Should I go back to Ported?

[cdy2179]

About a year ago I put 2 Fi IB18s in a manifold in the ceiling between and slightly to the left of center in relation to my mains in my theater room.
I'm pushing the two Ohm speakers bridged to 4 ohms with a Behringer EP1500.

At first it sounded really bad and after measuring i found a huge spike that went from 20 to 40 hz or so. Very odd. My ceiling was uninsulated because my roof is sprayed with foam.

So I added insulation to the ceiling and put a BFD on the system and put some pretty big notch filters in to level it out.

This made a huge difference and at first it sounded great, but after having it for a while and hearing other subs I feel it never really sounded as clean or powerful as my previous DIY 300watt 15" sonotube sub. Perhaps because of all of the electronic correction.

So now I'm thinking of either putting my spare sub on my seating area and taking the mic around the ceiling to see if I can move the IB to a better spot.
Or maybe build a ported box stage for my 18's and place the stage under the screen and forget IB.

here are some pics for room layout and IB install.
IB located just left of room center.


14x 18' long room seats backs at 14-15' from screen. columns have 5" x 6' long slit ripped out of the middle of the sonotube to let some sound through to the insulation inside the columns, not nearly as effective as corner wedges but using my old sub and the ears they did help. Please excuse the unfinished acoustic panel, the pics were taken several months ago before I completely finished the room.




up in the attic


manifold trimmed out and inside lined with faux black suede left over from columns, flash from camera washed it out in photo


here's the seating position with no EQ


And the nearfield

[ThomasW]

Oct 6, 2009 6:52:35 GMT -7 cdy2179 said:

but after having it for a while and hearing other subs I feel it never really sounded as clean or powerful as my previous DIY 300watt 15" sonotube sub.

IB's don't have the boost at Fb one gets from the port. They're the cleanest sub on the planet, some people however prefer the colorations created by a ported design..

All the EQ in the world won't make up for a improperly placed sub or a room needing acoustic traps suitable for low frequencies

IB specific drivers aren't designed to work well when placed in sealed or ported or ported boxes

Were I in your position I'd add more displacement by putting in another manifold with 2 more 18"s. I'd experiment with placement so the second manifold fills in the holes in the frequency response.

I'd also put 'super-chunk' style bass traps in the room.

[cdy2179]

With my peak being so big, I'm thinking of moving the current manifold if I can find a better place, I can add another acoustic panel to cover the existing hole so I'm not worried about leaving a hole.

My corner columns have the centers cut out and I have 4" of Compressed fiber board attached to the inside faces of all four corners. It's not as good as corner chunks but somewhat like the panel type corner traps. I'd like to keep them for aesthetic reasons of course.

Is my testing procedure for finding the optimal spot correct?? Put a boxed sub in the middle of my seating area and take my Mic to different places near the ceiling (standing on a ladder of course) and get freq. plots.

If I add 2 more 18s ,I don't think my current amp( EP1500) would push 4 18" Fi subs.

[weverb]

Can you describe more of what you don't like about the current IB sound? Have you looked into adding a "house curve"?

The EP1500 will not be enough for four 18's. You will need to step up to the EP2500 or add a second EP1500. With as close as they are in price, I would just sell your current EP1500 and buy an EP2500.

[cdy2179]

The bass just isn't super clean like I was expecting, it's not bad but sometimes it's not as clean as I think it should be, sounds muddier at times than previous ported subs I've built.

It's plenty loud enough and gets down to 3Hz. Before I put the BFD on it I'd set the level and all was OK until it hit the peak frequencies and ahhhhhh the room and my head would scream. It was very loud, I'm sure electronically cutting that much from the signal to flatten it can't be good.

[ThomasW]

Oct 6, 2009 9:10:25 GMT -7 cdy2179 said:

The bass just isn't super clean like I was expecting, it's not bad but sometimes it's not as clean as I think it should be, sounds muddier at times than previous ported subs I've built.

IB's by their nature are 'super clean'. They have the tightest bass of any sub. If you're hearing something different it's a function of the geometry of room, the location of the IB, the location of the listening position, the lack of adequate acoustic treatments.

4" traps aren't nearly thick enough for low bass. So you have a choice, looks or performance....

Cutting a peak has minimal impact on SQ as long as the filters are wide.

The other issue you have is the seating is too close to the rearwall. If you're going to sit that close you need diffusion for high frequencies and a thick bass trap.

[weverb]

I think we need to see some waterfall graphs. That should tell us a lot.

When I installed my first manifold with two 18's, I had a similar sound to what you are describing. I have been adding more and more "thick" traps in the correct locations and things have gotten much tighter. Now that I have added a second manifold, I need to add even more traps. Overall, this IB sounds/feels so much tighter than the box subs I had before.

This is a great read and may be of some help:

www.realtraps.com/lf-noise.htm

It looks like you have the mid to high areas covered very well. The columns are just not thick enough or maybe in the wrong place to help with the very low stuff.

[cdy2179]

The highs and mids are very clean and clear, panels are spaced off the wall to extend a little lower and they made a huge difference, so i'm good there.
In the corner traps I have placed the isnulation about 18" from the corners and are basically Panel style bass traps.

My head when seated is 5.5' off of the back wall, the room is 18' deep, am I sitting too close to the back wall?

