sealed box with BFD?

[KeithM]

I have plans to build a sealed sub out of the dayton titanic 1200(the first one). I found it for a good deal and here are the specs.
I plan a 5 cubic foot box with a Qtc of ~.707. My brother has plans for a vented enclosure(I'd reather get sealed and a BFD) because he says if I use the BFD to equalize the frequency of the sealed box to around 20 hz(20 hz at -8db), the voice coil of the sub would fry. I don't see how the coil would fry when all you're doing it "turning up the volume" in one frequency area. Would he be right saying that an 8 db gain would fry the voice coil on the sub? Sorry if the wording sounds confusing.

[TacoD]

You need a lot of power to lift with 8 dB, but if the Dayton can handle the extra power, you're save. I do not have the calculations at hand, but I think Thomas has the knowledge for that :-).

[ThomasW]

increasing the output +8dB requires approx 6.4 times more power.

That driver isn't a good candidate for +8dB of boost at 20Hz

[KeithM]

Thanks for the input. How much boost would be safe on a driver like this at 20hz?
Would it be better for me to just get a vented box?

[cjd]

Out of curiousity, is it 8dB required to bring it flat? If so, you may not need that much boost due to room gain. Then again, you may.

I have about 3dB of gain dialed in on the Tumult at 16Hz (in 2.5cu/ft) I built my dad (he has it but I helped set it up). It's in a fairly large room but tucked in a corner out of the way with a couple plants on it now.

C

[kgveteran]

What you are attempting is a linkwitz transform. I attempted this with my BFD and the problem is that the BDF won't do the inverse if the 12db rolloff at the F3.A dedicated LT is the way to go.You will need to get the sub built and into position before you can begin to calculate how much boost you will need.Room gain will be in your favor to a greater or lesser extreme. Adding boost is tricky.As posted it requires power and Xmax.I would suggest you build and test.Then you can determine where to go fom there.

Cheers KG

PS I am boosting my quad Tumults about 5-6db with an outboard Marchand BASSIS but still only down to about 16hz.It requires lotz of power.

[ThomasW]

He shouldn't use an LT circuit with that particular driver.

Keith,

If you want the max output at 20Hz, build ported box tuned to ~18-19Hz then dial in boost to fill in whatever room gain doesn't provide. Understand that a single 12" can't take much boost at those low frequencies unless it has a HUGE Xmax

I hope those drivers are a very good deal. They've been discontinued for quite some time, and certainly won't live up to the marketing hype posted on that link.

[kgveteran]

I prefer a sealed box to a tuned enclosure.Keep the search for drivers that will fit the bill.Remember one driver in a sealed enclosure will need to be a real performer.The real deal with subs IMHO is multiple drivers and multiple mono amps followed by parametric EQ and a quality LT.

Movies these days are putting more demand on subs.Also think of the demand of a sub that has to produce bass from all six or seven channels and the LFE, to boot. Thats alot to ask.

What size is your room and how far from the listening position is the sub going to be.

[Davey]

I'm not sure everybody's clear on what the Linkwitz Transform (or any type of equalization) can do. You can electronically "boost" all you want but this won't increase the maximum output capability that the driver has. That is a defined limitation based on the drivers surface area and excursion capabilities. Equalization can make the response more useable over a wider range but thinking of this as "boost"ing the raw performance is faulty.

Frying the voice coil of the sub.....it might happen. If you were already pushing the driver to its limits and you then applied an extra 8db gain obviously you would have to turn down the volume by 8db. So, there really isn't any more power required when equalizing a response......if you see what I mean. No free lunch.

Sorry if that's redundant to some of you, but it seemed to me not everybody was talking about the same thing.

Cheers,

Davey.

[Bent]

One of the things I've found out recently is that the best deal in the world on are superb value driver is almost worthless if you make one mistake (or if there was a manufacturing defect on your particular driver) and have to do a re-cone when there are none left..

My BP-1503 required a re-cone, and I did manage to purchase the continent's very last re-cone kit, and UPS managed to lose it in shipping. Now I have a pretty 45 pound paperweight that looks like a 15 inch driver...

[ThomasW]

Davey,

Yep +8dB of boost isn't a big deal if the overall output level is kept in check, unfortunately that's usually not the norm....

[kgveteran]

You are correct about the boost.I guess they discribe the effect as boost but in fact it is extension. Extention will rob your system if all area's are not capable.For the beginner a simple tuned box may be the way to go.

WTS nothing beats overkill.The three area'e of overkill would be, the driver or drivers, the cabinet and the amps. If you design well above your needs (at least 50-75% ) you can boost and tweak to your hearts content.The world is full of overkill designs and we live with them on a daily basis.

Also correct is one wrong move and the advantages of a world class driver are moot.You have to be aware of the systems limitations.

Cheers KG

[KeithM]

I prefer a sealed box to a tuned enclosure.Keep the search for drivers that will fit the bill.Remember one driver in a sealed enclosure will need to be a real performer.The real deal with subs IMHO is multiple drivers and multiple mono amps followed by parametric EQ and a quality LT.

Movies these days are putting more demand on subs.Also think of the demand of a sub that has to produce bass from all six or seven channels and the LFE, to boot. Thats alot to ask.

<b>What size is your room and how far from the listening position is the sub going to be.</b>

My room is not exactly the perfect "audiophile room." It's around 14 x 16 with 7 foot ceilings, but it extends into a whole basement(rather large basement). I'd prefer to get a sealed alignment too. How would you calculate room gain for the sub at low frequencies? Also, I sit around 6 feet from the sub, but that can be adjusted if needed.
And to the person who asked, I got the sub for 50 dollars, so if I don't like it I don't lose a whole lot. And I realized that they wouldn't be as good as the website said. The main thing I realized about it is that the Fs is at 16, so I'm giving it a try.

[PMazz]

You should probably get at least 4dB of room gain @20Hz so you may only need a slight boost 2-3dB to be flat to 20Hz. This is all speculation however. As was said, you need to build it and measure to be sure. I wouldn't feed it much more than 100W or you may have a blowout.

If you want a .7Q, build a 4 ft^3 box and stuff with fiberglass. Vb gain due to stuffing should do the rest.

Pete

[kgveteran]

Room gain is pretty unpredictable. I would say build it and try your best to get it in the best spot, then take some sweeps to see where the smoothest location is.
Like I said , I did use the BFD to make a quasi-LT circuit.It had the effect but not as smooth as a dedicated LT.