The subwoofer phase

[cobbpa]

If any of you are familiar with the project I've got going with my uncle's home theater, you know that we are building the 3-way towers & center channel for the front 3 in a room my uncle are constructing. Now he's agreed that bass is needed Across the front of the room will be a stage-like area that the towers and center will stand on. On each side we can fit a 2' x 2' x 18" box. I'm suggesting dual 15's, probably the SoundSplinter drivers. I'm guessing that's the most cone area useable for that amount of space. There is a possibility of doing it IB, but the back of the "stage" area will be drywalled, so it's hard to say that enough air will be getting to the drivers to do that. Anyway, running with the idea of dual 15" drivers, one on each side (both LFE output)...should I be concerned with cancellation issues between the subs or possibly the subs and the towers? Anyone want to make amplification suggestions? And of course, design plots & tuning ideas are very welcome I'm busy the next couple of days but will try and turn up some of my own to discuss soonish. If you see anything wrong with this plans or have opinions or improvement ideas, let me know!

[cobbpa]

Well, then I'll post up some of what I've come up with and maybe spark some discussion. First, when I'm modeling 2 drivers in Unibox I'm putting in 2 drivers in series, 2 ports, the power going to 1 driver, setting it to "2 drive units in series", and inputting the total volume for the drivers even though they'll be in identical, seperate boxes. Is all that kosher, or do I have to model them individually since each driver will be in its own enclosure? I'm using 750 watts per driver...they'll get that or 870 (if I choose the Nady).

Beyond that, I've started to toss around other ideas. Probably will use the Behringer EP 2500 or Nady XA-2100 for amplification. I'm considering the Fi Audio drivers in addition to the SoundSplinter RL-p15's I mentioned earlier. I read through most of Ryan's (---k---) thread and found a lot of good info there. I believe I have a little more volume than he did and have been working at ported designs. I'm using 110 liters each for my effective volume. 2' x 2' x 18" are my external dimensions, so does 110 L sound about right when all is said & done?

Alright, onto some models...see what kind of feedback I can get.

Here's my best effort for two dual 2 ohm SoundSplinter 15s:


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To compare, here's what I came up with for Fi Audio Q 15" drivers. They have a little more xmax than the SoundSplinter drivers.


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Lastly, although I doubt we go with this setup, here are dual 18" Fi Audio Q drivers in a vented box. I feel like I'm not modeling their performance very well; shouldn't they be more capable? Regardless:


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I modeled these sealed as well and it's not too different, really. I would consider running them sealed at 2 ohms each instead of 4 ohms, but the Qtc was .85 with heavy fill. Is that bad, or ok for primarily home theater use?
Here are the graphs for those sealed:


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Would it be a waste of excursion?


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Of course, if the way I have Unibox setup is wrong, these may be pointless.

That may be too many graphs for one post, but hopefully it can garner some comments! I'm not sure if I could talk my uncle into 18" drivers, but if it's the absolute best setup..it's possible. How much room of excursion do you like to have for transients / peaks / explosions? I feel like these all have some wiggle room, but am not certain. I would have no problem further examining sealing up either 15" sub, especially seeing the success Ryan has had, but we may not be able to do much measuring & tweaking after building, so I would like to do all we can to ensure solid output to 20hz through box design. So, comments / questions / ideas / criticisms / fatal errors... :W ...anyone?

[ThomasW]

2' x 2' x 18" external dimensions means 18.5" X 18.5" X16.5" so about 93L internal volume with 1.5" thick walls before subtracting for the woofers.

So one driver per box and a DEQ2496 to create a LT circuit to lower the "Q" and boost the low end output.

BTW, thanks for the discs.... With our blizzard I haven't had the time to mess with them yet.

[---k---]

That first graph you have says "Vented Box". Are you looking to build a sealed or a ported box? Based on your's and Thomas's post, I thought that this was going to be a sealed project.

93L is about what my sealed project ended up as. Should work well for you. If this project is in Wheaton, let me know when you get it finished. I would be interested in hearing it.

[cobbpa]

Thomas, I was planning on a single layer of BB ply with a double face and a window brace and that's how I arrived at 110 liters. Is the doubled walls a better option? I'm not sure yet if a DEQ will be in the budget. Let me know when you get to check out those discs, what you did / didn't like & all.

Ryan, I was looking mainly at vented designs but am open to sealed as well. I modeled the 18's in a sealed box. This one won't be in Wheaton..wish I could have stopped by to hear yours when I was up there last week though!

[---k---]

Oh, that is going to be tough. I think I did the same model as you. In your model, you'll notice that the port length is 55cm or 22". That is going to be tough to fit in your box and have proper clearance. Next, your port velocity is like 60m/s. generally it is best to have it down around 25m/s. Finally, the models really change when you switch it to a single driver in a 110L box.

I think if you are really limited to 2'x2'x18", you're going to have to go sealed with an RL-p15.

Thomas?

[cobbpa]

Okay...sealed should be fine; less hassle to build anyway I'm always open to guidance.

