Dual Duty Woofer Build

[AcridSaint]

Hey folks - I've been around the forums for quite a while but not posted much. I am a "new" diy audio-er, but not completely new to the audio scene. I've installed a fair amount of car stereo systems and am familiar with products in that realm (although that familiarity is getting pretty dated). I've mostly worked with out of the box stuff.

I have decided to venture into the diy sphere with a simple woofer project - I plan on sticking it in the back of my truck cab for the time being, but plan to move it into the house when the wife finally agrees that she's ready to put sound on the TV. This is not a "sub-woofer", it is a Dayton woofer. I know it won't get as low as a sub, but it should be fine for my immediate needs and always gives me an excuse to get something "cooler" later

This will be my first experience with a DIY vented enclosure. I've heard well-made enclosures that sound great and I've also heard some that don't, so I'm here to run my initial design past you all and see where I need to make changes/improvements. I hope I've got this in the right area.

I am attaching an image of the basic box design, no it's nothing spectacular, but it fits the area I need now with the woofer facing the rear seat. When it comes out of the truck, I will install rubber feet on the "face" to have a downward facing speaker. Are the ports OK in these locations considering the speaker position in and out of the house?

The design calls for 3/4" MDF, 1.5x6" ports and very moderate bracing. After the displacement of the woofer, ports and bracing, I should have an internal volume of just over 1.5 cu. ft. I can't spare much more room than that.

Here is the spec sheet for the woofer:
http://www.parts-express.com/pdf/295-310s.pdf

The frequency response on this woofer goes down to 29Hz and this box should give me an F3 very close to 33Hz. Is this an appropriate value? I am less concerned with SPL and more with SQ at the lower end of what the woofer is capable of.

Also, I have read where many folks are just running full-range audio into their woofers. I have the ability to cross it over at 120Hz, but do I need to do so? Is 120 too low a crossover point for a speaker like this?

[AcridSaint]

By the way, I posted this is the "subwoofer" forum, because I thought it most closely matched since it's by no means intended to be full range or multi-way.

[Brian Steele]

Originally Posted by AcridSaint

By the way, I posted this is the "subwoofer" forum, because I thought it most closely matched since it's by no means intended to be full range or multi-way.

You don't need to go down to 33Hz for a car audio subwoofer, particularly one that's going to be mounted in a truck's cabin. Aim for a sealed design that's good down to about 40 Hz or so, with as much SPL capability as possible. For example, you can easily do that with one good 12" in that same 1.5 cu.ft. box.

[AcridSaint]

Hi Brian - I already have this driver on the way, I kind of wanted the challenge of doing as much as possible with a small, cheap woofer. I don't know if this woofer will get into the 40's or really much below 70 in a sealed box. I can't get BassBox to design below an F3 of 68 with this woofer and sealed enclosure, which is one of the reasons I decided to go vented.

Since I plan to remove it from the truck and put it in the house later, I wanted to get a very low tuning, do you think that a 40Hz sealed design will also work well in that application if I can get the woofer to cooperate?

[Pancakes]

120Hz cutoff is sweet for car s/woofer. Don't run it full range and expect it to sound nice. I would agree with Brian Steele, with the gain you'll get from the truck cabin tune for max SPL from 80 to 40HZ. The ports on your model look too small, I would make them as big as possible until the length is 4 (maybe up to 5) times the diameter. You'll be hard pressed to make one box for your truck and lounge that will suit both. Would also face the speaker back w/ the port back or up or the speaker down as it sounds like you want too with the port back. Make sure if you face the speaker down there is enough clearance around the sides (1.5 sd minimum) or you'll be loading it sorta 4th order style

[Pancakes]

You'd almost want to run one or two of those/ side for your house and pick up a cheap JBL or something for the car

[AcridSaint]

With larger vents I ran into problems with the depth of the box, but if I change them to the "top" then I could lengthen and enlarge them. How close can I come to the other side of the box with a vent? for simplicity and box volume I'm trying to avoid vents that have to bend around the box. Would I be better off switching to one vent?

[chris661]

Here's an idea.
Make the box so it's the right size for a vented enclosure, then don't add ports when you put it in the truck. The cabin gain will flatten the response nicely. When you want to put it in your home, add the ports. This way, you can get the box to do fairly well for both places.

[AcridSaint]

Hi Chris - that is a brilliant solution. I see that I made some mistakes working up the sealed enclosure and I can get F3 down to around 60Hz while keeping the box the same volume. It doesn't change significantly with larger or smaller boxes, so this looks to be a nearly ideal situation for this woofer and my slightly unorthodox applications.

Thanks for the suggestion!

[chris661]

You're welcome.

Remember that, when placed in your truck, it will go much lower than you've modelled - cars, trucks, and small rooms will add extra bass, which will mean your sub will go really low.
Larger rooms add bass, but only at really low frequencies.

With regards to the vents - it's best to have at least 1 vent diameter away from everything else - this helps air flow greatly. Switching to one vent could help, but make sure it's more than 2" (51mm) diameter, or you'll get lots of port noises.
I've just checked the woofer you are using, and I've used a pair of the dual voice coil ones in a sealed sub. They're good performers - you won't be disappointed.
Happy building
Chris