Sub Design question (1 Viewer)

[Dennis_H]

I'm looking at designing a new sub for the house. My current DIY is OK, but could be much better. What I'm looking at is moving the AV system into another room. This room is on a raised concrete slab of about 12". On the right side is a recessed area with seats around the fireplace. This is going away and will leave me with an area of approx 144" X 72" X 16" that will be filled in. I would like to use this area to house a new sub. I'm looking at a Tempest or maybe a couple of Shivas driven by the AVA250 amp. This lets me get rid of the big box I currently have while improving the sound considerably. I am looking for suggestions on what to do to keep it under, or just over $400. I thought of using some kind of bandpass box with just the ports coming up through the floor. I do have 4 kids, so I'm guessing if the driver is mounted in the floor, I'll need a steel grill over it. I'll be doing it in 4 - 6 months and am really just looking for ideas at this point. The volume of the room is pretty large. The ceiling slopes from 8 foot high to 20 foot high in the span of about 12 foot. The room is about 20 foot wide and there really is no close back wall to the sitting area. I really don't listen at that high volume, but would like to be able to when the wife and kids are out of the house. I am starting to consider an IB with a couple Shivas, but it looks like the roll off with an IB configuration is about -4 or 5 dB at 20Hz. Is this the case?
Thanks,
Dennis Hoenich

 

[Jack Gilvey]

If I'm understanding correctly, you've got a volume of approximately 96 cu.ft. which can be used as an "enclosure".
In this case, I'd use two Tempests on a minifold since you've got the space for just over 4x Vas. As far as response, the anechoic response will be about 5-6db down @ 20Hz, but the rolloff is so shallow you may be flat to below that in-room. Alternatively, you could leave one voice coil of each woofer open, raising the Qts of the driver and leaving you with a response almost flat @ 20Hz. In fact, you can "tune" the driver this way, achieving almost any response you'd like.
I'm sure there are other drivers suitable for this (some on the stryke.com site come to mind), but Tempest is what I've used, and the specs (particularly the low Fs) seem ideal for it.
I've done something almost the same, I've just got a little more volume (128 cu.ft. closet) to play with.
Check this page out, the idea is the same as what Rich Kraus did in his pristine installation, using the same amp:http://klone-audio.virtualave.net/page100.html
[Edited last by Jack Gilvey (who can't stop editing)on July 19, 2001 at 12:15 PM]
[Edited last by Jack Gilvey on July 19, 2001 at 12:15 PM]

 

[ThomasW]

Oops didn't see Jacks post

Well the answer is the same as given when it was posted on the HTT forum.
6th order bandpass will give you terrible transients, just think of a Bose sub, they are 6th order bandpass= all boom, no roar!.
You'll get the best sound from an IB. You need a mininium of 4X+ the Vas for each driver used, 10X Vas is better You've got 96 cubic ft. That's enough room for 2 Tempests/4 Shivas, etc
Should kick some serious butt, and is much easier to build!
BTW, personally I don't recommend using the RDO control for the second voice coil, this cuts the power handling by 50%
Roll-off for a IB is the same as a sealed box. So to get optimal performance, use something like a Behringer DSP1100P, to "tweak" the sub
"Cult of The Infinitely Baffled"
[Edited last by ThomasW on July 19, 2001 at 01:21 PM]

 

[Dennis_H]

I really kind of expected to hear some ported box designs too. I thought they might be a little more efficient. But, you guys pretty much have me convinced. I'll try to go for a dual tempest IB design. I guess mount them on a V-shaped mount at about 45 degrees, or they won't fit without the drivers being very exposed. I'll put in a steel grill with speaker cloth over it. My only real concern at this point with it is if I have to remove a driver or change something, I'll have to rip up the floor. I'll route all the VC connections to a single place and tie them together there so I can hook it up however it needs to be. I guess the other concern is that it is going to already be over budget with 2 Tempests and an amp. But maybe I can sell off the old sub locally to someone. If the 90 ft3 is on the edge, can I put poly fill in the pit to 'increase' the volume like a standard sealed box? And is 250W going to be enough to make it worth it?
Thanks for the ideas...
Dennis Hoenich

 

[Jack Gilvey]

An IB is much more efficient down low than any other sealed design, and the 250 watts from the AVA250 will be enough to drive the Tempests to Xmax. In other words, they'll get about as loud as linearly possible given the alignment with that amp.
I guess you could try the polyfill, but you'd need a truckful.

