Building two subs, how?

[fackamato]

Hi, I've two Tempest-X, DCX2496 and an EP2500 at my disposal. I have no idea if I'm going sealed or ported. Many people say "just build two sealed boxes, 8^3 each". I don't know. First, they'll be huge. Second, if I go ported, I'll get more output. I can add a subsonic (highpass) filter with the DCX2496 to protect the drivers from bottoming out, which probably is necessary in a ported enclosure. Application is 50/50 music/film.

Which simulation program gives the most accurate results? I'm currently using WinISD and Bassbox 6 Pro.

Here comes some graphs using WinISD. I'm aware that the Tempest-X likes BIG boxes, but I'm trying to cheat it.

In a 250L sealed box the Tempest-X reaches 33mm excursion at 10Hz, using 600 watts.
In a 200L sealed box it never goes up to 30mm excursion, using 600 watts.



Excursion: SPL: Transfer function magnitude:

There is no xmax left for raising the bottom end with EQ. Just to clarify, I would probably be very happy with two sealed boxes but I'm just trying to get the best that I can get, even if I don't "need" it . Building ported boxes would require a slot port otherwise the length of the tubes would be way too long, so slot port is not a problem for me. (it would be a first time building them though)

So, how about some ported simulation...

250L ported, tuned to 15Hz, slot port (mm) 500x50x1200, versus 250L sealed. 600 watts @ both. The ported box has a 4th order Linkwitz-Riley highpass filter at 10Hz.

Airspeed: Excursion: SPL @ 600W: Transfer function magnitude:



And some final graphs comparing 250L ported, 250L sealed and 200L sealed:

Excursion: Group Delay: Impendance: Impendance phase: Maximum SPL: SPL: Transfer function magnitude:

Any comments, ideas? Did I miss something? Will the long slot port become a problem (noise, resonanse)?


Thanks,

Mathias

[thxgoon]

Looks like you've done your homework. Everything looks pretty good for both designs. I would go ported if you don't mind the extra work. The additional output looks pretty substantial in your case. Is 250 the largest you're willing to go?

[fackamato]

thxgoon wrote:

Looks like you've done your homework. Everything looks pretty good for both designs. I would go ported if you don't mind the extra work. The additional output looks pretty substantial in your case. Is 250 the largest you're willing to go?

Thanks! I've been playing with all the speaker software available now for.. 4 months.

Yeah I'm thinking of going ported too, I'm just worried about the excursion limit. Perhaps the DCX2496 isn't able to act as the highpass filter in a frequency that low? (10Hz)

I haven't actually bought the DCX2496 yet, but it'd be nice to EQ the two mainspeakers as well as the two subs, with one device.

Since I'm going for 2 subs at (maybe) 250L each, I think I'm stretching it a bit already. I have no choice but to have them standing, or make them a part of the furniture.. (using them on the floor, as a shelf for TV etc).

Regarding ports, I think I'm forced to use square (slot?) ports, no? If so, does it matter where the port exit ends up?

Edit: If not using a slot port, but using "pipes" instead... When is the length a problem? Is two 4" pipes 40 inches long, too long? What will happen? (200L)

Another question: it's the total port area that sets the frequency, right? How do I convert forth and back between pipes and slot/square ports?

[Mike P.]

The Xmax of the Tempest-X is 27mm.

I'm just trying to get the best that I can get, even if I don't "need" it

Then go with ported. As long as vent air speed is acceptable,(In this case it is) port length is not an issue if the the first port resonance is 125 hz or above and you use a 4 th order crossover at 80 hz, which most receivers have. A SSF probably isn't necessary since cone excursion isn't exceeded until 12.4 hz.
For comparison, in sealed, Xmax is exceeded at 26 hz requiring a SSF at 15 hz to keep Xmax within limits at 27mm. Both models below are with 600 watts applied.

[fackamato]

Thanks for the swift replies! Let's see if I can get some building going on during christmas.

[SteveCallas]

Is one of your goals to stay within 250 liters? Ported gives you many advantages as you have probably already noticed, but that FR can be made to look even better if you use a larger enclosure. You mention you are building two subs - so you have a few other options as well. You could maybe consider building one larger, better LLT with a Maelstrom X 18, or possibly dual LLTs that would be smaller in size using the Mach5 IXL 18s.

