My New Fi Q18 Sub Project -Input Wanted Please

[Martianpc]

I just moved into a new place and set up my HT room, I am not satisfied with the output I am getting from my current sub which is a Klipsch RW-12d. I want to build a new sub most likely using the Sound Splinter RL-P18

I do not have an amp or drivers currently so I need advice on what to buy for the amp. I considered using an ep2500 for the sub but I have no idea what sort of active crossover I would need. I think I may be able to use the sub out built in crossover in my Onkyo 805. (can be set between 80 and 120hz).

My current equipment is an Onkyo sr805 receiver, all Klipsch reference speakers RF82 up front, RF 52 in the rear and an older model KLF-C7 center.

The room is about 13x18 when the blackout curtain is closed and if that is not closed the room is open to the rest of the basement.

I want a loud but deep sound from the sub, should be able to feel them strongly during good actions. The room is mostly all concrete and I still need to try to treat the walls somehow.

Here are some pictures so please give any advice that might help me. Thanks







back of the room curtains partially open to rest of room. They close all the way though and black everything out.




Here is what I am planning so far. I would like to position it in the front of the room under the screen.

72" Wide
23" Tall
23" Deep

Made of 3/4" MDF with corner and cross bracing.

The port would be a slot port along the bottom that would be 21.5" wide on the inside (23" deep - 1.5" for MDF wall themselves) and 5.5" tall while being 59.89" deep. This will give me a tune of right around 16hz. Obviously the EP2500 will have more than enough power for this sub, but it allows me to build a second in the future if so desired.

The internal volume should be around 18 cubic feet after the port and sub.

Here are some rough sketches of my current plan.







If my Winisd is right, I should not have any port noise with around 50 ft/s peak at 14hz, I should be able to reach high spl and not bottom out. I have included the Winisd file as an attachment for anyone who cares to see the plan. This is not a final decision but a strong possibility. I do not know if I need a crossover besides my Onkyo because I would not have a subsonic filter to the best of my knowledge.

Specifically looking for pointers on:

-The Box design
-The Amp
-Built in crossover on RX going to be ok?
-Subsonic filter needed?
-Port issues?
-where to brace that box?

Thanks in advance for any help, I am new to HTS and was suggested by an AVS member that this is the place for DYI projects. Thanks!

[Mike P.]

First let's deal with the modeling.

The low pass filter should be 4th order at 80 hz. There's no need for the high pass 2nd order at 8 hz since it isn't doing anything. As you have it modeled the cone excursion is exceed at 14 hz with the amount of input power you have entered. Should you find the sub is bottoming out, depending on how hard you push it, you may need a add on High Pass Filter.

The first port resonance is too low. Change the port height to 4" and the air speed is well under 26 m/s and this raises the port resonance to 160 hz.

[Martianpc]

Hi Mike, thanks for the quick reply. I went ahead and changed the modeling to reflect a 4" x 21.5" port and fixed the filters. I also modeled up a Fi Q 18 that actually looks like it might actually preform very well under the same box without risking bottoming out. Not to mention it is 100 dollars cheaper to buy.

Do you think the crossover in my Onkyo set at 80hz will be sufficient to manage the output to an EP2500 amp?

I have included the model for the Fi sub as well. I appreciate the help and expertise.

[Mike P.]

The Q18 models close to the RL-p18. They both exceed Xmax at 14 hz when pushed hard.

I don't recall if anyone had insufficient voltage on a Onkyo to drive a EP2500 or not.

The 4" x 21.5" is longer then the 5.5" x 21" port. You'll have to recalculate the volume of the box to see if there is a difference in net volume.

[Martianpc]

Not to be a pain, but I am confused, I checked my model again and I am showing a port length of 42.43in which is shorter than the previous port of around 5.5" which had a length of about 59.8. You mentioned the port would become longer, however I am seeing it as shorter in length as a result of moving to a 21.5" X 4" opening.

[ironglen]

I thought my 14.5hz tune would be safe, and maybe I'm a bit fearful as the driver has so much travel to give, but I think a hpf would be a good safeguard, especially with movies like LOTR, Titan AE My Mal-X moved alot the other day, and it wasn't even turned up- scared me a bit as it would be an ordeal to lose the driver.

[Mike P.]

Martianpc wrote:

Not to be a pain, but I am confused, I checked my model again and I am showing a port length of 42.43in which is shorter than the previous port of around 5.5" which had a length of about 59.8. You mentioned the port would become longer, however I am seeing it as shorter in length as a result of moving to a 21.5" X 4" opening.

Sorry about that, I meant to say shorter. My bad.

[Mike P.]

ironglen wrote:

I thought my 14.5hz tune would be safe, and maybe I'm a bit fearful as the driver has so much travel to give, but I think a hpf would be a good safeguard, especially with movies like LOTR, Titan AE My Mal-X moved alot the other day, and it wasn't even turned up- scared me a bit as it would be an ordeal to lose the driver.

I agree on having a safeguard in place. It's well worth the $100 price tag for a add on High Pass Filter to ensure the safety on the sub. There's a big difference between relaxing and enjoying a movie as opposed to worrying if the next hit is going to damage the sub.

[Martianpc]

Do you have a recommendation for a certain HPF? I am trying to stay inexpensive on this project. Although I am starting to wonder if I will need anything to help manage the high output levels expected from this beast.

[Mike P.]

I suggest you build the sub and try it out first. Depending on your listening habits maybe you don't need a HPF. No sense spending more money then you have to.