Help a Newbie choose a sub for HT (1 Viewer)

[Highplainsdakota]

OK Let's say I've decided on the Fi IB318 driver x 4. Two in each manifold. Should I be getting the Single 2 or Single 4 in order to wire them in the proper resistance? Any links to wiring diagrams? Thanks

 

[Robert_J]

I'd go with single 4. Wire each pair of drivers in parallel and each manifold to one channel of the amp. The amp will see a 2 ohm load per channel. That is the exact reason I went with single 4 for my IB subs.

The Behringer amps put out about 75% of their stated power. So the EP-2500 / EP-4000 does about 800w RMS per channel into 2 ohms. So with a pair of subs on each channel, that's 400w per sub. It doesn't seem like a lot but remember there is no air spring behind them. The cone movement is relying on the driver's spider and surround for control. It takes very little power to push a free-air sub to xmax or even xmech.

At the 24 second mark, you hear the clank noise. That's the voice coil hitting the back plate of the motor. In this case it wasn't that hard and no damage was done. I've see subs where the coil looks like someone tried to squash an aluminum can. By the way, that's a sub I built. It's an odd basket I picked up from Car Audio Classified dot Org. The TC-7 motor came from a blown sub I bought where I only needed the basket. The coil and spider came from a TC-2000 https://web.archive.org/web/20070402025448/http://www.tcsounds.com/tc2000.htm that I got cheap because someone had overpowered it and deformed the cone. The cone was surplus from Sundown Audio. I like to build franken-subs.

 

[Highplainsdakota]

With an IB system like the one we've been describing, how do I know when to stop on volume to avoid damage to my subs? If I put on a movie and have it turned up, what if a sceen comes on with lots of base? I guess what is the safeguard?

 

[schan1269]

With an IB system like the one we've been describing, how do I know when to stop on volume to avoid damage to my subs? If I put on a movie and have it turned up, what if a sceen comes on with lots of base? I guess what is the safeguard?

Safeguard?Enough power not to clip. The Behringer has soft clipping...so it will tell you it is running out of power, before running out of power.And...like we discuss elsewhere, you need to understand volume doubling.

 

[Highplainsdakota]

So I guess I can safely assume that by choosing an IB design that pushes ~ 29 L of air into an 1800 L room (which freely communicates with another room that's 7000 L); where I'm sitting, I'll have the desired SPL before the subs reach Xmax in all likelyhood? I turn up the gain until the desired effect is reached or the speakers clip, or the clip light on the behringer amp stops me right?

 

[schan1269]

Speakers don't clip. Otherwise, yes.

 

[Robert_J]

As Sam said, speakers don't clip. As they are pushed to the limits, distortion increases. Why? If you look at the bottom 2 graphs (suspension stiffness and mechanical compliance), they are both increasing with excursion. Compare that to the force factor graph. The magnetic force decreases with excursion. TC Sounds (or John J. from AE Speakers depending on who tells the story) created one way to counteract this. The LMS (Linear Motor Structure) using a voice coil with variable windings with more layers on the top and bottom. So as the coil is moving towards its limits in the magnetic gap, the magnetic force from the coil is increasing. This makes the BL curve look more like a flat line with steep drops on either end.

If you notice one thing about IB sub drivers, they have small motors and loose suspensions. Loose suspensions give them a low Fs (resonant frequency) and large motors aren't required because the drivers don't have the air "spring" inside the box to work against. That helps to prevent over excursion and driver damage.

If you had chosen a single 15" sub for your IB then it would sound very similar to a 15" sub in a large, sealed box. You are going with four 18's. FOUR!!!! You are doing that to keep the distortion down. By the time the amp clips or your speakers are driven into audible distortion you will worry about your house.

 

[Highplainsdakota]

Ok. That's good.

I have chosen the Behringer inuke 3000DSP for the subwoofer amp. That gives 1500 W per channel (x 2) into 2 ohms. My two 4 ohm 18" per manifold in parallel give 2 ohms with a combined RMS of 1100. This looks perfect, but someone said the Behringer's give 75% of their rated power, putting it at 1125. Since more headroom is always better, and the cost between the two is minimal, should I go with the inuke 6000 DSP? This has 2 x 3100 W into 4 ohms, or 2 x 1600 W into 8 ohms.

I could wire each dual 18" in series to get 8 ohms, and 75% of 1600 is 1200. It's really not much more.

The final option would be inuke 12000 DSP (2 x 6000 W into 2 ohms or 2 x 1700 into 8 ohms). I could do either, giving me 4500 W or 1275 W at 75%, respectively.

Again, I'm not trying to blow my house down, but for an extra $100-200 I want to do the right thing for the system. I'm guessing it would be better for all the equipment to run a more powerful amp at a lower percentage of it's max. I'm sure all would work, but what would be "Best"?

 

[Robert_J]

The 6000 DSP is really a pair of 3000's in a single chassis. It is not 2 ohm stable. The theoretical difference between 1125w and 1500w is about 1db. In reality, it isn't audible. Don't sweat that one and stick with the cheaper amp.

During normal playback you will be pushing about 100w to 200w most of the time. Rarely will your peaks even get close to maxing out that amp. My EP-2500 really does about 800w per channel into 2 ohms. With dual 15's I have never had the clip light even start to glow much less completely light up. At +3 on my receiver's volume control I am shaking pictures on the other side of the house. I've even knocked my projector out of alignment. You will have 3 to 4 times the bass capability that I have.

 

[Highplainsdakota]

Ok, that sounds great. I'll use the 3000 in that case. That makes a lot of sense after my rigorous lessons from Sam. That completely answers my sub power/setup questions. I think I've got it figured out as close as I can at this stage without the house being built.

Also, I really don't intend to push all these speakers or my receiver to its max, it's just that this is my first set up that isn't completely plug-n-play, and I'd not forgive myself ruining something due to ignorance. I'm sure everyone on here understands.

 

[Robert_J]

I understand even though I've never owned a plug-n-play system. As far as I know, they didn't even have them when I was getting started. The only "all-in-one" type system looked like the picture below. In fact, I had that exact model. I may still have it somewhere in this house.

 

[schan1269]

I understand even though I've never owned a plug-n-play system. As far as I know, they didn't even have them when I was getting started. The only "all-in-one" type system looked like the picture below. In fact, I had that exact model. I may still have it somewhere in this house.

Please don't tell me you carried it on your shoulder...

My first had 8-track.

 

[Robert_J]

Please don't tell me you carried it on your shoulder...My first had 8-track.

I could lie and say that it was on my shoulder while I roller skated but that's stretching the truth way too much. Back in high school I could run through the ropes any way my football coach told me to but I can barely stay vertical with wheels on my feet.

I will take back my 'all-in-one' statement. I hijacked my parents system as my first and it had 8-track recorder as well as a record player.