My First Ever DIY Sub - Page 2

That isn't necessarily true. I have two sealed 15" subs in a room that is open to the rest of the 2300sq-ft house (as in the room only has 3 walls and the missing wall is one of the long ones) and I get appreciable room gain. Room gain is dependent on so many factors you don't really know if you're going to get it or not until you measure.

he said his room is 35'x17'x(9-15)' (sloped ceiling). that is a lot of room to try to get 20hz out of a 2.1 cubic foot sub with a 12" driver and 350 watts. pressure vessel gain will not be kicking in around 30hz in that room.

2.1ft^3 is a little too large given 500W and 22.9mm of xmax. Your comparison also ignores the effect of the 20hz HPF necessary to protect the driver in the ported box.

The situation looks more like this:

"Your comparison also ignores the effect of the 20hz HPF necessary to protect the driver in the ported box."

yes. i was comparing native frequency responses. if he goes with a plate amp, he is probably going to end up with a high pass filter with the sealed too.

here they are again with a 2nd order highpass at 20hz w/ a 350 watt plate amp.

edit: if the amp is actually 540 watts, here is what you get (no overexcursion in either enclosure):


Edited by LTD02 - 9/28/12 at 7:35pm

Are you sure that Dayton amp has a 2nd order HPF @ 20Hz? The 1000W model will play below 20Hz. I'm not sure about the 500W one.

Build a sonotube sub.

http://www.subwoofer-builder.com/sonosub.htm

Fairly simple to build and relatively inexpensive. All you need is a router to cut the circles. Just plug your woofer into the above software and BOOM it tells you all you need to know.

Without a subsonic filter in a 5cu-ft ported box tune to 20Hz you're limited to about 95W of power at 10Hz before you run out of driver excursion. With a 2nd order subsonic filter at 19Hz you can apply 500W to the driver and still have about 2mm of xmax left at the worst frequency (15Hz).

Excursion 5Hz HPF (2nd order) with 500W


Excursion 19Hz HPF (2nd order) with 500W


As you can see the HPF is important!

BTW, I used a 5Hz HPF instead of no HPF because most electronics roll off around 5Hz.

"Besides, as long as I can gain match properly and not take the driver to its extreme limits, won't that ensure I won't blow it out?"

it used to be the case that you could run a ported sub with a low tune for music and not have any worries because the music itself tended to be high-passed around 25hz to filter out rumbling.

these days, with home theater having some big content bursts around 10hz, it would be possible to damage your driver. you can see in stereodude's first plot that excursion goes WAY past xmax at 10hz. typically, there is some room past xmax, but for home audio subs it tends not to be double.

"Technically that's the total area of the kitchen and living room combined..."

you specified it correctly. for pressure vessel gain, the sub will see one big room.

That's the info I found as well.

After having built a number of subs, especially the two 12" ones I built last summer, I can tell you that you won't be happy with 100dB at 20Hz for movies. You have to remember that 100dB at 20Hz sounds/feels much more quiet than 100dB at say 1000Hz. Don't get me wrong, I love my subs, but they don't even come close to being enough for movies. I have two of them, by the way, in a room much smaller than yours. For movies, you want to be able to hit 115dB. This is the loudness that will rumble and make you feel the sound like at a movie theater.

However, if you're set on using that 12, then I suggest you find a horn loaded subwoofer design. They are the most efficient and will get you the most dB for power, which you are strapped for with that amp. Instead, I'd look to design your sub to play to about 25 or 30Hz. You'll get much better results since you don't have to compromise the box design by getting it to play low.

Now, with that out of the way, I suggest as the others have that you ditch those parts. Buy yourself a Dayton RSS390HF, cheaper than the TC sounds epic, and build a Tuba HT. You won't be disappointed. These play very low and very loud. They are large, but such is a requirement for low and loud in a big room. I don't have one. Instead, I built a clone of the JBL 4645C cinema subwoofer. It is huge, sensitive, and plays super low. There's absolutely no comparison when I put my two 12's against it. I reckon you'll have similar results with the THT.

