Olorin Posted April 28, 2004 Share Posted April 28, 2004 Hey, Rather than maybe hijack the other thread, I thought I'd just open a new one for this question. Those dipoles of yours look like a great bang/buck proposition -- the kind of thing someone with an extra amp, a circular saw, and a weekend can get a lot of joy out of. I wonder if you could share some of the resources you used in researching that thing, and maybe some of your thought process that led you to the drivers and design you have now. Thanks! Quote Link to comment Share on other sites More sharing options...
chops Posted April 28, 2004 Share Posted April 28, 2004 Well, it's a long story, but I'll try to shrink it down some. I am an active member of the www.DIYAudio.com forum elsewhere on the web. I was just roaming around the forum one day when I saw a topic pop up that looked interesting. It had something to do with crossover design and history. So I stopped in to take a peak. Part way through it was a link to Seigfried Linkwitz website.... (http://www.linkwitzlab.com/index.htm) I obviously went to his site to see what it was all about. Come to find out, he designs and builds alot more than just crossovers! I saw all these neat looking loudspeakers and started reading up on them. Then the thing that really caught my eye was something about dipole subwoofers. Since at the time I was using a pair of Magnepans which are dipoles, I figured that a matching pair of dipolar subwoofers would work perfectly. After doing much reading on Seigfried's site, (almost the whole thing!), I went back to the DIY forum to do a search on dipole subs 'n such. (hehe, get it?! ) A-hemm...... Anyway, I just wanted to see what people were doing, if anything with dipole designs. Most of what I found was geared more towards the "point-source fullrange single driver" designs. I think there were only a few small threads actually devoted to dipole subs, so I of coarse read them and asked questions. What I found out was that there are certain things to look for in the T/S parameters. Just to name a few is a low Fs, a high QTS, and a high Xmax. The first one is needed, then second one I feel is needed but alot of people do what they want (more on this one in a minute), and the third I have proven is not required. Also, almost all the people I spoke to said that a traditional (monoploe) sub is required to reach the lowest octaves because their dipole subs could only reach down to about 40Hz. This is another one that I have proven wrong! Alright, now for the goods..... The drivers: After doing some hunting on the web, I came across these Pyle Pro PPA15 15" drivers. They are cheap, (about $35-45 each), 2.5" voice coil, Fs of 26Hz, Qts of .67, Xmax of 6mm, SPL of 93dB @ 1 watt, and can handle 250 RMS and 800 watts peak. Why did I choose this driver? Well, first off the price! Secondly, the specs match up pretty close to what's needed for an infinante baffle. The Fs (free air resonant freq) is 26Hz. The lower this number is, the lower the driver can reproduce bass. The Qts (or Total Q) which is Qms (measurement of the mechanical suspension system) and Qes (measurement of the electrical suspension system) combined is .67. The higher this number is, the better the driver keeps control of itself at the Fs. The Xmax (Maximum Linear Excursion) is only 6mm. Beyond this and the voice coil begins to leave the magnetic gap, the suspension becomes non-linear, and you get potential woofer damage and/or failure. Now for the baffles. I decided to go with a much larger baffle and larger drivers than anyone else because unlike them, I don't have a wife running my life, telling me what I can and can't do, and I don't care how big and ugly they are as long as they sound good. A good rule of thumb is that the larger the baffle, the lower the bass the subs will be able to reproduce. Mine are 48"H x 24"W x 24"D. Yes they're huge, but so are all the Heritage Klipsch. Except the Herseys. This is where I proved everyone wrong the first time about not being able to reproduce bass below 40Hz. For one, they make their baffles too small, and two, they use drivers with a much lower Qts of .40 - .50. When they do this, the driver gets sloppy around its Fs. Also, because they're using smaller drivers (10" - 12"), those drivers require a larger Xmax (due to their smaller cone area) to move enough air to reproduce any true sub-bass. Plus, those drivers are inefficient and require alot of power. Because of these drivers everyone uses, they have to build complex passive crossover networks with equalization built into them to help take out a huge peak in output around the crossover freq. They also have to use some type of subsonic filter well above the Fs of the driver to keep it under control and not get damaged. Because of these reasons, that's why everyone ends up using a traditional monopole sub (sealed/ported) to take over from 40-50Hz on down. Me on the other hand, made my baffles nearly double what Seigfried recommended. Remember, the larger the baffle, the farther the bass waves have to travel before they cancel eachother out, hence the lower freq output I'm getting. Because my Qts is higher, the driver has very good control of itself, giving a smoother freq response which means I need very very little equalization at the crossover freq, and no subsonic filter at the bottom end. On top of that, my drivers are efficient, meaning they require less power and a smaller Xmax. (Ever notice how little your Heritage Klipsch 15" drivers move at high volumes?) Same this goes for my dipole subs! Let me know if I left anything out. And please, by all means, go out and buy yourself four of these 15's, build yourself a couple of these baffles, and after breaking them in for a couple days, let me know what you think! You really can not go wrong for less than 200 bucks and get this kind of true audiophile grade bass. Quote Link to comment Share on other sites More sharing options...
chops Posted April 29, 2004 Share Posted April 29, 2004 Quote Link to comment Share on other sites More sharing options...
chops Posted April 29, 2004 Share Posted April 29, 2004 Oh yeah!!! I almost forgot the most important picture of all!!!!!!! This is what she was doing when I was play Jimmy Buffet's Banana Wind cd at pretty high volume levels! She was under my right Maggie! Silly kittie. Look how happy she is!!!! Quote Link to comment Share on other sites More sharing options...
Olorin Posted April 29, 2004 Author Share Posted April 29, 2004 LOL -- my cat likes to sit on the sofa and glare at me when I've got Stevie Ray Vaughn cranked up. She could go just outside, but sitting and glaring seems to satisfy her more. Great write-up and pics -- thanks for sharing that! I might just have to give it a whirl when I get into the new house and have a room of my own to play with. Unlike you, I do have the WAF to account for. Quote Link to comment Share on other sites More sharing options...
chops Posted May 1, 2004 Share Posted May 1, 2004 If you or anyone else has any more questions, please feel free to ask away! BTW, what in the world is a "WAF"??!! Quote Link to comment Share on other sites More sharing options...
jt1stcav Posted May 1, 2004 Share Posted May 1, 2004 WAF - "Wife Acceptance Factor"...something us single guys with no wives or girlfriends have to worry about. Quote Link to comment Share on other sites More sharing options...
Olorin Posted May 2, 2004 Author Share Posted May 2, 2004 Alternately, "Wife Approval Factor." I think I'll test it with a dipole array along the back wall of the HT room when we get the house. Chops, thanks again for the info. I'll probably pester you some more when I get closer to the build phase. Quote Link to comment Share on other sites More sharing options...
TheEAR Posted May 4, 2004 Share Posted May 4, 2004 Good show,nice little system you have here.See the cats know quality speakers when they hear them Quote Link to comment Share on other sites More sharing options...
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