figuring port length

I am thinking to redo my enclosure with the sub facing up and port rear-firing. Do I find the port length based on the enclosures net volume? I am thinkng 5ft^3 net with 65 sq inch port @ 35 hz..  The enclosure will house an 08L7154 wired to 2 ohms, sub amp is 08zx750.1.  I have it in a 4.75 net enclosure 65 sq in port tuned to 40 now but still am not convinced I have it sealed properly. Any pros or cons to the new enclosure size/tuning I am considering? I have done the big 3 upgrade and the back half of car (96 cavalier) is dampened. The reason for facing the sub up is to make it harder to steal. We have some young punks around here and I wanna make it as difficult as possible to get at. I already have to remove the entire back and 1 front seat to get the enclosure in, plus rear interior panels and bend some sheet metal along rear deck. Anyway do I figure port length on net enclosure size? Thanks in advance.

thatfloorguy wrote:

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Anyway do I figure port length on net enclosure size? Thanks in advance.

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Yes.

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Thank You. I thought so,but thinking can sometimes be catastophic.. So any pros or cons to this design other than rear deck vibration and more than likely losing the 6x9 connections? I plan on eliminating them for compononts later anyway.

Ok with this design I will be able to go 15" high to allow 2" clearance for driver movement. I figured a port opening of 4.5x13.5 for 60.75 sq inches, 25.5 deep puts me a little over 32 hz. Will this be be ok or am I pushing the driver too far? I am planning to resin the interior of the enclosure and adhere polyfil. I am looking for a low deep bass responce,without putiing too much stress on the driver.

So I came up with a gross enclosure of 6.13ft3^ port is 60.75 sq inches tuned to 35hz. Will this be ok for this driver/amp combo, or am I asking for trouble? I don't want to keep building enclosures, it is quite a bit of work just getting them into my car. I figured on a 5ft^net,   .3 for driver/brace displacement, and  .82 for the port displacement. That was 6.12 gross. Will the difference in my final design affect the performance that much?

That's a very large port opening.  I can't imagine you need to give that much enclosure volume to the port structure on the basis of quieting port noise.  Are you looking at a port noise model as you come up with this design?  WinISD or anything?

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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

6X9 for a comp in the rear? Get outta town. Whats up with a bandpass box? Actually I run comp speakers in my Frontier's rear doors. Just the driver though, HPF like 130+/-. Do you Solder?



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https://www.caraudiotalk.com/audio-forum/showthread.php?t=7014 I was designing my enclosure using this site. I was looking to get a lower deeper responce than what I now have. The enclosure I have now has a 65 sq" port opening tuned to 40 hz. I was under the impression the smaller ports produced more noise.I was also considering the use of poilyfil to help smooth out the responce.  As far as the comps in the rear I have already made custom panels for the rear as I have my amps mounted underneath them.They are in the sides where the doors would be in a 4door model.(1996 cavalier). I have an 08zx350.4 so was considering 2 sets of comps front/rear.  My revised design is allowing .2 for driver/brace port is 4.5x13.5x23.5, 5ft3^ for enclosure for a totalof 6.06ft3^ gross.It is tuned right around 33 hz.I haven't put on the top yet as I wanted to resin the interior. I can still change the port if need be.I am open to suggestions. I just saw where Kicker's 6ft3^ enclosure was tuned@ 30 hz w/ around a 58 sq" opening and my current enclosure is 65, so I went somewhere in between hoping to err on the safer side if that is possible. Should I stay closer to the 58 and tune to 35 hz as opposed to 33? I want a low deep smooth responce without port noise.  and yes I can solder I didn't even consider soldering the leads, just accepted they were going to vibrate loose

You have a Kicker L7?  5 cuft tuned to 33Hz should work out pretty well.  I'd use a 58 sq-inch port opening (3.5 X 16.5 inside measurements.)  For 33Hz in 5 cuft it would be about 11.5" long.  Don't forget a subsonic filter.

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I am limited as far as the enclosure size. I have 13.5 high inside that will allow for 4.3 wide, at 58 sq". Will adding to the thickness of the port wall be sufficient, or will it take up too much volume? I figured on .3 for driver/brace displacement(guessing). I am pretty sure the amp has a subsonic filter. (08zx750.1)  I think I can remove the port and make my adjustments, I haven't put on the top yet. If not I will start over GRRR. I knew I should have waited before doing the port. Again the driver will be facing up to deter removal without bringing the enclosure into the car. That is why I am restricted to a hight of 15". This allows 3" for driver movement before the deck. The port will be rear firing allowing 6" from the trunk.

I am assuming you guys would reccommend I keep my day job, as there isn't much call for pot noise models these days!!

The actual geometry of the port matters far less than the opening size and length.  As far as port noise, with that large an opening you shouldn't have audible noise at any power level short of destroying the driver (in a vented enclosure an L7 is power limited to less than 750 watts.)  Up-firing should be OK for that woofer as I've seen it done, but I don't know the exact T/S parameters to tell you if that further limits the power handling capability due to sag,  I don't understand your statement about "leaving 3" before it hits the deck"??  Do you mean between the face of the woofer and the nearest surface?  The L7 will not move that far (indeed no woofer currently available will.)

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Yes from the face of the driver to the bottom of the deck is 3" min 4" at most of the area. I doubt I am getting 750 rms out of the amp. I had 2 cvr 12's in a common chamber ported enclosure one with a bad VC and they never died. They are only 300 each in the ported enclosure. I had just under 4ft^3 for the both combined. So is putting another 1/4" along the inside port walls not a good idea? I thought to use 3" triangular braces to minimize displacement if so.I wasn't aware that the driver facing up will affect the handeling, interesting.Also will I get a smoother responce by attaching polyfill when I resin the interior, or would you not reccomend it in this enclosure design?

re: battery discharging and amplifier gain setting.  If the battery is discharging through the cap then you either have a defective cap or it is installed incorrectly.  Please read the "How to set your gain" sticky in the Hot Topics forum.  Using bass boost to adjust the relative volume level of the sub is one way to fry your voice coils as the amplifier will clip if bass boost is over-used.  And you absolutely should not operate your system if there is no fuse on the main power cable at the battery, for safety reasons.

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