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Old 16th June 2009, 07:43 AM   #11
h@kan is offline h@kan  Sweden
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Quote:
Originally posted by johngalt47
Fascinating!

I'm really interested in your hot wire saw. Did you make it yourself? What kind of wire is it? What voltage?
Yes it's a diy saw, the wire is 0.65 mm stainless steel wire. The voltage comes from a car battery charger 13V 5A. Im sure 12V 2A is enough.

Quote:
Originally posted by jackfish
For those who are attempting this in the future, straight delimonine will dissolve polystyrene. It is a little less volatile than other solvents.
delimonine MSDS http://www.supercoproducts.com/msds/MSDS-FLOAT.PDF
It would definitely be great to find a less intoxicating method to get the polystyrene out. I wonder how much delimonine cost? And most of all I wonder what it's called here in sweden

Quote:
Originally posted by bjorno
Hi h@kan,

Nice project! Your hot wire saw set-up is genius, I will copy using the closeness of a window to avoid the smell of hot polystyrene.
Do you know that light weight ' EPS cement', http://www.epscement.com/ , have 85% less density than ordinary concrete mix, i.e. the weight could be reduced from 60 kg to about 9 kg without sacrificing good mold stability.

b
I will check into that! I wonder how that product works with thin structures as in mine (25mm)? It's worth investigating because the weight is a bit of a problem.

Quote:
Originally posted by planet10
Well done... not a whole lot of taper in the TQWT?

dave
starting with 3.2 sd and ending with 1.7 sd. Would a higher ratio be preferable?

Quote:
Originally posted by yan6
I'm not sure on the scale, but I am wondering if the polystyrene could be replaced by plumbing, ie: 4 or 6" sewer pipe. This way you wouldnt have to melt it out and it would be smooth inside. Of course you are then limited to the shape of a circle?

Are these for outdoor use? What kind of driver will you use in them?

Great project! this sure sparked my interest if for outdoor use.

Keep us posted
Yes some kind of pipe was my first thaught More specifically this type of formable alu-tube

Click the image to open in full size.

I did'nt manage to taper it in a good way so I skipped it.
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Old 16th June 2009, 08:09 AM   #12
h@kan is offline h@kan  Sweden
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I wish I had more experience in loudspeaker measurements.

Feel free to correct me if my measurement setup is incorrect.

The pipe is stuffed (polyester) quite light in the second section and more heavy in the first section (where the driver is placed) I think some more stuffing is required but I post this first result anyway. The helmholtz resonator is tuned to 200 hz.

Audio sector gainclone (quick and dirty) and diy mic-preamp.

Click the image to open in full size.

I measure in the center of the port and flush the backside of the speaker.

Click the image to open in full size.

Click the image to open in full size.

The driver...

Click the image to open in full size.

The frequency response from the port

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Port and driver in the same graph

Click the image to open in full size.

If the constant raining will end soon I will measure free field this evening.
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Old 16th June 2009, 07:29 PM   #13
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Quote:
Originally posted by h@kan
Quote:
Originally posted by planet10
Well done... not a whole lot of taper in the TQWT?

dave
starting with 3.2 sd and ending with 1.7 sd. Would a higher ratio be preferable?
Closed end is 3.2? Then it is not a TQWT, but a (not quite) 2:1 TL.

As to how it works, i'd have modeled it with MJK tables at least before building. I'm guessing you used Classic techniques which sometimes work, sometimes not.

dave
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Old 16th June 2009, 07:57 PM   #14
h@kan is offline h@kan  Sweden
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Quote:
Quote:
Originally posted by planet10

starting with 3.2 sd and ending with 1.7 sd. Would a higher ratio be preferable?


Closed end is 3.2? Then it is not a TQWT, but a (not quite) 2:1 TL.

As to how it works, i'd have modeled it with MJK tables at least before building. I'm guessing you used Classic techniques which sometimes work, sometimes not.

dave
Okej! Did not realise there is a breakpoint in tapering ratio and when going under a given ratio it becomes a X:1 TL. Is there any other design differences between a TQWT and a X:1 TL?

Regards H@kan
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Old 16th June 2009, 08:25 PM   #15
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TL is beginning to have as many meanings as the eskimos have words for snow...

If a line has a taper (closed : open) of n:1, n=>1 then its is typically called a TL. If n<1 it is a TQWT. But TL is also being used for all of those in the sense that they are all quarter-wave resonators.

And then there is a really strict definition of a TL which includes damping.

dave
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Old 16th June 2009, 08:52 PM   #16
h@kan is offline h@kan  Sweden
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Quote:
Originally posted by planet10
TL is beginning to have as many meanings as the eskimos have words for snow...

If a line has a taper (closed : open) of n:1, n=>1 then its is typically called a TL. If n<1 it is a TQWT. But TL is also being used for all of those in the sense that they are all quarter-wave resonators.

And then there is a really strict definition of a TL which includes damping.

dave
Well explained. Thanks!

Regards h@kan
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Old 17th June 2009, 05:45 PM   #17
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Hmm. For the sake of interest, a TQWT traditionally was in fact a negative taper line, i.e. one that tapers toward the terminus, so strictly speaking, the definition actually holds good. At some point in the past, the definition got flipped, and started being used for a positive taper line, i.e. one that expands toward the terminus. That's what's generally meant when people use the term now, but technically, a positive taper line is a horn.

Sorry. Didn't mean to add confusion.
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Old 17th June 2009, 07:44 PM   #18
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Quote:
Originally posted by Scottmoose
[ For the sake of interest, a TQWT traditionally was in fact a negative taper line, i.e. one that tapers toward the terminus, so strictly speaking, the definition actually holds good. At some point in the past, the definitio
Where did that come from? I've never seen a TQWT that went that way.

I always thot that TQWT was just another acronym for a Voigt pipe?

dave
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Old 17th June 2009, 09:39 PM   #19
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I can't remember offhand -GM is probably the best man to ask WRT the history of it, but as I understand it, that's what happened. We're going back to the 1930s WRT this I believe, but I've taken to using that definition at least in my own mind, mainly because it makes horn definition easier -as far as I'm concerned, if something is expanding toward the terminus, it's a horn.
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Old 18th June 2009, 01:12 AM   #20
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Quote:
Originally posted by Scottmoose
a TQWT traditionally was in fact a negative taper line
Actually, saying something has a negative taper is a bit meaningless mathematically, so that can lend a lot of confusion. A taper is always >0, it is a question of whether it is greater to, equal to, or greater than 1. (and which end you choose to put as the denominator -- in a 1/4 w/l box, i would suggest the closed end. In a 1/2 w/l it ismore ambiguous.

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