DIY sealed - jaxvon induced curiosity

[mike c]

I have some questions re: building my own sealed box (sealed because it's simpler, right?)

1) how many drivers and how big a box do I need to make a 10hz tuned sealed box?
2) is it ok to use real hardwood? (I don't have access to MDF, and my contractor has access to all kinds of real wood)
3) cost of no consequence ... looking at TC sounds drivers

 

[nav]

I have some questions re: building my own sealed box (sealed because it's simpler, right?)

1) how many drivers and how big a box do I need to make a 10hz tuned sealed box?

Adding more drivers doesn't lower your -3 dB point, it just increases total output. To get sealed box with usable response down to 10 dB is pretty hard without equalization. When to flatten the response in the lower frequencies with an equalizer (or some other electronic filter), the driver will run out of excursion fairly quickly; which will result in not being able to get the total SPL out of the system as you would with it un-flattened. So, you then use more drivers to make up for it.

An example in WinISD (running under WINE ). Here's a TC Sounds TC-2000 15" in a 2.56 cubic ft box. (See picture one.) I can run 1000 watts through it with no problem and the resulting output is predicted up to ~118 dB, but the -3 dB point is a relatively unimpressive 41.3 Hz.

If I apply a Linkwitz transform around 40 Hz I can flatten out the response, but the driver will run out of linear excursion around 35 Hz at the same 1000 watts. So, I lower the gain to a quarter of what it was and add a second order high pass filter at 17 Hz. Now the predicted total SPL won't get any higher than ~112 dB, but this gets us a -3 dB point of 23.38 Hz; much better. (See picture two.)

This isn't anywhere near useful output to 10 Hz. I could keep adding drivers (more total displaced volume, less required excursion of each) and equalization and possibly mess with the Q of the enclosure (using the equalization to even out the response), but it gets kind-of burdensome long before we reach 10 Hz.

So, that demonstrates what a sealed box can get you and possibly that a ported box might be what you need for 10 Hz. Building a Linkwitz transform isn't something everyone is up to either. Many plate amplifiers have a small low-end boost and high-pass built in though. For something huge you'll likely want to use an external pro-amp. I'll run some more TC drivers through WinISD in ported enclosures and see what I can come up with.

2) is it ok to use real hardwood? (I don't have access to MDF, and my contractor has access to all kinds of real wood)

A lot of people like using Birch plywood. The right stiffness to mass ratio without costing too much is all that's necessary.

3) cost of no consequence ... looking at TC sounds drivers

I have a TC-1000 sitting in my closet waiting for me to finish building it a box . They model well in relatively big sealed boxes. The TC-2000 does better in slightly smaller sealed boxes. The TC-3000 doesn't model too well in a sealed box and is more suited for ported boxes. I haven't model TC Sounds LMS drivers yet.

 

[jaxvon]

I have some questions re: building my own sealed box (sealed because it's simpler, right?)

1) how many drivers and how big a box do I need to make a 10hz tuned sealed box?
2) is it ok to use real hardwood? (I don't have access to MDF, and my contractor has access to all kinds of real wood)
3) cost of no consequence ... looking at TC sounds drivers

Don't blame me!

You can make nice sub boxes out of 3/4" plywood then covered with whatever you want. You just need to brace them appropriately so you raise the panel resonance above the passband. Since you said you have 10 thumbs, I would recommend against veneering, as it takes woodworking finesse.

While sealed is the easiest, it is not the ideal enclosure. You can get awesome quality bass with ported or passive radiator systems. I would think that a passive radiator system would be optimal. It takes more work to build than a simple slot-ported system, but you completely eliminate the issue of port noise while retaining the qualities of a ported system. TC Sounds makes a passive radiator that, from what I have seen, is yet to be equaled by anybody. It isn't cheap, but it is fully variable in its tuning and has massive excursion capabilities, a trait that is important for passive radiators.

I would also look to use a good high power PA amp to power this/these sub(s). A single Behringer ep2500 will provide enough juice to drive two monster subs without any issues, and will also make things simpler. Without an amp in the cabinet, you only need to cut holes for drivers and passive radiators. Beyond that would be two small holes to drill for the binding posts. Going with an external amp also saves your subwoofer amp from the punishment of all that vibration from the driver. It also allows you to hide the amp with the rest of your electronics stack (you ARE hiding your stack, right?). Lastly, it prevents ground loop issues and also reduces the number of cable runs to a location you need to do (just speaker wire, not power and signal).

 

[mike c]

was thinking that I was gonna ask the contractor to build a box to my specs ... so hardwood is gonna be no problem (we pay about 4 bucks per board foot for the local hardwood)

so ... a passive radiator is a box with an active driver and a passive driver that can move in conjunction with the active one ... to counter the intense pressure of a lone active driver in a sealed box?

I was planning to use up to two EP2500s, one channel for each VC!

 

[jaxvon]

was thinking that I was gonna ask the contractor to build a box to my specs ... so hardwood is gonna be no problem (we pay about 4 bucks per board foot for the local hardwood)

so ... a passive radiator is a box with an active driver and a passive driver that can move in conjunction with the active one ... to counter the intense pressure of a lone active driver in a sealed box?

I was planning to use up to two EP2500s, one channel for each VC!

Now THAT would be overkill. Use one for both VCs, otherwise you might end up with a cooked driver. As for the hardwood, I would not recommend that. Hardwood tends to be resonant. This is great for acoustic guitars and pianos and the like, but not for sub or speaker boxes. Have him build you one out of ply to your specs then get a cabinet maker to finish it. The box shouldn't be hard to finish for a good cabinet maker, so the cost should be nominal, lest you desire a high gloss finish with super premium veneers.

 

[mike c]

im waiting for some prices from TC sounds ... taxes and stuff to canada. it will depend on that ... if the price approaches DD ballpark ... I might as well buy another DD

 

[jaxvon]

im waiting for some prices from TC sounds ... taxes and stuff to canada. it will depend on that ... if the price approaches DD ballpark ... I might as well buy another DD

I dunno. I've looked at comparisons on DD subs and other woofers, even a DIY model with a now-discontinued Infinity woofer, and the Infinity was actually a better performer than the DD-12, even in non-linear distortion, which is odd, since the entire point of a servo system is to lower distortion. I feel that a high-cost subwoofer like the DD-12 shouldn't lose to a low-cost, non-servo system in anything, especially non-linear distortion.

 

[mike c]

I saw that Kappa driver you guys were talking about ...

ok, maybe I'll play with a sealed box DIY ...