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Old 12th December 2004, 02:20 AM   #1
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Default Sonotube end cap thickness?

As of current I have my sonotube and two perfectly routered ends, they are 3/4 thick MDF. The driver used is the 15" dayton quatro from partsexpress. I'm wondering if I can get away with just one 3/4" endcap per end or do I need(or really want) the extra stiffness? The endcaps are 24" in diameter. Its ported, but sealable. It hasnt been assembled yet. All replys are welcome.
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Old 12th December 2004, 07:46 AM   #2
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Default 24" in diameter? I'd double it up.

24" is a pretty big open span, especially since you will be cutting a 14" or so hole in one of the caps. I don't know that you need the extra stiffness, but it can't hurt, right? Now this assumes you are just attaching the caps around the perimeter. If you run threaded steel rods through the end caps, you can then tighten them down with a nut on each end and greatly increase the stiffness. That's how I originally built my Emerald Towers, though that was just an easy way to keep the end caps from falling off. However, it made them not so easy to work on, and they vibrated at 100 Hz, so I removed them. If you use thicker rod though, they shouldn't vibrate. Mine were only 1/4" and being 66" long didn't help.

All that said, you still can't put them any closer together than the edge of the woofer, or about 16", just 4" from the edge, so I don't know that it's worthwhile. I'd just double the end cap thickness!


Aaron Gilbert
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Old 12th December 2004, 03:28 PM   #3
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xstephanx,

I used three layers of MDF for my sonosub. Two layers fit into the end of the sonotube and the third was about 1 3/4 inches larger in diameter and rested on the end of the sonotube.
The driver will flush-mount in the third layer of MDF.
Click the image to open in full size.

I also used 3/8 inch steel rods to tie everything together. Even with the my thicker end-caps, the end-caps still vibrate more then the side walls of the sonosub when it is in operation. I would use more then the 3/4 inchs of MDF you are proposing since I feel you might end-up with an eventual failure of the end-cap similar to the failure I experienced. (pics below)

You can see the end-caps here as I was preparing for final assembly. (sonotube is 18 inch diameter)
Click the image to open in full size.

I had originally routed a shallow groove in the outermost end-cap so that the end of the sonotube would fit into it and be hidden from view.

Within a few months the outermost single layer of MDF cleaved in two from the vibration. Note: it did not fail at a glue joint, the MDF split between the glue joints! I ended up rebuilding the driver end-cap replacing the outermost layer of MDF with baltic-birch plywood. I did not route any groove for the sonotube the second time. It is much stronger and should stand up the the pressures involved.

The pressure exerted by the driver in combiniation with the steel rods caused the outermost layer of MDF to cleave in half. The final blow was from a Klingon battle-cruiser.
Click the image to open in full size.

If you use a single layer of MDF and then use screws to secure it inside the sonotube, odds are high you will also have a weak-point in the middle of the edge of your end-cap similar to the one I had with my groove around the perimeter.

The MDF failure occured at the depth I had routed the groove for the sonotube.
Click the image to open in full size.

Reassembled. Ready for another battle with the Klingon's
Click the image to open in full size.

You will not believe the amount of pressure exerted by a decent 15 inch sub driver. My Adire Tempest driver is similar in many ways to the driver you will be using. It will take little time now to plan for stronger end-caps compared to the time it will take to rebuild.

I cast one vote for more then 3/4 innch end-cap thickness.

Joe L.
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Old 12th December 2004, 11:03 PM   #4
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damn! you did that with a tempest?and i guess i might as well get another 3/4 end and liquid nail it together. Shanks for the replys everyone!
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Old 14th December 2004, 02:26 PM   #5
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J. L.,

Klingons? and Dirty Dancing?
interesting taste in movies.
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Old 14th December 2004, 11:05 PM   #6
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Quote:
Originally posted by Aunkst
J. L.,

Klingons? and Dirty Dancing?
interesting taste in movies.
Well...

Dirty Dancing is one of my wife's favorite movies, but we both enjoy science fiction, including... Star-trek. It was a blast from a Klingon battle-cruiser that made the MDF on my end-cap split. Now, we were playing the movie pretty loud... but not to where it was distorting in any way.

The subwoofer is powered by a 250 watt PE plate-amp. That is plenty to provide reference level bass that goes really deep. Lower than I can hear, but you can sure feel it as it shakes the whole room.

I now use a BFD equalizer to flatten out the response a bit, but here is the Un-equalized response at my listening position about 12 feet from the sub before hooking up the equalizer.

the frequency response does drop off rather quickly below the port tuning frequency, but then, most subs drop off and -10db at 10Hz is not too bad.

Joe L.

This was not max output, just a moderate level to do an Un-Equalized frequency plot
Click the image to open in full size.
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Old 14th December 2004, 11:15 PM   #7
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pardon my french DAMN that is one pretty intense sub! how big is the room you are using it in? Im probably just going to get the tempest now. its gonna be in a 250 litre enclosure tuned to 19 hz i think. Do you notice any port chuffing with just a single 6.5 sonotube port? i might do the same! of course with a 24" diameter sonotube, i dont have to worry about height as much.
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Old 14th December 2004, 11:31 PM   #8
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My room is about 14 feet wide by 18 feet long with an 8 foot ceiling.

Sub sits near the right front corner about three feet out.

Other speakers visible are a DIY Audax Home Theater set I also built.

Click the image to open in full size.
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Old 14th December 2004, 11:41 PM   #9
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DAMN im jealous! maybe add in an extra seat,since 14 year olds these days watch movies with their friends, more often than with their wives.Which, (unlike wives) the more the merrier! what projector are you using? and what did you cover your sub with? looks purty.

And what about chuffing? is there any? youre only using one striaght 6.5" port!
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Old 15th December 2004, 01:45 AM   #10
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Actually, I'm usinig one 6 inch port. I did round over the outside edge to make a slight flair.

In this picture I had put a short (1 1/2 inch) length of port tube in place to hold the layers of MDF aligned. I then used a roller-bearing roundover bit in my router to cut the opening in the outermost layer of MDF even with the port tube making the slight flair.

No... I've never heard any chuffing.

Click the image to open in full size.

Projector is a CRT - a 10 year old Barco Graphics 1208. Weighs about 165 lbs - easily does HDTV at 1080i. I do DVD's at 720p.

Projector with lower cover removed

Joe L.
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