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Old 3rd September 2003, 03:22 AM   #1
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Default Swifts and other birds

Does anyone know what this "BASS-IC" thingy is?

http://www.6moons.com/industryfeatur...ic/bassic.html
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Old 3rd September 2003, 04:15 AM   #2
SY is offline SY  United States
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A good reading of Augsperger's patent columns gives one a cynical view.

When we piece together the few facts scattered amongst the Poor Man's Bob Carver prose, I would guess he peaks the woofer below resonance by interposing a reactance or two. There are a bunch of ways that this has been done, most notably the series capacitor approach of Clark and Geddes.

I'll run a quick search and see if he's got a patent application in on this. If not, draw your own conclusions.

Edit: Ran a search of applications and issued patents at USPTO with "McGinty" as inventor and "loudspeaker" as a search term. Zip. Nada.
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Old 3rd September 2003, 07:39 AM   #3
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most notably the series capacitor approach of Clark and Geddes
Which has a definite advantage over any loading that is using some type of "exhaust": It acts as a subsonic filter as well.

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Old 3rd September 2003, 01:17 PM   #4
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The title of the article says "new chip for bass", but the body of the article insists that the technique is completely inside the loudspeaker-nothing to do with amps, etc.

I guess we'll never know about the effectiveness of the technique until we see some Thiele-Small parameters for a speaker and a response curve for an enclosure employing that speaker.

I wonder if it isn't some variation of the old technique of using the bass reflex port as a trucated horn section, in order to get horn action on a very narrow band of frequencies. I saw a book from the fifties by Abraham Cohen that illustrated that.

Anyway, please tell me more about the series capacitor approach of Clark and Geddes.
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Old 3rd September 2003, 01:45 PM   #5
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Series capacitor:

Applied to a closed box, a series capacitor will interact with the impedance of the driver in a way that the box can be made smaller and go a bit lower. Because there is no free lunch (as usual) you will end up with a steeper rolloff (3rd instead of 2nd order) and slightly worse impulse response. AFAIK the impedance will also be a little lower below resonance (the increased radiated power has to come from somewhere in the end !).
Theoretically it would be possible to simulate this behaviour with current feedback.


About the bass-ic thingie:

http://www.meadowlarkaudio.com/pow/tl.htm

shows a picture of one their TML foldings.
They seem to use a 1st back-chamber followed by a 2nd one (30% smaller approx), then the line is narrowing for the first 2/3 (approx) and then it opens up again towards the end.

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Old 3rd September 2003, 02:34 PM   #6
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Much thanks, Charles.

It always occurred to me that since the idea is to take the back wave and reverse it, a series of chambers could be used, each one adding their own little delay. A back wave, delayed enough, goes into phase with the front wave and reinforces it.

I was always under the impression that a bass reflex and Transmission Line delivers the back wave 180 out of phase, and therefore in phase with the front wave. However, I found out a short time ago that is not completely true. In both the Transmission Line and the reflex, the back wave is 90 out of phase with the front-which still means that it reinforces the front somewhat.

I wonder if this multiple coupled cavity, connected to a Transmission Line thing that Meadowlark has doesn't alter that relationship somewhat. Could it be that these new enclosures deliver the back wave fully in phase with the front instead of 90 out of phase, and that is where the extra benefit comes from?

I am just guessing here, I freely admit.
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Old 3rd September 2003, 10:42 PM   #7
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That appears like a normal 1/4 wave TL to me :/
but the price tag...
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Old 4th September 2003, 03:47 AM   #8
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VEC7OR:

If you look closely, the top 2 dividers do not provide a smooth cross-section for the sound to flow down, like in a conventional Transmission Line. The space betwee the wall and the open end of divider is much smaller than the cross-section of the Line at that point. The top 2 dividers are not part of a Transmission Line, they are divideing the enclosure up into two chambers.

The Transmisson Line begins after the second divider, when the space between the dividers and the wall is equal to the flow area of the Line at that point.
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Old 4th September 2003, 03:53 AM   #9
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In both the Transmission Line and the reflex, the back wave is 90 out of phase with the front-which still means that it reinforces the front somewhat...

...Could it be that these new enclosures deliver the back wave fully in phase with the front instead of 90 out of phase, and that is where the extra benefit comes from?
90 at what frequency? And what happens away from that frequency?
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Old 4th September 2003, 04:14 AM   #10
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SY:

90 at the tuning frequency of the reflex and the Transmission Line. The phase shifts the farther you get away from that frequency.
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