[irishpatrick33]

Hello,

I am doing something... no matter how stupid it sounds.

So I am going to meld an entertainment center together with my speakers. My plan is to use 10" sonotubes to house WB Betsys and support a wooden shelf where my tv will sit. The plan is to mount the Betsys upside down underneath the wood shelf. The sonotube would obviously encapsulate the Betsy below the board.

My question is as follows. How do I port the bottom? Do I make multiple holes? Do I just have one port out the front? What size holes? Is one shape port better than another?

One worry I have is taking too much structural support out of the sonotube. I'm also considering wrapping the tube, kind of like Kvart and Bolge wrap their speakers and reduce resonance. Might also try some dampening materials inside of the tube.

Any thoughts? Thanks

[mresseguie]

Could you post a drawing or pics of the concept? Im having a difficult time picturing it.

Michael

[mcgsxr]

I will take a stab at it, based on my understanding of your description, but pics or a drawing would help for sure.

I have seen folks use a sonotube as a baffle for a driver before - it is usually left open at the end opposite the driver if it is  going to be considered an OB implementation.  Essentially the sonotube creates a U baffle.  You vary the length of the tube to vary the effect of the baffle.

IF on the other hand you are simply asking what if I want to use a sonotube AS the enclosure for my driver, and you intend to close off the tube, that is a different matter.  Then you are creating a "box".  Typically you would use a port on the opposite end of the tube the driver is on.  You would calc the volume of the tube, and port it according to what your specific driver wants to see.

That would not be OB though, so 40 lashes with the wet noodle!   

[Guy 13]

Hi Patrick,
a picture (Or hand sketch) is worth a thousand words.
If you want us to help you,
please help us with some pictures - drawings...

Guy 13

[irishpatrick33]

Thanks for the replies, apparently I had them turned off and wasn't aware.




I think the idea possibly counts as open baffle. It would be an "U-ish" baffle (or maybe this is a J frame). So instead of having the open end of the tube be the end of the open baffle, I will create some sort of port in the front or sides near the bottom. I am tempted to create an arch opening on the very bottom of the tube, but I worry that might take away too much structural integrity. Instead, I am considering a good size opening at the front facing side of the tube--this way the apparatus can be placed right up against wall.

Think of a Duevel speaker that is completely hollowed out internally. Oh, I think I am switching to 12" sonotube.

[irishpatrick33]

The sonotubes are merely a convenience. I would use square hollow pillars, but my resources and work space are limited. So clamping wood together and performing a lot of cuts is not an option. If I could figure out a way to easily add structural support to the tubes, I would try that as well (as I fear the board, drivers, and a television is a bit for the tubes to support long term).

[JohnR]

Hi Patrick, I suspect I am not the only person still mystified... is this an OB at all?

[mikeeastman]

Patrick,
 As far as strengthening the sona tubes you could place a larger sona tube over the 12" one and fill the space between them with either concrete or plaster of Paris, you should put some kind of heavy mesh in the middle of the space if you use concrete.

[irishpatrick33]

Hi Patrick, I suspect I am not the only person still mystified... is this an OB at all?

Perhaps you are correct. It's a hybrid design in my eyes. I'll take the thread elsewhere. Please delete this thread because it is unsuitable for this forum.

[mcgsxr]

From what I see, and I am far from an expert, it looks like a transmission line type enclosure.

I don't think we're so closed minded that you have to take your fun somewhere else, but you may get more valuable advice in the Enclosure circle.

From what I see you using, I wonder if you will get enough high frequency out of the drivers?  Are they to be mounted facing down?  FR drivers are usually pointed directly at the listener, but there is a TON out there I don't know about.

Have fun with the project!

[richidoo]

Hello Patrick!  Very cool idea!

You are right to want to add some ports, because without ports to let the sound out, it really isn't a speaker at all. It is a free air driver inside of a sealed box so the sound can't get out. So you are right to need some kind of hole to let the soundout. It would also be far better if you mount the driver so that a baffle separates the front of the speaker from the rear  rather than let each side's pressure waves cancel each other out at frequencies whose wavelength is > the diameter of the cone, otherwise you'll have poor bass extension.

