Deciding to go IB and choosing a driver

[mpick]

Hey, everyone. The folks from PE Techtalk directed me here and told me to look for Thomas. Below is the post I started about a potential IB project. I have worked with several sealed and ported systems, but this would be my first IB. I like the specs for the Fi IB318. Assuming the xmax spec is real, this driver should preform quite well in IB applications. This is a home application for both HT and music. I am thinking DLS Ultimax 18" sealed or Fi IB318 18" infinite baffle.

I've been looking at the ultimax drivers. I recently started to consider infinite baffle. I see alot of people like the Fi drivers for IB. The Fi has a considerable excursion advantage assuming the spec is true and distortion is reasonable. The ultimax looks like stiffer more durable cone material, dual opposing spiders, and shorting rings. The ultimax seems to have more distortion reducing features. Simulations look favorable for the Fi product. What do you all think about these drivers?

[ThomasW]

Hi,

Either driver will be fine for your IB.

The Fi cone is Kevlar reinforced pulp so they're very stiff, the Fi also have shorting rings they just don't advertise them..

The Fi T/S parameters are accurate so yes you get a bunch more displacememt for basically the same price as the Ultimax.

[mpick]

Feb 27, 2017 7:55:41 GMT -7 ThomasW said:

Hi,

Either driver will be fine for your IB.

The Fi cone is Kevlar reinforced pulp so they're very stiff, the Fi also have shorting rings they just don't advertise them..

The Fi T/S parameters are accurate so yes you get a bunch more displacememt for basically the same price as the Ultimax.

Thank you. That's good to know and helps to make me more comfortable with the Fi product. Now i just need to figure out implementation.

I'm trying to put two subs in opposite corners to tame some issues with uneven response in different locations within the room. I want to put these in the basement with a manifold opening to the room above. The construction is unfriendly and leaves few spaces for a manifold. the manifold will need to be long and wide (maybe 8" x 32") for each driver. will this manifold shape create any issues?

[ThomasW]

If you'd post a floor plan or pics of the room it would be easier to answer your questions.

[mpick]

Feb 28, 2017 7:19:41 GMT -7 ThomasW said:

If you'd post a floor plan or pics of the room it would be easier to answer your questions.

Here is a drawing of the room as it is now. The red box is the subwoofer. Green boxes are speakers. Behind the couch is glass. To the right of the couch is a fireplace. The listening room is open to the kitchen. Openings in the kitchen walls go to other rooms in the house.

[ThomasW]

You don't need a 8" X 32" opening for a single driver, 8" X 18" is fine

Have you done the room crawl to check proposed places for the IB's?

[mpick]

Feb 28, 2017 21:47:48 GMT -7 ThomasW said:

You don't need a 8" X 32" opening for a single driver, 8" X 18" is fine

Have you done the room crawl to check proposed places for the IB's?

I don't recall where these vent dimensions came from. Basically i want the effective vent area to be greater than 188 square inches so i am not accelerating the air above the velocity at which it leaves the driver. I believe this is beneficial. But may not be required.

I have not done the crawl. I do plan to make some measurements with the sub in multiple places. I have not been motivated to do this yet because box placement currently had only one option. That's a key advantage for IB in my space.

I am not sure if the crawl will tell me everything i need to know because i don't have two subs. I am planning under the assumption that diagonally opposite corners will help. I currently have a corner loaded sub and seating along the back wall. Seems like a worst case situation but choices are limited. The most offensive listening position is in the diagonally opposite corner from the sub as expected. In theory, i believe there is advantage in placing a second sub in this location. When operated in phase with the first sub, the second sub should be 180 degrees out of phase with the first at the room mode frequency along reach room dimension (besides height). This should prevent the response peak in the corners allowing less EQ that kind the response elsewhere in the space. I have seen data collected by others that sends to show that this works reasonably well in square spaces. Problem is the IB is kind of a commitment. You can't really move it around once you cut your holes. Have you ever tried this purpose placement? The uncertainty is holding me back.

[ThomasW]

8"x18" is 144 that's more than close enough to the Sd that it won't cause any audible issues. Going bigger means the sound will be bouncing around it too big a box.

Were I you I'd build and install the front IB then experiment with your box sub to find the optimal position for the rear IB

[mpick]

Mar 1, 2017 7:20:36 GMT -7 ThomasW said:

8"x18" is 144 that's more than close enough to the Sd that it won't cause any audible issues. Going bigger means the sound will be bouncing around it too big a box.

Were I you I'd build and install the front IB then experiment with your box sub to find the optimal position for the rear IB

Thanks for the advise on vent size. I have not done IB before so i am making some assumptions.

I will definitely do like you suggest, starting with a single IB before cutting the second location. I may also try my single box sub in the other front corner to see if there is any advantage.

[mpick]

So i have decided to use the Fi IB318v2. I plan to use two of them each in seperate manifolds. I would use two in each manifold for force cancelation, but i want to be reasonable with the budget versus performance needs. I think two 18's driven by an inuke6000 with a mini dsp for EQ and 10Hz subsonic filter should provide good performance in my room. I show two possible manifolds below. One had the diver at the bottom so the force pushes against the weight of the house and is parallel to upstairs walls. The other has the driver on the side and includes bracing to counteract the diver force. I think the upward firing option would be better to control forces and vibrations. I am concerned however that anything that falls through the opening will be directly on the driver. I am concerned that the side firing option will cause too much vibration. Any thoughts on this topic?

[underthebottom]

For half of each cycle, the driver will be pushing up against the weight of the house.  For the other half, it will be pulling down.

[mpick]

Mar 5, 2017 12:07:46 GMT -7 underthebottom said:

For half of each cycle, the driver will be pushing up against the weight of the house.  For the other half, it will be pulling down.

Yeah i get it. This seems better to me than side to side, perpendicular to the walls. Seems to me that would result in more unwanted vibrations. What do you think?

[ThomasW]

I'd go with the up facing driver. The opening into the room should be covered with some grill cloth that will prevent anything from falling in the hole

[mpick]

Mar 5, 2017 17:17:18 GMT -7 ThomasW said:

I'd go with the up facing driver. The opening into the room should be covered with some grill cloth that will prevent anything from falling in the hole

Yeah i can put some screen or grill cloth under the vent cover to keep small stuff out. If I'm having carpet replaced or something I'll have to take the drivers out temporarily.

[nicktf]

I've been running four of the original IB 18s from fi audio for 10 years with zero problems and they are every bit if not more impressive (recently upgraded receiver) as the day I installed them.