18" vs 20" sonotube (1 Viewer)

[tom_furman]

My original calculations had called for using a 20" tube for my Tempest sub. I have been hard pressed to find a place that sells 20" (I finally found a place an hour away) and even there I have to buy a 12' piece for $104.00(which will be good if I ever make a second sub). A place right down the street from me sells 18" tube at a good price.

By using the 18" tube, my sub will shoot up to 5'4" (without legs). I know there have been concerns on here about standing waves and taller subs, is there any concern for a sub that tall?

Also I plan on flush mounting my amp much like Warrick did with his. My calculations show that flush moutning a PE 250w amp will cause the back end of the amp to "stick into" the sub about 6" of 1/3 of the tube. Will this affect how the sub operates? Could the amp help "break up" any standing waves in the tube?

PS. I have no personal preference about width/height..just want it to sound good.

 

[Patrick Sun]

Just do it!

 

[Dustin B]

My sub is 5'11" (including 3" of endcaps and 6.25" long legs) tall using 18" sonotube. I stuffed a foot of insulation around the port at the top and have had no problems with standing waves inside the tube. And yes the amp mount will help break up the standing waves.
Like Pat said, just do it

 

[tom_furman]

Hum...ok...one last question before I'm sold on the cheaper, more accessible 18" tube. As I mentioned, I'm going to flush mount the amp. I saw Warrick put a support running from the bottom on the amp, to the bottom encap to take the weight of the sub off the tube wall. I dont think I'll have enough room in an 18" tube to copy his plan.
Do you think the 18" tube (with its tighter radius) will hold a 13lb amp without any bending or pressure?

 

[Dustin B]

You'll have room to do that. It won't be exactly like Warrick's, but I'm sure it can be done.

I think Warrick mentioned that he didn't think it was really necessary, but he did it as a precaution.

If the amp mount fits well (and is glued and caulked well), the tube should still be very strong and air tight. I don't see saging or bending of the tube being a problem.

 

[tom_furman]

Thanks Dustin...now my material selection and calcs are FINALLY complete. The 18"er it is. After pondering it a bit, I think I like the idea of a smaller footprint in my room anyway. The height I don't really care about.

Any problems with stability? A 6' sub might be a bit tipsy on my plush carpet. Should I get a set of carpet spikes?

 

[jeff lam]

I have a tempest in an 18" tube 4'4" high and used a baseplate with some rubber feet mounted on the bottom and it will take some strong amount of force to topple the thing over. You'll be very surprised at how stirdy it is. When it's all done and you feel it needs spikes, put them in after but I highly doubt you will need them, even with the thickest carpet.

 

[tom_furman]

Hey Jeff...any pics of your sub so I can show the wife what to expect? Your 5'4" is very close to what I had figured. I had 5'2" and I forgot to calculate how much room the amp would be taking up, so that should boost it up to 5'4" like yours.

What size/length port did you use?

 

[Dustin B]

No problems with stability for me either. Most tower speakers are alot easier to knock over. Putting a base plate on will actually make the sub more stable (there is one small point as far to the edge as possible that it will have to tip on).

 

[jeff lam]

Tom,
Here are some pics of my sub. I don't have a digital camera so I didn't get as many shots as I would have liked and didn't get a good shot of the sub itself but have a look anyway:
http://www.hometheaterforum.com/htfo...empest+sonosub

 

[tom_furman]

Very nice sub Jeff. I hope mine comes out as nice. Yours might look more impressive if there is not a basket of stuffed animals in the shot

 

[jeff lam]

That's my wife's Lamb collection. Ever since we started dating she collected stuffed Lambs because of my last name, and she thinks they are cute. I figure since she is so understanding of my HT stuff I at least owe her a little something in return.

My tempest design is the 175L, 17.5Hz tuning, .577Q, 64oz polyfill, 13"L 4"dia flared port(overall port length is 14" due to flares per Dan Wiggins, use an 8" center piece). It's an awesome design. Hank, Brian, and several others have also built this design with great success.

This design was perfect for me because I could still tune low, get a very low Q, and still have the enclosure size within limits. Lets just say a 10-12^3ft enclosure was out of the question(and I didn't want it that big either)!

 

[tom_furman]

One more question Jeff. I see you went with 175L for your design. Adire Audio recommends (for most applications) 220L +/-. Are there any benefits to cutting back on the volume as you did?

 

[Ryan Schnacke]

Jeff,

How did you calculate the Q for that alignment? I know you're pretty close to the Tempest Adire alignment, which is .577 so I believe your numbers. I'd just like to be able to calculate Q for ported subs.

 

[jeff lam]

Ryan,
The design was straight from Dan Wiggins himself. It's not my design. I'm not qualified enough to design enclosures for subs.

Tom,
The only benefit that I know of is a smaller enclosure. I wanted a nice tight sound for music as well as a low tuning for H/T but I also didn't want to make the 10-12^3ft EBS design(It would have been about 7' tall with a 18" tube). It was just too big. So when I found this design by Dan I jumped all over it.
My understanding of the design is you will sacrifice a little bit of max output compared to the EBS design, but you still maintain the low tuning and tight response and on top of that you get it in a much smaller enclosure.

Here is the direct quote on the design from Dan Wiggins:

 

[tom_furman]

ARGH! The choice, the choices!! I was like 99.999% sure of my setup, but now I'm not sure. Myself (and a few others on here) had come up with the design of 225L, and a 6" port 24" long. I ran that through the CAD program and all looked good. How does one figure out Q? I don't beleive I've seen that on here.


Hmm..my original idea vs. Jeff's. Size isnt really an issue for me. I can go as high as I want really.

 

[Dustin B]

If size isn't an issue, then I'd get up over 240L net and tune to 18hz or lower with a 6" dia port.

 

[Bryan Michael]

how about using a smaller tube like a 12 inch and make it look like a pillar then you can put 2 of them in the back corner of the room like a 18 inch box that is 10 inches high that steps up to the 12 inch tube and same on the other side and all you have is a vent in the top and botom would that work?