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Old 8th May 2018, 08:11 PM   #1
bentoronto is offline bentoronto  Canada
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Location: Toronto and Delray Beach, FL
Default 17 foot pipe sub 12-230 Hz 5dB

The sub has two parts, a base holding a 15-inch, 1965 Stephens 150W, and a 17x17x72-inch box mostly inch plywood weighing about 45 lbs, containing three tubes (with two abrupt bends) with sound exiting from the top.

The first pix shows an average of 3 mic positions near my chair. No EQ or crossover filter. Can't say for sure if bottom bass is as it should measure, but that's 12-230 Hz 5dB (which I ordinarily cross over around 130 Hz). Nice.

The second and third pix shows near field sound outputs at the driver and at top exit. In each, you see the very lightly absorbent versus final stuffed (roughly the familiar .5 lb per cu foot). You can see the weird pipe effects. Something's cooking at multiples of 8.5 Hz.

The fourth pix has five impedance curves. The top and bottom are 47- and 7-Ohm resistors to benchmark the curves. The big bump at 26 Hz is the free-air driver. The smaller bump is in the lightly stuffed. The all-but-flat final curve near the middle is the stuffed pipe.

B.
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Last edited by bentoronto; 8th May 2018 at 08:27 PM.
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Old 8th May 2018, 08:17 PM   #2
bentoronto is offline bentoronto  Canada
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Here are the missing pix.
Attached Images
File Type: jpg V full range 12-230 5 3 av.jpg (74.5 KB, 807 views)
File Type: jpg driver near field w and wo fluff.jpg (75.2 KB, 799 views)
File Type: jpg exit output w and wo fluff.jpg (69.0 KB, 795 views)
File Type: jpg 5 imped curves.jpg (84.9 KB, 781 views)
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HiFi aspirations since 1957. Currently working on motional feedback again... the final frontier in audio (and just posted data for a folded 17-foot pipe sub)
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Old 8th May 2018, 08:41 PM   #3
bentoronto is offline bentoronto  Canada
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Some construction pix. You can see the exit port at the near end in the first pix and reversed in second pix. Yes, mostly -inch plywood but with some strengthenings. The interior partitions are celotex which is a light-weight cellulose board with acoustic properties.
Attached Images
File Type: jpg Bottom with partition 2 in place.jpg (130.8 KB, 805 views)
File Type: jpg Top before centre partition.jpg (95.6 KB, 401 views)
File Type: jpg Voigt base.jpg (84.1 KB, 351 views)
File Type: jpg V in basement unfinished.jpg (96.2 KB, 338 views)
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HiFi aspirations since 1957. Currently working on motional feedback again... the final frontier in audio (and just posted data for a folded 17-foot pipe sub)

Last edited by bentoronto; 8th May 2018 at 08:49 PM.
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Old 8th May 2018, 09:27 PM   #4
freddi is offline freddi  United States
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quite impressive and a pretty build - a plan would be nice sometime and estimate of what modern drivers it may like
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Old 8th May 2018, 10:04 PM   #5
Brian Steele is offline Brian Steele  Grenada
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Quote:
Originally Posted by bentoronto View Post
Here are the missing pix.
Using REW for measurement?

Let's see what the THD looks like at 2.83V... :-)
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Old 8th May 2018, 11:13 PM   #6
bentoronto is offline bentoronto  Canada
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Quote:
Originally Posted by Brian Steele View Post
Using REW for measurement? Let's see what the THD looks like at 2.83V... :-)
Thanks freddi and Brian Steele.

Mic placed near field sort of midway between the ends. About 90dBC at mic but ranges from 80 to 96 in the near field... long pipes are different. 2.8 volts.

BTW, I never work with REW calibrated since there are so many control points in the measurement path that touching any (like to keep the mic from overloading the mic pre-amp) destroys the calibration. So please ignore those axis numbers on mic charts.

The distortion results, presented in normalized-to-fundamental format, are pretty reasonable for a sub, esp. the low bass where you generally see worse than 10% figures (AKA -20dB) and unusual to see any that play anywhere as low. Must be that -inch plywood construction or maybe I should firmly attach the pipe structure to the base... just sitting on it now.

