I finished my other speaker but have been having too much fun listening to music to finish write-up ... these speakers are seriously fun!
Bit of background. I have been listening to Magneplanars (plus diy 5ft ribbons) at home since 1995 and am acutely aware of box resonance whenever I listen to conventional speakers. I have heard many speakers with more slam and deeper bass but have never heard anything else with the transparency, detail and coherence from top to bottom of the Maggies. So on balance I have stayed with them for their particular strengths.
Then earlier this year my audio buddy chris bought a quad of Eminence Beta15s and built some H frames. The bass response without any eq is flat down to 30Hz! And of course their is no box resonance. So I am a slow learner and it has only just dawned on me that cone speaker doesn't have to be housed in a box - there is such a thing as an open baffle cone speaker. Who would have guessed?
So I didn't want to just copy what Chris had done - I am recently retired and have time to some research.. Lots of reading of many posts here, as well as Linkwit audio pages and Troels Gravesen OB designs. My current system consists of Magneplanar Tympani panels (2 per channel) crossing over to my hand mand ribbons at 500Hz (1st order, passive line level, bi-amped). I believe that some of the transparency of my system is due to having a simple 2 way set up with minimalist 6dB crossover and I was keen to follow a similar path. So driver selection is a key issue for me.
I soon found out that Eminence drivers are favoured among OB builders because as I have seen for myself, they can go low without eq. But more research tells me that this is due to hi Q of these drivers, they peak up at Fs due to weak magnets which offsets baffle roll-off. I don't want bass drivers with weak magnets and since I understand enough about electronics to design any eq I want, I quickly ditched any thoughts of Eminence drivers. Some reading of Troels Gravesen OB15 project lead me to the Faital Pro 15PR400. I also read some favourable comments regarding this driver somewhere on DiyAudio. I looked at the spec sheet, it's response looks nice and flat up to nearly 4k, and it doesn't have that horrible peak at 2k that all the Eminence drivers suffer from. And the FaitalPro can be bought for a good price in Australia, so they are in!
And a bit more reseach got me to Pure Audio Project. Obviously I am not going to buy one of their speakers, but I like the layout so I have gone for WMW layout. Four 15" woofers should give me just enough slam.
Bit of background. I have been listening to Magneplanars (plus diy 5ft ribbons) at home since 1995 and am acutely aware of box resonance whenever I listen to conventional speakers. I have heard many speakers with more slam and deeper bass but have never heard anything else with the transparency, detail and coherence from top to bottom of the Maggies. So on balance I have stayed with them for their particular strengths.
Then earlier this year my audio buddy chris bought a quad of Eminence Beta15s and built some H frames. The bass response without any eq is flat down to 30Hz! And of course their is no box resonance. So I am a slow learner and it has only just dawned on me that cone speaker doesn't have to be housed in a box - there is such a thing as an open baffle cone speaker. Who would have guessed?
So I didn't want to just copy what Chris had done - I am recently retired and have time to some research.. Lots of reading of many posts here, as well as Linkwit audio pages and Troels Gravesen OB designs. My current system consists of Magneplanar Tympani panels (2 per channel) crossing over to my hand mand ribbons at 500Hz (1st order, passive line level, bi-amped). I believe that some of the transparency of my system is due to having a simple 2 way set up with minimalist 6dB crossover and I was keen to follow a similar path. So driver selection is a key issue for me.
I soon found out that Eminence drivers are favoured among OB builders because as I have seen for myself, they can go low without eq. But more research tells me that this is due to hi Q of these drivers, they peak up at Fs due to weak magnets which offsets baffle roll-off. I don't want bass drivers with weak magnets and since I understand enough about electronics to design any eq I want, I quickly ditched any thoughts of Eminence drivers. Some reading of Troels Gravesen OB15 project lead me to the Faital Pro 15PR400. I also read some favourable comments regarding this driver somewhere on DiyAudio. I looked at the spec sheet, it's response looks nice and flat up to nearly 4k, and it doesn't have that horrible peak at 2k that all the Eminence drivers suffer from. And the FaitalPro can be bought for a good price in Australia, so they are in!
And a bit more reseach got me to Pure Audio Project. Obviously I am not going to buy one of their speakers, but I like the layout so I have gone for WMW layout. Four 15" woofers should give me just enough slam.
So next the hunt is on for a wide range driver that can cover from 500Hz to 20k, something that my ribbons do easily. I started a thread here at DiyA and got some great suggestions. But ultimately I found the solution right here in Melbourne. Forum member Hollowboy pointed me to Total Recoil in Thornbury which is only 10km from home. Boyd, the owner, does a lot of speaker repairs but he also assembles his own 8" wide range drivers. These have fibreglass cone, a whizzer and a phase plug. Boyd also glues a ring of felt on the main cone directly beneath the whizzer - I saw a pair of speakers in the shop which had some wool between the whizzer and the cone, but Boyd says that he now prefers the felt ring. There is another felt ring on the rear side of the cone just inside the surround.
