| 2 pi tower folding? [message #62984] |
Sun, 30 May 2010 13:39  |
grindstone
Messages: 46
Registered: May 2010
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Baron |
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I was gifting some two pi's and a sort of homebrew el84 se thing to a friend as a little intro to tubeville and I read how much the decware guys seem to love the towers.
My buddy doesn't want the form factor of the towers so...I think I know the answer but have to ask anyway--has anybody successfully folded these things?
I mean, I know it's no longer Wayne's design so if it sucks it's my problem. Just trying to get a little more bass than the regular two pi and make a shorter speaker for his pref.
If not, I guess, please kindly count me in for a set of two pi tower plans please.
Thanks for the time.
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| Re: 2 pi tower variants [message #62985 is a reply to message #62984] |
Sun, 30 May 2010 15:13  |
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Wayne Parham
Messages: 18786
Registered: January 2001
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Illuminati (33rd Degree) |
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I'll send you the plans for the towers, some additional thoughts below.
First, the two π tower isn't a transmission line or horn, so folding it is sort of non sequitur. Its tuning mechanism is Helmholtz, so the shape doesn't matter... with the following caveats.
I say it "doesn't matter" but in fact what I mean is the internal standing waves are attenuated rather than incorporated as a tuning mechanism like a horn or transmission line. But even that being the case, it is still important to consider internal standing wave behavior because it will be significant in a cabinet this size.
The only difference between a large bass-reflex cabinet and a large T-Line is that the fundamental standing wave mode in a transmission line is used wheras in a bass reflex, it isn't, or at least it shouldn't be. In a bass-reflex box, Helmholtz resonance is used instead. I suppose you could build a hybrid where both mechanisms were used.
In a transmission line, the port is physically placed where the funadamental node is in a pressure node. If you're building a bass-reflex box, the port should be placed somewhere else, where the fundamental standing wave node is not strong, but rather at a zero-crossing. That way, the only thing present at the port is Helmholtz resonance.
Whether the tuning mechanism is Helmholtz or standing waves, the harmonics should be attenuated with absorbent damping insulation. It also helps to position the port so that odd-harmonics fall on zero-crossings, like I mentioned above. This will also assist in attenuating internal standing waves. If you have pressure modes that line up with the port, they'll show up as little blips in the response.
Having said all that, you can build the two π loudspeaker in any shape you want, in any size between about 1.5ft3 and 5.5ft3, and tune the box to 40Hz. Smaller boxes will have higher cutoffs, larger boxes will go deeper. Put the woofer and tweeter on the baffle fairly close together. It's that simple, in theory. In practice, the larger boxes will start to have internal standing waves that line up in the lower midbass and bass range near where the port is tuned, too low for the insulation to absorb very well. So you'll want to position the woofer and port in the box where the port isn't in a pressure node, and you'll want to span the cross-section with insulation to help attenuate what's left.
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| Re: 2 pi tower variants [message #62994 is a reply to message #62993] |
Sun, 30 May 2010 22:03 |
grindstone
Messages: 46
Registered: May 2010
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Baron |
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Well, at my skill level, I'm counting the first two honks and not going high-order.
I mean, to state the obvious, making the volume into anything other than what you designed makes it something else so the question is what makes sense (no answer here, yet). I don't pretend to be making the same thing but more trying to save the most of a good thing while still fitting something into the guy's house.
The Helmholtz is cool, and to radically paraphrase you, a tall skinny box is gonna have modes and they'll need attention...and damping...and care locating port and driver.
Re OS, yeah linux here (slackware). Some *buntu's on other boxes. Probably should have kept a box running the other stuff but it was a partially religious conversion that was strongly motivated at the time 
The macro things are always extra work and the older I get the more I respect people that just use whatever tool they need to do their tasks. Life's too short for everything to be a hobby. Convert your files a few times and it's tough to be excited about the world requiring another switch to new formats...which gets back to the OT zealotry thing 
hornresp doesn't run crash-free in wine but it runs and always seems to even with all the changes so it's another thing in the world to be really grateful for (like pi speakers, this board, and all the time & energy you spend educating). You must not sleep at all.
I'm probably gonna need to post over on the hornresp thread to figure out how far afield i've already strayed.
As long as I'm here, thanks for making such great things available at such economical prices as the 2 pi stuff. I might not have any idea what I'll end up with yet, but I know that it'd be quite a few dB down if it weren't for your stuff. It makes my whole little gift plan even possible and that's just plain cool.
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