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DIY Proscenium Subwoofer


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108 replies to this topic

#1 of 109 OFFLINE   Joe L.

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Posted July 09 2005 - 04:23 AM

Anyone built a subwoofer into their stage?

I've often read of folks filling the interior of their stage/proscenium with sand and then placing their subwoofer on the stage. The sand used to kill any resonance.
I'm strongly considering building a DIY Subwoofer into my proscenium (and NOT filling it with sand :-))

The Fed-Ex guy just delivered a new Ascendant Audio Avalanche 18" driver and my wife had asked when I initally ordered it if I could build it into our stage/proscenium.
I said "sure, but the stage will have to be a bit bigger to accomodate it"

New Avalanche 18" Driver
Posted Image

The approximate external dimensions of the new proscenium-sub will be 15" high, 96" wide, and 36" deep at its center tapering to 28" deep at the ends. This gives me quite a large amount of internal volume to work with. I plan on a lot of internal bracing so I'm planning on building it as two halves. I'll bolt the two halves together once it is in place in the theater. (It would be too heavy to handle myself otherwise)

I was originally thinking of a ported sub tuned to 12Hz, but in doing the following rendering, I think it might be easier to make it a sealed sub and use two drivers. I'll make the final decision later. Fortunatly, the same volume enclosure would work in both a "single driver ported" or "dual driver sealed" alignments according to the samples shown on the Ascendant Audio web-site. I use a BFD equalizer, so I can handle just about any resulting frequency response.

I'm a beginner at 3D rendering, but this should give you an idea of what I'm planning. The drivers will be mounted downfiring attached to sloped baffles.
Posted Image

Ideas, comments, suggestions anyone? (as I get started) I'm off to buy some plywood and MDF.

Joe L.

#2 of 109 OFFLINE   SteveCallas

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Posted July 09 2005 - 04:30 AM

Have you considered mounting the drivers face up on the top part of the stage? It seems you would get more breathing room behind the sub this way.

#3 of 109 OFFLINE   MarkRoberts

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Posted July 09 2005 - 04:41 AM

Joe,
I think it looks great.I would mount the drivers forward facing but thats just me. I love the look of the ascendant drivers. I have 3Posted Image All atlas though I thought about the avalanche drivers but I decided to get two 15" atlas and a twelve for about the same price as a 18". Not that they will perform better. I am doing the ported 12" going to the bedroom eventually. I am going to do a 15" in a ported 24" cube. I actually already built one of those for my gf's brother-in-law.Soujded awesome was sorry to see it go. If and when that isn't enough I might build a second one or go IB.
What program did you use for the rendering?

#4 of 109 OFFLINE   Joe L.

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Posted July 09 2005 - 05:31 AM

SteveCallas,

Yes, I did consider up-firing. I'd be forced to use dark grill cloth across the entire width of the top, otherwise, the reflection from the screen would be very distracting. Currently, my stage is covered with the same dark brown velour fabric that matches my screen wall. If the drivers were not visible I'd be afraid of someone damaging them by sitting on the stage.

Even if I could control guests and their kids, I can't control the family cat. I also didn't want the pressure waves to be directed up towards the screen. It is thin vinyl VuTec screen material and it might vibrate with the sound.

I know I don't have too much room, but was hoping the sloped baffles could help in giving me as much clearance as possible behind the drivers and as much opening towards the viewers as possible.

MarkRoberts,
I used a free 3D drawing/rendering program named "blender" (blender.org) to do my drawing. It has the ability to to full animation (as in Pixar and Disney) Be forewarned, it has a very steep learning curve but there are lots of tutorials on the web.

I too would put the driver forward facing if I had the height. I don't. The screen is fixed in position and cannot be moved. I've only got 19" of room under it and want a few inches between the screen and the stage to allow for light spillage.

I currently have an 15" Adire Tempest driver in a 260L sonotube. The new Ascendant Audio Avalanche sub will replace it. The screen, the current stage/proscenium, and Tempest sub can be seen here. As I already said, the screen wall and stage are covered with a dark brown velour that absorbs nearly all light. The center channel has since been mounted above the screen.

