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View Full Version : Praying to the box design gods (planet audio FU 18")



brandontw
11-30-2004, 08:00 PM
I need help designing a box for a fu-18-2 for my Taurus, I want to retain as much SQ as possible with this SPL sub, I have 5 cubic feet, and will be powering the thing with my bx1500d

http://www.planetaudiousa.com/print/FU18-15-12.html

There is a link to the sub.
Here is a link to the specs:

http://www.planetaudiousa.com/user%20manuals/2003%20Woofer%20Specifications.htm

How should I build the port, which way should I face the sub (I have rattle problems)
which way should the port face. I am not totally new to building boxes, I built a dual chamber ported box for my hx2's and it worked out superbly, but I have never made a box like this, and still don’t quite get how to tune your box (how do you tune it lower or higher?)
I threw together this super ghetto drawing of what I was thinking in paint:

http://img56.exs.cx/img56/3559/untitled694.jpg


it adds up to like over 7cubes if I leave that number at 1.2, but if I put it at 1.1 then it will be 6.6 cubes, which is recommended, but I don’t know if I should count for port displacement or what. The sub would be facing up, toward my rear deck, and the port facing out into the trunk toward the back of my car, and I don’t know how big or how long that port should be

please help.
Thanks guys.

bigred78797
11-30-2004, 08:11 PM
If you wan't go to my website that's in my sig and email me at that email. The link for the sub specs wasn't working for me so just send me the sub specs in the email along with the maximum allowable L x D x H. Also give me a good description on how you want the box to look and the overall desing and ill have everthing ready for you in about a day maybe two. And don't worry it doesn't cost anything.

brandontw
11-30-2004, 08:35 PM
specs for the sub are:

Nominal Diameter- 18"
Basket Diameter- 17-13/16"
Mounting Diameter- 16-1/2"
Mounting Depth- 9-1/16"
Magnet Diameter- 8-3/4"
Magnet Weight- 300oz
Frequency Range- 32-200 hz
Nominal Impedance- Dual 2ohm
DC Resistance (Re)- Dual 1.8ohm
Resonance Frequency (fs)- 38.92Hz
Mechanical Q Factor (Qms)- 2.682
Electrical Q Factor (Qes)- 0.275
Total Q Factor (Qts)- 0.27
Effective Cone Area (Sd)- 190.960sq in
Equivalent Air Volume (Vas)- 4.64 ft^3
Dual Flat Progressive Spiders
Compliance (Cms)- 62.43uM/N
Moving Mass (Mms)- 263.39 g
Voice Coil Diameter- 4 inches
Voice Coil Winding Height- 23mm
Voice Coil Former Material - Anodized Aluminum
Voice Coil Inductance 368.804 uH
Force Factor (Bl)- 12.163 TM
Linear Excursion (Xmax) 10.33mm
Sensitivity (SPL)- 96 dB
Operating Power (Pe)- 1800 watts

DBfan187
11-30-2004, 08:44 PM
I don't know if it's me or what, but BB6P shows that sub in a ported box, 6.6^3' @ 28Hz with an F3 of 90Hz. WTF?.

brandontw
11-30-2004, 08:47 PM
whats bb6p, and what is f3? i do want it tuned low i think, but how do i do that?

bigred78797
11-30-2004, 10:26 PM
BB6P = BassBox6Pro i believe... that's the program you use right? I use a somewhat older version of LEAP 5 or something like that. And came up with similar results.

DBfan187
11-30-2004, 10:31 PM
BB6P = BassBox6Pro i believe... that's the program you use right? I use a somewhat older version of LEAP 5 or something like that. And came up with similar results.
Yup, it has baffooled me.

brandontw
12-01-2004, 12:19 AM
Yup, it has baffooled me.
y are you bafooled?

brandontw
12-01-2004, 03:20 PM
bump, man, y dont people want to help with this? is it weird?, tough? cmon, i just need a little input

bigred78797
12-03-2004, 02:58 PM
hey i finished designing the box for you. Let me know if this is ok, the dimensions are 30x18x23 tuned to 36.8hz.. that's a bit high but i should work good for ya with a good response and such. Well heres the pic let me know if it's ok so i can make out the cut sheets.

brandontw
12-03-2004, 03:55 PM
thanks buddy, its an awsome design

Spkrman
12-03-2004, 06:05 PM
why 2 ports? Why not bunch one port together on one side of the box, and bump the sub all the way over to the other side?

Also.. has fitting the box through the trunk lid opening been taken into consideration???

And... this sub hates low tunes... lol. It peaks high and it likes to stay peakin high... have fun tunin it below 40hz ;)

Also... this is a trunk car... you always tune higher than you "want" tuning because your in a tight space back there, it drops "tuning" about 5 hz, sometimes more.

brandontw
12-03-2004, 06:11 PM
yea

bigred78797
12-03-2004, 06:12 PM
Yeah i took all those into conscideration... i did two ports because I like symmetry and felt like putting the sub in the middle. I know the sub doesn't like low tones that why i put it at 36.8 hz I usually tune lower into the 28 to 30 range for someone who wants some decent SQ. I also built the box to his specs if he cant fit it in the car then it is his problem because he gave me the specs to built it too and i built it to them. Im aware of the tone shift and effects of a box in a confined space. I mean i didn't start doing this yesterday.

