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.
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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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. 🙂
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. 🙂
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?
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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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.
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
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
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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.
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.
Plywood Half Cylinders & more.....
Just found these recently for a wood source instead of sonotube....
Aitwood Anderson International - StoreFront)
Just found these recently for a wood source instead of sonotube....
Aitwood Anderson International - StoreFront)
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.
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.
Aitwood Anderson International - StoreFront
And they're very very cool.
Thanks jackfish,
I may try phase plugs down the road. For now, I'm working on bracing and sanding. To my ears, i found a 1 uF cap and a 4ohm resistor to be 'right'.
My 7yr old son took aim at a dustcap with his laser sighted Nerf gun. He did what 7yr olds do..... dented the dustcap. I was mad for about 5 seconds, then I realized I'd likely be putting these speakers 'under the knife'. I think I'll be attempting a mod suggested by Godzilla in the near future. I have learned that the WAF is still quite low so I need to get these puppies painted or design something smaller.
In general, I have to say that these speakers are proving to be quite enjoyable. Best at moderate volume but capable of delivering some dBs. the cabinets are lightly stuffed with some poly fill I scavenged from an old set of infinitys. I've currently got 'em connected to an Onkyo integra tx-88 but will soon try them on my NAD 3080 and Sansui 7000 for comparison. I'll be curious to see how the congestion/compression of the midrange changes (if any) with different gear.
I may try phase plugs down the road. For now, I'm working on bracing and sanding. To my ears, i found a 1 uF cap and a 4ohm resistor to be 'right'.
My 7yr old son took aim at a dustcap with his laser sighted Nerf gun. He did what 7yr olds do..... dented the dustcap. I was mad for about 5 seconds, then I realized I'd likely be putting these speakers 'under the knife'. I think I'll be attempting a mod suggested by Godzilla in the near future. I have learned that the WAF is still quite low so I need to get these puppies painted or design something smaller.
In general, I have to say that these speakers are proving to be quite enjoyable. Best at moderate volume but capable of delivering some dBs. the cabinets are lightly stuffed with some poly fill I scavenged from an old set of infinitys. I've currently got 'em connected to an Onkyo integra tx-88 but will soon try them on my NAD 3080 and Sansui 7000 for comparison. I'll be curious to see how the congestion/compression of the midrange changes (if any) with different gear.
Uhills,
Can you share the dimensions? How long (tall) and how deep you cut the wood for the sides.
Thanks,
Mike
Can you share the dimensions? How long (tall) and how deep you cut the wood for the sides.
Thanks,
Mike
mikje,
The cabinets are about 25.5" tall with the wooden sides being 6x24 inches. I routered the back edge with a bit of a roundover to give it some shape ( i think this visible in the pics). I use 1"x2" pine to attach the sonotube to it's 'stabilizer rails' and the rails provided a surface to attach the sonotube to the rest of the cabinet.
The front Baffle (just the pine) is about 8" wide and 24" tall. The sides and top caps were attached to the outside edges of the baffle (all .75" MDF). I attached a 'half moon' shaped piece of MDF to each of the end caps that provided a surface to screw in the ends of the sonotube (somewhat visible in pics).
This project is definitely more "proof of form" than "finished product". If I were doing this project again, I would change the construction a little.
I was shooting for approx. 1.3 ft^3 and I think I'm fairly close.
For a prototype, I'm pleased.
The cabinets are about 25.5" tall with the wooden sides being 6x24 inches. I routered the back edge with a bit of a roundover to give it some shape ( i think this visible in the pics). I use 1"x2" pine to attach the sonotube to it's 'stabilizer rails' and the rails provided a surface to attach the sonotube to the rest of the cabinet.
The front Baffle (just the pine) is about 8" wide and 24" tall. The sides and top caps were attached to the outside edges of the baffle (all .75" MDF). I attached a 'half moon' shaped piece of MDF to each of the end caps that provided a surface to screw in the ends of the sonotube (somewhat visible in pics).
This project is definitely more "proof of form" than "finished product". If I were doing this project again, I would change the construction a little.
I was shooting for approx. 1.3 ft^3 and I think I'm fairly close.
For a prototype, I'm pleased.
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