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Reducing Internal Volume In Existing DIY Sub

post #1 of 22
3/25/09 at 8:19pm
Thread Starter 
Less than a year ago I had completed my IXL18.4 LLT build. It's current volume is 13.34 cu feet tuned to 14.5 hz.

I started thinking last night about altering the design, reducing the internal volume by 1.34 cu feet which would then yeild 12 cu feet with a 15.27hz tuning freq. I'd gain some extra SPL due to increased power handling and my cone excursion would be less than XMAX. My current setup exceeds XMAX by 2mm at around 23hz according to WinISD.

I was wondering if anyone had any good ideas on an easy way to reduce the volume?

I started thinking about using some 4x4 fence posts and lining the existing interior with them. Would say a foam block that comes with electronics work or is that not dense enough?

Any other ideas?
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post #2 of 22
3/25/09 at 8:47pm
Foam will not be dense enough to greatly reduce the volume. You could very easily build a small box to put in the box to reduce the volume. By the way how much will the extra port volume reduce volume? This will need to be taken into account as well.
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post #3 of 22
3/25/09 at 8:58pm
Edit: you don't need to cut the ports back, if you make the box physically smaller.
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post #4 of 22
3/25/09 at 10:04pm
When I review the Unibox model of my sub in a ported box, reducing volume at a constant port size increases box tuning frequency and adds a bit of a peak. Seem to be what WinISd is saying, too.

In a sub like yours, there's one obvious way to take up internal space - add internal bracing. I'm thinking specifically of constraint layer damping: glueing massive panels (1" oak?) to the flat areas. It'll take up space and do something beneficial. I doubt you can reach the far segment, but the front and middle ones are accessible. This is one reason I'm thinking of bolting on one end of my end table sub's driver enclosure - you never know when making one of a kind when it might need a little adjustment.

Have fun,
Frank
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post #5 of 22
3/25/09 at 10:18pm
You are correct... I was wrong, I just checked as well. Ok, so if you reduce the volume, you need not shorten the ports. Eek.
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post #6 of 22
3/25/09 at 10:19pm
Quote:
Originally Posted by fbov View Post

When I review the Unibox model of my sub in a ported box, reducing volume at a constant port size increases box tuning frequency and adds a bit of a peak. Seem to be what WinISd is saying, too.

In a sub like yours, there's one obvious way to take up internal space - add internal bracing. I'm thinking specifically of constraint layer damping: glueing massive panels (1" oak?) to the flat areas. It'll take up space and do something beneficial. I doubt you can reach the far segment, but the front and middle ones are accessible. This is one reason I'm thinking of bolting on one end of my end table sub's driver enclosure - you never know when making one of a kind when it might need a little adjustment.

Have fun,
Frank

Phone books 2x4's ream's of paper will all work.
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post #7 of 22
3/25/09 at 10:57pm
Rigid styrofoam works well.
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post #8 of 22
3/25/09 at 11:17pm
Bricks, pavers or sandbags.
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post #9 of 22
3/26/09 at 2:36am
Quote:
Originally Posted by mynym View Post

I started thinking last night about altering the design, reducing the internal volume by 1.34 cu feet which would then yeild 12 cu feet with a 15.27hz tuning freq. I'd gain some extra SPL due to increased power handling and my cone excursion would be less than XMAX.

you are a genius. you could write the next stimulus bill.
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post #10 of 22
3/26/09 at 7:47am
Thread Starter 
Thanks for some suggestions. I should have mentioned that I'd like this to be temporary so I can try out a few different configurations and remove them if need be.

I was thinking about adding pillows but I am sure they'd act as dampening and actually do the opposite of what my objective is.

Was thinking of lining the enclosure with some eggcrate foam or something to see if I can reduce some of the hollowness sound as well.

Ideas?
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post #11 of 22
3/26/09 at 10:05am
Seems like bricks would be the easiest solution. You could put in as many as needed and they should be easy to place, as well as easy to remove.
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post #12 of 22
3/26/09 at 10:34am
Thread Starter 
Quote:
Originally Posted by fsrenduro View Post

Seems like bricks would be the easiest solution. You could put in as many as needed and they should be easy to place, as well as easy to remove.

The problem I see with bricks is the placement and securing them, at least with my setup:







I can just see a brick moving around falling down on the back of the sub!
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post #13 of 22
3/26/09 at 11:55am
Use a bit of ingenuity to figure out how to stop them moving around.
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post #14 of 22
3/26/09 at 12:33pm
It appears that the rectangle opens in your bracing are approx 9.75"x6". Build 4 air tight boxes out of 1/4" MDF (to keep weight down) that are 9"x5"x13" (outside dimensions). Insert boxes up into the middle section of the enclosure, rest them on the bracing, and use double sided tape to temporary attach the box to the side walls. The volume of each box is approx .338 cu ft. Add or remove boxes to change the overall volume.

Edit: This may restrict the airflow to much between the bottom and middle sections. You could use two boxes from above and also make some smaller boxes to fit in the bottom section. How much room do you have between the side walls and the driver on the baffle?
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post #15 of 22
3/26/09 at 2:08pm
Fill a bunch of ziploc bags with sand and place them where needed. It might be tough to figure out how much volume they're taking up though.
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post #16 of 22
3/26/09 at 4:27pm
for the bricks you could lay them out like this



with a small dab of hot glue to hold them in place, then once you get what you want use construction adhesive.
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post #17 of 22
3/26/09 at 5:40pm
Thread Starter 
Quote:
Originally Posted by Cy-Gor View Post

for the bricks you could lay them out like this



with a small dab of hot glue to hold them in place, then once you get what you want use construction adhesive.

Thats a pretty good idea.

I like the location and it doesn't obstruct the existing bracing. It's also easy to get at. The only thing I may change is using blocks of wood, say 3x3x? with perhaps a compression fit against the walls?
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post #18 of 22
3/26/09 at 9:42pm
If you like the brick/block idea, why not glue bigger bricks/blocks to the middle of the walls and gain some cabinet damping? You'd need a great deal more than a dab of glue to get an effective damping layer, but it's a way to make the volume reduction more than a tuning change.
Frank
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post #19 of 22
3/27/09 at 1:33pm
likely the balloon depending on the internal pressure would be seen as a part of the air space.

i would bet if you could get a balloon that wouldnt expand so much and have it be at very high PSI then maybe it would work.

something at least the psi that the sub is capable of generating.

sand bags bricks or blocks of wood are probably easier solutions.
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post #20 of 22
3/27/09 at 3:38pm

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post #21 of 22
3/28/09 at 2:51pm
Thread Starter 
haha yeah that great stuff is killer. As you mentioned though, It would be kinda hard to be precise with that. Fun none the less.
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post #22 of 22
3/28/09 at 3:11pm
I agree its somewhat uncontrollable, not impossible to remove, you can cut it out with a knife, but for sure difficult to seperate the bond from the internal wood, but It would work.
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