In my coutry many build car stereos usings 15 inch sub woofers designed for cars. The car subs are relatively cheap but i know nothing about how good they are for home theater use.

What subs can be used to make a good sub for home use? What should I look for in specs? Are the omhs important? What about the amp? Can you car amp be used?

This is actually a fairly loaded question.
Depending on how you wire it, just about any sub can be adapted for home use. If you get a 4 ohm model, you might need a special sub, but you could always get a dual coil and wire it for 8 ohms. OR you could wire two together...Like I said, there are a lot of ways to do this.
The most important thing to look for is DETAILED specs on the woofer itself. If you get a good description of its characteristics, then you can use a program ( there are some decent freeware ones out there...) to construct a box that will take full advantage of the speakers abilities.

Personally I would go with a woofer that is dedicated to home use. That way you are guaranteed the quality you are looking for and they really aren't that much more expensive. A decent dual coil 15 inch woofer might run you 120.00 US. and the amp to run this one is about 100.00 US.

What you save in one area, such as parts, you will loose in another area, such as accuracy or even money to make adapters and step down for car amps. In the end, it will be your choice. What I would do is a search on Google for DIY sub woofers and go from there.

Good luck.
This can be a daunting task...

SJ

I've been doing car audio projects for a lot of years now.

Car speakers are always a compromise. Bar none, the best material for a speaker cone is paper. It's lightweight and stiff. This makes it the choice that will be in the vast majority of the world's best speakers. Not in car speakers, though. This is because car speakers have to put up with a harsh environment. Temperatures range from -40 to +80 degrees C, and can change rapidly with heating or A/C. Humidity levels can range from 0 to 100%. There's physical shock and vibration, exposure to water and any number of other hazards that a car speaker must take in stride. No home speaker is expected to stand up to these extremes.

Even the speaker coil itself is a compromise. Car speakers are typically 4 ohms because in a car, the available voltage is severely curtailed. The supply is only 12VDC. If you want to get any power out of the speaker, you have to cater to this limitation. Certainly high power amps can use a SMPS to increase the available voltage, but even then, this comes at a cost of drawing huge amounts of current, so there's a law of diminishing returns there.

In short, the best speaker will never really be a car speaker.

All that being said, if you have access to car speakers they can certainly be made to do the job. Home theater subwoofers are not really high-fidelity speakers, they're usually there more to make things rumble, rather than produce real bass sound.

The things that you need to do:

1. Check if your receiver can handle a 4 ohm load on the sub channel. Many cannot, and you may need to either wire a DVC sub in series, or use 2 4 ohm subs in series in order to get an acceptable load.

2. Build a suitable cabinet to house the speakers. You can be as careful as you want, here. If you plan on using the subwoofer syustem to listen to music, I'd recommend that you design a tuned enclosure, but if it's just going to be for movies, then whatever fits will probably work perfectly well. (For Home Theater use, an undersized sealed enclosure may actually work better.)

3. Do some careful listening to make sure that the sub isn't cancelling out your speakers at the crossover point. (This is necessary with ANY subwoofer system!)

i have been running a couple car subs in my stereo for 6+ years now

using an normal composite LR cable could come from a stereo, dvd player or tv. im using a reallly old bose 5.1 system

using a power converter to get 12v and using 2 car crossovers to get 12db of boost at both 40hz and 90hz

then the signal goes to a pyramid 800x ( 800watts x2 @ 4 ohmz)

from there i am running a 12in and a 15in
currently both are in bass tubes (made from a concrete pilar form )


they added TONS of bass to the lacking bose - my room has been shaking ever since
for movies 15in all the way but i kinda like the added sound the 12 puts out ( you have to have it turned a little higher since it moves alot less air even though its a better woofer). if you go this route with the crossovers be prepaired to have some crazy looking db hz graph a few frequencies falloff quick depends on what your listening to i usually don't notice

to fix this simply have a sub output and use it instead of the crossovers

4 gauge wire from the amp to the sub collects a lot of dust btw

just make sure your ohmz match from your amp to your sub and your good to go

The subwoofer is one of the areas were DIY can yield a very high return on your money. Especially if you are willing to allow the subwoofer enough space to make a reasonably sized cabinet.

