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Discussion Starter · #1 ·
HI guys,


After reading through about 20 pages of the Marty sub thread I think I have a model that might work.


I have an AT screen with limited room so i'm trying to make a shallow taller version for my Dayton 18 HO's with a bottom slot port. I'm trying to hit a tune of around 18hz.


Overall cabinet demensions: 24w x 17D x 44H


Effective Internal volume with double front baffle and bracing, etc: Around 7 cuft


Slot port demensions: 2.75H x 21W x 36L


From everything I've read, i'm giving this a best guess at around 18hz??? Can someone verify or give a best guess?


any glaring problems with velocites or resonances? I'm new to ported builds.


side concern: Is there a minimum distance I should be aware of for clearance of the back of the sub itself to the back wall of the cabinet. With this design, with the port bending up the back wall, I'm looking at the back of the sub being about a little less than 4" off the back wall. Not sure if that matters.


16.25" internal depth - 3.5" port Height - 9" driver depth= 3.75 inches of clearance.


Thanks!
 

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Quote:
 Overall cabinet demensions: 24w x 17D x 44H


Effective Internal volume with double front baffle and bracing, etc: Around 7 cuft


Slot port demensions: 2.75H x 21W x 36L
 

That port length will tune the box to 23hz. You want something like 2.75 x 12 x 34" to tune a 7cu ft enclosure to 18hz.

 

If the driver has a pole vent, you need some breathing room. About the diameter of the pole vent so around 2" is good enough assuming the vent is 1" in diameter.
 

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Discussion Starter · #3 ·
Thanks for the reply. What if I went with the same size slot port as the Marty Cube. Looks like its around 22.5 x 2 x 39. I know it's tuned to around 20 hz, but oddly when you type those numbers into WinISD it spits out around a 22 hz tune. I think they figured the "end correction" thing is off in WinISD.


If I went with the same size port as the Marty Cube, in a slightly bigger box, wouldn't it bring the tune down to around 19 or so?


Is there an advantage in going with a 2.75" high port at 12 inches wide vs a 2" high port at 21" wide? velocitiy wise?


If I end up with a 6 cuft volume, I show a 2"H x 21.5"W x 39L port giveing me a 19Hz tune and first port resonance of 173. Would this work??
 

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Discussion Starter · #4 ·
How does this look? Are port velocities ok?


outside box demensions of 17x24x42 including double baffle.








It seems as if everyone is getting a slightly lower tune than expected on these, so i'm guessing this would end up around 18Hz tune. Sound correct?


This give about 3.75 inches of clearance from the back of the woofer to the back wall.
 

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If you change your tune to 21hz you’ll see that it shortens up the vent by 4” which wont make a big difference. WinISD doesn't notice a few things and leaves one to contemplate. Say if a guy breaks the rule and runs the end of a 4” round vent 2” away from the enclosure wall it will most likely drop the tune. The same happens with a slot vent since the driver sees the vent extending because one of it’s walls keeps running. There are other things that contribute also, but in short that’s the jest of it. Some online calculators apparently factor all this and give a much shorter length. They don’t ask for the full picture though from what I have seen.
Quote:
so i'm guessing this would end up around 18Hz tune. Sound correct?

Most likely pretty close? 18-19ish
 

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Discussion Starter · #6 ·
Thanks Steve. Looks like this design would work then as long as no one sees a problem with the shallow cabinet that i'm not seeing.


I'm a little nervous to make the switch, I finally dialed in my sealed boxes, but like everyone around here, i'm wondering if I could get a little better.


My current graph is below, so i'm getting some great room gains in the lower frequencies which is one of the reasons some go from sealed to ported. I'm curious as to what I would gain overall. As it stands right now, I don't have the subs turned up all the way when I listen to movies, it just gets a little too boomy.


A little bit of a different subject, but what if you had twenty 18" subs in a 3000 cuft room? There is no way you're going to max out your sub volume, even if it's clean, because it would overtake the rest of the sound track. So if at reference level, with a balanced amount of bass, I still have some headroom with my current setup, what would I gain by adding more? I've never had the pleasure of listening to some of the larger bass builds around here, so i'm honestly curious.


Anybody made the switch from sealed to ported that could comment on the perceived gain? I'm wondering if it's worth the switch. I'm hoping for a "hell ya" so I can start cutting wood again


 

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Headroom was my first question but then you followed through and answered that. From looks alone I wouldn't want to mess with what you have going now though. Are you using a LT? You mentioned boomy, what is it that you have going now then?
 

