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Old 7th July 2003, 06:48 AM   #1
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Default tapered pipes vs others

ok, i've seen a few designs for tapered pipes and such, with the few points of consensus being:

use a good damping material like dense polyester fill or prefably loog wool.

the pipe should have an ending width no larger then Sd. why?

but then the next part is where the designs diverg. the one design has the spekaer mounted at 1/3 the length of the pipe, and the taper gets larger until it reaches the exit, which is equal to Sd.

the other design starts at about 1.5 Sd and decreases the taper until it reaches Sd. the spekaer is mounted at one end of the pipe.

from reading, the first design reduces distortion, but lowers output slightly.

i would appreciate any explaination of the differances, and mainly why the small exit area?
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Old 7th July 2003, 08:51 AM   #2
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Default Re: tapered pipes vs others

Forget classic TQWTs, you don't get lucky often.

A TQWT is just another quarter-wave design, and as such can be modeled with Martin King's SW. Bob Brine's has some good commentary on what works & what doesn't.

The restriction of the terminus mass-loads the line & improves its low-pass function... and it yurns out that 1/2 way along the line (oe close) is the best place to position the driver.

dave
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Old 7th July 2003, 04:18 PM   #3
GM is offline GM  United States
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Quote:
and it yurns out that 1/2 way along the line (oe close) is the best place to position the driver.
Please define 'close'. It's been my experience that the optimum point can be from <10% to >80% of line length depending on the area of the closed end or terminus and flare rate (taper ratio). Indeed, 50% is optimum for only one taper ratio, whether expanding or reverse flared.

GM
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Old 7th July 2003, 04:32 PM   #4
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Didn't Augspurger say 1/5th of the pipe's length away from the closed end?
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Old 7th July 2003, 04:36 PM   #5
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Hi, this is just my opinion, so I!=fm sorry in advance if I didn!=ft hit your point.

Some of QWTs seem they have the driver in the midpoint of enclosures. But correctly, it is 3/4 position in the whole length of the pipe.

As you see, pipes generate acoustic wave by resonance, and its wavelength is 4 times longer than pipes, which is utilized in QWTs to strengthen the low.

But there!=fs another resonance, which generates 4/3 longer acoustic wave than the length of pipes. In frequency scale, it comes 3 times higher than the base resonance.
The effect of 4/3 times resonance is weak. But it may be troublesome, if it goes far over than the range you target for reinforcing low.

The driver, attached at 3/4 position of pipe lengths (that is also at the beginning point of flipping wave) has the purpose to knock down 4/3 times resonance, by its acoustic vibration.

Even if you completely ignored this effect, it may not cause anything practical because of its weakness. But you can!=ft tell in advance whether something bad appears or not.
I think this is why you see different positions of the driver among QWTs.

As for the different superficies of ending, I!=fm sorry I can!=ft figure out any convincible reason. In my opinion, the differences of ending superficies don't seem getting something distinctive, except the extreme cases that spoil the effect of QWT.

In some cases, you see the attempt to mix different effects. Attaching ports to mix QWT and Bass Reflex, or taking in exponential curves to mix with Back-horns. Although any of them haven!=ft made remarkable success yet, I think.

One exception may give you the reason for small exits; it looks like a version of Voight Pipe. What I am mentioning is Reverse-horns. Attaching horns reverse way, horn!=fs exit to drivers, narrow entrance for exit.

Nautilus of B&W (the model we nicknamed as escargot) has this figure, aiming the ideal absorption of backpressure to purify the quality of sound. Its ending is closed, but it affects as such if it opens slightly.

If you adapt Reverse-horns to the driver extends to low range, horn!=fs length will be very long. That is why B&W took on the eccentric figure.

In DIY, it is difficult to build escargots, so that easily be shaped looks like as reverse versions of Voight Pipe. Resonant effect in this case is almost filtered out by the narrowed exit. But there may be some people trying to mix Reverse-horn and QWT, as above.
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Old 7th July 2003, 05:30 PM   #6
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Quote:
Originally posted by GM
Please define 'close'. It's been my experience that the optimum point can be from &lt;10% to &gt;80% of line length depending on the area of the closed end or terminus and flare rate (taper ratio). Indeed, 50% is optimum for only one taper ratio, whether expanding or reverse flared.
I puposely left things a bit fuzzy due to just this. Maybe a better statement is that in lines based on geometry similar to Matin's ML-TQWT 50% seems to be close to the optimal placement. In the end optimal can only be found by playing with the model.

MJKs new alignment tables have a section on offset that can give a quick feel for what works.

dave
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Old 8th July 2003, 05:06 AM   #7
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the book i have gives the estimate for the optimal point being (apporimately) 1/(2 + (At/Am)^0.5) for the voight pipe, wher At = 0, the location is at 1/2.

i'll look into this modeling thing. any links or keywords to search for?
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Old 8th July 2003, 05:59 AM   #8
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Quote:
Originally posted by theChris
i'll look into this modeling thing. any links or keywords to search for?
http://www.quarter-wave.com/
Quarter Wavelength Loudspeaker Design

http://geocities.com/rbrines1/
Bob's Speaker Stuff

dave
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