Joe L.
Posted Image

#5 of 109 OFFLINE   MarkRoberts

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Posted July 09 2005 - 06:54 AM

Joe,
Nice theater!Posted Image What do you have for a projector?
I didn't realize the stage was already built. I don't really see any other way of doing it. Except for the up firing. Which I understand why you can't do that. Cats have a mind of their own. Keep us updated as it goes. Oh yeah, thanks for the link.

#6 of 109 OFFLINE   Joe L.

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Posted July 09 2005 - 07:13 AM

MarkRoberts,
Projector is a Barco 1208 (8" CRTs).

The stage you see in the picture is the current one. It is only about 8 inches high and is empty. (since my subwoofer was not on it or real near to it, I did not fill it with sand) It is free-standing and simply rests on the carpet in front of the screen wall. It is purely there for appearance. It originally held the Audax center channel speaker I built, but the center channel speaker was mounted above the screen over a year ago.

The current stage/proscenium will be replaced with the new proscenium-subwoofer once I build it.

Joe L.
Edited by Joe L. - 7/30/2009 at 05:30 pm GMT

#7 of 109 OFFLINE   SteveCallas

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Posted July 09 2005 - 01:11 PM

Any chance of building a new, bigger, and better sonosub? I'm doing just that with the same driver and the projected results are astounding. If not, I fear that there won't be enough breating space behind the driver and it might not sound very nice.

#8 of 109 OFFLINE   Ryan Schnacke

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Posted July 09 2005 - 01:37 PM

I believe that Ascendant is now out of stock of everything except the 12 inch Avalanches. Not absolutely sure, but I think this is the case. So you might want to focus on single woofer alignments.

#9 of 109 OFFLINE   Brad E

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Posted July 10 2005 - 12:20 AM

Joe, I'm just putting the finishing touches on my stage/sub now. Outside dimensions of mine are 8' wide 3' deep and 27.5" high. It's actually 2 subs, so it was movable. Even then, these things are heavy. If you have to go down stairs then moving straps are a must. I placed my 2 Atlas 15's forward firing with 2 4" ports (also forward facing) in each sub tuned to around 13 hz. Listening to the machine voice in the Matrix revolutions it got a little windy, so if that is going to bother you then forward facing might not be the best choice. I did a brief test the other day with one of them. My in room response was very good. Slight peak of 4 db below 20hz but otherwise fairly flat. I also cut out a notch for my center to sit in. Can't wait to to get it up and running already, but I've just been to damn busy to get the last little bit done. I also found out the hard way that you don't need much to power these things. I bottomed my Atlas out pretty hard on the flyby scene in Star Wars AOTC.

#10 of 109 OFFLINE   Joe L.

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Posted July 10 2005 - 01:15 AM

Brad E,
How much power were you using when you were testing and bottomed out your new sub?

I was advised to use an 8 inch diameter port for the Avalanche 18. As I said, I'm still not decided which alignment to use. Guess it depends if I can get a second driver.
Either way... we will have far more subwoofer than 99.99% of most folks with a home theater. Posted Image Posted Image Posted Image

Good luck with your project... post some pictures when you can.

Joe L.

#11 of 109 OFFLINE   SteveCallas

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Posted July 10 2005 - 01:44 AM

Joe, sent you a PM.

#12 of 109 OFFLINE   Brad E

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Posted July 10 2005 - 06:59 AM

Joe an 8" port is a good idea, especially with a monster like the Av 18, but the length of that port may end up being longer than you might like. For me, swithing to 6" ports, a little more than doubles the length. I have cutouts for 4" right now, but if I can find some 6" pipe, I'll probably go that route. Rythmic Audio 350 plate amp is what I was using to power the Atlas. Gain was a little less than half. I did a quick calibration and had the LFE set about 5db hot (close to 10 db hot from 15-20hz. Lower than that, I don't know), but the receiver volume was only set at -20. Reference volume on my setup is around -5. I'm hoping that the 2nd Atlas will pick up the slack of the first.

#13 of 109 OFFLINE   Joe L.

