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Old 7th November 2012, 02:10 PM   #11
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some pics of the sub coming together:

Click the image to open in full size.
Click the image to open in full size.
not much to look at (yet)

Click the image to open in full size.
I used 3/8" plywood for this box - because it's designed to be placed on the back seat of a car. And I didn't want it to be so heavy that it would screw up my seats. But you can see the 'bowing' of the plywood will create some challenges.

Click the image to open in full size.
At every step in the build process, I'm using weights to flatten and straighten the boards. It's a bit of a hassle, but I'm hoping that it will pay off with a light rigid subwoofer enclosure.

Click the image to open in full size.
In this picture, I'm STANDING on the center tunnel of the sub box. I did this to demonstrate how rigid/strong it is. Due to the very thin plywood I am using, I believe a lot of cross braces are a pre-requisite for this thing to work properly. (IE, if I'd used 3/4" plywood instead of 3/8" plywood these types of braces wouldn't be as important.)
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Old 7th November 2012, 03:10 PM   #12
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Hey Patrick,

Let's see,you started the Lazy & Impatient thread in July, should we expect to be impatient with your lazy build until sometime middle of next year ;^) ?

Put on some shoes and git er done!

Art
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Old 7th November 2012, 08:03 PM   #13
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Quote:
Originally Posted by Patrick Bateman View Post
I used 3/8" plywood for this box - because it's designed to be placed on the back seat of a car.
On the back seat??

Hmm.. it looks like aesthetics and safety are not high on your priority list
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Old 8th November 2012, 01:29 AM   #14
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Pat I thought you gave up on tapped horns for cars and wanted to use monopoles?
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Old 8th November 2012, 02:03 AM   #15
jbell is offline jbell  United States
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monopoles???



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Old 8th November 2012, 02:04 AM   #16
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Just started watching that show lol love It!
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Old 8th November 2012, 03:08 AM   #17
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Quote:
Originally Posted by m R g S r View Post
Pat I thought you gave up on tapped horns for cars and wanted to use monopoles?
yes, I think sealed boxes are the way to go in a small room or in a car IF you want the most output per liter. In fact, one of the ideas I'd considered instead of this box was using a pile of small woofers in a sealed box.

There were a few things that tipped me towards a tapped horn again:

1) as long as you have plenty of power, output will be mostly dictated by woofer displacement.
2) a tapped horn has very low displacement at the tuning frequency
3) while a sealed box is 'theoretically' superior for a car, if you combine the low excursion of a tapped horn with a highpass filter to lower excursion below fb, a tapped horn can handle a crapload of power


Bottom line - six or eight of the Alpine woofers in a box that's about the same size will likely get louder. But the box, woofers and amplifier will cost about $1000, versus less than half that much for the tapped horn.


Also, I'd actually come *really* close to doing a front loaded horn for the Alpines, but they don't work so hot because their QTS is so high.
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Old 8th November 2012, 07:10 PM   #18
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Quote:
Originally Posted by Brian Steele View Post
On the back seat??

Hmm.. it looks like aesthetics and safety are not high on your priority list
Something I wrote in rec.audio.car about 8 years ago:

... forces of 40 to 50 G are routinely recorded during the standard 30 MPH crash tests. Your sub box weighs, for example, 50 pounds. Multiply that by 50: 50 x 50 = 2500 pounds.

That's well over a ton. If you were to suspend your car nose down, then stack over a ton of weights onto the back of the seat, do you think the seat locks would hold? Would you be prepared to be buckled into the driver's seat while the weights were stacked? What do you think would happen to you if more than a ton of weights landed on you? It'd be ironic if you were to hit something, be saved by the seat belt and airbag, then be mashed to strawberry jam by your sub box.

Bolt that sub box to the vehicle frame. NOW.

It needs to be bolted down as securely as a trailer hitch would be mounted. This means high-tensile bolts and big load spreading washers. The bolts should run right through the box- it's no use just bolting the bottom down, the rest of the box will likely rip off it and go flying.

If you doubt that, just take a sledge hammer to an old sub box sometime.(*) I'll wager that it'll only take one big swing to break out the bottom or a side if you hit it from the inside near one edge (puts the joint under maximum tension). The sledge head weighs 20 pounds or less and is moving less than 30 MPH. I'll bet your sub drivers weigh 20 pounds or more, and they will be moving faster in even a moderate collison.

(*) Yes, I have done this. They were water and smoke damaged and had to be written off. We broke them up so they'd pack flat in the dumpster.


In Patrick's case, I would suggest designing the box so it can be restrained by the rear seat belts. It's not ideal, but it's better then nothing. If the belts are too short to fit around the box, consider using (safety approved) seat belt extenders.
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Old 8th November 2012, 07:30 PM   #19
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Quote:
Originally Posted by Don Hills View Post
Something I wrote in rec.audio.car about 8 years ago:

... forces of 40 to 50 G are routinely recorded during the standard 30 MPH crash tests. Your sub box weighs, for example, 50 pounds. Multiply that by 50: 50 x 50 = 2500 pounds.

That's well over a ton. If you were to suspend your car nose down, then stack over a ton of weights onto the back of the seat, do you think the seat locks would hold? Would you be prepared to be buckled into the driver's seat while the weights were stacked? What do you think would happen to you if more than a ton of weights landed on you? It'd be ironic if you were to hit something, be saved by the seat belt and airbag, then be mashed to strawberry jam by your sub box.

Bolt that sub box to the vehicle frame. NOW.

It needs to be bolted down as securely as a trailer hitch would be mounted. This means high-tensile bolts and big load spreading washers. The bolts should run right through the box- it's no use just bolting the bottom down, the rest of the box will likely rip off it and go flying.

If you doubt that, just take a sledge hammer to an old sub box sometime.(*) I'll wager that it'll only take one big swing to break out the bottom or a side if you hit it from the inside near one edge (puts the joint under maximum tension). The sledge head weighs 20 pounds or less and is moving less than 30 MPH. I'll bet your sub drivers weigh 20 pounds or more, and they will be moving faster in even a moderate collison.

(*) Yes, I have done this. They were water and smoke damaged and had to be written off. We broke them up so they'd pack flat in the dumpster.


In Patrick's case, I would suggest designing the box so it can be restrained by the rear seat belts. It's not ideal, but it's better then nothing. If the belts are too short to fit around the box, consider using (safety approved) seat belt extenders.
Click the image to open in full size.

So you're saying that Unity horns on the dash and tapped horns on the back seat are a recipe for disaster?

:O :O :O
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Old 8th November 2012, 08:16 PM   #20
Djim is offline Djim  Netherlands
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Quote:
Originally Posted by Patrick Bateman View Post
So you're saying that Unity horns on the dash and tapped horns on the back seat are a recipe for disaster?
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