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SonoTube and SewerPipe BP6 Subwoofer
SonoTube and SewerPipe BP6 Subwoofer
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Old 29th October 2017, 01:53 PM   #11
DonVK is online now DonVK  Canada
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Quote:
Originally Posted by David McBean View Post
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.
Fair enough. I loaded the most recent 42.40.

There is a difference at around 200Hz as the peak increased, so I lowered my LP filter from 160Hz to 150Hz, reduced chamber #2 from 10L to 7L, and decreased the port2 area from 500cm2 to 360cm2 to compensate. New graphs and design file posted.

Quote:
Originally Posted by Brian Steele View Post
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.
I have reduced the chamber2 volume and port size for both design reasons and the updated HornResp. I can now use 2 * 6" pipes for the front exit. The simulation indicated some front volume is required.
Attached Images
File Type: jpg HornResp Power 2017-10-29.jpg (45.1 KB, 150 views)
File Type: jpg HornResp Impedance 2017-10-29.jpg (44.7 KB, 145 views)
Attached Files
File Type: txt sono_bp6_v1.txt (958 Bytes, 3 views)
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Old 29th October 2017, 02:21 PM   #12
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Quote:
Originally Posted by scottjoplin View Post
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
I agree, the voice coil would still want to move, so there would be force applied to both the suspension edge and voice coil bond. I was thinking a soft stop edge would decelerate it enough to avoid a hard impact or shock. I'm not expecting music below 20Hz, it was more of an observation the Xmax was exceeded for VLF.

The alternative is also unpleasant, as the voice coil movement is stopped by its connecting wires, or is damaged from exiting its magnet chamber.

I will test this. I know the amp rolls off at <20Hz, and when I use REW RTA I see very little power in the <20Hz region. Older amps used to have a filter switch to prevent turntable rumble from trashing your woofers from Xmax. My Yamaha AX900 calls it a "subsonic filter" and its great.

Last edited by DonVK; 29th October 2017 at 02:28 PM. Reason: filter
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Old 29th October 2017, 10:22 PM   #13
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Default ABEC model internal pressures

I thought it would be interesting to model this in ABEC. I had to initially guess at a few parameters so I'm not done yet. Its interesting to see how the internal pressures change with frequency. Use the pressure legend because ABEC autosolarizes each graph seperately, so not all colours are equivalent in each pic.

I've removed skin in all but the first pic. More plots coming as I fill in more model data and add the filters. Overall it looks like its working as a BP6. I should add that the woofer is driven with 1rms, so 1^2/4=0.25w (future pics will be the std 1w)and the distance to the right edge is 1m.
Attached Images
File Type: jpg SonoSub avg.jpg (46.0 KB, 143 views)
File Type: jpg SonoSub @25Hz.jpg (50.4 KB, 146 views)
File Type: jpg SonoSub @40Hz.jpg (49.4 KB, 142 views)
File Type: jpg SonoSub @70Hz.jpg (49.8 KB, 17 views)
File Type: jpg SonoSub @124Hz.jpg (50.1 KB, 23 views)
File Type: jpg SonoSub @200Hz.jpg (50.1 KB, 32 views)

Last edited by DonVK; 29th October 2017 at 10:28 PM. Reason: power
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Old 31st October 2017, 05:59 AM   #14
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Default ABEC sim

I've updated more ABEC parameters, but its not entirely accurate yet. I'm not sure what the wall impedance of a pvc pipe or a sonotube would be. I also don't know where the 2nd impedance peak went (compared to HornResp). In fairness, I'm not an expert in either tool.

If I use pic#2 below and 80db as my end points I get 27Hz-150Hz. It could go higher, but I have a BW4@150Hz rolling off the high end. I've also increased the port#2 length to 50cm to get a flatter response. Although there is still a small bump at 45Hz that I can't explain.

