the port to the wall & also from the position the flare 4" from all edges.

I am not sure what I am doing wrong.

 

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I have to leave a 4" gap from the end of the port to the wall & also from the position the flare 4" from all edges.
Ideally it would be one port diameter away from the walls, it will work with less. I'm away from home at the moment, I'll run the numbers as soon as I can.
 

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Don't be overly concerned with the location of the port outlet in reference to the baffle. Just make sure that there's at least 4" clearance between the port inlet and the rear of the enclosure. The real problem lies with your design.......a single 4" port is going to chuff at higher output levels with port air speed reaching above 40 m/sec. Given the Oaudio manual, there appears to be a HP filter at 20hz 12db/oct which will be cutting it close for a 20hz tune. I'd tune lower.
 

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Discussion Starter #16
Don't be overly concerned with the location of the port outlet in reference to the baffle. Just make sure that there's at least 4" clearance between the port inlet and the rear of the enclosure. The real problem lies with your design.......a single 4" port is going to chuff at higher output levels with port air speed reaching above 40 m/sec. Given the Oaudio manual, there appears to be a HP filter at 20hz 12db/oct which will be cutting it close for a 20hz tune. I'd tune lower.
Mayhem: I am actually planning on a rear port. I just listed it in the front as it was easier than making two separate drawings. So I guess the same rule applies? 4" clearance between the port and the front of the enclosure?
 

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Front,back,sides.....it doesn't matter. The same rules apply. But as i said earlier, you'll need a larger diameter port...or multiples of the same or smaller. Three 3" ports (SVS style) bring the air speed down to 26 m/sec, but port length increases to 34" which may require some elbows on the ports.

I haven't read your original thread so i don't know the room size for this build BUT......any reason you chose ported over sealed with this driver? The Titanic is clearly better suited towards a sealed alignment given the TSP's and in a smaller space with available room gain might be the better option.
 

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Discussion Starter #20
Front,back,sides.....it doesn't matter. The same rules apply. But as i said earlier, you'll need a larger diameter port...or multiples of the same or smaller. Three 3" ports (SVS style) bring the air speed down to 26 m/sec, but port length increases to 34" which may require some elbows on the ports.

I haven't read your original thread so i don't know the room size for this build BUT......any reason you chose ported over sealed with this driver? The Titanic is clearly better suited towards a sealed alignment given the TSP's and in a smaller space with available room gain might be the better option.
I went with the recommendations given in the other thread. I will be using it for both HT and Music maybe that's why ported was recommended?
 
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