[OvalNut]

OK, here goes.

The bottom line is that adjoining my HT room, I have a utility room with a volume of 1475 cu. ft. (over 20x the Vas of 4 Fi IB3 18" subs). Though my HT room is set up on a screwy diagonal for livability purposes (hey, I like it this way!) the IB manifold would be right behind the TV between the mains.

The HT room itself is roughly 24'd x 15'w x 8'h. It is a basement room with studs and drywall backed by R13 insulation over concrete walls. The floor is padded carpet over concrete. The ceiling is smooth drywall throughout with a layer of R16 insulation between the ceiling and the floor joists approximately a foot above it.

The surrounds are set in a 6.1 configuration. I used in-ceiling speakers for a clean look. What I did right here was that when I finished the basement I built in 3/4" MDF enclosures between the joists and filled them with insulation prior to installing the ceiling. The engineers at HTD were great about helping me get the box volumes right.

FYI, I am also is the midst of upgrading my mains (TBD), for what that's worth.

My thoughts are:

- Build a manifold with drivers on 4 sides, 15” or 18” each. I like the 18” idea though I may not quite need to excess SPL.

- My design goals are: Retain as much punchiness as possible, while still getting cleanly below 9hz flat at over 110 db.

- The 18’s may be just too physically big, but perhaps worth it?

- The HT room itself is about 2500 cu. ft. with an adjoining 1400 cu. ft. room to the side via a 5 ft wide entrance.

- Use a Behringer EP2500 amp in 4 ohm mono(?) for power.

- I am using a FBQ2496 and REW for EQ.

- Retain existing bass traps and acoustic treatments.

- A friend of mine 2 doors down is a finish carpenter and will be available to assist with the manifold build and installation.

- I am open to insulating the carp out of the utility room if that will help both the IB performance (perhaps), and make a significant impact on limiting the effects of the IB being felt throughout the rest of the house (doubtful).


Pictures of both the HT room and utility room are shown below. The approximate manifold opening is shown via the X filled square in the photos. The white door you see in the HT room picture is to a bathroom unconnected to the utility room.


…I would like to open this for discussion and hear your thoughts.

Much thanks in advance,


Tim
:drive:

 

[OvalNut]

I've been mulling this over some, and I how about a 2 sided manifold with 2 sets of opposing drivers? Something like the following. Also, I would mount it down at floor level (see the red areas in the pictures below) to pick up some output from the floor. My only concern is if it would have any bad effects on the RPTV in front of it.

Anyway, more food for thought:

 

[Mike P.]

Your ideas look good. I'm not sure about the floor mounted manifold in front of the TV. It would be great if someone could verify that it's acceptable before you build it and find out the hard way that the TV can't take the vibrations.

 

[Sonnie]

Should be interesting. This is the same equipment setup I plan to use... with 4 Fi IB3 18's and the EP2500.

I would take that PC13 you have and place it where your main listening position is... run REW sweeps with your mic about a foot out from the wall where you plan to install the manifold. Maybe place it right above the display, but I would not move the display if that is where you plan to keep it. This should give you a fairly good idea of what kind of response you will be dealing with.

 

[OvalNut]

This looks pretty workable. I put the PC13U on the couch in the main listening position, then set the FBQ2496 to Bypass. Then I took a few measurements with the mic as you'd described, "about a foot out from the wall where you plan to install the manifold. Maybe place it right above the display".

With the PCU13 in 15hz tune, I ran REW sweeps, and here's what I got. You can ignore the big dip at about 125, as that's a main reason why I'm looking into new mains too. The target line shown includes a 5db house curve.

 

[Sonnie]

Not sure you'll get to 9Hz flat, but that looks very good to about 16-17Hz nonetheless. You might could recheck it by plugging all three ports on the PC13 and that should resemble an IB configuration a little closer.

 

[OvalNut]

Good idea Sonnie.

I repeated the test with the PC13U, but in Sealed mode this time, and the FBQ2486 set to Bypass. The results below speak for themselves it seems(?) The first graph is unEQ'd, and the second graph is the projected response after adding some filters in REW.

It does look like I'd be paying about an 8-10db headroom penalty to EQ it flat, but that's another reason why to use multiple large high Xmax drivers in an IB, right?

 

[Sonnie]

Yeah... I think with 4 of those Fi IB3's (I think I would prefer the 18's)... you'll be jolly fine. :T

 

[OvalNut]

So, the other questions left remain:

1. Is an EP2500 enough amp given the headroom hit I'll take to EQ this? Would I be better going with a bigger/better amp, or perhaps 2 EP2500's? I really want to keep the signal clean and avoid signal induced distortions and heating of the voice coils... but I also don't want to crater 4 big drivers by mindlessly overdriving them . :wits-end:

2. How to even consider breaching this idea to my wife, who loves me dearly, as do I her. But, she really does think I've already gone over the edge with some of this audio tweaking already. And now I'm considering cutting a big hole in a perfectly good wall while the sound I already have is exemplary.