It'll be interesting to compare to the actual. Parts are arriving.
Attached Images
File Type: jpg SonoSewerSub pressure.jpg (46.7 KB, 27 views)
File Type: jpg Bode SonoSewerSub .jpg (15.5 KB, 30 views)
File Type: jpg Impedance SonoSewerSub.jpg (17.3 KB, 26 views)
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Old 1st November 2017, 11:51 PM   #15
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Default Build pics

A few pics of the build in progress. It should be assembled tomorrow, and I'll start test and measurement.

The woofer throat plate will allow 8mm movement before the rubber surround touches it (Xmax is 9mm).
Attached Images
File Type: jpg DSCN2303 reduced.jpg (622.7 KB, 27 views)
File Type: jpg DSCN2302 reduced.jpg (654.7 KB, 26 views)
File Type: jpg DSCN2305 reduced.jpg (577.0 KB, 31 views)
File Type: jpg DSCN2307 reduced.jpg (481.9 KB, 42 views)
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Old 2nd November 2017, 09:58 PM   #16
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Default More build pics

This is the last of them. They will remain unfinished until better weather arrives.
Attached Images
File Type: jpg DSCN2309 reduced.jpg (573.3 KB, 40 views)
File Type: jpg DSCN2312 reduced.jpg (533.0 KB, 30 views)
File Type: jpg DSCN2317 reduced.jpg (624.5 KB, 38 views)
File Type: jpg DSCN2316 reduced.jpg (455.7 KB, 61 views)
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Old 2nd November 2017, 10:15 PM   #17
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Default Initial measurements

These are from a dry fit to get a first impression. There could also be minor air leaks until I chalk the seams. So far it looks good.

My class D amp board has not arrived yet, so these measurements used an additional 4ohm series resistor to raise the driver impedance for my HT amp. The 4Ohm was subtracted from the measurement in the graph.

There are peaks at 15Hz, 40Hz, and 200Hz as predicted by HornResp.
Attached Images
File Type: jpg sono nearfield1 at port.jpg (71.8 KB, 58 views)
File Type: jpg SonoSewerSub Impedance.jpg (85.6 KB, 34 views)

Last edited by DonVK; 2nd November 2017 at 10:18 PM. Reason: corr meas
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Old 4th November 2017, 06:33 PM   #18
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Default Updated - after sealing ports + fittings

Its bolted together and sealed now. Their was some minor change and its a bit flatter.

The bump @45Hz predicted by ABEC is definitely there. I have EQ'd it out (but not posted here) to see if I could hear it, but its too early for a conclusion. I would need my amp board (still waiting) and music and listening time. So far, by using sweeps and the REW generator I'm happy with it.

The graphs below show a -3dB point (from 125dB nearfield) of 28.5Hz which is close to the predicted and sufficient for me. The impedance peaks are in the right area (13Hz, 38Hz, 202Hz) but the two lowest peaks are not equal in height suggesting a possible tuning issue. I'll see if I can replicate this condition in HornResp or ABEC before fiddling with the physical.
Attached Images
File Type: jpg Sono FR nearfield.jpg (72.8 KB, 35 views)
File Type: jpg Sono Impedance.jpg (69.9 KB, 30 views)
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Old 5th November 2017, 07:23 PM   #19
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Default Effect of adding fiberglass fill

I tried adding various thickness of pink fiberglass insulation in the top (60L) V1 chamber. Mostly out of curiosity, to see if it would smooth things out or extend the FR. The fill starts at 45cm from woofer mount plane (approx midway).

Graph provided below. It does have some effect on smoothing the FR, especially at the higher end (>200Hz) which I'm not interested in. It also causes the low end to sag before 30Hz, which I'm also not interested in. This effect is like increasing the volume in HornResp. To counteract it, I would need to make the port P1 length shorter or diameter larger and it would actually extend a flat low freq roll off. Either of these changes require too much material change for a minimal benefit.
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File Type: jpg SonoSub effect of filling.jpg (87.1 KB, 33 views)
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Old 6th November 2017, 03:45 AM   #20
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have you read Nelson's El Pipo article?
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