Its time for a sonosub! (1 Viewer)

[Jerry Parker]

Well, next week I am probably going to start working on my *Final* box for my Blueprint 1803. I am going to go with a 14cuft box tuned to 18hz. The enclosure will be a sonotube 24" in diameter and about 6 feet tall. That should come out to around 18.8 cubic feet, but after the port and driver displacements, along with the endcaps will probably be pretty close to 14 cubic feet. For the port, I was thinking about making a square port out of MDF, 10 inches by 10 inches inner diameter, around 55 inches long. Will I get any port noise with this? The port displacement is over 3cubic foot!!! For the endcaps I was thinking 3 layers of .75 inch thick MDF. Do I really need 3 layers, or would 2 suffice? I need to be able to transport this thing!!! I will be using a Behringer Feedback Destroyer for equilization. Surely some of you have built a similar box! Anyone have a webpage with pictures? I need to do a *perfect* job on this, since the materials will probably cost me around 100 dollars! Also, how do those of you who build sonosubs cut out the driver and port holes? Do you do this before laminating the 3 endcaps or after? My guess is before. Ill post a picture of my planned enclosure... Thanks guys!

 

[Anthony_Gomez]

Hey Jerry,

You may want to talk to Brian Owens. He did a 12ft^3 sonotube with the 1803 tunned to 18hz. He used an 8in port. IIRC he didnt have any port noise except with extreme volume levels. He had only two problems that I remember.
1) his enclosure was too light and as a result, his sub "jumped" a lot. My advise is to use 2" thick end caps and a 1-2" thick base. That should add enough mass.
2) use somethings BESIDES screws. Tnuts or anchor/bolts will work. Brian actually busted all but like 2 of the screws from the SPL the driver created! Ask him about it. Kinda funny=)

Use a router and a Jasper jig to cut all your holes. You will also be cutting out the holes before laminating.

Feel free to ask any more questions.

 

[Greg Monfort]

The vent's long enough to have significant standing waves that will comb filter with the rest of system's response. How audible/obnoxious it will be I can't say.

FWIW, I get a 14% mach vent speed, so if driven to the limit, vent noise may be audible, especially when combined with the organ pipe resonance's.

Two layers of 3/4" MDF glued together is somewhat stiffer than 3/4" BB plywood, so is plenty stiff for the application. That said, since the sonotube is long enough to have standing waves down into the sub's BW, either additional layers or layers of acoustic tile on the top endcap is a good idea.

I cut out everything beforehand.

GM

 

[Greg Monfort]

1) his enclosure was too light and as a result, his sub "jumped" a lot. My advise is to use 2" thick end caps and a 1-2" thick base. That should add enough mass.
2) use somethings BESIDES screws. Tnuts or anchor/bolts will work. Brian actually busted all but like 2 of the screws from the SPL the driver created!
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Good advice! Smart design is to use threaded rod anchored to a substantial baseplate, then up through the driver mounting to hold it in place, and anchored to the top endcap. Now the driver is part of a stiff/damped system.

GM

 

[Jerry Parker]

 

[Jerry Parker]

Thanks for the responses guys, but dont the port resonances come into play around 200hz with that long of a port? It will most likely be crossed over around 100hz by my reciever, but the Feedback Destroyer can substantially reduce any peaks caused by port resonance. I can go with a larger box though! I think my maximum enclosure height is around 7 feet though. I need to be able to get it through doors. Any disadvantages to going bigger? A loss of power handling in the 25 to 30hz range perhaps? Also, I dont think I can go with a port wider than 10 by 10! I cant believe their is port noise with such a big port! What do you guys suggest? Should I go to a 12" by 12" port? To fit the port in the box then, I would have to make it at least 7feet tall. If I need a 12" by 12" port for no noise, I will go with an 18cuft box, that should be a 57 inch long port. Also, do I need to brace anything? And what would you guys suggest to use for legs? They would need to be pretty sturdy. And, I assume for cabinet dampining, I could just buy a foam mattress thing at wallmart, cut it up, and paste it to the inner walls of the tube. Any more suggestions? Thanks guys!

 

[Patrick Sun]

It's much easier to just go to Home Depot or Lowes and just buy a 8"/10"12" wide Quikrete tube to use as the port. You have measure what they have in stock, but you'll find one that fits the bill (or design for what diameter of tube you do have.

 

[Anthony_Gomez]

You may also want to put the driver on the bottom. 50lb driver on top may make it a wee bit top heavy.

 

[David_Lew]

wow that's a missle silo in the making

 

[Jerry Parker]

Thanks guys, but how do you cut the sonotube for the port and the enclosure? Will they cut it for you? If not, what do I use, I guess a jigsaw? That does not sound very accurate.