3. Honestly.... how will the Sound Quality compare to the PC13U? I mean, the sound quality I get now is truly amazing.. .... I just want more, better, deeper. With even more IMPACT!

4. What would the perceived and/or measurable differences be between using 15" vs 18" drivers? From what I have read about the IB3 drivers, the 15 and 18 both seem to share the same motor size and structure (?) while the 18 has a more massive cone. If I'm right in that, will I suffer a responsiveness hit by going with the 18" drivers, but with a lower Fs due primarily due to the larger cone size? I'm thinking of it as power to weight ratio kind of a thing....


Tim
:drive:

 

[Sonnie]

Here's a comparison I did which includes 4 IB3 18's vs. 8 IB3 15's...

If you double your power you only get a 3db increase in volume, so I do not see two EP2500's helping enough to be noticeable. I would start with one and if you felt he need, add another.

I don't think you will ever notice any responsiveness hit with the 18's either.

As far as sound quality... that is going to be subjective. Some folks like the sound of an IB, some don't. Rodny claims his IB did not have the impact of his SLLT (same drivers, same location, same amp)... and I have read where the SVS subs actually seemed to have more "impact" than an IB, yet the IB would be cleaner and extend deeper, albeit a rare occasion. However, keep in mind that you have your PC13's tuned to 15Hz... there ain't a lot out there other than a very few scenes that you will ever get any benefit of anything below 15hz. It's a once in a very infrequent while that you will get the opportunity to experience it. Most heavy hitting movie scenes are going to be above 15Hz... that hit me in the chest type impact is generally 50-60Hz or so. What you get below 20Hz is generally a little bit of rumble here and there. With music... most of the low stuff doesn't extend below 25-30Hz, unless you happen to own one of the couple of pipe organ CD's that are available.

The wife thing... man... I am just not sure how you get around that one. To me, that is the absolute biggest hurdle of a decision you got to make. :dumbcrazy:

 

[Sonnie]

Here's 4 x 15's (yellow) vs 4 x 18's (green) with HPF's on each to keep from over excursion and at 1900 watts, about the max you'll get out of the EP2500.

 

[weverb]

4. What would the perceived and/or measurable differences be between using 15" vs 18" drivers?

Aren't the 18's going to move 1.4 liters of more air each? That would mean 5.6 liters more if you get a set of four. I would think that would equate to more "kick".

What does his current SVS sub do compared to four Fi 18's at 24.9 liters of air?

I am also in the research/planning phase of an IB set-up. I would be curious to hear/read your thoughts Sonnie and Tim. I have only one 12" sub playing 15-50Hz. and two 12's from 50-80Hz. I would think two Fi 18's would have more impact (kick in the chest) even if the REW graphs looked the same.

 

[Sonnie]

I suspect that might depend on how pressurized your room is, but I am not sure.

 

[jagman]

Sonnie... could you please model the 2 Ohm IB3 18 version? For some reason I can't get it to work. When I try to download the WindISD file for that driver from the Shack download list, I get the following message... "Not a valid WindISD save file!".

The reason why I ask is with four of the old 2 Ohm IB drivers hooked up to an EP2500 such that a pair is on each side wired in series so the amp sees 4 Ohm stereo, one would not need a hi pass filter (although they would technically bottom at 4 Hz if the amp is driven 100%). Having them set up this way would give up 1.5 dB max SPL above 25 Hz but you'd gain 3dB at 10 Hz when compared to four of the 4 Ohm version wired series/parallel so the EP2500 sees a 4 Ohm load in bridged mode (if a hi pass filter is set at 12Hz to keep the 4 Ohm drivers from bottoming). Since the sub would be level matched with the mains above 25Hz, if four of the 2 Ohm version keeps up with the mains (which should easily happen), then he would effectively get a 4.5 dB "boost" without EQ or ports at 10 Hz... and this "boost" would be present at all playback levels (not just max SPL). If the IB3's model similarly, this would be a way to get better VLF output without doing an LLT. Considering the output of four 18's, I would think this would be a viable trade off to get good VLF output while maximizing spouse approval and getting great bass.

 

[Sonnie]

I am about to crash, so it will be tomorrow, but tell me more about what the problem is. You say you cannot get them to model... are the files corrupted or are you saying it just does not look right?