The ideal solution would be to cut a hole in the shelf, and mount the speaker to the bottom of the shelf, firing upward, so the sonotube is a sealed box surrounding the back of the speaker driver, and the sound comes out of the top of the shelf. Then you'll have a sealed enclosure. You can install a hidden enclosure floor inside the tube at whatever height creates the enclosure volume you need to make the kind of bass you desire. The internal volume will affect the bass EQ of the loudspeaker by adjusting the "loudspeaker Qtc." You can google that one if you are curious. A good Qtc to shoot for would be in the range of .57-.71, but higher and lower will also work.

Cutting a few holes in the side of the sonotube to let out the sound of the free air driver will make terrible sound. The free air driver (without a baffle separating the front and rear sides of the driver) will cancel the bass, and the mid and treble will echo around inside the sonotube and sound very muffled and smeared when it exits the hole.

But the sonotube is a good idea for a box since it is inexpensive, strong and resists vibrations along the length due to the curvature. Vibrations can still occur in the sonotube travelling around the circumference, but you can damp that with dynamat if it is noticable.

Another idea would be to mount the speaker in the side of the sonotube, facing out, with solid shelf on top. But the mounting would be more difficult because of the radius of the sonotube. You'd have to make a mounting from wood that is flat on one side and rounded on the back to mate them together without air leakage.

To make a open baffle design as you originally suggested, you could mount the driver in the shelf facing up, and then cut a lot of holes in the sonotube to let out the rear wave. But you'd get a lot of echo inside the tube before the rear wave gets out, I don't think you'd be as happy with that. Certainly would not be what open baffle sound quality is capable of, and you would be giving up a lot of bass compared to the sealed box.

One last suggestion, is you could make a bass reflex box. This is similar to the sealed box, but you install a small resonant pipe inside the box which has an outlet on the outside of the box. The pipe resonates at low frequencies and amplifies the bass. If you have a small speaker drivers with limited bass response then this might sound better than sealed. The pipe length and diameter have to be calculated according to the box size and the driver you will use. It is a resonant system so the design of it and the building of it have to be kind of precise to work well. Nothing you can't handle though. We can design the reflex port and box volume for you if you can build it.

So what we need is some more info. What's the height and diameter of your sonotubes? And what are the brand and model number of the speaker drivers you plan to use? We can simulate the box design for you after we discuss which design you prefer, pros and cons, etc.
Rich

[JLM]

The Wild Burro Betsy's are extended range drivers, typically used in open baffles (Qts = 0.78).  The Betsy-K is the model designed for enclosures (Qts = 0.46).  Which are these?

Yes, the extended range drivers should be pointing towards the listener (unless you have some defined sort of reflectance in mind to maintain high frequency response).  Upward firing drivers are typically used for ambience, not as primary sound sources.  If that's your intent full range response isn't necessary.  I'm running upward firing ambience tweeters that are located on floor behind my floor-standers (inspired by John Romeyn's Late Ceiling Splash concept) to great effect (boosts treble response and enlarges/solidifies the soundstage).

Shape of enclosure and location of driver(s) and port(s) do matter.  Putting ports near the driver will tend to nullify enclosure effects.

If the O.B. Betsy I'd recommend a simple 3-sided enclosure (driver mounted on the front, back open).  Add straps to join the sides at the back if needed.  Could be built with pre-finished shelving or have the lumberyard make the cuts for you, leaving you to doing the finish work.  If you have Betsy-K just add a full back panel.  Simple sealed/ported formulas will predict proper cabinet size.  Excess volume can be filled with sand.  But keep any port near the middle of the cabinet to avoid turning the cabinet into behaving like an acoustical pipe (common mistake that manufacturers make).

[irishpatrick33]

Thanks!

The board is going to have two cutouts for the drivers. The drivers will be mounted there upside down. This way the drivers are omnidirectional (pointing up to ceiling and then down into sonotube), something I desire. The hardest part about building an omnidirectional for me is to create a diffuser. So I am cheating using the magnet to disperse the sound, in theory.

I have the OB version of WB Betsys. I also have neighbors, so I am not so inclined to "enclose." Earthshaking bass is something to avoid and I tend to like the open sound as well. Hooray for Top Gun references.