El Pipe-O subwoofers
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 26th October 2008, 07:48 PM #1 Banned   Join Date: Sep 2008 el pipe subwoofers I have a question regarding the pipe subwoofers which Mr pass has written an article about here. www.passdiy.com/pdf/el-pipe-o.pdf Since I had an 8 inch car woofer lying about i thought about trying to find a pipe. Now my questions are what length should the pipe be? i dont know what kind of woofer it is I have so do measurements matter MUCH or is it just a case of find ing a long pipe to fit on top and then filling it with a blanket? And how low would it go? And how do you go about fixing the pipe to the woofer? thanks..
 26th October 2008, 07:53 PM #2 frugal-phile(tm) diyAudio Moderator     Join Date: Oct 2001 Location: Victoria, BC, NA, Sol III Blog Entries: 5 For a straight pipe, the length should be a 1/4 wavelength of the Fs of the driver (or a bit shorter) and the CSA is determined by the Vas & Qts (essentially -- you'll need some other numbers to do the math or look it up in the MJK tables) dave __________________ community sites t-linespeakers.org, frugal-horn.com, frugal-phile.com ........ commercial site planet10-HiFi p10-hifi forum here at diyA
 26th October 2008, 11:42 PM #3 Banned   Join Date: Sep 2008 But I don't see how I can achieve 20hz given that the ceiling height in my room is 8 feet which means a tube length of say upto 7 feet, which equates to a resonance at 1100/28 which is approximately 40hz. So is there any way around this without using a 14 foot long tube?
 27th October 2008, 12:14 AM #4 frugal-phile(tm) diyAudio Moderator     Join Date: Oct 2001 Location: Victoria, BC, NA, Sol III Blog Entries: 5 You either have to fold it or heavily taper it. dave __________________ community sites t-linespeakers.org, frugal-horn.com, frugal-phile.com ........ commercial site planet10-HiFi p10-hifi forum here at diyA
 27th October 2008, 12:45 AM #5 Banned   Join Date: Sep 2008 what effect does using a bigger drive unit have?
 27th October 2008, 01:28 PM #6 diyAudio Member     Join Date: Aug 2002 Location: Gaithersburg, MD I think fixing the pipe to the woofer is covered in the article. What I don't recall from the article (or subsequent discussion here on this very forum) was whether anyone had tried laying the pipe on its side. __________________ Would a woodchuck bother to chuck MDF?
 27th October 2008, 02:23 PM #7 diyAudio Member   Join Date: Jan 2006 Location: Cleveland, OH I have built the el-pipo to approximately 13 foot length and have it lying on it's side. I built it using sono-tube and a 12" car subwoofer I had laying around. I am powering it from an old plate subwoofer amp I had laying around. It really sounds good!
 27th October 2008, 04:44 PM #8 Banned   Join Date: Sep 2008 how low does it go in your room?
 27th October 2008, 06:48 PM #9 diyAudio Member   Join Date: Jan 2006 Location: Cleveland, OH I get usable output to 18Hz. I think the resonant frequency for my tube is about 25-27hz. I have the amplifier low-passed at 35 hz. It really adds a nice presence to music, and when desired can really pump out some clean loud low bass.
diyAudio Member

Join Date: Oct 2004
Location: Ottawa, Ontario, Canada
Mini El-pipo

Hi Guys,

I've been looking for a place to post this project, so I figured this thread would work.

I designed and built a miniature version of the El-pipo using a 6.5" Tangband W6-1139SL, which you can get on sale at Parts Express for \$29 right now. It's a long throw driver with a neodymium magnet and a huge rubber surround.

The pipe was designed using MJK's worksheets, and then measured using Speaker Workshop to verify that things were as expected.

MJK's worksheets gave me the following criteria based on the driver's parameters and a chosen tuning frequency of 40Hz.

Dz = 38.858
Dr = 0.095
Sl/So (taper) = 1
Cross-sectional area = 22.22" square
Length = 82.4"

Since the driver diameter was only about 6.75", I used a 6.5" section of Sonotube for the pipe. This yields a cross sectional area of 33.2" square, but it's easy to reduce the pipe's area later if need be.

The pipes are available in 8 ft lengths, so I purchased one and cut it down with an Exacto knife to the correct length of 82.5". The pipe fit perfectly in the recess of the back of the woofer's frame, so I used some industrial strength hot melt glue to attache the driver to the pipe and create an airtight seal. It's remarkably stong, and there aren't really any other options since the pipe is smaller than the outer diameter of the woofer, making a wooden fitting ring impossible.

The woofer is mounted with the cone facing out, and four small feet (capacitors) are attached to space the driver about 2" from the floor. I have attached a few pictures to show the details.

I drilled two small holes in the side of the pipe and fitted binding posts before gluing the driver in place. This allows for easy connection to an external amplifier.

So how does it work? I'd say remarkably well. I have attached a few measurement made outside in a large parking lot, and as you can see it's flat down to about 37Hz, and in room response should be even better than that. There is no stuffing in the pipe, which explains the peak at 40Hz and the peaks/valleys at and above 120Hz. Since I'm using a 4th order lowpass at 80Hz, the response ends up extending to about 125Hz and then dropping off. I later wired up a dual op-amp to add a bandstop filter between 140Hz and 250Hz, which eliminates the second peak and leaves the next closest peak down by about 40dB

Adding stuffing to the pipe would drastically reduce the peaks and valleys, and enough stuffing would almost completely eliminate them. I experimented with this, but found that adding stuffing drastically reduced the output, and didn't provide that much audible benefit once the low pass crossover was in place. It seems a little strange, but it works.

So how about the downsides? Well, there aren't really any except that most people probably don't like the look of a 7 ft tall pipe in the living room. I covered mine in a wood finish, which makes it look a little more acceptable, but certainly not invisible. I guess you could say it makes a good conversation piece.

Cheers,
Owen
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