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Obsidian Audio 18 Enclosure Assistance


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Good day all = )

I am in search of some assistance with specs for an Obsidian Audio 18. Made some attempts but getting extremely confused overall. Working with a max of 7.0 ft^3 gross. Would like to tune to 33-34 Hz. Will be putting 1200w on it. Was considering firing sub upward & porting backward or sub & port facing upward (Wagon). External dimensions available are anywhere between 41W x 15H x 25D.

Any assistance would be greatly appreciated. Thanks!

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The OA18 sub has a bit of a weak motor for the amount of cone area it has.  This causes its output to begin to roll off on the bottom end at a bit higher frequency than other subs might.  My suggestion would be to tune a bit lower (say 30 hz or so) and make the box as large as your space will allow.  6 cu ft net would be great, but it you can't get that much it will be OK.  

"Nothing prevents people from knowing the truth more than the belief they already know it."
"Making bass is easy, making music is the hard part."

Builds:

U7qkMTL.jpg  LgPgE9w.jpg  Od2G3u1.jpg  xMyLoO1.jpg  9pAlXUK.jpg

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Well that's extremely depressing news = ( Not exactly what a new owner wants to hear about their sub they were hyped about, you know? But I always appreciate the feedback. Do you think it was a bad idea to swap the SA 15 for it? Or will it better maximize my 1200w?

I was going to do the box tomorrow/Monday. Here's what I came up with:

Gross - 7.02 ft^3, Net - 5.13 ft^3, Port - 1.75" x 22.75 x 32" (2) (Again with the "bad" port ratio. I know you especially frown on anything over 1:5), Total Port Area - 79.625 in^2, Tuning - 33.5 Hz, Box firing upward. Sub to middle. Ports to either side.

If that is all wrong, I just worked out something more straight-forward after reading your message.

Gross 7.02 ft^3, Net 5.0 ft^3, Port 5.875" x 13.5" (1) (Muchhh better port ratio), Total Port Area - 79.3125 in^2, Tuning - 31 Hz, Sub firing upward, port firing backward on passenger side.

Thanks again for the help bro. Checked out some of your work. Jaw dropping. I am honored.

 

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I wouldn't lose sleep over the weak motor thing.  Its not an uncommon situation for many 18" subs and the OA18 you have will still be louder than the SA-15 would be in every single way.  Its just what happens when they use the same motor for the 10", 12", 15", & 18" subs in a product line.  The 10" subs end up having too strong of a motor and the 18"s end up a little weak.  

As far as your first proposed box specs go I think you will be fine.  You are right, I don't like the aspect ratio of your ports, but you have enough port area that it shouldn't matter.  With a 22.75" wide port I'd suggest putting a brace piece in the middle to keep the panels from flexing.  Bracing is a important thing to consider with a box the size of yours, regardless of your port dimensions. 

Your second box specs do have a much better port aspect ratio and I'd prefer the lower tuning, but if you think the first box with ports on each side will make you happier, I would go with it.  

 

 

"Nothing prevents people from knowing the truth more than the belief they already know it."
"Making bass is easy, making music is the hard part."

Builds:

U7qkMTL.jpg  LgPgE9w.jpg  Od2G3u1.jpg  xMyLoO1.jpg  9pAlXUK.jpg

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Will try not to @ lose sleep. lol. Make sense @ same sized motor across the board. Was worried that you meant in comparison to most other 18s. Relieved to know that it should be a step up from the SA.

Surprised to hear you give an "Ok" on the first spec. Wasn't expecting that. Was intending on bracing the port. Not sure how just as yet. Will supports along the port be an issue in terms air flow? Or they will be negligible? Any suggestions? Will the box itself need to be braced? Or will the ports act as enough of a brace?

Will the second box perform better in your opinion? Looking at peaking around 36, preferably 38 for the most. Don't want 40+ to be overwhelming, more on the downward slope. Firing up would allow me to push the enclosure closer to the tailgate, which was recommended. Was also advised against tuning as low as even 33 but I insisted on not going much higher that that preferably.

Thanks for the time/patience & expertise! = )

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Sooo, thinking the tuning got thrown off somewhere. The inside opening of the port ended up being short off the wall (2.75" when port is 1.75" wide). Still breaking in a little & experimenting a bit but from appearances, it's not giving the kind of low end output I was hoping for. I crossed it a tad higher on the deck just to check & the 40-50 Hz range difference is loud as hell.

On doing some more research I found a guy who said he got a recommendation of 5.25 ft^3 tuned to 28-29 Hz from Jacob. That rang a bell since you suggested tuning lower & going a larger net volume if possible. Dropped the port area & went with a better port ratio. I came up with a similar spec to the second option posted earlier. 5.25 ft^3 net, tuned to 28 Hz. Port is 13H x 4.75W x 34L. Sub firing up, port firing back & will be on passenger side. If after some adjustments & breaking in it doesn't perform as I hoped, will be doing this box. How do those specs sound? Is the port area too small? Thanks!

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Sorry I haven't responded earlier.  I'm in the middle of my busiest time of year and I just don't get much time to get back to people. 

Regardless of how you arrange your port, your box should be braced internally.  Here is a post I made on bracing techniques: 


Your box specs of 5.25 cu ft net tuned to 28 Hz with ~62 sq in of port are should be fine. 

One thing you might do with your current box is verify the tuning frequency.  Sounds like it might have come out higher than you intended.  You can verify your tuning frequency by playing sine wave tones at moderate volume while watching/lightly feeling your cone.  Adjust the sine wave frequency up and down until you reach the point were cone movement is at a minimum, that will be your tuning frequency.  

"Nothing prevents people from knowing the truth more than the belief they already know it."
"Making bass is easy, making music is the hard part."

Builds:

U7qkMTL.jpg  LgPgE9w.jpg  Od2G3u1.jpg  xMyLoO1.jpg  9pAlXUK.jpg

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No reason to be, no explanation needed. Didn't think you were sitting around doing nothing & all that amazing work is appearing out of nowhere, lol. Very much appreciate that you took the time to drop in.

Thanks for the link. I did actually brace the last box & usually use some form of bracing when required. I took the box for a guy working at the dealership to hear & we messed around with it. Although it seemed to be tuned to 33 it was peaking around 50. Very strange indeed. Sometimes going simple is the best way. Especially with my limited experience. Was going to do over an entirely new box but decided to mod the old one. Went with 5.25 ft^3 net tuned to 30 like you initially suggested. Port is 63.75 in^2, 5 x 12.75 x 29.75. Sub up, port back. It's currently in progress. Hoping to finish it tomorrow (Saturday). Will probably add a brace. Ended up pushing the sub furthest away from the port. Have a better feeling about this spec. Hopefully it works out well = )

Keep up the great work!

Thanks again!

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Small update. Completed the modification on the box. It sounds 10x better than the last one, thanks to all the help. My one possible issue is that the port firing backward is basically 5" from the tailgate. The port is 5" wide. How big of an issue is this? & does it warrant another do-over?

Apart from that, my biggest issue at the moment is rattles O_o. Trying to take care of that one piece at a time. Next upgrade to system will be an Xs d3400r at the end of this month. Looking forward to that very much. Will there be any audible difference? Running a stock current setup with a big three upgrade atm. Curious. Thanks!

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