I just built my first subwoofer. I have built many speakers in the past but this was my first sub. I used a Dayton 12 inch driver and a Dayton plate amp.

The cabinet is built for optimum tuning for this driver so it's quite large. At 4 cubic feet. I tuned the box slightly lower to roll off the driver a little sooner and to give stronger really low bass. I have no bass boost on and I would say that with room gain it is flat at least to 18 Hz.

The box was built of MDF and scrap plywood. 1.5 inch thickness with lots of shelf bracing. I would say I spent about 250 dollars total and this sub literally destroys anything that I have heard in a store or audio shop at any price. It even completely blows away 2000 USD Carver and Velodyne subs.

Watching the DVD Master and Commander it feels as if the house is being wripped apart during the ship battle scenes and the deep bass hits you in the gut hard and fast with no overhang and good transient response.

The trick is not how much you spend but knowing how to select the right kind of driver. Most car drivers are made to fit in small boxes and are not suited to going down really low and accurate.

Hezz: care to share those plans on here with us all

I have been looking in to this for a while but the sonotube subs seemed a little more challenging to build as there would be multiple circular cuts.

Well, any sub you build would require at least one circular cut. A router and a homemade jig make it pretty easy to do repeat cuts. FWIW, I haven't built a sonosub, but I did build this end table sub for ~$275 (with 15" Quatro & 250w plate amp from ParsExpress) and with EQ I have it flat from 20Hz to 80Hz (crossover point).


l]

Lots of good examples on AVS in the DIY Gallery.

nintari,

I don't have detailed 2D drawings but I do have a 3D solid model that I will post. I can also take a picture of the subwoofer. Except that it is tucked behind some other furniture in the corner.

The cabinet is easy enough to build that you won't need plans. It uses butt joints which are easy to make for the DIY'er. All you need is a circular saw and a staight edge and a couple of C-clamps.

Be back in a minute with a picture of the solid model.

OK,

Here are the plans that I have. They are not too detailed because I was just making them for myself but if you have any questions you can post here. And I will try to answer.

This subwoofer uses Dayton DVC310-88 12" DVC SERIES SUBWOOFER from parts express. 110 USD. You can use any amplifer that you wish. Because it is a dual voice coil driver you can use an old surplus stereo amplifier to drive each voice coil. This will give you the current and power of both channels to take control over the driver motor. This can make the project even less expensive and with good results. I use a DAYTON SA240 240W SUBWOOFER AMPLIFIER. This is actually a very good sub amp and only 130 USD. But it is a little noisey. I finally had to lift the ground to get it to be quiet enough since it was putting noise into my whole system. Use the non bass boosted amp unless you are going to be in a really large room. In my room which is not real big (about 12 x 22 feet) I'm estimating that I'm flat down to 17-18 Hz with room gain.

For a medium size room, room gain should be around 1 db at 30 Hz and 6 db at 20 Hz. So the subwoofer is tuned one or two Hz lower than the butterworth tuning which makes the speaker roll off a little sooner but go a little deeper.

Cabinet volume is around 4 cubic feet internal volume. The vent ends up being somewhat shorter than it shows in this model.

By the way. This Dayton driver is an amazing 12 inch subwoofer driver and performs very well. It has just the right parameters to get killer bass in an acceptable size box. Meaning large but not too large to be unlivable. Since you only have to have one of these in the HT it's not really so bad.

The vent is four inch ABS pipe.

Here are a couple of 2D plans that I remembered that I had made for dimensions. The walls are laminated sheets of .750 inch MDF or plywood to create a 1.5 inch thick wall and front baffle.

For a subwoofer one thickness of MDF and one of plywood is good because the plywood is lighter and stiff. There is no attempt for constrained layer dampening here. You can often find scraps of plywood in the dumpsters at new building projects.

The rear baffle only uses one .750 wall thickness but using 1.5 thickness would be better.

I do not have any actual measurements but subjective sound quality is of a subwoofer that essentially gets out of the way sonically and does it's job. You won't hear much at all until you have some really deep bass and when you hear it it is well defined. No significant boominess or bloat. The sound quality is reasonably fast and articulate. Dynamics are huge with soundtracks like Master and Commander. Much better bass definition than smaller subwoofers that I have heard. And better transient response due to the near butterworth alignment.