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Posted July 10 2005 - 08:58 AM

Brad, 10dB is 10 times the level. You might have been closer to maxing out the 350 watt amplifier than you think. In any case, I'm only using a 250 watt Parts-Express plate amp on my 260L Adire Tempest sub. I've learned one thing, you cannot go by the relative gain setting on these plate amplifiers since they all seem to have an very large range of available gain (to be able to handle almost any level connected to them) and even small adjustments represent many dB. You can get both 6 inch PVC and Plastic sewer pipe at Lowes in my area. Joe L.

#14 of 109 OFFLINE   Brad E

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Posted July 10 2005 - 12:44 PM

True enough, I wasn't going by the gain setting though. I calibrated the sub beforehand. Just letting you know where it was set at. I set it hot because I really wanted to see what it could do.:b I got the 350 amp because I'm going to be wiring the subs in series so it should work out to be around 250 watts into a 8 ohm load. I'll be sure to post some pics soon.

#15 of 109 OFFLINE   stephanX

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Posted July 10 2005 - 01:57 PM

FIRST off, atlas subs are physically not posasble of bottoming, the cone will hit the frame before the VC will hit the backplate, second, it doesnt have nearly enough motot strength to do that, the coil will burn up before you make the cone hit the frame. I know from experience that the motor has enough strength to get about 2" of stroke out of the woofer. Also 250 watts is NOT enough for two, you will more than likely end up clipping severly, much more frequently than acceptable (imo no amount of clipping is really good). I would reccomend buying another 360 watter, and use a dmm to calibrate the subs output to the voltage corresponding to 300 watts, when the reciever is set to reference, then boost the sub level on the reciever by 3 or 5 db (if you want to continue running the subs hot) and dont play over -3db. You wont kill the atlas by giving it 360 clean watts for short transients, itll just suck it up as exess heat, no matter HOW low it is. You will easily kill at atlas with clipping. the avalanche however is a different story, you can bottom that thing out, but usually its prettu difficult, even with extreme use(gien the proper alignment). However, i dont think any avas have been returned for warrenty with misaligned/deformed(not from heat)/ shattered voice coils. That said i would definately keep the one 18" you have right now, and just run it ported in a big box(or stage as you put it). It would probably be difficult to find another 18 ava. Also, very nice theater, i doubt ill have anything approaching that nice before im 20.
Can your 450$(cad) sub hit 120db at 40hz?

#16 of 109 OFFLINE   Joe L.

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Posted July 10 2005 - 02:45 PM

stephanX,

Thanks for the comments about my theater. I didn't have anything like it when I was 20 either... I had a hand-me-down black-and-white TV that I repaired by unwinding and fixing the open deflection yoke winding if I remember correctly. (My grandmother had given the broken set to me when they found the repair was too expensive and elected to buy a new color TV instead)

Now, that was a few years ago... When I was 32 I purchased a 72 inch Sony CRT front projection TV. That was in January 1983... 22 years ago. (I was a bit ahead of the home-theater curve)

The current projector and theater I've had for about 4 years. It has a Barco 1208 CRT projector, 110 inch DIY screen made with VuTec 1.5 gain screen material, and DIY Audax Home Theater signature series speakers combined with an DIY 15" Adire Tempest sonosub.

At reference levels, at very low (subsonic) frequencies, the sonosub is unloading and is reaching its excursion limits. I've had to reach for the volume control a few times already when extreme LFE effects sneak up on me. Posted Image I figure it is time to make more sawdust and build a bigger sub.

I know the current 250 watt PE plate amplifier may not be enough and will be clipping when I turn up the volume way before I get to the Avalanche limits, but I do have two monaural amplifiers I built in the mid 70s that I measured as putting out over 500 watts into 4 ohms, so I may not have to purchase anything new.

The amps are DC coupled and have a frequency response down to DC. (two input jacks, one capacitor coupled, the other bypassed the input cap) I used to watch the cones on my Ohm-F speakers move in sync with the warps in LPs. (33.3 RPM would be roughly .5 Hz) I might use one monoblock amplifier on each driver if I get a second Avalanche. They should work fine as subwoofer amps. Might be interesting as they are currently unused in my present HT.

