Suggestions on DIY sub (1 Viewer)

[boomski]

Hello fellow HTF Members,
I have two cerwin vega dx7 3 way floorstanding speakers that I do not use in my current HT setup. I want to take the 12" subs from these speakers and build new enclosures for them to use as 5.1 subs. I have plenty of experience just fiddling with car stereo and building sub boxes but nothing was ever done mathematically, (most were built to fit area in trunk and modified with foam or porting). I could possibly try some sub enclosure software but I have no experience with it and do not know some of the specs for these speakers that the programs need inputted. I can certainly construct the box and know of the importance of materials used, bracing, air tightness, etc, I would just rather not guess on the dimensions and waste alot of time and material trying to find the right size and type of enclosure. any and all help would be greatly appreciated, and a million thanks for a useful reply!

 

[Robert_J]

Those are not subs, those are woofers. Big difference. They are designed to play low but not as low as a real sub. Also, you can't get the Theile/Small parameters of those drivers without testing them with Woofer Tester 3 ($100 from Parts Express).

What you can do is create a generic box and install them with the expectation that you will replace them at a later time with better drivers. For example, a 4cf box tuned to 20hz would probably sound good with about 100w. You could later upgrade to the 12" Dayton DVC for about $120. With a 250w amp, you would get about 3db more output since the excursion of the Dayton is probably double that of the CV.

-Robert

 

[boomski]

Thanks for the reply robert

My mistake I should have know better than to call them subs! I like your suggestion, build the enclosure for a future sub purchase, theres definitely possibilities there. As I stated in my previous post the only experimentation I have with subs is with car audio, the volume of space in the house is enormous compared with what I have experience with
Any suggestions out there on a specific type of enclosure I should focus on,
Sealed
Ported
Bandpass, 4th order, 6th order
isobaric
compound, (push-pull)
my theater is 11 feet by 16 feet and will soon be sealable from the rest of the house by french doors.

 

[Robert_J]

Sealed or ported will work fine. It depends on the driver you pick, the amount of real estate you are willing to give up and your budget. Ported will be larger unless you want to go the passive radiator route. That's more expensive. Sealed requires more power to get the same output (thank Hoffman and his Iron Law for that). That usually means a more expensive driver and amp.

Bandpass - If you design your ENTIRE system around them, they will work. Make a mistake and they are a one note fart box. Bose is the only large home theater company using this design and you see what kind of response they get around here.

No need for isobaric. That was popular back when sub motors were relatively weak. Now they have motors that will lift a small kid (yes, there's a video on You Tube of it) and weigh up to 75 pounds. Don't get hung up on the motor/magnet weight either. Newer materials like neodymium have more magnetic strength with less weight.

Compound is easy. That's just putting two drivers in one enclosure with one inverted. That eliminates some harmonic distortion. It makes the enclosure larger and will make it more difficult to build if you have to hide the back of a speaker. Now if you had a nice looking basket like this, you would want to show it off.

You left out IB subs. The best bass around but they are not for everyone. You have to modify your theater by cutting at least one hole in the wall. You need an attic, basement, garage or closet touching the wall where you will install your IB to catch the rear wave of the sub. Output is lowest of all subs so we usually use multiple drivers.

I need to know your maximum budget for the driver and amp combo. What movies/music do you watch/listen to? Do you crank the volume to reference levels? How much area are you willing to sacrifice for the sub? Can you buld tall (think SVS cylinder series)?

Every person has different goals. For example, your theater is a little smaller than mine. I'm currently using a pair of 15" TC-3000's (like this but a different color) powered by a 2,400w Behringer EP-2500. I use a Behringer Feedback Destroyer to flatten the sub's in-room response. I've -3db at 16hz and -6db at 12hz. Output is down right scary. I can flex the walls and make the door to the room shake violently. I can rattle the china in the dining room. My wife can feel the vibrations in the concrete foundation on the other side of the house. It's not enough for me so I'm upgrading to quad 18's in an IB configuration.

Answer the questions and we will narrow down the list in your search for perfect bass.

-Robert

 

[boomski]

Your right I did forget completely about Infinite Baffle setups, Ive seen a few of those setups on this forum before and Ive even heard of them in car audio before, but never dealt with that type of setup. I do have an attic and as for your question of space I really have been trying to go with a very clean design in the theater, I would rather not have a huge floor to ceiling sub enclosure sitting in the room and your suggestion of The IB setup does have some definite advantages to the look Im trying to achieve in the room, but Ive also been trying to design the room to be relatively easy to convert back to a regular room, (just incase we decide to sell the house down the road). I think Id be willing to compromise this though if I was sure I was going to get a more powerful and even response from the IB setup than the sealed/ported cube option.

I Use the room as a theater only, (kids occasional video game in there too), I tend to watch lots of action flics mainly for the surround sound also an occasion music DVD or two, and hardly ever just music CDs. I generally set the volume 5-10 dbs below reference and a little lower after 9/10pm. As for budget Id probably like to keep the sub/amp purchase around $500 but could go higher if i wait a little while, maybe $1000 but I dont know if I could justify going higher than that to myself. also if were talking about IB the roof trusses in the attic are spaced 2 ft apart.

now if were talking about a pair of subs, they are in separate enclosures right? (thats how ive always pictured doing it) If so are they both to be tuned identically or should they be tuned differently to help give a more even response across the frequency range? I realise in an IB setup they would both be in the same enclosure anyway.

I know it seems like a lot of questions for only one aspect of the theater but in my opinion the .1 in theater surround is just as important as the center channel. I just want to try to put as much effort into getting it right the first time. Ive currently got those cerwin dx7s (full cabinets crossovers and all)sitting in a corner of the room wired up in series to the 6th channel of my receiver at 120 watts max. they sound pretty good for as cheep as that setup sounds, and I know if I just put some effort into that .1 channel setup I might have great sound from it! anyway thanks for your continued help robert.

 

[King Ghidora]

I originally posted a question in this thread but I decided I probably should start a new thread for my question. So please ignore this post. I tried to delete it but apparently that isn't possible. I'd appreciate anyone helping me in the thread I'm starting.

 

[Robert_J]

An IB is very easy to convert back with a piece of drywall, some tape, mud and a few screws. Within an hour, even a novice home repair guy can have it fixed and ready for painting. With 2 feet between trusses, you could easily do something like this. Fi Car Audio will even sell you IB specific subs at a discount if you mention you are a member of Home Theater Shack or Cult of the Infinitely Baffled (check each site for details). Four 18's and an EP-2500 pro amp is enough for even the hard core bass addict. If you want to spend less, Mach 5 Audio or Elemental Designs have less expensive subs and you can go with a smaller amp.

If you go with a pair of ported subs, you want to build them identical. Their are phase issues with ported subs and if you mix tuning freqencies, you may get less output than with a single sub.

If you want to go with something similar to the SVS PB12 NSD/2, then Fi again is blowing out pairs of 12" drivers for $160 shipped. Pair that up with the 500w PE amp on sale for $240. You have $100 for ports and wood and you are right at your $500 budget. If you don't think that's enough, then build 2 for $1,000. AE Speakers is blowing out some of their subs as well. 15" models with aluminum cones and 23mm of xmax for $125. You have dozens of choices so once you decide on box or IB, we can start working on drivers and a design.

-Robert