I made some small changes to subwoofer to make it easier to assemble but if you follwed this plan it would be successful. Since I painted my whole cabinet black except the top I used long sheetrock screws to hold the shelf braces in place while the glue was drying. These were countersunk below the surface and then bondo was used to cover all holes. If you decide to cut dados in the walls to hold the shelf braces that works really well. But you may have to increase the dimensions of the braces slightly.

I am sure anything along this line or worse is better than what I have thanks

right now I am using a Philips surround sound system that is 100W per channel and uses little sattelite speakers. The sub is a 100W WooX sub. Not much but was waaaaaaaaaaaaaaaaaaaaaay better than anythign I found in the pricerange at the time (original retail not what I paid lol)

Paid $125 for the receiver and speakers, was originally $399 I believe. Still sound great and really is good for my setup for now, but I want to put surround sound back on my bigscreen and have another system where my projector is. Since I wont find antyhing close to what I have for the same price, I might as well move up in the world

BTW I had went a few times to check out this Onkyo set that was always on sale @ circuit city for like $399 and everyone raved about..... personally I thought my system at home was way better..... I am by no means an audiophile but that Onkyo set just seemed to lack something. I know though that it isnt a fair comparrison though cause it was in store and not at my house.

I have had five Onkyo stereos and A/V receivers and I can say that you can't go wrong with Onkyo. In my opinion I have always found them to be at the top tier of sound quality in the mass market price range HT receivers. And I have compared them to all major brands. But in a store demo you don't really know what you are getting. The digital switching system that they use degrades the sound a lot and they rarely make wise decisions when selecting components to put together so they never get the best out of any setup. For instance I have seen the cheapest small speakers paired with the best A/V deck in the store just because they were small and meant to impress the wife.

I just recently got a killer deal on a TX-NR901. It was two years old and never sold. In 2004 it was 1500 USD and I got it for 650 bucks.

One thing I would suggest if you can budget it is to get a receiver that has preamp outputs. Then you can use a couple of cheap Audio Source amps as the fronts as monoblocks. They can be bought for around 100 USD each. There is a lot of energy in the fronts and if you do this it will improve the dynamics and sound quality of the whole system tremendiously. Because the main power supply of the A/V receiver won't be so starved for current for the other channels. It will also improve the sound quality of the front channel a great deal.

IF you decide to built this subwoofer you may wish to do something I did to make it more pleasing to look at.
Because of it's size it can double as a table. I made the very top out of hardwood and stained it. The rest is painted black. But it looks a lot better and blends in somewhat better. I had some scraps of hardwood left over from some old projects.

I was almost thinking of making two subs to put on either side of the room, but I hope to build floor standing speakers so there may be enough bass to only need one sub.... but I love the feel of good bass so there more than likely wont be a such thing as enough bass for me lol. Although I am sure the neighbors will beg to differ lol.

If you have a large room you could build two of these and then use them as the stands for some largish upper two-way speakers. Kind of like a large over-sized Watt/Puppy.

In all honesty you won't need two of these though unless your room is really big. The other day when I was testing the system I had turned the subwoofer volume up a little more than usual and I was using Master and Commander DVD to test the system. This DVD is totally awesome for testing a HT system. The DTS soundtrack is good sounding and the reference sound levels are kind of low. THat is until the battle scenes hit.

I went upstairs to get something to eat and all of a sudden the door going down to the HT room is almost coming off of it's hinges. I mean this thing can easily shake the whole house and the HT receivers was only at a modest level.

/me wipes the drool from his chin

I should also point out that while the house was shaking there were no significantly discernable bass distortions from the subwoofer. In other words, even with prodigious amounts of bass output the sound was quite clean and strain free.

However, building some floor standing full range front speakers can add a lot of dynamics and improve things. This is because there is a lot of bass information in the front channels. In fact, in many soundtracks there is not much LFE information at all and most of the bass is in the front channels. So even with only one subwoofer it's best if the fronts can do some pretty good bass. However, better to emphisize quality over quantity at the fronts since a lot of music is involved.