 

[Kevin Beck]

Jerry,..
I believe Pat has it on his site, but the simple thing that can be done, is to take a roll of fairly wide peper. say, a roll of wrapping paper left over from christamas, or a roll of god ol brown packing paper, and wrap it around the tube on the mark you have measured out for length. Line up the edges when you overlap a few inches, with no slack in the paper. Now trace the line all the way around the tube, and you have asquar line to cut on. Same same for a big port if it won't fit in a chop saw.
>>>--->
Ps,..if you haven't been to some of the Sonosub pages yet, its a very good place for info with pictures to boot.

 

[Greg Monfort]

Thanks for the responses guys, but dont the port resonances come into play around 200hz with that long of a port?
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It's a function of diameter and length, so for a 10"^2 x 52" pipe, the 1st mode will be ~123Hz, 246Hz/2nd, etc.. Note that these are not affected by the XO, so the more the vent is energized, the louder they will be.
The main tube's standing waves will modulate the driver, and begin at a lower frequency, but EQ will help here.
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> It will most likely be crossed over around 100hz by my reciever, but the Feedback Destroyer can substantially reduce any peaks caused by port resonance.
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Not per se. You can't boost the nulls, and the peaks can only be attunated globally, like a room reflection.
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> I can go with a larger box though! I think my maximum enclosure height is around 7 feet though. I need to be able to get it through doors. Any disadvantages to going bigger?
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No, this thing looks really good in 19.25ft^3 net/18Hz Fb. Any lower and the vent's way too long IMO.
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> A loss of power handling in the 25 to 30hz range perhaps?
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No, there's a slight gain, but not enough to be obvious.
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> Also, I dont think I can go with a port wider than 10 by 10! I cant believe their is port noise with such a big port! What do you guys suggest? Should I go to a 12" by 12" port?
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I suggest you ignore my previous remark. At the time I wrote that it didn't seem right, but that's what the program said. Later on, it gave me some numbers in another sim that I knew for sure was wrong, so closed it and loaded it again; it seems to be OK now, and lists a 4% mach speed for your vent, which seems much more reasonable. Sorry about that.
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>Also, do I need to brace anything?
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My 'smart design' suggestion below is all you'll need.
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>And what would you guys suggest to use for legs?
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If you follow my suggestion, then all you need do is slide some pipes over the threaded rod/nuts.
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>And, I assume for cabinet dampining, I could just buy a foam mattress thing at wallmart, cut it up, and paste it to the inner walls of the tube.
====
Line just half the tube wall, with plenty on the top end cap. No sense overdamping it.
Like they said, driver at bottom, and use a Quikrete (or equal) tube for the vent. 3" end caps are overkill, but whatever floats yer boat.
GM

 

[Jerry Parker]

Thanks! Ok, I guess I can do a 19.25cuft box, I was under the impression that 14cuft was good though? Is there any disadvantage to going to bigger and bigger boxes? I mean, why not use a 30cuft refrigerator if size is not a concern? Isnt their a loss of power handling above the tuneing?

As for the vent, a Quickete 10" tube will work fine for the port? I get a length of 27 inches in a 19.25cuft box.

As for the endcaps, will 2 .75" layers be sufficient? The total would be 1.5", that should be enough shouldnt it?

Looks like I will be mounting the driver on the bottom. How much clearance is necessary? I was thinking about 4 or 5 inches would work?

 

[Greg Monfort]

14ft^3 is fine too, I was just confirming that it looked good in a sim of the larger cab since it has sufficient Xmax. There's a point of diminishing returns though, and the difference in perforance probably won't be audible. I just answer questions as best I can. The one disadvantage is the standing wave modes fall in frequency, making them harder to attenuate due to their greater acoustic energy. The shorter vent is a plus though.
I've already given my thoughts on construction.
WRT spacing, I use the reasoning that the max 'slot' area between the perimeter of the baffle/floor be ~the driver's useable Vd (2*Xsus*Sd) to ensure free flow up to this point, with some acoustic loading above it to help protect it if pushed harder. I normally use Xsus = 1.5*Xmax since it isn't usually readily available.
I haven't done any elaborate testing, but haven't measured any obvious impedance increases until the driver's pushed hard, nor heard any 'vent' noise.
Anyway,the 1803's estimated Xsus = ~1.02"*1.5 = ~1.53" and Sd = ~188.7in^2, so Vd = ~188.7in^2*~1.53" = ~288.7in^3. If it's used in a 24"i.d. tube, then the perimeter is 24*pi = ~75.4", so ~288.7in^3/75.4" = ~3.83" min. between the baffle/floor, though if carpeted and only using legs I would make this to the top of the pile. I'm not a fan of just legs though, much preferring a relatively massive base such as dense wood, marble, slate, concrete, etc., to attach the tube legs to.
GM

 

[Anthony_Gomez]

I personally think 12-14ft looks better than 19.25ft.
30ft gives you a big saddle with a big hump at 18hz.

Have you throught about using PR's? would let you shrink your enclosure a considerable about. (since you did mention possible making a fridge)

1.5" endcaps should be just fine. Make sure you use a pair (or more) wood or metal rods to couple the two end caps together.

4" of clearance should be fine.

You should really contact brian owens to see if his 8" diameter ports were sufficient.