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soundminded

Sweet Sixteen blast from the past

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I recently had a chance to re-read the "sweet sixteen" design article in January 1961 Popular Electronics. In that article, a design was presented using sixteen five inch table radio speakers in a square array in a sealed enclosure using 1/2 " plywood for the front and back and 2X6s for the side rails. The thrust of the arguement for the design was that when two speakers are closely coupled, their in box resonance frequency is halved and when doubled again, halved again. So for a speaker driver with a free air resonance of 320 hz, sixteen in such a configuration would have an in box resonance frequency of 20 hz and that with 256 drivers you could go down to 1 hz. They internally braced the box at various intervals and added a tweeter to extend the high end.

Does anyone have any experience with this design and does it work as they claim? The intuitive answer is no it would sound like 16 crappy table radio speakers but they are very definite about their claim. Any comments? I'm thinking of trying it myself. I've got a few boxes of 4" drivers hanging around at least as good as the ones they used.

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Guest radkrisdoc

Hi!

While I have not experienced it directly, I do know someone who has....my Dad. Of course, I've read the article and I clearly remember Sweet Sixteen. My dad said the only impression that lasted long enough was the bass. It was more than enough and not "tight" but warm and enveloping (room-filling). Kinda like a bass reflex, but definitely not the kind of bass from an acoustic suspension enclosure. His friend had completed the project more than two decades ago.

I guess if you experiment with different drivers you might have more luck with it...but the speaker's radiation pattern would be of concern. There will be severe combing effects and lobing if the radiation pattern was mapped out. Kris

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I'm thinking of bringing the drivers about as tightly together as I can to try to create as close as I can get to the effect of a single large driver. The Quam speakers in the article were of very mediocre quality. I can do a lot better even with was is already in my house. The recommended add on tweeter was also very highly directional. The theory says that the bass can be extended to a very low f3 due to the acoustic coupling effect. In 1961 when the article was written, graphic equalizers for home use didn't exist. It should be interesting if I ever get around to it.

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Guest radkrisdoc

Well, if you are worried about lobing and comb effects, you can read articles on line arrays and see what works best for a sweet sixteen mod, making its radiation pattern more acceptable for stereo imaging....I found a nice article titled "Design Guidelines for Practical Near Field Line Arrays" by Dr. Griffin. I dont know about the author, but it looks like a pretty reliable source. You can obtain the article by plugging in the title on Google. The information you are looking for is how near or how far away drivers can be placed with respect to their highest operating frequency. You will find that info on page 11, under the sub-heading "Driver Separation". Hope that helps in building a really good sweet sixteen system.

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