Brian,
Some have made bifurcated (symmetrical split path) TH, but that uses more wood for the same path length, and although it equalizes pressure left and right, it still does not provide even loading for the cone top to bottom.
The cone loading changes with frequency, and it is possible that only one frequency will excite a cone rocking mode. The rocking may not show up with most musical signals, while can be (very) apparent with the right sine wave signal.
At any rate, a stiff cone with a double spider (like the BC18SW115) goes a long way towards "cone correction" ;^).
Art
As I expected, I have to settle for a smaller restriction of 4.5L.
On the bright side, this is still 50% more than my previous restriction
With some spreadsheet wizardry, I managed to come up with a method that will give me a restriction that can be adjusted by simply adding or removing panels.
e.g.
1. For a restriction of 4.5L, I use all 10 panels listed (or 1-9, which is close enough)
2. For a restriction of 4.0L, I use panels 1 to 6 and leave out the rest
3. For a restriction of 3.5L, I use panels 1 to 5 and leave out the rest
4. For a restriction of 3.0L, I use panels 1 to 4 and leave out the rest
Oh, and to get these into the TH, each "panel" that is more than 28 cm wide is actually two panels that will be joined together in the TH. Joy. Shouldn't be that difficult to whip them out quickly via circular saw however.
Tomorrow I'll cut the panels out, and given the time, I might actually be able to start some testing, if the beers don't start calling first ...
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Hmmm...
Hmm...
According to my spreadsheets, that triangle wedge to the left and the stack of wood to the right are supposed to have the same volume - 3L.
My eyes are telling me otherwise.
Oh well, I'm going to start off the experiment with the "new" 3L stack, and do some impedance and FR measurements to see how they stack up.
Hmm...
According to my spreadsheets, that triangle wedge to the left and the stack of wood to the right are supposed to have the same volume - 3L.
My eyes are telling me otherwise.
Oh well, I'm going to start off the experiment with the "new" 3L stack, and do some impedance and FR measurements to see how they stack up.
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First up, the impedance curve. In blue is the POC3's impedance curve with no cone compensation, in red is the impedance curve with the "new" 3L of cone compensation. Basically no change below 53 Hz, some minor changes up to 100 Hz, and then some interesting changes after that. The peak at 129 Hz has decreased somewhat and the peaks above that have shifted a little and become sharper.
129 Hz is around where the POC has a dip in its FR, so I'm wondering what this is going to mean for the frequency response?
129 Hz is around where the POC has a dip in its FR, so I'm wondering what this is going to mean for the frequency response?
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Oh well...
FR results below. Yeah, I got rid of the "dip" around 130 Hz. And a good portion of the response between 60 and 100 Hz as well. Not good, not good at all for a TH designed for PA use.
I'm pretty sure that the new CC has more volume than the old one I had in place, so the lesson learned here is do not apply more restriction at S2 than that identified in the HornResp sim - you're going to lose output.
FR results below. Yeah, I got rid of the "dip" around 130 Hz. And a good portion of the response between 60 and 100 Hz as well. Not good, not good at all for a TH designed for PA use.
I'm pretty sure that the new CC has more volume than the old one I had in place, so the lesson learned here is do not apply more restriction at S2 than that identified in the HornResp sim - you're going to lose output.
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Yep, to the first approximation, down low it's all about displacement, though in a true compression horn you get more peak power per unit displacement, so more restriction nets higher SPL over a wider BW as a 10:1 CR W.E./Lansing/Altec/GPA or similar design compression driver proves.
Unfortunately, AFAIK the closest you can make a TH compression horn is to couple together a bunch of ones that individually will under perform similar to yours and a 10:1 CR compression bass driver would be huge and super expensive to manufacture, so not a viable option.
GM
Unfortunately, AFAIK the closest you can make a TH compression horn is to couple together a bunch of ones that individually will under perform similar to yours and a 10:1 CR compression bass driver would be huge and super expensive to manufacture, so not a viable option.
GM
Hi Brian,
Compensating the full volume of baffle cut-out and cone volume in a 'straight' fold-section at the driver, will 'narrow' the path and increase the compression-ratio of the horn. Full volume compensation needs a curved horn-path that follows, more or less, the curve of the cone.
Cheers,
Djim
Compensating the full volume of baffle cut-out and cone volume in a 'straight' fold-section at the driver, will 'narrow' the path and increase the compression-ratio of the horn. Full volume compensation needs a curved horn-path that follows, more or less, the curve of the cone.
Cheers,
Djim
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