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Old 1st July 2003, 05:59 AM   #1
JoeBob is offline JoeBob  Canada
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Default Uber good, just a little less cheap.

I started a thread a while back about an open-baffle TB W3-871S speaker that I toyed with. Since then I tried alot of other drivers, in many configurations, but kept coming back to the TB. I tried the TB driver in ported, sealed, TLs but here again I kept coming back to the W3-871S in an open-baffle, I like it THAT much.

Well, I wanted a small speaker, so I decided on a folded-baffle. I wanted it small to conserve space and so it wouldn't cost to much to use a real wood and not particle board or MDF, I ended up using solid birch. But while the mid-bass/midrange/tweeter combo had been settled on and I liked it so very much, all I needed was bass that was just as amazing and also, great (and I mean really amazing) bang for the buck.

I thought about using TLs, but stereo bass in a TL would just have to be too huge, I wanted LOW bass and an TL to go as low as I wanted would have to be enormous. And while a ported box could be made to go as low as I wanted, it would also have to be huge, and I never really liked the quality of a ported box. But, when I had originally toyed with the W3-871S in an open-baffle I used it with a cheap stryke 7" woofer, also in the open-baffle, the bass wasn't super low, but it was remarkably good. So I decided on dipole bass as well... As it turns out, it was a very good choice indeed...

Now, in the end the speakers measured 16" wide, 24" tall, and had two side 12" deep, a nice size for my room. Since they were to be this size, I didn't want a 15" woofer, it would have just been too large, I wanted 12", no smaller either. I searched for a long time to find a woofer with all the qualities I wanted in the price range I was looking in (under $100 CND each, ended up being $125 CND with shipping and tax and everything, I was very pleased). Yet, even in this price range I wanted a driver that seemed to be well built, a quality driver always seems to sound better, although isn't always more expensive.

I found a driver that was 12", had an xmax of 6mm one way (wich was good enough for me, it is being powered by a single-ended Class-A MOSFET amp, so it doesn't have power to push it past it's excursion, I believe that quality amplification really matters for the bass, not just the mids and highs). I wanted a rubber surround, low enough fs (ended up with 28Hz, good enough). It was the MCM 55-1465, it's well built, VERY well built for the money.

The only thing is, no bass driver would go deep in the "enclosure" I specified above. I knew this and had decided form the begining to use equilisation on the dipole rolloff. But I wanted a driver that would rolloff as slowly as possible, so luckily the driver I had my heart set on had a Qts that wasn't too high at all. It ended up rolling off at pretty close to 6dB/octave until a bit under it's fs, then it dropped.

So I implemented a 6dB/octave boost starting around the mid 20s, I get bass a bit lower than 30Hz, into the 20s, but after that it drops like a stone, but to me bass in the 20s is VERY low since it is flat down most of the way. I added a potentiometer before the gain stage in the equilisation so that if I place the drivers on the floor I can adjust the bass level, and also because I knew not how much gain to give the eq'ed bass. I implemented all this in the preamp/cross-over/dipole eq box, all together and I kept it as simple as possible. And I crossed over the fullrange driver 1st order at 150Hz, so the bass driver doesn't go high and the fullrange doesn't go anywhere near it's xmax, it barely moves.

The end result? Very, very nice. I have never heard bass this good, I can't stress that enough, it is a cheap driver, but cheap doesn't mean bad, it sounds amazing. And with a bass driver filling in the lower octaves, the W3-871S is really allowed to shine, and shine it does, ALOT. I've built numerous loudspeakers before and they all sounded great (well, most, there were flops), but this last system (the speakers can't really operate without the preamp/crossover and acceseries) really sounds much better, I atribute it alot to the dipoleness of it. Many threads have been started with people toying with dipoles lately, and it isn't hard to realise why when you've heard one.

Well, I've been re-listening to my colection now and I just thought I'd give an update to the growing design that started with my thread a little while back. Sorry for the length of this thread, I'll just post a couple pictures, and sorry for the picture quality, I was going to take better ones after, but the bateries in my camera died on me...
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Old 1st July 2003, 06:02 AM   #2
JoeBob is offline JoeBob  Canada
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first pic...
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Old 1st July 2003, 06:05 AM   #3
JoeBob is offline JoeBob  Canada
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and a second one... The tube box is the preamp/crossover/all that in there...
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Old 1st July 2003, 03:58 PM   #4
Rudolf is offline Rudolf  Germany
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Congrats,

these must be the first „bookshelf-size“ dipols I see in my life.

Your original thread about the Tangbands in an open baffle helped me start into OBs myself. And there seems no way back.

Still I am wondering how you could place the TB so near to the baffle edge. Guess it´s no more than 12 cm distance. Following Linkwitz´ theories you should suffer from a heavy dropping in SPL downward from ~1200 Hz. Do you have measurements of the system?

I am asking because I want to cut off some of the „overhead“ of my open baffles for aesthetic reason, but don´t know how much I can risk before compromising the frequency range.

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Old 1st July 2003, 09:31 PM   #5
JoeBob is offline JoeBob  Canada
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Actually the TBs are about 15cm from the side, but there is a 30cm side panel on each side of the baffle. I tried placing the W3-871S on many test baffles to see if there were any problems, the final position was where I liked it best (both for looks and for sound). Unfortunately I haven't taken full measurements yet, I'll have to do that, but I'm just so busy listening to all my music again.

If you're worried of losing frequency response, just do what I did, try it on a test baffle. If you don't want to use wood I saw someone else on the forum once use cardboard as a test baffle, could be a good idea...
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Old 1st July 2003, 10:57 PM   #6
Rudolf is offline Rudolf  Germany
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Thanks JoeBob,

actually I was only worrying about the distance from the TB to the top of the baffle. Did you find a HUGE difference between the actual position and some other placement nearer to the center of a board? Or was it more a matter of taste?

I will keep an eye on your postings - in case you find time to take some measurements.

Happy listening.

Rudolf
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Old 1st July 2003, 11:40 PM   #7
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Joe....nice set up and good article

Joe
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Old 11th October 2003, 10:33 PM   #8
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joebob, do you have a schematic for you bass boost circuit...Thanks Lee
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Old 11th October 2003, 11:17 PM   #9
Bose(o) is offline Bose(o)  Canada
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What were you using for the EQ? I have been thinking about EQ, but was wondering about purchasing a parametric EQ or building a fixed Eq.
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Old 16th October 2003, 06:52 PM   #10
Coolin is offline Coolin  Netherlands
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Default T/S parameters

Hello Joebob,

Looks like a great project!!

Do you have the T/S parameters for the woofer?

Have you compard it to other high quality woofers besides the Strike you mentioned?

Do you think its posible to match the levels of the units pasively?

Hope you can help us out.........

CO
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