The performance during movies is more important than music here. That said, I understand I should be targeting a Q around .7, correct? I don't know what the Q actually represents, but have read enough numbers / preferences to have an idea of what number I should shoot for. Let me know if this is a poor choice.

I'm now using 110 and 90 liters..kinda checking how the volume changes affect the performance; if 90 L can bring similar results the reduced cost of MDF over BB ply would be nice. It's hard to really know what to do since we likely won't be buying the DEQ, a BFD or anything like that...although I am 100% certain whatever subs / setup go into the theater, my uncle & family will be pleased and impressed. So I guess I'll just spend a bit comparing the few drivers, amounts of fill & such, see what looks best...I'm guessing the SS ones win out.

[ThomasW]

Basically "Q" tells how 'damped' the system is.....

Qtc .707 = maximally flat, is IMO the highest "Q" you would want. It has the potential to get a bit boomy depending on what happens with room gain.

You really should consider somekind of EQ. It goes a long way toward taking a sub sound 'good'. The $99 for a BFD is a small investment when one is making a real HT

[cobbpa]

I see. Just to clarify...maybe dispell the idea from my mind...two 15" drivers probably isn't enough for an IB setup, right? And a 4" x 12" vent in the rear drywall to each sub probably doesn't give enough breathing room either, does it? It's an idea that's sticking in my mind and I really doubt it's an optimal condition for it, or that we'd gain much...right? :?: I'll look around the Cult some

In my models, the SoundSplinters have the a Q of a little over .5 and an F3 of 55 hz. The 15" Fi Audio Q drivers Qtc is .665 with an F3 of 39 hz. This seems like Unibox is telling me the Fi Audio drivers may be worth the few extra bucks in this application.

If IB is possible, the 18" Fi Q's look to do well. I think I'll be clicking through your cult's propganda some today, Thomas, maybe answer some of the questions I posed..

[ThomasW]

If IB is possible, the 18" Fi Q's look to do well. I think I'll be clicking through your cult's propaganda some today, Thomas, maybe answer some of the questions I posed..

Propaganda?

Hey! lets get one thing straight, everything from "The Cult" is 'truth', just like any other hardcore fundamental extremist group.... :B

Just to clarify...maybe dispell the idea from my mind...two 15" drivers probably isn't enough for an IB setup, right

Depends on the size of the room and the distance from the IB to the listening position

And a 4" x 12" vent in the rear drywall to each sub probably doesn't give enough breathing room either, does it?

Nope that's a no go for two reasons. First yes the opening is way to small, second if there's only one sub in the room, it shouldn't be behind the listeners.

IB owners have used both SS RLp-15" and the Fi 18"s with great success. If you want a small sealed box sub the lower "Q" of the RL-p15" makes it the best choice.

[cobbpa]

There would be 2 subs..in the front of the room..I'm saying the back of the drivers would have drywall behind them and I doubt my uncle would want to do much more than a small vent in that wall to give them access to extra air. Seating position is about 12'-15' away, I'd guess. The room is large and open to the rest of the basement, so there is a lot of volume. Regardless, from your response & skipping around some of The Cult's truths, it isn't ideal without more effort / sacrifice on my uncle's part. Fine by me, I'd like to hear one sometime though.

Now, the lower "Q" of the RL-p15...being that low is ok for HT use? From what I've read .5 is "tight" (musical?), anything .8 or above is "boomy" (sloppy?) and .7ish is good for HT. But Thomas, you feel that basically lower Q = improved bass quality in most any scenario? (Down to .5 or so..not trying to put words in your mouth) It's the F3 that scares me, but I probably need to do more reading about how "Q" influences sound and how lower frequencies are influenced by the room to better understand your preference. I should have some time to do that the next couple of days; no rush on this project really. We're still working on the 7 other speakers :lol:

[ThomasW]

IB subs can't be mounted in a stud bay. They need a bunch of space (10 times Vas for each driver is recommended) to work properly.

Other than a 10 times Vas IB, the "Q" is always goes up when the driver is put in a box.

Our recommendation are fairly simple to understand without knowing a ton about "Q".

With EQ it's easy to make a low "Q" sub sound like a high "Q" sub, doing the reverse is impossible. So we recommend using a critically damped Qtc= 0.5 design. Since it's not a big deal not have it sound like a higher Qtc if needed/wanted.

[cobbpa]

I think I may be able to get away with a single layer of MDF, thus gaining volume and keeping a low budget. I can screw the box back, bottom, and one side to studs. The top would have an inch countertop or finished plywood on top. I'd still do a 1.5" face though & a window brace or two.

Also, this is going to be in an area where people and kids will be running around. Therefore, grills will be necessary. Any ideas on how to protect the sub while not getting in the way of xmax?

[ThomasW]

This is a high excursion driver in a small box. MDF is worthless for strength. If the walls of the cabinet vibrate, those vibrations cancel output from the woofer. So use doubled MDF or a single layer of BB ply.

There are grills for car audio woofers. The other choice is expanded metal lath.