If my previous subs sounded tighter wouldn't it tend to lean toward bad placement rather than the need to add more traps. It seems like if the room demanded more traps any sub would sound bad.

[ThomasW]

You came here after building your IB. We don't know anything about the room when you where using the ported sub. Where was it located?

As a experiment put the ported box in the rear corner. What does that do to the in-room response?

[cdy2179]

Actually I came here a year before I built and during my build.

My previous sonotube sub was in the front left corner and sounded great. The IB is about 4' to the right of this position just left of the center of the room.

I knew better than to build it without verifying the location but I hadn't used REW at that time and only did the ear test. I figured it was close to where my old sub was and got building. It's not the first time I've jumped the gun.

As far as the rear of the room goes... after building columns and panels we stuck the sonotube sub behind the chairs in the right rear corner to get it out of sight. It sounded terrible . Distorted isn't the word... it was bad. But it helped me easily convince my wife to agree we needed a new sub system.

[cdy2179]

Just thinking..... if a spot on the floor test pretty flat..... will it also be good at the ceiling?

[ThomasW]

The measurement needs to be taken at the ceiling

[ThomasW]

cdy2179 said:

I'm assuming even the IB 18 in a sontube should have way ore output than the IB config...

Nope, above the tuning point of the port, a single driver in an IB and one in a ported box will have the same output.

[chrisbee]

My fuzzy logic suggests that prior to a ceiling IB build a normal subwoofer should be lifted to ear height at the hot seat. Then measured with REW at the ceiling where the IB is intended to be placed. There is often a strong vertical component to frequency measurement. A few inches up or down can make a huge difference in my typical attic room. It follows that the test subwoofer should be placed at ear height.

It would be interesting to hear if anyone has ever fitted a ceiling and a floor manifold in the same room and measured the results. It has been said that the SVS cylinders are kinder to a room than the boxes. This may be the result of the considerable difference in height between the output of port and driver.

There may be room for a better raw response curve from vertical separation than from using front and rear IBs. Vertical arrays already offer considerable spread which may partly account for their (claimed) better SQ. Where one has a ceiling IB it is relatively easy to place a box sub temporarily in various positions on the floor to judge the effect on the response. Any IB EQ would have to be bypassed for this test to make any sense.

[weverb]

Thomas, Chris,

Do you think he would be better off leaving the existing one and measuring for a second location to improve things?

[chrisbee]

Thomas is far better qualified to answer but I can't imagine anyone being satisfied by going backwards to ported subs once an IB is heard. Adding more drivers will also increases output and headroom and reduce distortion and cone excursion. Doubling the number of drivers was a huge step up for my IB's SQ once I had the different drivers properly balanced. Nobody else would have that problem.

After reading the OPs doubts I tried my big SVS cylinder again today to remind myself of its capabilities on organ music. It was amazingly loud at times but had none of the effortless character rendition of the IB. The cylinder sounds far too much like sinewave test tones to me. Without any of the timbre, subtlety, timing, weight, speed, expression or depth of my IB.

Any organ fan would probably be delighted by the addition of the 16-46 into their music system. Until, that is, they heard an IB. If you own any other sub and can't fit an IB into your music room then it's probably best not to hear one. You will never be satisfied again. IMO, of course.

[cdy2179]

I have plenty of output so adding another sub isn't really desired, I'd rather try to relocate the sub and see if that helps.

It's hard to describe the distortion I hear, at times the sub sounds good but a certain frequencies I can hear it.

ex.
over the weekend me and my little girl were playing Halo, in the soundtrack of the game at a few points there is a deep heartbeat sound (may be when you've been hit), when it hits it sounds deep but has a slight blurp or distorted sound, not perfectly clean and tight like my 15' sonotube played the sound. It has to be placement and the huge 30db peak and the many filters i had to add to flatten the response.

[ThomasW]

Oct 14, 2009 9:38:54 GMT -7 cdy2179 said:

not perfectly clean and tight like my 15' sonotube played the sound

Unless the 18"s are damaged this makes no sense.

The 18"s have the ability to move about triple the air moved by a single 15". If the 15" isn't distorting neither are the 18"s unless something is wrong.

Are the 18"s and the 15" playing the same SPL when this occurs?
Do you know the frequency where this is occurring?

Possible issues are these.

The amp is distorting
You're hearing a resonance in the building or furnishings
Is the BFD being driven to distortion?

[cdy2179]

This happens when the volume is at moderate levels and I keep the receiver sub output turned down so that even the Nemo "glass tap" scene doesn't clip or go red on the BFD or the amp.

It doesn't sound like a blown speaker or anything, it just doesn't sound clean. I have my amp bridged (2 ohm subs run in series for 4 ohms)

should I maybe put one sub on each channel and see if maybe it's one of the drivers or one of the sides of the amp?

FYI the sonotube contained a 15" dayton Quatro with about 10mm of Xmax so the 2 Fi 18s should spank'em.

[ThomasW]

A Quatro can't possibly reproduce all that's recorded in the Darla 'tank tap'.

An IB will try to reproduce everything including the 5Hz data. Doing this will cause all kinds of rattles and shakes in the structure (this can sound like distortion).

If you want the IB to sound like the Quatro, just use a high-pass filter set to remove everything below where the Quatro rolls-off