DIY Proscenium Subwoofer (1 Viewer)

[Joe L.]

After getting more input and advice I rendered a new 3D image of my proscenium subwoofer project.
I am trading the opposite mount of the drivers and possible reduction/cancellation of vibration for a larger opening in the front of the stage.

I was advised that optimally, the opening should equal the "Sd" of the drivers, otherwise "compression" will occur.

Since the enclosure and drivers combined will weigh about 300 lbs, I'm not too worried about it walking across the floor on its own.
I'l be using a lot of internal bracing, so I'm not concerned about the vibration of the enclosure walls.

In any case, here is the most recent 3D rendering I made last night:


And here, a 3D rendering as re-drawn by AVS member Scott Vonhof showing the internal bracing as he envisioned it. I'll probably make openings in the bottom corners of the outermost front-to-back braces. he only showed the top part opened up as he cloned the part of the enclosure next to the drivers. I'll also make the brace between the drivers solid, and in that way, each half becomes its own sealed enclosure.

Scott Vonhof's rendering of my project:


I'll post actual pictures this weekend as the sawdust starts to accumulate.

Thanks to all for the suggestions and ideas. Special thanks to Scott Vonhof for his 3D rendering.

Joe L.

 

[Rob.J.B]

Wish you luck with the cutting/nailing/gluing. Please keep us informed on how this turns out. I have very similar plans for my riser. I intend to have the subs up-firing as the couch will span the area where the subs are so there should be no worries about stepping on them. I am very interested in your experiences so keep us updated!

 

[Rob.J.B]

Not sure if you had started construction yet but something to consider is just making a simple square box and building the stage on top of it. That would make construction much simpler and allow for simple joints... Not to underestimate your abilities!! My plan was to use two boxes (shiva 12's?) and build the stage around them, putting the deck on top. The subs will have grills and be under/behind top seating. Just some more thoughts. Looking forward to pictures / results!

Not allowed to post url's yet...
[http]://chewyoatmeal.com:81/albums/album09/aab.sized.jpg

 

[stephanX]

Good luck! box building always seems intimidating till you start, then its just plain fun!

Happy building!

 

[Bryan Michael]

i have 4 18 in a ib ava that is and it is insane and it makes the wall move.

 

[SteveCallas]

Joe, any updates? Did you finish building one of the sections yet? Also, set you a PM once more.

 

[stephanX]

I also demand pictures and a follow up!

in the most polite way of course

 

[Joe L.]

Steve,

Since you "demanded" an update so politely...

I've spent the past week or so trying several different "mock-ups" of the driver mounting arrangement... Reason was, my original plans could not physically built.

Now, if the basket on the Avalanche driver was shaped like the one illustrated on their web-site, I might have angled it as I had originally planned, and been able to fit it within the 16 inches of hight I was targeting.

Unfortunately for me, the basket on the Avalanche is a 12 spoke basket and even if I tilt the driver, the height it occupies does not change very much.

Here you can see the driver mounted in a 20 inch square piece of scrap plywood. The basket spokes extend almost straight back from the baffle.


The current 12 spoke basket shape does not let me angle the driver and fit it in the targeted height. That put me back to the planning stage once more. I gave a bit more thought and came up with the following idea.

Basically, a shorter sub, about 15 inches high, with the two drivers upward facing. To protect the drivers, I plan on a top-plate spaced several inches above the woofers. This should result in enough open area so that "compression" does not occur. (According to ThomasW the open area should equal the combined "sd" of the drivers)

Notice the top plate does not extend all the way to the back of the enclosure, therefore, it does not matter if it is higher and closer in height to the bottom of the screen. It is there to protect the drivers and only needs to go back about 24 inches or so...

I might close the back of the top plate so that all the sound is directed forward to the viewers, but I'll better judge if I need to once I can see it in action. I do not want the subwoofer to visibly shake the screen behind it.

In any case, here is another "rendering" of what I am now building:


And here... construction has started.
I'm in the process of laminating multiple 1/4" layers to fashion the front of the stage.


My wife summed it up well... It is big It is 96 inches wide, 36 inches deep at the center tapering to 30 inches deep at the ends of the stage. The pieces holding the curved front as I glue it are a temporary jig, but the correct size and scale of the eventual enclosure. Once the front is glued up, I'll cut it in half and use each half for the front of the two sealed enclosures.