As for building subs, Bill Fitzmaurice gives very detailed instructions when you buy the THT plans. If you don't want to build a horn loaded sub and instead opt for a simple box, all I can say is brace the living crap out of it. If you don't have a table saw or a good circular saw and a straight edge, buy your wood and go to a local cabinet maker. One of my local guys in Kirkland, WA quoted me about $50 for all the cuts I needed for the 4 speakers I wanted to build this summer. Don't bother with any fancy joints. Simple butt joints with Titebond II will hold fine. I panicked and used a nail gun to put finishing brads in the joints every couple inches. You don't need to do this if you brace and glue correctly. Also, use 1" MDF if you're going bigger than 2ft^3. 3/4" MDF vibrates too much and 1" isn't that much more expensive. NOTE: Be prepared for dust. Always wear a mask or respirator when working with MDF and close all the doors and windows near where you're working. You may not see it, but the dust gets EVERYWHERE and is a bitch to clean up.

Port: Don't use PVC for the port tube. It is over priced and doesn't paint easily. Go to Home Depot or wherever and buy a concrete form tube. A 4' tube will run you about 5 bucks and they're quite easy to cut. JBL uses cardboard tubes in all their professional subs; there's no need to pay extra for some fancy port. The same goes for port flares and the like. You won't notice the difference so don't bother with them, especially if you don't have good box building skills.

Bracing: You can certainly make some fancy CNC designed gobbledygook, but 2x4's work great. Cut them about an eigth of an inch long to pre-load (push out ever so slightly) the walls. Use 2 2x4's in a cross configuration every 2 feet. Glue to the walls and then screw them into place from the outside. Either countersink or drill out your holes to make room for the screw head and then fill the hole with spackle, Bondo, or wood putty.

Finishing: Depends on what you want. At the very least, prime the MDF or seal it before putting a finish on. Nothing sticks well to MDF and the ends will soak up paint like no other. Sand the edges as fine as you can before putting primer or sealer over. Then, sand again until it's the same smoothness as the surfaces around it. A lot of people finish their speakers with Duratex, but that may not be the best for putting in a chic living room. You have to choose on that one. Veneer, paint, vinyl wrap, etc. are expensive and the cost adds up quick. Factor in between $100 and $200 to finish it.

Amp: I'm not sure if that amp will play a THT to its loudest, but that's a decent amount of power. You should be fine, but don't expect miracles. Tried and true sub amplifiers are the Behringer EP1500, 2000, 2500, and 4000. Tons of power, tons of reliability, and they actually put out pretty close to as much as they say. Don't forget that you want headroom in your amp for 3dB spikes. If your speaker is rated for 500W, get a 1000W amp. If you turn your sub up to watch Transformers or something of the like, you'll want that headroom in for all those Michael Bay explosions. If you don't have that headroom, your sub will clip and sound like junk.

EQ: Depending on how you design your box or if you go with the THT, you'll likely want some form of EQ to extend a bit lower. The Behringer DSP-1124P is the holy grail of sub EQ. It's mega cheap and works great, what more could you ask for? If you use the THT, give it a 6dB boost at 20Hz and you'll be good to go. You may see some over-excursion, but it won't kill the driver and you won't notice the distortion.

Lastly, get some good spikes or pads for the sub to get it off the floor. Anything from this page will work great. Don't buy the ones from Parts Express; they're way overpriced. If you're on hard flooring, get some foam yoga/exercise mats - the thick kind - and stick them under it. You won't see them, the sub will look like it's floating, and it'll sound much better.

This is all I can think of off the top of my head. If you're really stuck to the TC driver, I'm sure you can make something great. But in the world of subs, displacement is everything and the smaller drivers simply can't produce as much as the big ones without a lot of excursion, which comes at a very high price. Do yourself a favor and ditch the TC sounds, grab the parts/plans for a Tuba HT and be on your way. Look around the web for a used Behringer EP amp. Ebay, Craigslist, and the classifieds here are a good start. Don't pay more than $250 for the EP2500,4000 and no more than $200 for the EP1500,2000.