TimberJon
12-03-2004, 06:14 PM
Why not drop one port out the box opposite the other port. fire each port towards the SIDES of the trunk. Ive gotten better results from side porting, and you feel the bass a bit more IN the cabin. the cars on your flanks feel the pain too if your subs are powerful enough.

Also, for Twin 12, 13, or 15" sub enclosure designs, Sometimes i port one out of each side, and the other pair towards the rear of the trunk. 6-port designs are brutal if you design the box right. You can just about point a port in any open-air direction.

bigred78797
12-03-2004, 06:19 PM
There is no way to consistenly determine the effects of facing a port in a certain direction. What works for your car may not work for another car.. most of the time port direction only adds a fraction of a decible which a person would not beable to notice only and instrument such as a TermLab Mic would be able to do so. And i was also conscidering the fact that he gave me a sides limit of 33 inches... blocking a port by a wall or object is not the brightest thing in the world to do and will completely negate any calculations determined for that box causing unexpected results.

BASS OUTLAW
12-03-2004, 06:23 PM
hey Well heres the pic let me know if it's ok so i can make out the cut sheets.
http://www.caraudio.com/vb/attachment.php?attachmentid=2971

hey how did u draw that 1?
what program ?
thanks

Spkrman
12-03-2004, 06:27 PM
Yeah i took all those into conscideration... i did two ports because I like symmetry and felt like putting the sub in the middle. I know the sub doesn't like low tones that why i put it at 36.8 hz I usually tune lower into the 28 to 30 range for someone who wants some decent SQ. I also built the box to his specs if he cant fit it in the car then it is his problem because he gave me the specs to built it too and i built it to them. Im aware of the tone shift and effects of a box in a confined space. I mean i didn't start doing this yesterday.

Your figuring tuning will be EXACTLY 36.8hz... tuning doesnt mean much - its what the sub does in the box. Theoretical tuning and actual tuning are very rarely the same...

You obviously didn't take the trunk into account saying "its tuned to 36.8hz" and you normally tune to the 28/30 range... which you just don't need to in a trunk if the box makes proper use of the trunk

And you can't design a box for a trunk if you don't know if it'll fit through the lid...


There is no way to consistenly determine the effects of facing a port in a certain direction. What works for your car may not work for another car.. most of the time port direction only adds a fraction of a decible which a person would not beable to notice only and instrument such as a TermLab Mic would be able to do so. And i was also conscidering the fact that he gave me a sides limit of 33 inches... blocking a port by a wall or object is not the brightest thing in the world to do and will completely negate any calculations determined for that box causing unexpected results.

its a trunk - everything is unexpected.

I better stop now ;)

bigred78797
12-03-2004, 06:35 PM
Yeah i know that i can't EXACTLY tune a box to an EXACT frequency in an UNKNOWN UNCONTROLLED environment. I just use past box building and Installation experience i mean i only worked in a shop for 2 years as one of the custom box builders. When someone gives me dimensions i expect for them to take into accout wheather or not it will fit through the trunk or no. In most of my trunk installs i tune low, I just tend to have better more reliable result when i do.

bigred78797
12-03-2004, 06:37 PM
Oh and bass outlaw i use 3dstudio max, i could use autocad but i like 3dstudio better as i can do more scene editing.

Spkrman
12-03-2004, 06:55 PM
Yeah i know that i can't EXACTLY tune a box to an EXACT frequency in an UNKNOWN UNCONTROLLED environment. I just use past box building and Installation experience i mean i only worked in a shop for 2 years as one of the custom box builders. When someone gives me dimensions i expect for them to take into accout wheather or not it will fit through the trunk or no. In most of my trunk installs i tune low, I just tend to have better more reliable result when i do.

Tuning low when rear firing into a trunk is really the only way to go... because normally the acoustics of the trunk won't let you tune really high anyway... cuz it just doesnt work.

From *my* personal experience... the box design that was originally drawn would work a heck of alot better than the one you threw together. Not saying those exact dimensions or placement of things, but that design works better in a trunk... especially when you take the trunk lid opening into account. Your not getting 18" of height in almost any trunk... not through the lid at least.

2 years as a box designer doesn't mean a heck of alot... I can hammer nails in crooked all day, and hey, they probably hold..... but it doesn't mean its the best way to do it, and it doesnt mean i'm learning anything.

bigred78797
12-03-2004, 07:10 PM
Hey i just built the box to his specs. if he feels that 18" can fit into his trunk then im gonna build the box 18" high. I personally go more in depth into car audio than the average "box builder" in a shop. One of my main thing is trying to completely learn is everything about how speakers react, i have a nearly complete understanding of all of the characteristics of speakers in boxes from sealed enclosures to enclosures utilizing the quarter wave therory. If you wanna get on my aise about it then fine. And no i didn't just nail the boxes or just spray the fiberglass or just put on the carpet, I did from start, design concept, to finished product. Never had a complaint or blown anything in any of my setups. Even recieved compliments at local car audio shows from other car audio stores. The only thing that i really changed from the original design was having two ports instead of one which really wouldn't make a large audible difference. The sub is facing up.. because the guy asked me to face the sub up.

Spkrman
12-03-2004, 07:41 PM
alrighty ;)

brandontw
12-03-2004, 07:49 PM
hey man checfk your pm's