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Old 8th February 2004, 02:04 AM   #1
dooper is offline dooper  Canada
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Default Seeking comments on (new?) design

Here's an idea I've been working on recently. The cabinet has a gross internal volume of 8.19 liters, and would most likely house a single full range driver. I'm not sure if this has been done before....

TriBox Project

The idea is simple. Take a conventional rectangular speaker cabinet design based on the Golden Ratio, and slice it in half diagonally. The ratio of height to width to depth remains 1.618 : 1.00 : 0.618. The ratio of the length of the sloping panel to the width will be SQRT (3) : 1, or about 1.732 : 1.

The TriBox is ideal for use in situations where a small internal box volume is required, and a conventional enclosure would not be wide enough to house the chosen driver. For example, assume that an eight inch driver is to be mounted in an enclosure with a gross internal volume of about 8.3 liters. In a rectangular GR design, an internal width of eight inches would yield a gross internal volume of about 8.39 liters. Problem – how can you mount an eight inch driver on a panel that is only eight inches wide? Solution – use a TriBox. With an internal width of ten inches, the gross internal volume would equal about 8.19 liters.

Another advantage is that the TriBox has only one pair of parallel surfaces, compared to three pairs in a conventional enclosure. This, along with suitable damping material, will help to eliminate standing waves inside the box.

A few math calculations will reveal that the base angle of this right triangle is very close to 69 degrees, and the angle at the top of the triangle is approximately 21 degrees. If you fear math, that’s all you need to know. If you don’t….

The Golden Number is equal to (SQRT (5) – 1) / 2, or roughly 0.618. In any GR box, if the width W = 1.00, the height H = W / 0.618 = 1.618, and the depth D = W * 0.618 = 0.618. Armed with these numbers, the base angle can be calculated. The angle will equal arctan (H / D) = arctan (2.618) = 69.09 degrees. An even 69 degrees will be quite close enough.

The triangular shape leads to a number of possibilities. For rear surround applications, the box can be mounted upside down on the side or rear wall, and the height can be chosen based on the listening position, making use of the 21 degree angle. For front L / C / R use, there are numerous options. If rectangular side panels are used, and the drivers are mounted on the sloping panel, the cabinets will look just like conventional speakers from most angles.

For internal bracing, I suggest the following. Use triangular braces for the sides, and increase the width of the bottom, rear, and sloping panels accordingly. For example, if the internal dimensions are to be 10” W X 16.18” H X 6.18” D, and if Ύ” MDF is used throughout, the side braces will be right triangles measuring Ύ X 6.13 X 16.05”. Use two by two softwood such as spruce, trimmed to one inch square, to brace the joint between the bottom and rear panels. Trim another length of two by two to one inch square, then miter cut it lengthwise at a 69 degree angle. The resulting two pieces will be used to brace the remaining corners. The three corner braces will be 9 7/8” in length.

The remaining dimensions will be as follows:

Sloping panel / baffle: Ύ X 11 ½ X 20.22”.

Bottom: Ύ X 7 ½ X 11 ½”. Panel will be miter cut at 21 degrees off vertical, then trimmed so internal depth = 6.18” and external depth = 7.22”.

Rear: Ύ X 11 ½ X 18 ½”. Panel will be miter cut at 69 degrees off vertical, then trimmed so internal height = 16.18” and external height = 18.14”.

Sides: For rectangular sides, Ύ X 8” X 20.22”. For triangular sides, Ύ X 7.63” X 19.64”.

NOTES:

1. External triangular side dimensions are approximate.

2. All dimensions may be rounded to the nearest 1/8”.

3. Edges adjacent to the baffle are to be rounded using 3/8” radius.

4. The driver may be mounted on the surface of the baffle, and a rectangular piece of hardwood of the appropriate thickness may be used to achieve flush mounting. In this case, the rounding radius will be greater.


Comments, coaching and criticism will be welcomed.

dooper
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Old 8th February 2004, 02:11 AM   #2
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What?
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Old 8th February 2004, 02:22 AM   #3
dooper is offline dooper  Canada
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Not enough pictures? This is all on the drawing board right now. I could fire up the scanner and burden the server with my sketches and notes, if need be. I thought the words would have been clear enough, accompanied by the cheesy JPG created with MS Paint.

I'll return to my cave now ;-)

dooper
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Old 8th February 2004, 02:59 AM   #4
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There are many ways to get the correct internal volume when dimensions are restricted.

A wedge shaped box has been done before. It's nothing new.
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Old 8th February 2004, 03:17 AM   #5
dooper is offline dooper  Canada
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Thanks for your reply, and g'day! Like I said, I'm wasn't sure if this had been done before. It's kinda like what I tell my 16 year old son - there's nothing new under the sun.

I will post pictures when this prototype is done.

dooper
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Old 8th February 2004, 03:55 AM   #6
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Are you talking about something like this?
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Old 8th February 2004, 08:47 PM   #7
dooper is offline dooper  Canada
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Looks very nice, Timn8ter. My idea is bookshelf / stand / wall mounted boxes, with the sloping panel used as the baffle. I hope to use them as satellites in my HT system. The sub to satellite crosspoint is 90 Hz, so the sats won't really need to provide very much bottom end.

dooper
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Old 8th February 2004, 09:41 PM   #8
Mats J is offline Mats J  United States
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It sounds kinda like your trying to describe the old SPICA TC-50 and TC-60.

http://www.enjoythemusic.com/magazin...spicafever.htm
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Old 8th February 2004, 10:09 PM   #9
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Oh yeah. The John Bau quote that has become stuck in my mind:
Quote:
I lost interest once audio became a video accessory.
Hey Mats J: Are you coming to the DIY meet in April?
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Old 8th February 2004, 10:24 PM   #10
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Timn8ter, sounds like fun. It doesn't say at what time, just the date.
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