My dipole project

My dipole project

Postby gt4702e » Fri Dec 28, 2007 2:38 am

One year later, my dipole project slowly marches on. I've settled on a first order crossover; series for the tweeter/mid and parallel between that network and the woofers. The response measures nicely and sounds very good too. Bass reaches down to the 60s and should mate easily with a sub. They are remarkably efficient for dipoles, I'm guessing about 90 db at 1 watt, and capable of concert levels when relieved of sub-bass.

At the moment, I've stopped tweaking and taken everything apart so I can finish the baffles. I also need to order some more crossover parts now that I have a better idea of exactly what I'm going to need.

I'm really excited about finishing these speakers in the spring. I've been doing the DIY thing for a decade now and these represent the culmination of my collected experience.

Early baffle testing:
baffle1.jpg
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baffle2.jpg
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Finished baffles waiting on stain/varnish:
baffle3.jpg
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Re: My dipole project

Postby Chromedome2000 » Sat Dec 29, 2007 1:10 am

Looking good! More info on the drivers, crossovers and baffle would be great as would response measurements. Also what size room are you using them in and how far from the rear wall do they need to be? I have a rather small listening room and was wondering if dipoles were much of an option in smaller rooms.
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Re: My dipole project

Postby gt4702e » Sun Dec 30, 2007 6:31 pm

I posted some details previously on the email list, but to recap...

Drivers are:
1x B&G Neo 3 PDR (rear cup removed)
2x Seas Excel nextel cone 5" mid woofers
2x Peerless SLS 12" woofers

Crossover is still a work in progress. The mid/tweeter network is basically a textbook series filter @ 2.8kHz with the addition of a .1mH coil in series with the tweeter to tame it's rising response a little bit. The woofer/mid is parallel; 2nd order electrical on the woofer @ about 350 and first order on the mids at about 400. I tried using an all series crossover that measured equally flat, but I could never get the mid/woofer transition to sound right. I also tried various Zobels and found that they didn't seem to be helpful beyond shaping the response a decibel or two and making the load more amp friendly.

The baffles are constructed of 3/4" oak ply laminated to 3/4" birch ply. The front has a 3/4" round over and the rear has a 1/2" round over. They are about 4' high and taper from about 9" at the top to 26" at the base. There will be an additional "wing" added to the base to make things stand upright. It's essentially a right triangle 14" high and 9" at the base.

I didn't design these with any specific room in mind (I hope to move soon), but it will likely end up in a fairly small space. I would guess no larger than 15 x 20 x 9. I've found that concerns about dipole placement are often overblown. The highs can be absorbed with good wall treatments and the lows will be dominated by room nodes anyway. The major upside is greatly reduced side wall reflections. Setting these 24" out from the rear wall will probably be fine, but there's no really god way to know aside from experimentation.

I haven't saved any measurements while I've been playing with the crossovers. I honestly probably won't have time to take anything meaningful until Feb....
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Re: My dipole project

Postby gt4702e » Fri Mar 07, 2008 9:39 pm

One more update:
I have the "wing" attached to the baffled and have started applying the finish - a reddish chocolate colored stain followed by numerous coats of satin varnish. It's going to look truly beautiful when it's finally completed. I know - I need to get pictures up.

I've also been thinking about a center channel. I think I'm going to build it as a little table and keep the dipole thing going. I have a 720p projector so it can be big, but it can't stick up too high. For drivers, I was thinking of using the 4" Tang Band bamboo cone full rangers as mids, flanked by Dayton Reference Series or Peerless SLS 10" woofers. Tweeter would be another BG Neo 3 PDR or maybe a HiVi RT1L. Of course, there is probably wisdom in just using a cheap neo dome too keep the mid-tweet spacing sufficiently low. I figure I'd probably cross 5-6 kHz so it does seem like something worthy of consideration.
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Re: My dipole project

Postby gt4702e » Thu May 29, 2008 12:12 am

Okay, I'm a little late on getting a response graph up. Anyway, I think it's worth the wait. This was taken from my listening position in a fairly small bedroom so the lower frequencies are not completely accurate, even with a gated sine. I also think some of the roll off on the top end is the mic. In any event, I think you'll agree that things look pretty good. I also did a measurement of the individual drivers as best I could. That should provide a good idea of how everything shook out in the crossover.

One speaker is still running on a temporary crossover for easy tweaking, but this is probably going to be the final design unless anyone offers some brilliant suggestions. The sound is nothing short of stunning.
Attachments
response_graph_indv.jpg
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response_graph.jpg
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A few more updates...

Postby gt4702e » Thu Jun 12, 2008 1:01 pm

Here is a picture of the (nearly) finished product. I just need to finish up the crossover board for the right channel.
dipoles.jpg
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I added a bypass cap to make a proper RLC notch filter in the tweeter circuit. This lifts the response above 15 kHz a few db and makes for a notable improvement in "air" on certain tracks. I'll try to get updated measurements up soon. I may also get ambitious and measure outdoors.

I've slowly started moving on a center channel too. Parts Express had the Neo 3 PDR on sale so I picked one up along with a pair of the Tang Band 4" bamboo cone mids. I hooked one up yesterday and gave a listen. It sounds good in the midrange, but the high end has some nasty distortion and beams like a flashlight. I have no idea why they market these as full range drivers. They would be positively horrid in that role.
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Re: My dipole project

Postby llung » Fri Jun 13, 2008 3:14 am

Beautiful work.
I hadn't noticed your cat before. Looks just like mine! Does s/he try to scratch the drivers?

-lou
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Re: My dipole project

Postby gt4702e » Fri Jun 13, 2008 6:33 pm

Thanks Lou. The cat belongs to my roommate, both of which have moved back to the midwest since that picture was taken. She never seemed at all interested in all of the drivers and assorted computer equipment laying around the house. I guess she worked out her feline impulses chasing critters in the yard.
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