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Old 18th October 2011, 03:55 AM   #1
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Default A few simple questions

I was asked by a high school student for assistance to build some home speakers for a school project. He is a good kid with some woodworking abilities, but I was hesitant for 2 reasons:

1. He seemed convinced that he could buy some raw speakers and cross-overs on-line, throw them in a box and it would sound great. (Oh to be young and optimistic again)
2. I have had success building amps but the speakers I built many years ago sounded less than desirable and left a bad taste in my mouth. Wanting to spare him the disappointment of building some crappy sounding speakers caused me to think about a pair of Atlas FAP82T speakers left over from a recent job and how they might be a perfect donor for his project. They are a two way tuned port speaker in a metal enclosure used for PA applications, 8 woofer and a 1 tweeter. http://www.parts-express.com/pdf/242-808s.pdf

My thought was to build a MDF cabinet of approximately the same cubic inches as the metal enclosure and use the same speakers, crossover and port diameter. However, having no experience building a good sounding speaker, I had a few questions.

How critical is the port location?

Because the original case is metal and cylinder shaped, what effect will a rectangular wood cabinet have on the sound? In other words, should we make the wood case smaller, larger or same size?

Keep in mind that his primary interest is a good looking cabinet, so I am merely interested in getting these speakers to sound reasonable. Later if he enjoys this project, I plan to help him build some more serious speakers.

Thanks for any advice you might give.
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Old 18th October 2011, 04:27 AM   #2
AllenB is offline AllenB  Australia
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These speakers were designed to be mounted flush in a ceiling. Although I have no idea how well they achieved their objective, in theory mounting them on a box would leave them somewhat bare with a crossover change needed at the least. I suppose failing other options you could use as wide a frontage as didn't look too out of place, and adjust the tweeter level later if it didn't sound right. Leave the port and internal volume the same.
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Old 18th October 2011, 05:58 AM   #3
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Allen, thanks.

Yes, they are designed to be ceiling mounted, but I picked the FAP82s because they had a lower dispersion rate (100 degrees) than most ceiling mounted speakers. We put a pair of these on my bench, forward facing and about 8 feet apart. We stood back about 10-12 feet, played various music thru them and they sounded remarkably well. Again I realize these speakers have some limitations, but he heard the 8" woofer and was convinced that was what he wanted to use. (Something about young men and booming bass)
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Old 18th October 2011, 06:10 AM   #4
AllenB is offline AllenB  Australia
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And dispersion. This year I am using 15" midrange drivers for this reason. You'll probably prefer the wooden cabinets. They may be a little more solid and less resonant, and an improvement on the round frontage of the units currently when freestanding. You should also add a little stuffing to the box.
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Old 18th October 2011, 03:53 PM   #5
sreten is online now sreten  United Kingdom
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Hi,

You will have some "hifi" issues using that speaker in a normal
box but it will work in a fashion, though not that optimally,
as its designed for flush mounting. In a box you will get
weak bass due to the "baffle step" a box introduces.

Something like Zaph|Audio - Bargain Aluminum MTM
would be in a entirely different quality class. The
floorstanding version has very good bass extension.

rgds, sreten.

undefinition
(see if nothing else, the excellent FAQs)
Zaph|Audio
FRD Consortium tools guide
http://web.archive.org/web/200909021...esigningXO.htm
RJB Audio Projects
Jay's DIY Loudspeaker Projects
Speaker Design Works
HTGuide Forum - A Guide to HTguide.com Completed Speaker Designs.
http://www.troelsgravesen.dk/Diy_Lou...r_Projects.htm
Humble Homemade Hifi
Quarter Wavelength Loudspeaker Design
The Frugal-Horns Site -- High Performance, Low Cost DIY Horn Designs
Linkwitz Lab - Loudspeaker Design
Music and Design

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Old 19th October 2011, 01:54 AM   #6
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Screten, thanks for the links. If he enjoys the 1st project, these links will give us many choices for future projects.
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