 

[OvalNut]

...
The reason why I ask is with four of the old 2 Ohm IB drivers hooked up to an EP2500 (with a pair on each side wired in series so the amp sees 4 Ohm stereo), one would not need a hi pass filter (although they would technically bottom at 4 Hz if the amp is driven 100%). Having them set up this way would give up 1.5 dB above 25 Hz but you'd gain 3dB at 10 Hz (when compared to the 4 Ohm version wired series/parallel for 4 Ohm bridged load with a HPF at 12Hz). Since the sub would be level matched with the mains above 25Hz, if four of the 2 Ohm version keeps up with the mains (which should happen), then he would effectively get a 4.5 dB "boost" without EQ or ports at 10 Hz nor any of the negative effects of a HPF. If the IB3's model similarly, this would be a way to get better VLF output without doing an LLT. Considering the output of four 18's, I would think this would be a viable trade off.

You guys are nutz, but I like the way you think! That is a beautiful scenario. :daydream:

Looking forward to the modeling results!!!


Tim
:drive:

 

[jagman]

Sonnie... when I download the WinISD Pro file from the Shack, the following error message shows up:

"Not a valid WinISD save file!"

I tried downloading a couple times and the same thing happened each and everytime. I do have an older version of WinISD along with the new PRO APLPHA, so that may be the issue. I think I'll go ahead and uninstall both WindISD programs and then re-download and re-install the latest version. That may do the trick.

BTW... I modified my above post (#14). Please reread it and tell me what you think... especially if you get the chance to model the two scenarios: (1) four 4 Ohm IB3 18's wired series/parallel and hooked up to the EP2500 so it sees a 4 Ohm bridged load (with a HPF set at 11 or 12Hz), and (2) four of the 2 Ohm IB3 18's wired with a pair of drivers on each side in series such that the EP2500 sees a 4 Ohm stereo load (no HPF necessary). Thanks!

 

[jagman]

EDIT: I got it to work! With the proper models for the S2 and S4 drivers, the increased sensitivity of the S2 vs the S4 at 10Hz relative to the peak of the SPL curve is 4dB instead of 4.5dB. This relative gain is of course dependent upon the S4 requiring a hi pass filter but the S2 not needing one. Regardless, that is a relatively large gain in VLF output at all volume levels given you'd only give up 1.5dB max SPL. Very compelling to say the least. The only problem is I couldn't figure out how to print the plots .

 

[Sonnie]

I do not see a difference if you feed them both the same power.

 

[jagman]

Sonnie... you are right. If given equal power, they essentially perform the same. But in this situation, they wouldn't get equal power. Let me explain... and then please tell me if I have it straight!

When four 2 Ohm drivers - a pair on each side with each pair wired in series resulting in a stereo 4 Ohm load - are wired to a EP2500, the result is 650 watts per side, 1300 watts total. 325watts per driver will in theory cause the driver to bottom when the amp is driven 100% and fed a 3 Hz signal... and since that won't happen, in theory, the drivers should be safe from bottoming provided the amp isn't driven to the point of clipping. So, no hi pass filter is necessary. But, when four 4 Ohm drivers - all four wired series/parallel resulting in a mono 4 Ohm load - are wired to a EP2500, the result is total of 2400 watts. 600 watts per driver will in theory cause them to bottom when the amp is driven 100% and fed a mid teen Hz signal. If the signal is in the range of 10 Hz (common in many recent action movies), then the drivers could easily bottom when the amp is driven far less than 100%. Thus, a high pass filter is necessary (a 4th order filter at 11 Hz would in theory work nicely). With the filter in place, when the amp is driven at 100%, the four 4 Ohm drivers hooked up the the EP2500 would have 1.5 dB greater efficiency above 25Hz, but 2.5 dB less efficiency at 10 Hz when compared to four 2 Ohm drivers without a hi pass filter. Thus, when level matched to to the mains, the 2 Ohm speakers hooked up to the EP2500 would be 4dB more efficient than the 4 Ohm drivers (with the hi pass filter in place) at 10 Hz... and all drivers (whether 2 Ohm or 4 Ohm) would be equally safe from bottoming. Obviously this is specific to these drivers hooked up to this specific amp, but given the application, I think the 2 Ohm drivers are the better choice. He would get signigicantly more VLF output with the 2 Ohm drivers with this amp wired as I explained above... and no port would be necessary.

Interestingly enough, four 4 Ohm drivers wired series/parallel, as above, but hooked up to an EP1500 would result in a total of 1400 watts... just 100 more watts (25 watts per driver) than the 2 Ohm speakers hooked up to the EP2500. This would result in the 4 Ohm drivers bottoming when the EP1500 is drive at 100% and fed an 8 Hz signal (if memory serves me correct).

Based on all this, my recommendation... if my numbers are correct above... would be to go with the EP2500 if you're getting four 2 Ohm drivers and the EP1500 if you're getting the 4 Ohm drivers. One thing to remember, bridging the amp and giving it a 4 Ohm load doubles the distortion and is a heavier load on the amp. Driving them with a 4 Ohm stereo load is much easier on the amp with half the distortion. So, I still stand by going with four 2 Ohm drivers and an EP2500.

Sonnie... does this seem right to you?