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Discussion Starter · #8 ·
I have two 4cf sealed Dayton 18" HO's being eq'd with a miniDSP.


Is that what you were asking? not sure what "LT" is?


I was trying to maybe get a litte bit more of that "throaty" sound, for lack of a better description. Maybe the boomy side of things means I could use more headroom, lol. I don't know.


If I turn the gain up on the EP4000 it seems like movies become a little muddied. Audyssey actually try's to turn the subs down around 4-5 db from where I currently run them.
 

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I see your response raises 10dB starting at about 17hz. Have you tried flattening that out a little? Sometimes bass can have a heavy feel to it with a low freq gain like that. Off the top of your head do you know how much if any fill/dampening you have in your subs?
 

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You might try pulling all of it out and try that, and then put half of it back in while leveling your response down low and see what you come up with. I would try each with the response you have and each ratcheting down your low-end. You might find you like one of these options much better??
 

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Quote:
Originally Posted by Gomdaf  /t/1522981/tall-marty-slot-port-tune-verification-and-advice#post_24500460


Or screw it and just build two ported because I feel like building something and they look bad ass

Lol What a novel thought! http://www.4smileys.com
 

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Discussion Starter · #14 ·
Looking for the final stamp of approval from the experts before I start building Dayton 18 ported...


Internal box demensions: 24w x 42H x 16D

Volume before bracing and woofer: 7.64 cuft

Guessing on a net volume of: 6.5 cuft

Tuned to 20 hz in WinISD

Slot Port: 21"w x 2"h x 38"L


from what others have said I should be ok with the shallow cabinet. It would put the driver only about 4" off the back wall when taking into account the port going up the back.

Also, the tune should probably turn out around 18-19hz figuring in the end correction that people are seeing.


Any problems that anybody could point out or does this look like its good to go?


thanks!

Phil
 

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I'm no expert but your vent alone is next to 1.3cf http://www.hometheatershack.com/forums/enclosure-volume-calculator/ sq inch calculator at bottom of site after vent calculation. You have to account for the wall of your vent also. Something you might want to think about is you would be better served by going a 3/4 length down the middle of your vent (two vents) as to help with bracing.
 

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steve, with the slot port effective at 21", it looks like he is accounting for two braces down the slot port and one wall thickness on each side for a total of 3" of reduction from the external dimension.


"Any problems that anybody could point out or does this look like its good to go?"


so long as your sure that you have clearance from the back of the driver (you don't need a lot, 4" is fine), your numbers look good to me.


the cab volume seems about right. i double checked the port. should be a good performer. i'd like to see a smidgen larger port, but that would complicate things in this case more than it would help performance, i think.
 

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Quote:
steve, with the slot port effective at 21", it looks like he is accounting for two braces down the slot port and one wall thickness on each side for a total of 3" of reduction from the external dimension.

I guess so.. I can't know that unless it's communicated though? I just plugged it in to verify the tune as suggested in post 4 and go from there before looking at anything closer. Unless correction has also been added since? the vent will take up displacement factor.
 

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Discussion Starter · #19 ·

Quote:
Originally Posted by LTD02  /t/1522981/tall-marty-slot-port-tune-verification-and-advice#post_24514794


steve, with the slot port effective at 21", it looks like he is accounting for two braces down the slot port and one wall thickness on each side for a total of 3" of reduction from the external dimension.


"Any problems that anybody could point out or does this look like its good to go?"


so long as your sure that you have clearance from the back of the driver (you don't need a lot, 4" is fine), your numbers look good to me.


the cab volume seems about right. i double checked the port. should be a good performer. i'd like to see a smidgen larger port, but that would complicate things in this case more than it would help performance, i think.
Quote:
Originally Posted by LTD02  /t/1522981/tall-marty-slot-port-tune-verification-and-advice#post_24514798


"Anybody made the switch from sealed to ported that could comment on the perceived gain? I'm wondering if it's worth the switch."


haha...you must have missed the mother of all all switches:

http://www.avsforum.com/t/1516234/8x-18-lms-5400-ultras-sealed-to-27-cube-15hz-ported-build/

LTD is correct on the slot volume for a net of 21" after walls and 2 braces. when you say you'd like to see the port a "smidgen larger", are you talking port height or length? I might be able to spare a quarter inch higher but I'd be about 3.5" off the back of the driver. How would this help?
 
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