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Old 14th December 2005, 01:34 AM   #1
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Default Deep HT Sub With a Twist

Let's say you wanted to make a subwoofer that could play really low (let's say 20hz f3 as the maximum), and you wanted it to be moderatly small.

But here is the part that should make it interesting/easy: I only need it at output levels of 90db maximum, in a small room. I live in an apartment, and I like to watch action movies, and I took a db rating of what I normally listen to movies at, and it was around 65dB talking, and peaks of 80-85 during heavy action. I can't turn it up more than that, because I don't want to bother other people.

I was thinking a sealed box with a LT, but what driver would you choose, especially if you were on a budget?
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Old 14th December 2005, 02:37 AM   #2
owdi is offline owdi  United States
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I'm in a similar situation, except the -3db point for me needs to be around 25hz. Right now I have a single 10" sealed subwoofer, with plenty of throw and a 250 watt amp. It's loud, but it doesn't go low and has tons of harmonic distortion.

My solution is two fold. First, to avoid bothering my neighbors I need to avoid room modes. +12db peaks shake walls, and -12db dips mean I need to turn it up even more. The only way to counter this problem is by using multiple subwoofers.

The second part of my solution will be using small (for subwoofers) 8" speakers in sealed cabinets and mass loading them to get my desired response. I believe mass loading will result in less harmonic distortion than simply boosting low frequencies. I'm still researching this part, but I think I'm on the right track.

Looking forward to more posts in this thread....

Dan
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Old 16th December 2005, 03:41 PM   #3
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I have an AE Speakers AV12 woofer in a 3 cubic foot enclosure with the Parts Express 500W amplifier, and dual 1400g passive radiators also built by AE Speakers. I like it a lot. It will give you information to about 18 Hz, but only as loud as 115dB. I overbuilt my box with double-layer MDF, plus some extra MDF for a set of end-caps on the top and bottom to give the grilles some cosmetic trim, but I cannot recommend that you try this, because my box weights a fair bit over 120 lbs fully loaded. I do however recommend the driver and passive radiator combination. Availability of the AV12 woofer is highly variable but I think it's worth it to check and see if you can get one, because for the money, I think they are still pretty much the best value out there in a subbass driver. The cost of admission is high compared to some of the other more commonly used long throw sub drivers, but if you can make that, you end up with a driver that's a great value for what you pay for it.

You can do this sub combination for about $550. That's what it ended up costing me.

I have plenty of stories of demonstrating this sub to other people and watching their jaws drop and then they run down the hall to get their friends, etc (I live in a college dorm).

To get the low distortion you want, you need to use a quality subbass driver. That's one reason I like my AV12 - very clean and musical. It definitely falls under the 'high-end' category, inhabited by AE Speakers, Adire Audio, Exodus Audio, and Ascendant Audio, as well as the Dayton Titanic and RS subbass drivers. Some people have even found SoundSplinter.com drivers to work fine but I understand they don't go very deep without some EQ. For an 8" woofer, I imagine you could do well with the Tang Band W8-740C woofer that Parts Express has. Use it with a 12" passive radiator. Again, I recommend the AE Speakers passive radiators for their quality but you could use just about anything if it's got plenty of displacement. For your very small application, this could serve you quite well.

The best way to get the low tunings you want from the small box you want without a lot of port noise is going to be with passive radiators. Here's another, ultra-budget option you might consider: Parts Express has the Dayton Shielded Dual Voice Coil woofers. Not extremely insane performers like the AV12 woofer I mentioned but a 12" shielded DVC woofer in a 14"-16" cube with two of the matching 12" passive radiators (one on each side of the box with the active driver front-firing or down-firing but there's no advantage to a down-firing driver so front firing is best) can be tuned to 25 Hz. Throw in a 100 watt plate amp and you're set for a good low total price, under $200. This leaves you plenty of extra budget to build a good solid box with walls of 3/4" MDF and a brace from the top to the bottom of the box.

I'll run some numbers here and see how viable the Shielded DVC woofer option would be. If it models well, it could turn out to be a very sensible option for your application.
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Old 16th December 2005, 05:10 PM   #4
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Addendum: Boy, the 12" Shielded DVC subwoofers from Dayton really don't model that well in anything small. The smallest box I could get to model well was 16" by 16" by 24" and it's only good to about 30 Hz when it's tuned to 25 Hz. It has the same F3 point as it would have if it were tuned to 30 Hz, but the 30 Hz tune would have a flatter response and more output level. It bears mentioning that this design would have very high output, around 115dB with a full 150 watts, but it wouldn't be as good sounding or deeply extended or distortion-free as my AV12 sub. I also have suspicion that power compression would set in a lot sooner, and the voice coil would be leaving the gap to produce this kind of output. I really need to get WinISD Pro so I can see what kind of cone excursion we'd be talking about. I have a feeling it's just a calculation based on Sd and sensitivity measurements. Hopefully I'll be getting HarrisTech BassBox Lite for christmas, which should be more powerful than WinISD.