With any of the drivers being considered, you don't really need a highpass filter if you will be tuning below 15hz. Most electronics naturally start rolling off in the single digits or sooner, driver suspensions become less efficient when approaching their limits, xmech affords more travel for "safety" purposes, a ported sub typically winds itself down a bit below tuning, and then lastly you have to consider how few scenes really have very spirited output in the single digits. You add all these things together and you get a pretty good margin of safety with high excursion drivers tuned below 15hz.

[fackamato]

SteveCallas wrote:

Is one of your goals to stay within 250 liters? Ported gives you many advantages as you have probably already noticed, but that FR can be made to look even better if you use a larger enclosure. You mention you are building two subs - so you have a few other options as well. You could maybe consider building one larger, better LLT with a Maelstrom X 18, or possibly dual LLTs that would be smaller in size using the Mach5 IXL 18s.

With any of the drivers being considered, you don't really need a highpass filter if you will be tuning below 15hz. Most electronics naturally start rolling off in the single digits or sooner, driver suspensions become less efficient when approaching their limits, xmech affords more travel for "safety" purposes, a ported sub typically winds itself down a bit below tuning, and then lastly you have to consider how few scenes really have very spirited output in the single digits. You add all these things together and you get a pretty good margin of safety with high excursion drivers tuned below 15hz.

I already have the drivers, that's why I'm building with them.

I'm also going to build a box based on Neodan's easy button table design (6.375cu ft) with a Maelstrom-X for my dad, but these two tempest-x are mine.

250L is pretty big, and I think the F3 I'm getting is pretty okay... I guess. I live in a really crowded place

[fackamato]

By the way, a few more questions:

* Does it matter if the port goes to the rear of the box? I.e. against the wall in the room.

* Do you know of a simple 3D modelling program that I can use to model the box? Neodan's pictures of the buttontable for example...

* Should the driver be placed in the middle of the baffle, top, or bottom? What about the port? (if on baffle)

Little late, but happy thanksgiving

[thxgoon]

fackamato wrote:

* Does it matter if the port goes to the rear of the box? I.e. against the wall in the room.

* Do you know of a simple 3D modelling program that I can use to model the box? Neodan's pictures of the buttontable for example...

* Should the driver be placed in the middle of the baffle, top, or bottom? What about the port? (if on baffle)

The port can go on any side of the box that is convenient. Just make sure that there is at least 1 port diameter of clearance on all sides of the port from any walls or driver magnets etc... Mount the driver where ever you like

NEODan uses google sketchup. It is free and by far the easiest cad program I've ever used.

[Blaser]

Mike P. wrote:

The Xmax of the Tempest-X is 27mm.



Then go with ported. As long as vent air speed is acceptable,(In this case it is) port length is not an issue if the the first port resonance is 125 hz or above and you use a 4 th order crossover at 80 hz, which most receivers have. A SSF probably isn't necessary since cone excursion isn't exceeded until 12.4 hz.
For comparison, in sealed, Xmax is exceeded at 26 hz requiring a SSF at 15 hz to keep Xmax within limits at 27mm. Both models below are with 600 watts applied.

Attachment 10565

Attachment 10566

Looks great, but if possible use slightly bigger enclosure. You'll get better efficiency down low...

[fackamato]

250L is big, with 19mm MDF (38mm baffle), external dimensions are 1427xt500x470mm (h * w * d) (or 56x20x18.5 inches).

[Blaser]

That's not that big if you have the space...Check my signature

[fackamato]

Yes of course, if you have the space. I don't have any space at the moment, I'm currently living abroad, and I don't have a house/apartment in my home country, so I'd have to live with my parent(s) when I get home in some months. I'll go home briefly over christmas, and build the subs. place them with my dad in an empty small room... Or, maybe have them laying down at the front with the tv. We'll see. 2 tempest-x and 1 maelstrom-x. Why not. It'll sound horrible.

Just kidding, he'll just use the maelstrom.

[Blaser]

I understand the space limitation issue, but the problem is the drivers won't understand

[Mike P.]

but the problem is the drivers won't understand

Sure they will, Blaser, they'll do as they're told!