Joe L.

 

[SteveCallas]

Sounds like a good plan. Maybe even mount the drivers as close to the front edge as possible and then slightly angle the top plate up towards the front.

By the way, I know you ordered your second driver on the same day I ordered my two drivers. Have you recieved yours yet or at least a shipping / tracking number? They told me mine was supposed to ship last Wednesday, but nothing, and now then they were out of the office until Monday.

I'm sure everything is fine, but with these delayed shipments, dust cap leakage issues, and supposed inaccurate fs issues, it's got me a little worried.

 

[Joe L.]

Steve,

I spoke to Chad's father on Thursday. He said my second driver had been shipped. He also said he and Chad would be out of the office on Friday to attend some industry show (or something like that) and they would be back in the office on Monday. He predicted my driver would be delivered Tuesday or Wednesday. He said he did not have the shipping number but would call Fed-Ex on Monday to get it and then mail it to me. He said they did not use the same technique as last time with the advance issuance of shipping numbers.

I did check the dust-cap on my first Avalanche driver and it is solidly attached. I also tried using the driver (without an enclosure) with my current 250 watt plate amplifier and it sounded just fine. (Not as loud as the current Tempest driver in its ported enclosure, but very clear and no trace of distortion) I'm not worried at all about the second driver. From what I've seen so far, these drivers will be awesome.

I hope to have a bit more done on my pair of new sealed enclosures by Wednesday... wish me luck. I'll post more pictures as I take the laminated curved front off the assembly jig and attach it to the actual enclosures.

Joe L.

 

[SteveCallas]

Joe, not trying to get off topic about your subwoofer, but just after I made that post yesterday, I went out to dinner with my friends. Sure enough I came home and there is a FedEx slip on my door that says they were there at 7:48 PM with my package. I never knew they made deliveries that late - now I'll have to wait until Tuesday.

 

[Joe L.]

Looks like I should put a note on my door to the Fed-Ex guy in case it is delivered earlier than Dale predicted.

Currently doing a little research on best glue for the laminations of the front of the stage. I'm considering one of the polyurethane glues that expand to fill the cracks and voids. Expensive, but might be easier than others in that less clamping pressure is needed.

Don't know if I mentioned it before, but get your sonotube and use a 2 or 3 inch band of it as a guide when you make the end-caps as the size sometimes varies. (some manufacturers nest the cardboard tubes for ease of shipping, so sizes could be off by 1/4")

Joe L.

 

[SteveCallas]

Yep, had them cut me 2 70" pieces and 1 4" piece. The actual inside diameter of my 28" sonotube is about 27.75" - it varies slightly at different points.

 

[Joe L.]

Steve,

The Fed-Ex guy delivered my second Ascendant Audio Avalanche 18 driver today... right on schedule.

I need to get busy with the new enclosures.

Joe L.

 

[SteveCallas]

After realizing just how heavy these drivers are, I think mounting these things in an up-firing position would have been my best option as well!

 

[Owen Bartley]

Hey Joe, I know I'm a bit late with this, but I just saw something similar from Bag End... who knows, may give you a little inspiraition.

http://www.bagend.com/bagend/d18e-ad.htm

By the way, how is the project coming?

 

[SteveCallas]

Yeah I've been wondering how this has been coming along as well. I'm starting to think that having two front firing ports on the front edge, one for each enclosure, would have been a good idea. You'd be getting a big boost in spl and extension and probably get less distortion as well. I can tell you without a doubt that this 18" driver in a ported configuration does not sound boomy or muddy at all - it's highly detailed, uncolored, and very dynamic.

Let us know how it's going.

 

[Joe L.]

Owen,

Thanks for the link... Looks like you can fit two 18" subs in a 15" height enclosure. (If you have shallow drivers that can be tipped at an angle) Looks like they used a 3 cubic foot enclosure for the two drivers... that is really small (read inefficient)

Each of my sealed enclosures will be about 12 cubic feet in volume. My enclosure alignment "Q" should end up about .6. I know I will need to equalize the low end a bit, but then, the Bag-end subs in their 3 cubic-foot enclosures need a LOT of equalization and big power amplifiers. My sub will be fed with about 500 watts to each driver when I am finished through a BFD equalizer, but for now...