Just out of curiosity, I simulated a 14"-cube sealed box with my AV12 woofer to see what it would be like. This gives a sealed enclosure with a Qtc of 0.65 (good for music but with less damping than a critical Q box so that it won't sound wimpy on home theater). With 500 watts, it also does 115dB. If you wanted a high-end but sufficiently-small option, I'd consider going with this if you can afford the $175 driver and a $300 500-watt plate amplifier from Parts Express.

Next up, I'm simulating the Tang Band W8-740C in a passive radiator box with one 12" passive radiator. It would need to have some displacement capability, though, like the AE Speakers PRs. Generally, the AE Speakers passive radiators are always available (it's not highly-variable like with the AV series woofers). I think the Parts Express passive radiators based on the DVC woofers are overpriced. Anyway, this gives an EBS-ish response with a peaked low end in a box that's 2 cubic feet. I recommend putting the active driver and PR both on the front of the box. This has a nasty group delay spike, though, so I don't think I'd recommend it. Instead, a 1-cubic-foot box with the same driver and PR looks more promising, with a much lower group delay spike, only 30ms at the tuning frequency. This only tops out at 105dB simulated. You could do a down-firing driver with this driver, because it has a nice, stiff suspension that will support the cone even if it's mounted downwards. You might find this to be more cosmetically acceptable than having the driver on the front and the passive radiator on the side, or the passive radiator on the front and the woofer firing out the side. This gets down to 27 Hz. The 12" passive radiators aren't listed on the web store anymore, but I know the proprietor, John Janowitz, will still build them if you want them. This should be a good option if extension is your priority, not output. In addition (as a nod to your original desire to get 20 Hz stuff from this thing), if you tune the box to 20 Hz, you get a shelved response not unlike an EBS. You get a shelf that's 6 dB down from normal, which room acoustics might boost up somewhat. Though that sealed AV12 would work hand-in-hand with room acoustics and get you some much more musical bass, but at a higher price as well and probably not reasonably flat down to 20 cycles (though certainly usable at that frequency).

I hope you got some good information from all this about some potential designs you could do. Parts Express also is getting another high-excursion 8" woofer from TB, which has a 12mm Xmax and neodymium magnet assembly so that would also be another interesting option.
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Old 16th December 2005, 07:15 PM   #5
khanh12 is offline khanh12  United States
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BAM

Can you share with us the details of your sub? Can you x-over it at 100hz? Pictures? Plans? anything?

Thanks
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Old 18th December 2005, 05:40 AM   #6
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When I had my TLs in my bedroom I found some very punchy and low bass. Even now in an avereage sized living room it gets down to about 23 Hz with decent output. In your situation a sub might not even be needed. TLs get down low and their roll-off being not so steep means a nice integration with room gain.

Another idea: subwoofer headphones!
Place one either side of your chair. Room modes have less impact this way. Try it out first as you might not like it.

Another option is dipole - more bass for you, less for the room. You can do this with a pair of monopoles, wired with reversed polarity on one. Draw a line through the two of them and out one end comes the front wave, the rear out of the other. In the middle of them is a null. If the party wall runs parallel to the axis that runs through the two separate subs set up to function as a dipole, then the wall will be at a null.

If SPL is limited you might consider limiting extention as the lower you go, the lower the SPL will have to be as it gets harder to keep it in the room.

Another idea - put an open baffle dipole in as a footstool!
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Old 18th December 2005, 02:52 PM   #7
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khanh12 - which one are you interested in? Those were just some ideas that WinISD told me would work. That's usually what audio DIYers do before they build their subs - building and testing prototypes is prohibitively expensive, and the simulations of modern programs are very accurate. If you need me to make you some plans for any of those, I can do it. If you want to see the WinISD response curves, I can post those as well. The drivers used in both subs should handle a 100 Hz crossover with aplomb, but I don't recommend crossing that high as a general rule unless you are planning to build two and use them in stereo.

Or are you interested in MY sub?

This is the last sub I ever built without the aid of a router and a circle cutting jig. The one I built for my friend with my old 10" driver looks a lot better, but its performance is not as awesome. This photo shows both the driver and one of the two 15" PRs, to prove that I have both and that they are in a box and working, and I'm not just blowing smoke when I say I've done this before. Typically the driver and both PRs are covered with fabric grilles, which produces an interesting effect when you can barely see the shine of the aluminum cone through the grille fabric.

The room was very messy that semester. That black, blue, and white strap you see is from one of a set of drum cases that one of my roommates stored his drum kit in.
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File Type: jpg sub_w_pr.jpg (26.0 KB, 704 views)
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Old 19th December 2005, 12:05 AM   #8
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BAM how high are you crossing your AV12s? The highest xo point I've used was 80 Hz with a 4LR and I wasn't happy with the result - upper bass was a bit boomy, not even close to the bass from my mains so I cross them low ~ 40 Hz.
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Old 20th December 2005, 10:19 PM   #9
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My XO is ~50 Hz to suit my mains.
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Old 8th August 2006, 03:52 AM   #10
preiter is offline preiter  United States
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Check out this project:

http://sound.westhost.com/project48.htm

It's an intriguing design and just may fit the bill for what you need.
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