Follow what I've advised and you'll have a bomb-diggity sub without breaking the bank. Expect to be out around $600 when it's all said and done.

Another idea, depending on where you're located, is to just buy a good sub. This is the same sub I have. It's used in many movie theaters around the world and sounds, simply put, epic. It won't play below 20Hz, but the stuff you get 20Hz and above will the the best you've ever heard. New from JBL these are around $2000, so this one is a lucky find. I'd look into the cost of shipping, or see if he'll part out the driver to you. If you go this route, PM me and I'll give you all the information you need to clone it with that 2242H driver. It'll probably cost you about the same as if you went with a custom design, maybe a bit more, but not much. I got the 2242H driver for $300, and built the box for about $75. I'm using a Behringer EP2500 bridged mono which I got for $200. Turned up half way this thing is scary. Those prices add up to about what it'd cost you to use the TC sounds, the SPA500, and a custom box with finishing.
Edited by Frosteh - 9/29/12 at 9:49pm

I built a very similar sub to the one you are considering. I used the TC Epic 12, O Audio BASH 500 amp, and a roughly 6.3 F3 dual ported box (22.25H x 27.25L x 18.25W interior dimensions and 24" long 4" round ports). I got a lot of help in these same forums to help build it. Listen to LTD02, he was very involved in helping me. While it is a little bigger than I originally wanted, I'm glad I chose what I did. It rocks!

I was trying to decide on those two drivers as well, but the Dayton would work well in a large sealed box. If you want to port it, it needs to be HUGE. I went with the epic 12 as it works very well in a 3 cubic foot ported cabinet (which still isn't small according to my wife) and has almost twice the Xmax of the Dayton. As much as I like the Dayton I'd say save yourself a few bucks and go with the yung 500 watt amp. It is very well built, has tons of power, and it's what CSS sells. I built two of the epics with two yungs and this system bests my sealed 18, well maybe not at 10hz but who cares.

Dan

I'm sorry, but one 15 inch Polk is not going to keep up with 4 epics. Efficiency is a good thing to have, but almost worthless at the lower frequencies. At that point it comes down to air movement. Take the sd of the driver multiply by stroke and you get swept volume. That's what's important. It looks as though the momo has 9.5mm Xmax which isn't alot.

Dan

"What's the advantages of using a dual voice coil sub over a single one?"

flexibility. the coils can be wired in series or in parallel in order to provide two different impedances, e.g. two 2 ohm coils can be wired to net either 1 ohm or 4 ohms. in many cases, you want to run with as low of an impedance as your amp is happy with.

Sorry, but the numbers don't exactly back your claims

Here's a comparison of a 150L box tuned to 20Hz with:

• 2 MoMo 15's getting 500W (total)
• Epic 12 getting 500W
• Titanic MkIII 15 getting 500W

HPF disabled

Do you have any limitations on the enclosure size? If not, I'd use this driver (15" Titanic Mk III) and make a large sonosub. Something like 300L tuned to 17Hz. Sonosubs are pretty easy to build.

dual-ported, 3 cubic footer, tuned to 20hz.

that means that either you have a really long enclosure or the ports are too small.

have "chris at pe.com" check the port velocity on his design. i'm getting 47 meters/second with two 2.5 inch diameter ports, which would have to be 20 inches long. two 3.5" ports will reduce port chuffing, but in a 3 cubic footer, they would have to be 40.5" long to tune it to 20hz.

as a sub gets smaller, the ports must get longer in order to tune it to the same frequency. this is why you almost never see a low tuned ported small enclosure.

I didn't screw up anything. Your graph seems to be 300L with 2 Polk MM1540DVC drivers and not 150L with 2 Polk MM1540DVC drivers.

You're like a dog with a bone when it comes to the Polk MM1540SVC & MM1540DVC. Regardless, they model pretty similarly in 300L tuned to 17Hz.

you are putting 500 watts each for 1000 watts total into the 2x 15" model.

stereodude's post was accurate.

the mm has a 2 inch voice coil and can't take a ton of power, so it is going to be power related in just about every application other than a very large sub. for $280, no thank you.