I know I have not posted any pictures lately, but progress is continuing as I find time in the evenings.

so far...
I've cut the curved front I was assembling in two. Each half is now being used as the front of a sealed enclosure. The two enclosures side-by-side will be the "stage" beneath my screen. Once I had cut the front in half, I started to finish the balance of the enclosures and their internal bracing. That is where I am at this point, in the middle of adding the internal bracing.

Now, in the interim, my wife and I have had the chance to watch about 4 of 5 movies with the new stage physically in place under the screen. (I am assembling it, amd gluing it in the theater, but doing all the cutting outside in the driveway) In between assembly steps, I move it under the screen so I can get an idea of what it will look like once completed.

I did order 3 yards of velvet material to cover the top of the stage as reflections of light from the screen were very distracting. Since the top surface of the stage is that much closer to the screen, and the angle of light to our eyes more shallow, this was critical. For the first movie or two we watched I used a piece of brown fabric similar to what I have on my walls. The next two movies we watched were with the dark brown velor I have on my screen wall. Both reflected lots of light from the screen and it was very distracting... My wife agreed, the top must not reflect light.

The last two movies we watched had the stage in place (without the internal bracing or subwoofer drivers) and the velvet I had ordered worked exactly as I wanted on top of the stage. No distractions from reflections.

Now... Once the stage was in place my wife and I decided that it would look nicer visually if it did not have the top plate covering the drivers sticking up in the front 2/3rds of the stage. Thinking about it, I then perched the entire stage up on a few scraps of wood and asked her opinion of how it looked down-firing, but with about a 3 inch opening around the entire perimeter of its base and the top of the stage about an inch below the screen.

She liked it. I liked it. Doing the math, the opening around the entire bottom perimeter is easily equal to the "sd" of the drivers, so I think that this will be the actual configuration I will use. (Those 3D renderings I made helped, but the full sized enclosure helps even more to visualize how it will look when completed)

The down-firing design did require me to re-engineer one part of the enclosure, but... it was not too difficult. (Can't say enough how great it is to have my wife's support in this project. It is even better as she and I both are involved in the physical design.)

I know it is not a perfect enclosure configuration, a 4 or 5 inch opening around the bottom would be better... but... I'm sure we will have plenty of bass to go around once it is done.

Be patient with my progress, it is just a bit slower when we are watching movies and enjoying the theater in between sessions of making sawdust. After all, my current "small" 260L 15" subwoofer can keep up with most of what we watch... and we watch a lot of movies.

Joe L.

 

[Joe L.]

Steve,

I can always convert my sealed encloses to "ported" if I find I do not have enough extension. I'll keep that in mind as we watch the first few movies once the subs are completed.

Great news that your sub is completed and you have had a chance to evaluate it with various program material. Didn't you build two subs? Are they both completed? or did you just get one operational at this point?

I'm waiting to see pictures of your new Subwoofers.
(hint hint)

Joe L.

 

[SteveCallas]

I only built one so far, all the parts for the second one are sitting here in my office right now staring at me, just waiting to be assembled. That will NOT be happening anytime soon. From Sunday until last night, I have only been listening to music, mostly classical. As I said in the other thread, sounds spectacular.

Tonight I wanted to up the ante a little bit. I put in Matrix Revolutions and went to the scene were the machine speaks. I normally listen to movies at 42-45 (arbitrary numbers on my receiver) in this apartment. I didn't know what to expect, so I had it at 32. The machine said "Speak" and I swear to you my entire apartment flexed in an instant and then in an instant it was gone. I immediately turned the dvd player off and won't be listening to anything else tonight - my neighbors must have been scared shitless. I am scared I will have a note on my door tommorrow after work about this, it was that powerful - and 32 is NOT very loud. My sub was calibrated to my mains and was not running hot.

I have heard some decent subs before, but nothing had as much raw power and air moving capability as this. I don't know how I will go about watching movies now. I will have to speak with my neighbors and try to work something out. I wish I already owned a home.

I will have pictures and all that good stuff up after this weekend.