Boyd also recommends a small AMT driver (4 ohm) to fill in the top end. He recommends a series cap of 2.2uF which should give a cross over of 18k if I can calculate. Now I am 55 and probably can't hear above 12k, but Boyd designs these speakers and I can only assume that that he knows more than me so the AMT is in. You can see it nestled between the wide range and the top woofer. Hollowboy calls it a wee hole, that's because its a wee driver, it not for weeing. Oh and I also see that the AMT looks suspiciously like one sold be Parts Express (Dayton AMT mini).
Boyd advise that Fs is around 70Hz, and sensitivity around 93dB. Now that sounds like a good figure, because I know that I will need at least 9dB of eq on the Faital Pro, if one FP gives 99dB then 2 give 102dB, take off 9dB and we get to 93dB. A match made in heaven.
Boyd also recommends a small AMT driver (4 ohm) to fill in the top end. He recommends a series cap of 2.2uF which should give a cross over of 18k if I can calculate. Now I am 55 and probably can't hear above 12k, but Boyd designs these speakers and I can only assume that that he knows more than me so the AMT is in. You can see it nestled between the wide range and the top woofer. Hollowboy calls it a wee hole, that's because its a wee driver, it not for weeing. Oh and I also see that the AMT looks suspiciously like one sold be Parts Express (Dayton AMT mini).
Boyd advise that Fs is around 70Hz, and sensitivity around 93dB. Now that sounds like a good figure, because I know that I will need at least 9dB of eq on the Faital Pro, if one FP gives 99dB then 2 give 102dB, take off 9dB and we get to 93dB. A match made in heaven.
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Now for eq. Boyd recommends that I crossover at 250Hz. I have already got crossovers built into my power amps, 1st order 500Hz. So this is what I am using right now. I have bought a few caps on eBay to adjust the crossover down to 250Hz, this is something to do next time it rains. For bass eq, I have built a simple passive shelf filter, lower F3 at 60H then dropping 9dB at 6dB per octave. As anticipated, the level of the woofers after eq is spot on with the wide range. There is no need to adjust the level of either drivers, good luck or good management but it has come out just right.
The baffle is built from cheap 30mm pine ply from Bunnings. Although the driver layout was copped from Pure Audio Project, the construction was inspired by Troels Graveson OB15. 3 layers of polyurethane and the speakers have passed the all important WAF test. They match nicely with our bamboo floating floorboards, and SWMBO has said nice things about the look of these - in 25 years of marriage this is the first time that she has complimented the look of anything I have built so I am pretty pleased about that.
So finally how does it sound? Well they are only cones and don't have the transparency or clarity of my older system. In particular, my 5ft ribbon is one of the best hf transducers I have heard (in my own very HO) and no cone or dome driver comes close. But this new system has about 10dB better sensitivity, it goes LOUD and its FUN. The bass is flat down to 60Hz but I don't feel that I am missing anything. I might adjust the eq down a bit but its not a high priority. I normally listen to classic rock and my wife usually complains about the volume so this morning I played her Saint-Saens Organ Symphony. It sounded like we were in the auditorium with the Boston Symphony. Not only does she like the look of these speakers, she really enjoys the sound they make. So now I have a pair of speakers that my wife likes. They should be keepers - but now that I have time on my hands, I have another 5 projects I am dreaming about
The baffle is built from cheap 30mm pine ply from Bunnings. Although the driver layout was copped from Pure Audio Project, the construction was inspired by Troels Graveson OB15. 3 layers of polyurethane and the speakers have passed the all important WAF test. They match nicely with our bamboo floating floorboards, and SWMBO has said nice things about the look of these - in 25 years of marriage this is the first time that she has complimented the look of anything I have built so I am pretty pleased about that.
So finally how does it sound? Well they are only cones and don't have the transparency or clarity of my older system. In particular, my 5ft ribbon is one of the best hf transducers I have heard (in my own very HO) and no cone or dome driver comes close. But this new system has about 10dB better sensitivity, it goes LOUD and its FUN. The bass is flat down to 60Hz but I don't feel that I am missing anything. I might adjust the eq down a bit but its not a high priority. I normally listen to classic rock and my wife usually complains about the volume so this morning I played her Saint-Saens Organ Symphony. It sounded like we were in the auditorium with the Boston Symphony. Not only does she like the look of these speakers, she really enjoys the sound they make. So now I have a pair of speakers that my wife likes. They should be keepers - but now that I have time on my hands, I have another 5 projects I am dreaming about
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Hello, thanks for sharing your project, that wideband driver looks very interesting, I like the arrangement on the baffle a la Pure Audio, and they do look good have you tried moving them further away from the wall for critical listening? I found my OB speakers sound best about five feet away
have you tried moving them further away from the wall for critical listening? I found my OB speakers sound best about five feet awayThanks for sharing your OB Project, I bet they sound fantastic! I pretty much followed your same path – at an audio show last fall I heard the Pure Audio Project system and was blown away with the clarity and purity, and its simplicity.
