Converting sealed Tempest to ported (1 Viewer)

[Benihana]

I have a 230L sealed tempest. I want to convert this to ported, similar to the adire alignment. However, I need to know how to approach this. First question is, is the 230L LowQ model volume before or after driver displacement?
I also have the amp built into the side, so i'm guessing that will take like 3L of air?? I need to know the net volume so I can tune it to 15.4hz. I can't use the adire alignment port length because that box is just a bit smaller, and after some calculations it loox like i might need to make the port either shorter or longer. I already drilled holes for the ports, I just need to install them. Much help will be appreciated.

 

[ThomasW]

Any box modeling program gives the 'net' volume needed after you subtract for the driver, the amp, the port, bracing, etc...

 

[Benihana]

after some consideration, I've decided to tune the box to 18hz , and just plug the ports when listening to music with the sub, which is not often. So in the end I get like a 225L sealed low q for music, and 225L ported 18hz. Should be some fun.

 

[Owen Bartley]

You might want to tune lower for HT, especially if you're going to plug the ports for music. My Tempest (210L) is tuned to 19 and the one thing I'd change if I did it again is tune lower to probably around 15Hz. I start to roll off a little too early, and am not helped much by the 19Hz rumble filter in my amp, but I'd like a little bit more low end extension. Just my 2 cents though.

 

[Chris Popovich]

I would think twice before tuning that low.

15hz tuning is LOW, you're not going to be getting much out of that port until you're really dipped far down in the ferquency spectrum, and seriously increasing the chance that your driver will bottom out around the 30Hz range. The "saddle" in the frequency response is very significant... and it won't go THAT much lower than your 19Hz tune... just food for thought.


-Chris

 

[ThomasW]

Unless his room is really lossy the saddle will be filled in by room gain.

Going with a lower tuning helps protect the driver from unloading if bass lower than the tuning is sent to the woofer

 

[Benihana]

isn't there usable response down to 15hz when using a 18hz tuning? I remember dan wiggins saying if you want a big HT destroyer, build a 8cf vented box and tune to 18hz.

Maybe your rolling off to early because you have a 19hz rumble filter? you can change that.

 

[Owen Bartley]

I think mine is a combination of the rumble filter, and the tune. I was going to disable the rumble filter, but with my box tuned to 19 Hz, it would quickly unload below that frequency, so I am going to keep it. If I had tuned lower I could remove it without worrying too much.

 

[Benihana]

from the graphs i've seen and modeled, it seems like it will waste alot of energy from like 17hz-40hz if tuned at 15hz compared to 18hz. The 18hz tuning has output to 15hz(-3), which is plenty low enough.

 

[ThomasW]

No problem, just don't play any DVD's like WOTW or Batman Begins, without a rumble filter

 

[Benihana]

I justed tuned it to 18hz, and WOW!!!!!!!!!!!!

 

[Benihana]

at what frequency should I set the subsonic filter to with the sub tuned at 18hz? Is 14hz too low?

 

[Patrick Sun]

Might as well set it at 18Hz since the porting will, more or less, protect the driver down to that frequency.

 

[Scott_Vonhof]

BTW, not that it matters now, but for your sealed design, you need to caculate that based off of the added volume of the inside of the ports as well, since they are not sealed on the inside edge of the port, but the outside edge (you plug it without taking the box apart).

No biggie though.

 

[Benihana]

Yes, it was 230L before the ports, but if you figure about ~5L for the ports, it comes out to 225L with the ports installed, sealed or not.

 

[Scott_Vonhof]

But the ports are open to the inside of the box, so your sealed sub is actually a 230L sub, but your ported sub is only 225L. :b

 

[Benihana]

lol, even better, best of both worlds.