B.
Attached Images
File Type: jpg 2.8v mid mic 90dBC.jpg (41.8 KB, 331 views)
File Type: jpg 2.8v distortion.jpg (38.2 KB, 171 views)
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HiFi aspirations since 1957. Currently working on motional feedback again... the final frontier in audio (and just posted data for a folded 17-foot pipe sub)

Last edited by bentoronto; 8th May 2018 at 11:24 PM.
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Old 10th May 2018, 01:26 AM   #7
bentoronto is offline bentoronto  Canada
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Quote:
Originally Posted by bentoronto View Post
About 90dBC...
That's 90dBC measured at 70 Hz. So the vertical axis that seems to say about 67dB at 70 Hz really should be 90 and 13dB added to the scale, if you want to know the absolute sound level at that near field spot.

As far as the listening results, that would be the swell first curve of post #2, not near field, particularly given the spatial and tuning anomalies of a 17-foot pipe when too close.

I judge my treble quality by listening to the orchestral anvil (no kidding) in band 7 of the Holst Band Suites. The less it sounds like an ordinary bell the more it sounds like an untuned, dull massive metal anvil.

Curiously, listening to the big orchestral side drum* in the same piece with this pipe sub is instructive too. The sound is now "duller" and more rumbly in the sense, I think, of being less peaked to the tunings of the enclosure.

B.
*ironically, electric RTA of this piece has very big peak at 40 Hz but some little rumbles at 12 and 18 Hz. Another good bass recording is Bach's old T&F in d, Murray/Organ Blaster, has substantial content below 30 Hz even below 20 Hz (see picture... you can see the individual pipes, eh). Anybody ever do an RTA of Dark Side of the Moon?
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File Type: jpg Bach.jpg (93.9 KB, 152 views)
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Last edited by bentoronto; 10th May 2018 at 01:52 AM.
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Old 25th May 2018, 02:53 PM   #8
bentoronto is offline bentoronto  Canada
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Quote:
Originally Posted by freddi View Post
quite impressive and a pretty build - a plan would be nice sometime and estimate of what modern drivers it may like
Thanks. Sorry to be so long in replying.

And sorry too that I'm an empirical guy and have to leave it to others to suss out the model. I couldn't say how my pipe behaviour relates to TL models. But here're some notes.

1. The three pipe sections are different cross-section shapes (that was intentional in following my taste for heterogeneity in audio design) but each is about 85 sq inches and that's about half the surface of the 15-inch driver and quite different than the Official TL size. Sure saves space if you're aiming for a long pipe.

2. I think the stuffed pipe is acting much like an IB. So there's no need for extra stiffness in the cone. Likewise, fairly efficient so no need for clumsy heavy VC.

3. I don't know why but there's good output below Fs particularly with the pipe standing in a room corner (and both driver and exit door are in the corners of the corner). So maybe no need for extra low resonance, unlike any other enclosure I can think of.

4. The -inch walls* sure vibrate in a way that would make you smirk for a sealed box. Not sure if the forces in a pipe are large or that the vibrations are too much of a shortcoming. For sure, the distortion and other specs within the sub passband are noticeably nice (distortion is spectacular below 35 Hz), so it can't be so terrible but then I'm biased.

B.
*an old guy had to be able to carry it around, eh.
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HiFi aspirations since 1957. Currently working on motional feedback again... the final frontier in audio (and just posted data for a folded 17-foot pipe sub)

Last edited by bentoronto; 25th May 2018 at 02:59 PM.
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Old 27th June 2018, 01:36 PM   #9
wilbur-x is offline wilbur-x  Tibet
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Great ! Two parallell ideas, but close enough ;-)

My tubed sub w/ 21" Hipower (ongoing) Ducts 500 & 400 with asymmetric transition.
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File Type: jpg Capture.JPG (35.4 KB, 125 views)
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Old 28th June 2018, 01:34 AM   #10
bentoronto is offline bentoronto  Canada
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Nice. Can you tell more about it?

B.
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