NicksHitachi needs your help. - AVS Forum
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post #1 of 8 Old 12-07-2012, 05:36 AM - Thread Starter
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I am building a DIY under seat truck sub for a friend and need enclosure and driver advice. I posted over in the Car audio forum but I know some of you guys over here in the DIY forum and wanted to ask for your input.

Man where's KW when you need him.frown.gif

THREAD HERE.

*ControlV*

I am designing a sub enclosure to go under the back seat of a truck for a friend. I need the help of you guys more familiar with car sub design. There are two variables which I need advice. Subwoofer driver choice and Box internal volume and alignment type. The maximum volume is already determined by the rear seat height and is 2.25ft^3.

The details

  • The enclosure maximum internal volume is 2.25ft^3.
  • He wants to spend approx $100-125 for each driver assuming two drivers in this enclosure so figure $250 budget for driver(s)
  • He wants to use a Kenwood KAC-9104D he already has.
  • His listening preference is Rock, Metal, Classic Rock. Think ACDC, Metallica, Nickelback, shutup i know this music is not very popular these days. tongue.gif
  • Mounting depth is shallow at only 6"


Now he like the Kenwood XR-W10F and I modeled a sealed enclosure in the volume he has. This driver likes a bigger box for flat response. It has a high Q bump at 50-60Hz, but since he likes rock music I thought he migh actually like that bump for the kick drum. I also modeled ported but it didn't yield any significant output and introduced more issues with excursion so I thought better to stick sealed.

I am pretty saavy with HT subwoofers but as far as Car audio i'm a little green. I don't know as much about small cabin gain in a car, and not sure how much extension is really needed in a car sub either so ADVICE IS GREATLY NEEDED. His amp choice works with those subs when wired to 8ohms. I assume the amp is capable of 250WRMS @ 8ohms based on its specs and excursion is under control with 125W/driver in that sealed volume.

He hasn't bought the subs yet, I just wanted to make sure nothing stands out as "just plain wrong" with this design before we move forward and see if another driver choice might work better.

Nicholas
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post #2 of 8 Old 12-07-2012, 05:50 AM
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what kind of driver depth and enclosure volume do you have to work with?

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post #3 of 8 Old 12-07-2012, 06:04 AM - Thread Starter
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6" mounting depth

2.25ft^3
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post #4 of 8 Old 12-07-2012, 06:37 AM
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I put an Earthquake sub sealed in my BMW planning to Linkwitz Transform it flat with a MiniDSP. I found that with cabin gain, I didn't need an LT or really any equalization. In case it helps, I've attached a cabin gain frd file created by JeffB's diffraction and boundary simulator. It is based on 11 ft maximum linear dimension in the cabin and 40% leakage (which is probably pessimistic for a car). RoomGain in car 11ft.txt 11k .txt file With this a single Earthquake SWS 12 models in 2.25 cu.ft. models -3db at 20 hz.
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File Type: txt RoomGain in car 11ft.txt (11.5 KB, 2 views)
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post #5 of 8 Old 12-07-2012, 06:49 AM - Thread Starter
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Thanks Jack!

Looks like a calc -3db @approx 50 is a good goal? Am I reading that right?
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post #6 of 8 Old 12-07-2012, 10:14 AM
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I'm not sure I understand your question. My graph shows the room gain kicking in around 60 hz with 3 db of gain at 50 Hz If that matches the -3db point of the woofer, the net result will be flat down to where the room gain curve starts to level off. Obviously, box size and the woofer T/S params determine the match. In other words try to find a woofer and sealed box size that simulate -3db at 50 hz or lower.
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post #7 of 8 Old 12-07-2012, 10:22 AM - Thread Starter
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Quote:
Originally Posted by JackNC View Post

In other words try to find a woofer and sealed box size that simulate -3db at 50 hz or lower.

Quote:
Originally Posted by NicksHitachi View Post

Thanks Jack!

-3db @approx 50 is a good goal?

Good thats what I was seeing, just wanted to make sure I interpreted it correctly.

Also thanks for the tip on the Earthquake subs, id didn't know about them. It looks as though they have a very good 10" slim model. I will model it tonight and see how it looks in the 2.25 cubic feet but they recommend like .33 cubes for a single so i'm guessing prob need to make enclosure a bit smaller but I won't know till playing with model.

Thanks for the help, I had no idea on the target curve for a car cabin.
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post #8 of 8 Old 12-07-2012, 11:03 AM
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You won't need to go smaller. Their recommendations are for the absolutely smallest box you can get away with. For the 12" model, their recommended minimum box size of .56 cu.ft. results in QTC = 1.5. Their maximum recommended box of 1.25 cu.ft. results in QTC=1. So you can go way bigger than what they recommend. Of course the smaller box will lessen the danger of overexcursion.

Also pay attention to their warning to leave lots of room in front of the cone. They really do have huge Xmech.

Jack
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