Pioneer BOFU build (sonotube) - diyAudio
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Old 6th January 2010, 04:13 AM   #1
Uhills is offline Uhills  United States
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Default Pioneer BOFU build (sonotube)

Hello All, I've been lurking around here for weeks and finally decided to try and build something. I became fascinated with single drivers and after lots of reading I decided to try a Pioneer b20 with rear facing tweeter. Essentially, a modified version of Godzilla's b20 + Piezo.

To make things hard on myself, I figured I'd try something different. I find the recent line of KEFs appealing because of the curvature of the back cabinets. I , have seen some pretty labor intensive designs that involved many layers of plywood sandwiched together. For some reason (I'm impatient), I couldn't bring myself to devote that much time to cutting wood. I instead decided to split a couple lengths of sonotube in half (lengthwise). I would use these half cylinders to add the desired curvature to the back of my cabinets. I've read pleanty about people using sonotube for subs and projects like the Indignias or some of the DIY projects over at Parts Express. I haven't seen any sonutube used in the way that I had planned. So I gathered up some spare MDF and some Pine for the baffle and started assembly.
For the rear facing tweets, I'm using some Infinity Polycells that I pulled out of some Infinity sm102 (from the early 90's). I picked these up on CL for a project like this. The old infinity's with the 1" tweet and 10" woofer sounded remarkably bad. The tweeters desserved a better fate than adorning some old fartboxes.
I have everything assembled and am still breaking in the Pioneers but I have a few thoughts about the sound. ( I don't have any measuring equipment........yet) The Single driver does a fine job of creating a decent soundstage and does a nice job of imaging. The rear facing tweet has a 20ohm Resistor across its leads and a .68uF cap on the Pos. side. I may try a smaller resistor to see if the sound becomes to bright for my tastes... but for now the little bit of sparkle and air is quite nice. The Pioneers are very listenable but do suffer a bit from that 'cupped' or compressed sound. I don't know how much of this is attirbuted to my shoddy woodworking skills but I'm pretty impressed, all things considered.
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Old 6th January 2010, 07:08 AM   #2
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Keep us posted... i've had ideas about doing something like this.

dave
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Old 6th January 2010, 10:11 AM   #3
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That enclosure is going to flex quite a bit (compared with a rectangular box). It needs braces from side to side where the sonotube meets the flat parts of the sides.
You appear to have sandwiched the two halves of the sonotube together. If it's going to be permanent (rather than a proof of concept), you might want to consider putting a different density layer between them - a thin sheet of foam or bituminous felt, or a thin sheet of lead.
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Old 6th January 2010, 12:46 PM   #4
Uhills is offline Uhills  United States
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Bracing and flexing were definitely on my mind. So far, a 3/4" dowel is going to be used to connect the sides and provide some stiffness.

I haven't decided yet If I should rebuild these or start sanding and painting. I have to say that I working with the tube was fairly easy and the appearance looks better to me than a box.
Thoughts?
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Old 6th January 2010, 03:13 PM   #5
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Great idea! Got to love Sonotube! There used to be a DIY company in late 70's- early 80's that built and sold parts for speakers using nested sonotubes with poly foam filling space in between. Never heard, but always kept idea in back of head. I did build the baby El-Pipe-o's from Nelson Pass design.
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Old 6th January 2010, 07:08 PM   #6
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This may help.

http://www.zillaaudio.com/b20-mod.htm

Btw, that dome tweeter does not require a resistor like the piezo does. The cap alone can be used and you can play with it's value to alter its sound. You can make what you have there sound better. Once the tweeter is matched correctly the cupped/veiled sound is minimized. Removing the dust cap also helps imo... but that character is always there, just minimized. After a while you don't hear it until you compare to something better. I have been enjoying my B20s this way for MANY years and just recently popped them into an open baffle - using a different tweeter - and it sounds excellent. They are one of the least fatiguing drivers i've heard even with their shortcomings.

Godzilla

Last edited by Godzilla; 6th January 2010 at 07:08 PM. Reason: bad url
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Old 6th January 2010, 07:18 PM   #7
Uhills is offline Uhills  United States
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Thanks godzilla!
The tweeter is one of the 'high output' polycells that is supposed to be very efficient. I think I'm going to play with resistor and cap values tonight. I like the 'air' that the tweeter provides. I was going to mount it on the front but after reading everything on your site, I had a change of heart. I'm glad I followed your lead as it seems to preserve the best attributes of a fr driver while providing the needed top end.
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Old 7th January 2010, 04:26 AM   #8
JoMoCo is offline JoMoCo  United States
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Default Plywood Half Cylinders & more.....

Just found these recently for a wood source instead of sonotube....

Aitwood Anderson International - StoreFront)
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Old 11th January 2010, 07:01 PM   #9
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Phase plugs from Planet10-HiFi should eliminate the constrained sound and open them up a bit. A good and worthwhile $50 addition. I arrived at 1.33 uF for a cap value, different tweeter though.
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Old 11th January 2010, 07:14 PM   #10
badman is offline badman  United States
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Nice work! Phase plugs do indeed make a big diff with this driver. I'm doing a build (not for B20s) with some of the aitwood wood semicylendars,

Aitwood Anderson International - StoreFront

And they're very very cool.
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