My research lead me to the OBL-15 too and choosing the FP 15PR400 for the bottom end, though I’m only using one per side (couldn’t imagine needing a second-must be impressive!). I chose the MarkAudio 12P for my mids (full range) and so far don’t hear a need for a tweeter, time will tell once “broken in” and design finalized.
“At my age”…(I got frustrated with the free on-line design programs) I didn’t do a lot of design simulation or pouring over spec’s and numbers, but more of a “seat of the pants” design approach. Inexpensive plywood and experimenting with what “sounds good” is my design tool.
My system will be bi-amped so one “high-tech” gadget I sprung for was the MiniDSP as an active crossover. An awesome tool and very easy to setup and use, allows me to play with different crossover points and EQ.
Did you do any dampening or treatment to the back side of your baffle? I’ve heard some builders do that but haven’t tried any myself.
Thanks again for sharing and enjoy your speakers… Dave
My research lead me to the OBL-15 too and choosing the FP 15PR400 for the bottom end, though I’m only using one per side (couldn’t imagine needing a second-must be impressive!). I chose the MarkAudio 12P for my mids (full range) and so far don’t hear a need for a tweeter, time will tell once “broken in” and design finalized.
“At my age”…(I got frustrated with the free on-line design programs) I didn’t do a lot of design simulation or pouring over spec’s and numbers, but more of a “seat of the pants” design approach. Inexpensive plywood and experimenting with what “sounds good” is my design tool.
My system will be bi-amped so one “high-tech” gadget I sprung for was the MiniDSP as an active crossover. An awesome tool and very easy to setup and use, allows me to play with different crossover points and EQ.
Did you do any dampening or treatment to the back side of your baffle? I’ve heard some builders do that but haven’t tried any myself.
Thanks again for sharing and enjoy your speakers… Dave
Thanks for dropping in Scott. I just checked distance from back wall, its only 4 feet (I would have guessed a bit more). I will try moving them around, but first priority is to change XO down to 250Hz. By the way, what is max XO freq to qualify for WAW status?Hello, thanks for sharing your project, that wideband driver looks very interesting, I like the arrangement on the baffle a la Pure Audio, and they do look good
Here is a picture from the back. You can just see my Class A mosfet amps in the bottom of the picture. The toroids you can see are not power trannies they are used as output chokes. The amps are balanced and I am able to use the secondary of a 240/25V toroid as a choke (dual secondary coils are joined in series and 'centre tap' is grounded). I am much more an electronics guy, I studied EE at uni and am pretty comfortable with analog circuits. But by some strange coincidence, one of my lecturers and thesis supervisor in final year at uni was a guest American fellow by the name of Dick Small. I didn't know any better back then, but later on I found out that he knows a thing or 2 about speakers. But since my thesis was on feed-forward error correction I did not ever bother to ask him about speakers .....
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Hi, 4 feet is a good distance, they looked closer than that in your picture that's why I mentioned it, still it could be worth experimenting. I'm not in the business of defining Xover frequency that defines WAW , it depends on the drivers, baffle, EQ, room set up etc., Usually the lower the better. Ideally each pair of speaker wires should be twisted together, close coupling and all that. I don't understand the need for the chokes?
, it depends on the drivers, baffle, EQ, room set up etc., Usually the lower the better. Ideally each pair of speaker wires should be twisted together, close coupling and all that. I don't understand the need for the chokes?Hi , Speakers were wired up with odd bits of wire that I had floating around. For twisted pair, would solid core Cat6 cable work OK? I have a few LAN cables I can cut up for free speaker cable.Hi, 4 feet is a good distance, they looked closer than that in your picture that's why I mentioned it, still it could be worth experimenting. I'm not in the business of defining Xover frequency that defines WAW
Toroids (chokes) in the picture are part of power amp - here is a schematic and explanation of operation.
http://www.diyaudio.com/forums/solid-state/212424-balanced-class-fet-amplifier.html#post3018407
Hi Dave, have you posted any pictures of your system on the forum? Mark Audio drivers were on my short list before I found the Boyd drivers, I bet they sound fine.
With regards to damping of panels - I have given a little thought to this but I have a few other projects I need to attend to first. On thing I might try is building a sand box in the bottom of the cabinet. The base of the cab is 600mm by 600mm, and loses about 75mm on the front and similar on sides due to wings. I could pour about 1 or 2 inches of sand in there, and would need to find a way to keep it from blowing around but that should help with vibration (not that I can feel a lot of vibration in the front baffle). In an ideal world with unlimited time and funds and better woodworking skills I would build another cabinet with sand filled baffles but that is probably not gonna happen.
Regards
Probably easier to keep the sand in containers (coffee sacks / pillow cases / stuffed owls / whatever) rather than have it loose. Especially if you'll ever cat sit for a friend.
A 20kg sack of rice will work just as well as a 20kg layer of sand, and will be a lot more handy during the next zombie outbreak.
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