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SonoTube and SewerPipe BP6 Subwoofer
SonoTube and SewerPipe BP6 Subwoofer
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Old 6th November 2017, 04:28 AM   #21
DonVK is offline DonVK  Canada
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Thanks, it's the first I've heard of it. I just looked up "El Pipe-O" and read the article. Great fun

I considered QWTL using concentric pipes to get the length in a shorter package. It always had too much ripple, so did BP8. It just looked like I could get what I needed with a BP6.

Last edited by DonVK; 6th November 2017 at 04:45 AM. Reason: typo
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Old 6th November 2017, 04:54 PM   #22
chris661 is offline chris661  United Kingdom
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Quote:
Originally Posted by DonVK View Post
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.
Get rid of that 4ohm resistor ASAP.

Try simulating in Hornresp what the added resistance will do. It ain't pretty.

Chris
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Old 6th November 2017, 05:08 PM   #23
DonVK is offline DonVK  Canada
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Yeah, I know its effecting the response. It was just a few test runs so I could check for leaks and try out the effects of fill.

I'll post again when my class D amp arrives. It's better suited for a load like this, and will not have any series resistor.
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Old 7th November 2017, 01:56 AM   #24
DonVK is offline DonVK  Canada
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Default Retested using a Class D amp

I finally got my amp and p/s and these are the near field results. Sure aa-ab31282 (200W class D) and a Qualtek QPDF-320-36 (36VDC supply, 320W).

I'm very happy with the response. I typically use a sub <=100Hz so its flat enough for me. I'm surprised at how low it goes, as I was expected a sharper drop.
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File Type: jpg SonoSub + Sure Amp.jpg (71.9 KB, 104 views)
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Old 7th November 2017, 02:59 AM   #25
DonVK is offline DonVK  Canada
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Default How low is required ?

That question is asked a lot. I put on a few tracks, with low freq content, and measured with REW RTA to see what's there.

The frequencies below 20Hz cannot be heard, but they can be felt. I have a mechanical stop (throat plate) than prevents woofer from extending more than 8mm. During some of those tracks, at moderate volumes, I can hear the woofer slapping the throat plate. I need to add a HP filter @20Hz to prevent these VLFs from trashing the woofer. This is also in line with the HornResp prediction of excessive Xmax for subsonics.
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Last edited by DonVK; 7th November 2017 at 03:09 AM. Reason: graph error
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Old 7th November 2017, 09:43 AM   #26
chris661 is offline chris661  United Kingdom
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Don,

I'm not convinced the stop plate is a good idea. The reason is this - most drivers have it built-in, to some extent or other.
What drivers are not designed for is having the cone physically hit something repeatedly. It'll fold the cone up if it hasn't already.

Chris
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Old 7th November 2017, 02:13 PM   #27
DonVK is offline DonVK  Canada
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The cone and surround are OK, I checked them. I only use low power when testing so the force is not too great. Even so, it's enough for me to hear it. I used a spacer block to measure the surround to throat plate gap via the front port. It's actually 10mm which is already more than Xmax (9mm). I suspect the rubber surround compresses like a bumper pad to decelerate the cone.

I'm not so sure that the woofer has some built in limiter. How would you determine that?

It's only very very few tracks than have this VLF. I'll be adding a HP before the amp to prevent them in future. I was just surprised the electronics allowed them to pass.

Last edited by DonVK; 7th November 2017 at 02:39 PM. Reason: actual gap
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Old 7th November 2017, 03:03 PM   #28
chris661 is offline chris661  United Kingdom
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Most drivers will mechanically limit before destroying themselves - they'll reach a point where the suspension will go no further, or they'll run out of motor force. That said, I did manage to fold the cone on a rather nice 15" by accidentally dumping >500w into it, way below port tuning.

Chris
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Old 7th November 2017, 03:16 PM   #29
DonVK is offline DonVK  Canada
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I'm doing a little reading on this subject now.

It appears that Xmax is purely related to the amount of voice coil overhang and the peak travel that results in "linear" performance (ie. low distortion). Its not necessarily a physical limit like I thought.

There is another parameter "Xmech" or "Xlimit" that is the physical limit, although at the cost of much higher distortion. I can't find it for the DCS305, nor can I locate a method of measuring it (non destructively). The driver spec claims "bumped back plate" feature but does not define it.

Last edited by DonVK; 7th November 2017 at 03:21 PM. Reason: wrong term
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Old 8th November 2017, 05:31 AM   #30
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Default ...after much reading on woofer excursion

It seems the issue of exceeding safe excursion limits is fairly common for subwoofers. Many of them implement a HP filter to attenuate the subsonics.

All of the resonant designs (BR, ABC, TH, BPx) seem to have this issue for subsonic frequencies. Even a sealed box can have this issue if the box is large enough. Very few non-pro drivers have specified the Xlimit or Xmech figures, but nearly all have the Xmax. There is no clear relationship between these figures. There are many who just turn up the volume, and when you hear significant distortion, you've gone a little too far past Xmax.

My BP6 design is reasonably well behaved and predictable displacement above 20Hz. Above 20Hz it should reach Xmax at approx 100w generating 108dB. Below 20Hz is a problem, and with just 8w @10Hz it will exceed Xmax. A 2nd order HP filter @20Hz will fix this.
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