Joe L.

#17 of 109 OFFLINE   stephanX

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Posted July 11 2005 - 05:08 AM

haha im not 20 I'm 15(still got a fair way to go), im familiar with the tempest, i made a thread a while ago about sonotube bracing on diyaudio, and you had pictued of your sub (and the split mdf bottom plate). 500 watts of juice could work insanely well, hell you could even run both, one on each coil, and be conservative on the gain! Also how much did you diy screen run you? im getting an infocus x1 in the next couple months.
Can your 450$(cad) sub hit 120db at 40hz?

#18 of 109 OFFLINE   Brad E

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Posted July 11 2005 - 11:04 AM


Whether or not the Atlas bottoms out in the conventional sense or not is irrelevent.
It reached it's excursion limit and make a distinct bang/pop/ting. (however you want to describe itPosted Image)
What else would you call that?

I agree that 250 watts may not be enough. I seem to get conflicting views on this.
One thing to consider is the size of the enclosure, which is bordering on IB characteristics. Though not an IB, it is free flowing enough that 2 350 watt plate amps would be overkill.

#19 of 109 OFFLINE   Joe L.

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Posted July 11 2005 - 01:57 PM

stephanX,

You certainly do not write like a 15 year old. I've seen many your age that would have a tough time putting together a coherent sentence... You are much more mature sounding than most. I can believe you will get whatever you want for your theater, if not by 20, then certainly by the time you get to my age.

I built my screen frame from select quality pine and engineered it so it would not warp or bow with "T" shaped frame members. It was about $50 in wood and about $100 for the screen material itself (Ordered it through AVS). Not cheap, but not real expensive either.

The frame prior to putting on the fabric is here

I used velcro to attach the vinyl screen material as seen here

My screen material is 1.5 gain. You probably do not want as much gain with your projector as I think it is much brighter than mine. I would use "blackout" fabric (used to line drapes to "black-out" a room) if I were you. A few dollars a linear yard at JoAnne's fabric store and you've got a great screen. The X1 is a great projector.

In any case, I spent some time on the phone today with Chad at Ascendant Audio and we talked about my proposed Proscenium-Subwoofer design and showed him the 3D drawing I made. He liked it. Even said he might build something like it some day. We discussed single-driver ported, dual-driver ported, and dual driver sealed possibilities and suggested I build it internally as two sealed subs...

Oh yes, he still had a few 18" Avalanche drivers left so I ordered the second driver. From what I read, SteveCallas also ordered his two drivers. Between us, we'll be making some sawdust...

Joe L.
Edited by Joe L. - 7/30/2009 at 05:31 pm GMT

#20 of 109 OFFLINE   stephanX

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Posted July 11 2005 - 04:02 PM

Thanks for the compliment. ill probably be using a roll down screen from ikea(tuppur), due to some good reviews, and some photos showing VERY good picture quality. Also, to the guy with the bottoming atlases, i cannot think whats happening, i played my atlas free air to its excursion limits(dont ask, it was a mistake) only noise from the pole vent, MAYBE the woofer topped out hard enough that it bent the cone a small bit. Maybe it was heavy heavy tinself lead slap, but i cant think of anything that would cause a "clack". maybe i voice coil hitting the sides of the magnetic cap, or the pole piece, but i dont know how it woudl get there under normal use. Also, no one ever said you had to use ALL 360 watts, think of it like this, buy the more powerful amps, calibrate them to a lower output power, that means pretty much no chance of clipping, less thd introduced by the amplifier(not exactly relevent here but still, for the sake of saying so). But giving 2 of those suckers would be about as unjust as putting motomaster tires on your ferrari(I'm really more a dodge charger person, but for the sake of the anaology ill use an import). Also, if you decide to move to a less efficient, burlyer sub in the future, youve got some extra power on tap there! and id reccomend going with another of the same amps, just so you know that all the circutry will all be the same, and that setting them up equal will be a breeze.
Can your 450$(cad) sub hit 120db at 40hz?




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