As far as ported designs go, I don't think it would be worth your trouble. You'd have to build a box behind the wall, as that enclosure is much too big for even four Tempests in a reflex alignment. And the sound quality of an IB vs. a reflex is no small consideration, of course. They (ported) will go louder with a given input and size, though, which is sometimes a big consideration.
The bottom line for me is, whenever it's possible to do an IB, do an IB.
[Edited last by Jack Gilvey on July 19, 2001 at 02:50 PM]
[Edited last by Jack Gilvey on July 19, 2001 at 02:52 PM]

 

[Dennis_H]

>As far as ported designs go, I don't think it would be
>worth your trouble. You'd have to build a box behind the
>wall, as that enclosure is much too big for even four
>Tempests in a reflex alignment. And the sound quality of
>an IB vs. a reflex is no small consideration, of course.
>They (ported) will go louder with a given input and size,
>though, which is sometimes a big consideration.
I realized I would have to section off part of the space for a ported system. That actually isn't any harder than what I am doing since it is just adding a partition in the floor space I'm filling. The extra (potential) volume and the flatter response of the ported system are the only things I still am wondering about. I guess I really need to hear an IB configuration. Is 3/4" plywood enough for the floor or does it need to be thicker? I think I can seal it pretty well by doubling up the 2x6s at the joints. I'm guessing there isn't a lot of pressure in the box since it is so big, you just have to kill the rear waves. I'll have 2x6 joists, 3/4" plywood, carpet padding, and carpet on top. Is this enough, or do I have to go to two layers of 3/4" plywood?
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[Jack Gilvey]

I don't know anyone who's gone the IB route who wishes he'd gone ported.

I've explained your options as far as achieving anechoic "flatness", and the much shallower rolloff of the IB vs. the ported makes for a lot of deep bass. A ported will definitely have the advantage in max SPL in the deep bass, as it's not limited in the deep bass by the displacement of the driver. If you define your SPL goals, that will help determine if an IB will get loud enough for you in your room.

I'm guessing there isn't a lot of pressure in the box since it is so big, you just have to kill the rear waves.

Exactly. The idea is to have the driver experience the same pressure on both sides, allowing it perfect linearity (almost). That's what the 4x vas rule essentially achieves. The bigger, the better. All the box is there for is to prevent that back wave from coming 'round the front.
I'll let someone else comment on the construction, that's not really my forte'.
[Edited last by Jack Gilvey on July 19, 2001 at 03:26 PM]

 

[ThomasW]

Dennis
If you wanted to line the interior of the "box" with 6" of fiberglass that would be OK. It's certainly not necesary to stuff it with anything. I'd suggest getting it up and running. If you feel the performance is lacking we could discuss adding the fiberglass or other options at that point.
The manifold should be stout enough to hold the drivers and not flex. IBs don't need to be massively overbuilt like standard sub boxes. I'd sugggest 2-3/4" layers. They can be a combination of any standard construction material. I use 3/4" MDF (machines/tools nice), laminated to 23/32" OSB (cheap and strong).
If you can build the metal grill as removable, then design the manifold so that the drivers drop in from the grill side. You do need to be able to remove them in case of problems.
quote: The extra (potential) volume and the flatter response of the ported system are the only things I still am wondering about. I guess I really need to hear an IB configuration. [/quote]
Yep, the proof is in the listening
A ported system certainly won't be "flatter". The output difference is not that much for what you get, which is the finest quality bass available regardless of cost.
Oh!, BTW, please photo document the project. I'd appreciate having copies for the "Cult" gallery. If you don't have a website, email them to me (after making compressed jpgs) and I'll post them.
Regards
Thomas
[Edited last by ThomasW on July 19, 2001 at 04:37 PM]

 

[Rich Kraus]

"I guess mount them on a V-shaped mount at about 45 degrees, or they won't fit without the drivers being very exposed."
my original plan (or, at least, one plan that got seriously considered) was to mount on a v shaped box as you have described. this was scrapped to ease build complexity. if its possible, it will be less frustrating to build a "square" box without all the issues that come from a "V" box.
im still trying to figure out your exposed driver problem. ('course i didnt have the space restrictions you have since i built in the attic.) maby you could surface mount the drivers from inside the box. let me be more clear- do the same thing i did, rectangular box with the magnets facing out, but with the drivers poked in from the inside of the box. you could pull them out of the box again withought ripping up the floor.
my box is as simple as they come, one layer of MDF with screws, and seems to work fine.
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'Till next time,
Rich (the kite guy)

 

[Dennis_H]

Hey, HTF is back up! After the last several days of thinking, I've definately decided to go IB. I certainly will take some pictures as I go. I hope to do this in 4 to 5 months. I think I'll do 2 15" drivers. That is why I need to go to the V-shaped enclosure. The depth of the area I'm filling in is only 16" so I need the mounting room, but don't want the drivers sticking straight up. (kids) I was pretty sure I was going to go with the Tempest, but am also looking at the PE DVC 15.
MDF for the floor somewhat concerns me trying to nail into it for carpet tack strips etc. Also there is the swelling issue if (or more appropriately, when, since I have 4 kids) something gets spilled on it. I'll probably just use a couple layers of plywood.
Again, thanks for all the help. I'm now really getting anxious to get started...
Dennis