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SonoTube and SewerPipe BP6 Subwoofer
SonoTube and SewerPipe BP6 Subwoofer
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Old 26th October 2017, 10:40 PM   #1
DonVK is offline DonVK  Canada
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Default SonoTube and SewerPipe BP6 Subwoofer

I'm looking to build a subwoofer from sonotubes and sewerpipes. I'd like a flat-ish response from 30-100Hz min. I only need 110db max, and its for music.

The BP6 has flat response and covers the range I need without getting too big or requiring transforms to fix it. The BP8 has 5db ripple that I could never eliminate. I realize a box may be easier, but I want a cylinder to match other speakers.

Below is a drawing of what I intend to build as well as the HornResp design. I have added a 4th order BW low pass filter at 160Hz. The structure is as big & tall as I'm willing to go.
Attached Images
File Type: jpg SonoSewerSubBP6.jpg (30.6 KB, 371 views)
File Type: jpg HornResp Tube BP6 schematic.jpg (35.8 KB, 368 views)
File Type: jpg HornResp Tube BP6 input.jpg (58.4 KB, 351 views)
File Type: jpg HornResp Tube BP6 power.jpg (43.5 KB, 342 views)
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Old 26th October 2017, 10:41 PM   #2
DonVK is offline DonVK  Canada
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Default Filling - will it lower the -3db point

First question.

I have a -3db point around 28Hz but would like 25Hz. Can anyone comment on the effect of adding fiberglass fill (or other fill) to chamber #1 to make this chamber "appear" larger so I can get a lower -3db point ???
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Old 26th October 2017, 11:55 PM   #3
Brian Steele is online now Brian Steele  Grenada
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Quote:
Originally Posted by DonVK View Post
First question.

I have a -3db point around 28Hz but would like 25Hz. Can anyone comment on the effect of adding fiberglass fill (or other fill) to chamber #1 to make this chamber "appear" larger so I can get a lower -3db point ???
That's a very interesting project you're planning there!

Fiberglass fill in a vented cabinet will reduce the resonance frequency and the "Q" of the vent output. Lining is ok, but stuffing might likely result in a reduction in output. I suggest just trying to detune it a bit by increasing the length of the vent connecting the two sections. For in room response, you might actually get better results with a passband response that gently slopes down to -3dB @ 30 Hz, rather than as flat as possible down to the lowest resonance frequency.

With your particular design, as the connecting vent is actually external, you could plan the build to allow you to swap in different lengths to get the best results.

From the diagram, it looks like you're planning to have three vents from one cabinet. This can make fine tuning a pain in the butt. I suggest using one large vent instead, like the 6" precision port available from Parts Express, and face it downward. That will leave only one vent to trim, and you can fin-tune the response by varying the distance from the end of the vent to the floor (i.e. raising the cabinet).

I'm looking forward to seeing pictures of the build!
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Old 27th October 2017, 04:05 AM   #4
DonVK is offline DonVK  Canada
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Brian, thanks for the advice on the fill.

All the tuning ports will be accessible to allow tuning if required. It would be easy to lengthen the external pipe P1, after the build, and slope more gradually into the 20's at the expense of some flatness and droop in the 30's.

If the bottom vents P2 are made from the same 10cm sewer pipe (78cm2). I would need multiple pipes around the bottom perimeter (maybe 5 pipes). I might rethink this. I could use a single larger pipe as you suggest. I could also do this by making the bottom port from a space between 2 discs and tune via disc spacing.
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Old 29th October 2017, 02:22 AM   #5
DonVK is offline DonVK  Canada
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Default Max power and displacement

Does anyone use mechanical stops to prevent exceeding Xmax?

I've provided a few more graphs that indicate the max pressure I can get is about 108db at 20rms (=20rms^2 /4=100W) at the Xmax of 9mm. I think this is at the standard 1m, but I'm not entirely sure what HornResp uses.

I'll be using a Dayton DCS305-4 (12"), Sure aa-ab31282 (200W class D) and a Qualtek QPDF-320-36 (36VDC supply, 320W). Parts should arrive over the next week.

In reality this amp can deliver ((36vdc-1vdc)pk * 0.703rms)^2 / 4 = 153W to a 4 Ohm load. The power supply has spare capacity for my future bi amp'd speakers est (2*75W + 2*30W + 100W = 310W). The amp also seems to have a high pass somewhere <20Hz, but they're not clear on it. I need to attenuate f<20Hz anyways as the x-displacement would be too large and not audible.
Attached Images
File Type: jpg HornResp MaxPower.jpg (42.0 KB, 276 views)
File Type: jpg HornResp Impedance.jpg (41.5 KB, 45 views)
File Type: jpg HornResp Displacement.jpg (39.8 KB, 35 views)

Last edited by DonVK; 29th October 2017 at 02:24 AM. Reason: wrong graph
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Old 29th October 2017, 05:15 AM   #6
Brian Steele is online now Brian Steele  Grenada
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Something's weird here. That impedance response suggests only one resonance frequency in the 20's. However, given a Vb of 12 litres and a port with area of 506 cm^2 will be extremely high resonance frequenccy, over 150 Hz. If that's the case, it may be better to not have a front volume at all. And given a rear volume of 62 litres with a vent of 4" diameter that's 43.5" long will result in a resonance frequency of 18 Hz or below.

I suggest validating the sim in another program that can simulate series-tuned bandpass enclosures before committing to a build.
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Old 29th October 2017, 12:40 PM   #7
David McBean is offline David McBean  Australia
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Originally Posted by Brian Steele View Post
I suggest validating the sim in another program that can simulate series-tuned bandpass enclosures before committing to a build.
Or perhaps use a more recent version of Hornresp, noting that relatively small changes to chamber and port tube dimensions can significantly alter the positions of the resonance frequencies.
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Old 29th October 2017, 12:47 PM   #8
scottjoplin is offline scottjoplin  Wales
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Originally Posted by DonVK View Post
Does anyone use mechanical stops to prevent exceeding Xmax?
How? I would expect any stop to do more harm than good
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Old 29th October 2017, 01:34 PM   #9
DonVK is offline DonVK  Canada
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How? I would expect any stop to do more harm than good
There would be a limit stop disc mounted in front of the woofer, with a small overlap with the rubber suspension ring. It would prevent the cone from extending too far and damaging the voice coil. The limit disc could even have a soft foam surface to cushion the impact and (hopefully) not crush the cone edge on impact.
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Old 29th October 2017, 01:44 PM   #10
scottjoplin is offline scottjoplin  Wales
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The voice coil would still want to travel and I worry this could put strain on the voice coil former to cone bond as well
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