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Old 17th January 2014, 05:43 PM   #1
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Default One Cubic Foot Tapped Horn Challenge

I need another subwoofer like I need another hole in my head...

But if that wasn't the case, I'd probably buy a pile of these:

Tang Band W4-992C 4" Subwoofer | 299-825

This is probably the first driver I've seen that's under 5" that could truly be called a "subwoofer"

There are some neat things you can do with this:
1) I was able to create a tapped horn with less than 3dB of ripple that has an F3 of 29hz
2) Due to the low QTS, it would be great for a vented box
3) It works nicely in a back loaded horn, but it needs a tweeter to get to 20khz due to the inductance

Here's some things I like about the woofer:
1) The Aurasound drivers make a lot of bass, but their QTS is very high. The TB, with a paper cone, has a much lower QTS. This makes it work better in vented boxes and tapped horns
2) It's way cheap
3) Due to the very low SD you can keep the box small, and this makes it work well for Geddes-type multi-sub arrays. At home I have four subwoofers and they take up a lot of space. Something smaller would be nice.

So...

What other drivers can be shoehorned into a tapped horn under 1cf?
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Old 17th January 2014, 07:08 PM   #2
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Quote:
Originally Posted by Patrick Bateman View Post
This is probably the first driver I've seen that's under 5" that could truly be called a "subwoofer"

There are some neat things you can do with this:
1) I was able to create a tapped horn with less than 3dB of ripple that has an F3 of 29hz.
So...

What other drivers can be shoehorned into a tapped horn under 1cf?
John,

By "create" do you mean "simulate"?

I'd guess the horn path would need to be around 9.74 feet (3 meters) long, is your one cubic foot an external size, and if so, what material thickness did you figure in the construction that would allow the long path in that overall size?

A quick estimate using 1/2" material comes out at the material and driver using up about 610 cubic inches out of the 1728 available in a cubic foot, leaving only 1118 cubic inches (18.4 liters) for the net volume.

What is the simulated SPL output in half space when the Tag Band W4-992C 4" driver reaches Xmax (3.5mm)?

Art
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Old 17th January 2014, 07:26 PM   #3
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Originally Posted by weltersys View Post
John,

By "create" do you mean "simulate"?

I'd guess the horn path would need to be around 9.74 feet (3 meters) long, is your one cubic foot an external size, and if so, what material thickness did you figure in the construction that would allow the long path in that overall size?

A quick estimate using 1/2" material comes out at the material and driver using up about 610 cubic inches out of the 1728 available in a cubic foot, leaving only 1118 cubic inches (18.4 liters) for the net volume.

What is the simulated SPL output in half space when the Tag Band W4-992C 4" driver reaches Xmax (3.5mm)?

Art
1/2" plywood is a reasonable material for a four cubic foot tapped horn using a 12" driver that goes to 40hz. Something like the TH-Mini comes to mind.

When you go down to one cubic foot, it's not just the driver that gets smaller, *everything* has to get smaller. I've built tapped horns with 2" drivers, 3" drivers, and 4" drivers. I generally used .25" MDF or 0.2" plywood.

Seems to work fine because the power levels are low and there's only so much force that can be generated by a 3" cone.

Click the image to open in full size.
Click the image to open in full size.

I *do* think that lots of braces and heavy thick panels are needed for large subs. Going back to the example of the TH-Mini, if you scaled all the dimensions by two it would go from four cubic feet to thirty two cubic feet. At that scale, 3/4" panels are a minimum and 1" would work even better.

Click the image to open in full size.

I built this twenty three cubic foot subwoofer a few years back. Coming from the car audio arena, I was accustomed to using 1/2" wood or smaller, and I used 1/2" for this one. I ended up trashing it because it was just too buzzy, and no amount of braces was able to address the problem.
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Old 17th January 2014, 07:44 PM   #4
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Originally Posted by Patrick Bateman View Post
1/2" plywood is a reasonable material for a four cubic foot tapped horn using a 12" driver that goes to 40hz. Something like the TH-Mini comes to mind.

I've built tapped horns with 2" drivers, 3" drivers, and 4" drivers. I generally used .25" MDF or 0.2" plywood...

I ended up trashing it because it was just too buzzy, and no amount of braces was able to address the problem.
John,

The DSL TH Mini uses 3/4" Baltic Birch, it does not make 1/2" ply come to mind for me.
Jbel's comments about measuring 3/8" deflection on his 1/2" SS15 does come to mind.

Using 1/4" material would reduce the material volume to around 300 cubic inches, but you did not answer either of my questions from Post #2.

Art
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Old 17th January 2014, 07:54 PM   #5
wg_ski is offline wg_ski  United States
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Originally Posted by Patrick Bateman View Post
I ended up trashing it because it was just too buzzy, and no amount of braces was able to address the problem.
Looks like some CDX plywood in that pile. That stuff is so full of voids it doesn't surprise me that the whole thing rattled. You can't fix it when it happens inside a panel.
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Old 17th January 2014, 08:04 PM   #6
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Originally Posted by weltersys View Post
John,

The DSL TH Mini uses 3/4" Baltic Birch, it does not make 1/2" ply come to mind for me.
Jbel's comments about measuring 3/8" deflection on his 1/2" SS15 does come to mind.

Using 1/4" material would reduce the material volume to around 300 cubic inches, but you did not answer either of my questions from Post #2.

Art
Art,

Would you mind letting me post on diyaudio without nitpicking everything I write?
I don't do this for a living, I have a day job, I haven't been doing this for as long as you have, I don't have as much experience.
When every post of mine is followed up with a post from you playing 'whack a mole', it really discourages any kind of experimentation. It should be obvious by now that I'm not from the school of 'measure twice, cut once.' I build fast and furious and I try to learn as much as I can before tossing the project into the dumpster.

And as much as I respect your expertise, there are a lot of people that seem to enjoy my half-baked ideas.

And for the record, you're right about the TH-Mini, as usual. It's 3/4", not 1/2".

Now if it doesn't offend you, can we get back on topic? What drivers are well-suited to a tapped horn of one cubic foot or less?
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Old 17th January 2014, 09:24 PM   #7
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"......there are a lot of people that seem to enjoy my half-baked ideas."

Yep, and I'm one of them. So please keep posting them.
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Old 17th January 2014, 10:44 PM   #8
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Originally Posted by weltersys View Post
Jbel's comments about measuring 3/8" deflection on his 1/2" SS15 does come to mind.
Ouch - that suggests "muddy midbass" to me. Panel flex of that amount would send me back to the drawing board.

Perhaps a mix of panel sizes would work for this 1 cu.ft. challenge, e.g. 1/4" braced internal panels to form the horn's path, 1/4" panels for the sides (which should be adequately braced by all of those internal panels) and 1/2" panels for the other sides. My POC #2 design used a mix of panel sizes and it worked out fine.

I'd probably aim for a cutoff above 40 Hz for this design though, as shoe-horning a longer path into a 1. cu.ft. box is likely to introduce unacceptable compromises.
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Old 17th January 2014, 10:58 PM   #9
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Originally Posted by Patrick Bateman View Post
Art,

Would you mind letting me post on diyaudio without nitpicking everything I write?

And as much as I respect your expertise, there are a lot of people that seem to enjoy my half-baked ideas.

What drivers are well-suited to a tapped horn of one cubic foot or less?
John,

If you can't stand the heat, get out of the glass house .

Sorry you find my questions to be "nitpicking", but you still have not answered my questions in post #2, so we don't know whether you are asking about one cubic foot gross or net, a rather basic distinction that makes real world differences.

And without an SPL level to compare to, how can we say if another driver is any more or less "well-suited" to a tapped horn of one cubic foot (gross or net?) than the one you already "half baked"?

Art
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Old 18th January 2014, 01:20 AM   #10
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